Sunday, May 31, 2009

Landscape and Nursery - Plant Phenological Indicators

A method of timing pest activity (and therefore controls) is ornamental plant development. Using Plant Phenological Indicators (PPI) involves observing certain plants whose bloom time (flowers, leaves, fruit, etc.) coincides with a life stage event of a specific pest. As temperatures rise in the spring, both plants and insects/mites begin development and continue throughout the growing season in response to this accumulation of heat units (GDD). Therefore, the development of plants can be correlated to insect activity.

Information from "Accurately Timing Pesticide Applications by Using Plant Phenological Indicators (PPI)" by Steven K. Rettke, Ornamental IPM Program Associate, in the May 14, 2009 edition of the Plant and Pest Advisory, Landscape, Nursery and Turf Edition from Rutgers University.

Landscape and Nursery - Good Guide on Cultural Problems

The following is information on a good guide for cultural problems in the landscape and nursery from the University of Massachusetts.

Cultural Practice Problems of Trees and Shrubs in the Landscape and Nursery

A concise compilation of the most recent research on cultural practice problems of trees and shrubs in the landscape and nursery. Highlights the many cultural practice pitfalls associated with woody plants in the nursery, landscape, and urban forest. Written for professional horticulturalists, landscape designers, municipal grounds managers, and master gardeners. $17.00

Go to to order.

Saturday, May 30, 2009

Landscape and Turf - Ants

The following is information on ants in landscapes or turf.

BLACK PAVEMENT ANTS (Tetramorium caespitum) are the most likely culprits if the mounds are relatively small, measuring 2-4" across. BLACK FIELD ANTS (Formica subsericea) are the architects if the mounds are large and relatively flat, measuring 1-3' across and only a few inches tall. Pyramidal mounds that are 1-3' across and 1-2' tall are engineered by ALLEGHENY MOUND ANTS (F. excectoides).

Black pavement ants are small and have pale legs, a brown to black thorax, and a black abdomen. Their habit of locating their underground colonies beside or beneath sidewalks gives rise to their common name. The ants scavenge for a wide variety of food including live and dead insects, honeydew from aphids, grease, etc. The ants are very protective of their feeding territory, and very intolerant of nearby colonies. They are well-known for their bare-tarsal brawls with battles sometime spilling across the entire width of sidewalks.

Black field ants and Allegheny mound ants are both relatively large with foraging workers measuring around 1/4" in length. Both are also associated with aphids, or other plant-sucking insects. The ants protect the sucking insects by fending off predators. In return, the sucking insects provide the ants with high energy carbohydrates in the form of honeydew.

Allegheny mound ants are one of the true mound-builders of the ant world. Their pyramidal mounds rise conspicuously above the surrounding landscape. Mound ants range in color from chestnut red, to black, to a combination of red and black. The ants are very aggressive, and they can use their powerful mandibles to deliver a noticeable pinching bite to a probing finger. However, their threat to people is inconsequential compared to their impact on plants. Mound ants are capable of killing small bushes and trees by injecting formic acid into wounds created by their mandibles. They use this capability to clear plants that shade their mounds. All vegetation, with the exception of large trees, may be killed within 40-50' of large, well-established mounds.

Black field ants are much less accomplished mound-builders. They form large, low-profile mounds of loose soil. These ants do not inject formic acid into plants, so they are not direct plant killers. However, they often heap soil over low-growing plants and they will pile soil high onto plant stems. Their plant-smothering mounds have been known to cause plants to decline and die. In particular, they are sometimes considered a serious pest of turfgrass. These large black ants are also very aggressive, and they will attempt to bite using their powerful, well developed mandibles.

Although both Allegheny mound ants and black field ants feed on honeydew produced by plant-sucking insects, they are also very effective scavengers and predators. The same is true of black pavement ants. The ants may be observed dragging live or dead cuisine back to their mounds to be surgically dismantled for protein. Since these ants are considered beneficial, management efforts should focus on dissuasion. For example, the pavement ants and field ants loathe thick, high-cut turfgrass. Repeated destruction of the mound ants abode can persuade them to locate elsewhere.

Information from the Ohio State Unibersity Buckeye Yard and Garden On-Line

Landscape and Nursery - Pine Needle Scale

The following is information on pine needle scale. Crawlers are now active in Delaware

Pine needle scale, Chionaspis pinifoliae, crawlers are actively searching for places to settle and feed. Crawler activity often begins when Forsythia intermedia is in full bloom, however peak crawler activity is 498 (range 63-1046) GDD base 50 . Crawlers are light purple in color until they settle and turn light yellow with a dark longitudinal line down the center. Crawlers, found on needles, may spread by crawling, wind or birds. This scale prefers pines, especially Scotch and mugho, but may also be found on firs, Douglas-firs and spruces. Adults appear as white oyster-shaped scales and when populations are large, give plants a frosted appearance. Untreated heavily infested plants may cause needles to turn yellow to brown and may cause twigs or branches to die. Females lay about 40 reddish colored eggs during the summer around 1622-2745 [2053 peak] GDD base 50 . The second generation of crawlers usually begins at 1791 GDD base 50 . Another closely related scale, Chionaspis heterophyllae (commonly called PINE SCALE or PINELEAF SCALE), is known to feed on pines predominately, but has been reported on fir and spruces. The differences between the two are only noticeable under a microscope.

Natural enemies such as the twice-stabbed lady beetle and parasitoids attack this scale species. Treatment options include: horticultural oil, insecticidal soap, dinotefuran, acetamiprid, pyriproxyfen, acephate, and synthetic pyrethroids such as deltamethrin. In some cases, such as on Christmas tree farms, removal of heavily infested trees reduces the likelihood of other nearby trees becoming infested.

Pine needle scale giving a frosted appearance. Photo by Whitney Cranshaw, Colorado State University,

Information from Brian Kunkel, Ornamental IPM Specialist, UD.

Friday, May 29, 2009

Landscape and Nursery - Choose Scab Resistant Crabapples

Nurserymen and landscapers should consider using scab resistant crabapple varieties. The following is more information.

Use scab-resistant or scab-immune crabapples in the landscape. Scab immune trees don’t get scab while scab resistant trees may show some lesions, but not enough to cause defoliation. Nurserymen should be growing scab-immune or scab-resistant crabapples; these may include the following: these may include the following: ‘Adirondack’, ‘Bob White’, ‘Brandywine’, ‘Callaway’, ‘Camelot’,‘Candymint’,
‘Canterbury’, ‘Christmas Holly’, ‘Cinderella’, ‘Coralburst’, ‘David’, ‘Dolgo’, ‘Evereste’, ‘Excalibur’, ‘Firebird’, ‘Foxfire’, ‘Golden Raindrops’, ‘Guinevere’, ‘Hamlet’, ‘Holiday Gold’, ‘King Arthur’, ‘Lancelot’, ‘Lollipop’, ‘Louisa’, ‘Manbeck Weeper’, ‘Mary Potter’, ‘Molton Lava’, ‘Pink Princess’, ‘Prairifire’, ‘Prairie Maid’, ‘Professor Sprenger’, ‘Purple Prince’, ‘Rawhide’, ‘Red Jewel’, ‘Sentinel’, ‘Silver Moon’, ‘Sinai Fire’, ‘Strawberry Parfait’, ‘Sugar Tyme’, ‘Tina’, ‘White Angel’, ‘Winter Gem’, M. baccata ‘Jackii’, M. floribunda, M. sargentii, M. x zumi ‘calocarpa’.

Do not grow these in the nursery or plant in the landscape:

Very susceptible: ‘American Masterpiece’, ‘American, Triumph’, ‘Harvest Gold’, ‘Indian Magic’, ‘Jewel Berry’, ‘Pink Satin’, ‘Red Jade’, ‘Royal Scepter’, ‘Spring Snow’, ‘Thunderchild’, ‘Weeping Candied Apple’, ‘White Cascade’.

Extremely susceptible: ‘Almey’, ‘Eleyi’, ‘Hopa’, (there are others).

Information from the University of Kentucky.

Landscape - Some Insects to Look For at this Time

The following are some insects to look for at this time in the landscape in Delaware.

Ambrosia beetles and symptoms have been noted. We are past the usual spray period for Granulate (Asian) ambrosia beetle but there is still time to control Brown ambrosia beetle. Go to for more information. Rose sawflies are active. Manually remove and destroy small infestations. Treat larger populations of larvae with hort oil. Euonymus scale crawlers are active. Control with hort oil, insecticidal soap, dinotefuran, or pyriproxyfen. Pine bark adelgids and spittle bugs are active. No treatment needed, unless infestation is incredibly high and the tree is small and recently planted.

Information from the "What's Hot" section of the Ornamentals Hotline from the University of Delaware Cooperative Extension.

Thursday, May 28, 2009

Landscape - Japanese Maple Scale

Japanese maple scale is a major problem in the landscape. I had a Japanese maple almost killed in my landscape by this scale until I got it under control. The following is more information.

Japanese Maple Scale

This scale has become the number one scale in nurseries and landscapes over the last 5 years - so pay attention and watch for this scale. Try to bring it under control before it overwhelms you.

Plants Damaged: Japanese maple scale is showing up in more and more landscapes and nurseries lately. Look for this scale on Japanese maple, Ilex sp., American red maple, dogwood, zelkova, lilac, yellowwood, pyracantha, privet, holly, euonymus, redbud, stewartia, cherry, magnolia, Itea, and Styrax.

Damage: This armored scale feeds directly on plant cells, not in the phloem tissue like soft scale insects. Heavy populations cause a slow decline of the tree. If high populations have resulted in dead branches on trees, prune these out before crawler hatch to reduce the number of scales potentially moving onto other branches and trees.

Life Cycle: The life cycle is poorly understood. The male and females overwinters as immatures and mature in early spring. There are two generations per year. The two generations overlap and crawlers are present from June through October. We will monitor and let you know when crawlers start emerging. Look for the white to gray, narrow oystershell-shaped female covers on twigs and main branches. Use a hand lens to look for the light purple crawlers.

Control: Applications of 1% horticultural oil and Distance should be made when crawlers are detected. This should have about 2 - 3 week residual activity. At that time monitor your plants again to see if you still have crawler activity. The twice-stabbed lady bird beetle provides some biological control of this scale.

Information from the May 22, 2009 edition of the TPM/IPM Weekly Report for Arborists,
Landscape Managers & Nursery Managers from University of Maryland Cooperative Extension

Landscape - Ash Rust

The following is information on ash rust, a disease now present in the landscape.

Ash rust caused by the fungus, Puccinia sparganoides, was observed last week on white ash. This rust produces bright orange swellings on the green stems and petioles; infected leaves are distorted and have numerous orange crown-shaped pustules. The infections are few at present but it can be pretty spectacular when leaves stay wet for long periods of time (6-8 hrs). In 2006, ash rust was everywhere. It is too late for any chemical control. The alternative host for this rust is Spartina spp. (marsh and cord grasses). Most of the real damage is to nursery trees that lose the new green twig growth. If symptoms are not present, preventative fungicide applications of labeled fungicides for rust are advised for nursery growers. Myclobutanil (Systhane or Immunox for homeowners) is the only fungicide registered for this disease.

Ash rust. Photo from the Iowa State University Plant Disease Clinic.

Information from Bob Mulrooney, Extension Plant Pathologist, UD.

Wednesday, May 27, 2009

Landscape - Poison Ivy Control

Poison ivy season is with us again. Landscape maintenance firms may be asked to control poison ivy on properties that they manage. The following is more information on the subject.

Poison ivy, Toxicodendron radicans, has fully leafed out throughout Delaware. This is a problem weed in managed woodlands, wooded properties, parklands, commercial sites, and overgrown properties. It is noted for its ability to cause allergic skin reactions. Poison ivy is woody perennial weed that can be found as an erect shrub, a trailing shrub running along the ground, or a woody vine climbing by aerial roots giving the vine a fuzzy appearance. It is identified by its leaves, newly emerged red in color then turning glossy green, consisting of 3 leaflets two to four inches long with pointed tips. Two of the leaflets are directly opposite each other and center leaflet stands out by itself, extended on a longer stalk. It spreads by rhizomes, stems rooting along the ground, and seed.

Control can be done in small areas by digging up plants making sure to get all the rhizomes. Avoid all skin contact using gloves, long sleeves, and long pants. Herbicides are best applied in early through late summer, but before leaves change color. Herbicides that are effective include glyphosate; triclopyr; 2,4-D; 2,4-D + dicamba; and fosamine. Apply as a broadcast spray to leaves. Multiple applications of these herbicides will be needed over several years for complete control. Vine and brush forms may be cut and gyphosate applied immediately to the cut stumps.

Glyphosate is recommend (as a directed or cut stump application) in landscapes and desired woodlands. Triclopyr; 2,4-D; 2,4-D + dicamba; and fosamine are most appropriate for non-landscaped areas, fencelines, and right of ways as they are general brush killers.

Gordon Johnson, Extension Horticulture Agent, UD, Kent County

Landscape - Poison Ivy Pictures.

The following are pictures of poison ivy. Poison ivy has fully leafed out now in Delaware.

Poison Ivy leaves. Note the middle leaflet of has an extended stalk and leaflets are in a group of 3. Photo by Richard Old, XID Services, Inc.,

Poison Ivy foliage. Photo by David J. Moorhead, University of Georgia,

Poison Ivy vine. Photo from the Ohio State Weed Lab Archive, The Ohio State University,

Tuesday, May 26, 2009

Greenhouse - Reducing Humidity

With rain and cloudy weather returning, it is good to review methods for reducing humidity in greenhouses. The following is a short article on the subject from the New England Greenhouse Update.

Cool, cloudy or rainy weather creates an ideal environment for Botrytis infections during production in a full greenhouse.

Once Botrytis develops, it cannot be effectively controlled with fungicides alone. The key to suppressing Botrytis is to keep the plant canopy dry especially from dusk until dawn. This can be accomplished by managing the greenhouse environment.

Ventilation allows the exchange of moist greenhouse air with drier air from outdoors. Heating is necessary to bring outdoor air up to optimum growing temperature, and also increases the capacity of the air to carry moisture, thus avoiding condensation. Neither practice alone is as efficient as both combined.

The method and time it takes for heating and venting will vary according to the heating and ventilation system in the greenhouse. To vent the humid air in greenhouses with vents, the heat should be turned on and the vents crack open an inch or so. When doing this the warmed air will hold more moisture (RH), escape from the greenhouse through the vents and be replaced with outside air of lower RH. This natural rising of the air will result in a greenhouse of lower relative humidity.

In houses with fans, the fans should be activated and operated for a few minutes and than the heater turned on to bring the air temperature up. The fans should then be shut off. A clock could be set to activate the fans. A relay may be needed to lock out the furnace or boiler until the fans shut off so that both the fans and heating system do not operate at the same time and flue gases are not drawn into the greenhouse.

The venting and heating cycle should be done two or three times per hour during the evening after the sun goes down and early in the morning at sunrise. The time it takes to exchange one volume of air depends on several factors including whether or not fans are used and, the size of the fans and vents. For some greenhouses it may take as little as 2-3 minutes air exchange. For greenhouses using natural ventilation, it may take 30 minutes or longer. Heating and venting can be effective even if it is cool and raining outside. Air at 50°F and 100% RH (raining) contains only half as much moisture as the greenhouse air at 70°F and 95% RH.

Information from Tina Smith, University of Massachusetts and Leanne Pundt, University of Connecticut in the New England Greenhouse Update:

Landscape - Know Your Invasive Species 2

This is the second in a series on recognizing invasive species in Delaware. This post is on Asian honeysuckles.

Asian Bush Honeysuckles; Lonicera maackii, L. morrowii, L. tatarica; Honeysuckle Family (Caprifoliaceae)

Form: Deciduous Shrubs
Flowers: May–Jun
Fruits: Jun–Jul, Oct–Nov (L. maackii)

Native Range: China, Manchuria, Korea
Introduction: Tartarian in 1700s, Amur and Morrow’s in late 1890s. Promoted by USDA for wildlife habitat and shelterbelts.
Mid-Atlantic Range & Habitats: Open woodlands, old fields, forest edges, hedgerows, throughout the region.

Ecological Impacts: Several similar species of bush honeysuckles of Asian origin occur in our region. These shrubs leaf out early in the season and hold their leaves longer than most native deciduous shrubs, thus reducing light availability to other plants for a long period of the growing season. Recent studies have shown that chemicals in L. maackii are capable of inhibiting germination of other plants. The nesting success of birds nesting in Asian bush honeysucklesmay be reduced because the plants provide less protection fromnest predators. In addition, foraging birds choose honeysuckle fruit as readily as some native species with greater caloric content. Honeysuckle seedsmay be dispersed over long distances by birds and deer.

Identifications: In the invasive honeysuckles, leaf margins are entire, the fruit a red (usually) to yellowish round berry, and the stem has a hollow pith (the hollow in the center of the pith is often quite small). The invasive species are often confused with native honeysuckles. The yellow flowers of our native Bush-honeysuckle (Diervilla lonicera) are in groups of 3–7 and turn reddish with age. The invasive honeysuckle species all have white to yellow flowers, with the exception of Tartarian Honeysuckle (Lonicera tatarica) that can have white to pink flowers.

Tartarian honeysuckle. Photo by John M. Randall, The Nature Conservancy,

Information from "Mistaken Identity - Invasive Plants and their Native Look-alikes, an Identification Guide for the Mid-Atlantic" by Matthew Sarver, Amanda Treher, Lenny Wilson, Robert Naczi, and Faith B. Kuehn. You can download the publication at:

Monday, May 25, 2009

Landscape - Know Your Invasive Species I

This is the first in a series on recognizing invasive species in Delaware. This first post is on Tree of Heaven, Ailanthus altissima.

TREE-OF-HEAVEN, Ailanthus altissima, Quassia Family (Simaroubaceae)
Broadleaf Deciduous Tree
Flowers: Jun–Aug
Fruits: Jul–winter
Native Range: China

Introduction: to Philadelphia in 1748 by a gardener.

Mid-Atlantic Range & Habitats: Disturbed forests, forest edges, old fields, roadsides, urban areas, widespread, in a wide range of soils.

Ecological Impacts: Tree-of-heaven releases chemicals into the soil that inhibit the growth of other plants. At the same time, the rapidly growing tree quickly reduces light availability to plants growing beneath it. Ailanthus has also been shown to change nutrient cycling and availability in invaded forests. Female trees produce huge numbers of windborne seeds.

Identification: Leaflets are entire except for one to several broad, rounded teeth at base; underside of leaflet with a round, thickened spot (a gland) near the base of each tooth
Fruits are large cluster of winged samaras. Leaves and stems of plant have a strong, unpleasant odor when crushed or bruised.

Ailanthus can be confused with sumac species (Rhus). Ailanthus has clear sap, whereas the Rhus species have milky, sticky sap. The young stems and petioles of Ailanthus are hairless. Smooth Sumac has hairless but glaucous stems and petioles and those of Staghorn Sumac are covered in dense hairs. The undersides of the leaflets of both species of sumac are whitish, compared to the green or light green of Ailanthus. The thin gray bark of Tree-of-heaven is distinctive, with diamond-shaped markings on younger trees, and pale vertical lines on older trees. The bark of the sumacs is very smooth with narrow horizontalmarkings. Sumacs do not grow more than 10 m (30 ft.) tall, whereas Tree-of-heaven grows to a height of 25 m (over 75 feet).

Tree of Heaven. Photo by Joseph M. DiTomaso, University of California - Davis,

Information from "Mistaken Identity - Invasive Plants and their Native Look-alikes, an Identification Guide for the Mid-Atlantic" by Matthew Sarver, Amanda Treher, Lenny Wilson, Robert Naczi, and Faith B. Kuehn. You can download the publication at:

Garden Center and Greenhouse - Care of Plants in a Retail Setting

The following is a good article on care of plants in a retail setting from the New England Greenhouse Update.

Plants on display in your garden center or farm stand require regular, gentle watering to maintain high quality. Watering should be completed during the daylight hours, to allow plants to dry before dark. The drying will help prevent foliar diseases. If plants are to be watered by hand, be sure to furnish sufficient time and personnel to water thoroughly. Anything less, and plant quality will decline rapidly.

Place hanging baskets in areas beside the aisles, not over aisles where water and fertilizer will drip onto customers and create a hazard.

Keep plants and surrounding areas in order and clean even during the busiest times. Removing dead and injured plants and spent flowers are essential at least twice a day even during the busy season. Customers get turned off when plants look bad and high ethylene concentrations from decaying plant tissue will causes premature loss of foliage and flowers. A skilled employee isn’t necessary for these jobs, but a competent one is. Employees should carry pruning shears and wear work aprons with large pockets where they can keep dead flowers and debris from plants in the sales area until they can find a waste can.

Plants in hanging baskets and planters will stay in those containers throughout the summer and will need to be fertilized in a retail operation. Depending on the plants, options include fertilizing on a weekly basis, using 400 ppm N or 200 ppm N at every watering or topdressing with a controlled- release fertilizer according to directions. Retailers should communicate with their wholesale growers to make sure controlled-release fertilizer has not already been applied prior to shipping.

Potted plants and bedding plants left over after the busy weekend will also need fertilizing, especially if they have been irrigated and spot watered with only plain water for several days. Inspect the root health and if healthy, fertilize, using 200 ppm N. Poor root health may indicate a need for a fungicide application.

Article by Paul Lopes, University of Massachusetts and Tina Smith, University of Massachusetts in the current New England Greenhouse Update

Sunday, May 24, 2009

Landscape - Controlling Ticks

Landscape maintenance, turf, and pest control firms are often asked by clients if they have anyway to control ticks outside. The following is a good article on the subject from Rutgers University.

During the weeks ahead, the peak activity for the immature stage of the Deer tick (Black legged tick) will commence. This stage is the vector of 70% of all cases of Lyme disease. The nymph is very small, about the size of a poppy seed. The tick is picked-up by brushing against low (4”-6”) vegetation. Since ticks don’t fly or drop from trees, they crawl up and wait on vegetation for a person to walk by and then grasp onto clothing to crawl up. Tucking your pants into your socks (so they don’t crawl up your leg undetected), wearing high rubber boots (too slippery to crawl up?), and wearing a repellent (to kill them upon clothing contact) are thus all precautionary recommendations to prevent a tick bite. The nymph stage will feed for 3 to 5 days, swelling with blood to the size of a sesame seed before it drops off.

The nymph prefers to live in the woods, or in adjacent vegetation, not in properly mowed lawns. A lawn is simply too hot and dry for nymphs to survive. Research shows that 84% of nymphs are found in the woods, 13% along wood-edged vegetation, and only 3% in the lawn. Reliable control of Blacklegged tick nymphs currently involves one application of a granular insecticide (e.g., Sevin G) broadcast 8-12 feet into the woods. Shaded turf adjacent to the woods is also treated. One application during late May or the first week of June has given >95% control of nymphs. Liquid insecticides are also labeled, but thorough coverage, by drenching foliage until runoff, must be performed. Only one pesticide application is necessary, because nymphs rarely move more than 10 feet from where they molted from a larva. Once they are killed within an area, they won’t re-infest again until the adult moves in via animal activity during the fall season.

Reprinted from the May 29, 2008 edition of the Plant and Pest Advisory Newsletter, Landscape, Nursery and Turf Edition from Rutgers University.

Landscape - Septoria Leaf Spot of Rudbeckia

The following is information on Septoria leaf spot of Rudbeckia in the landscape.

Septoria leaf spot on brown-eyed Susan, Rudbeckia 'Goldstrum' can be found on some very small plants in the landscape. Infection this early could develop into some serious defoliation. To keep some leaves on heavily spotted plants (irregular brown spots on the leaves with small black fruiting bodies on the oldest spots), make a fungicide application with Daconil or other labeled fungicide.

Symptoms begin as small, dark brown lesions that enlarge from 1/8 to 1/4 inch in diameter. Although the lesions are usually rounded, there may be angles where leaf veins limit the spread of the fungus. Symptoms of this disease may be difficult to distinguish from those of angular leaf spot of Rudbeckia. Microscopic examination of the lesion will reveal black, flask-shaped structures called pycnidia that contain thousands of thread-like spores. Spores are produced in late spring and early summer, causing leaf spots on the lower leaves. The spores of the fungus are dispersed by splashing water, with lesions first appearing on lower leaves and later developing on upper leaves as the season progresses.

To manage this disease, remove the infected leaves at the end of the growing season to reduce inoculum levels. Because leaf moisture is essential for infection to occur, increase air circulation around the foliage by properly spacing plants (and removing volunteer seedlings) to prevent over-crowding. As with other foliar disease problems, avoid overhead watering. Fungicides containing chlorothalonil or copper may protect new growth and reduce the spread of the disease. Preventative applications of fungicides should begin in late May to early June prior to the onset of symptoms.

Information from Bob Mulrooney, Extension Plant Pathologist, UD and "Diseases of Rudbeckia" by Janna Beckerman, Extension Plant Pathologist, University of Minnesota.

Saturday, May 23, 2009

Landscape - Aphids on the Increase

Aphid activity in the landscape is on the increase at this time. The following is more information.

Aphids are abundant on many plants (from climbing roses to copper beeches). However, our earlier rain and cool temperatures have also produced many beneficial insects (i.e. lady beetles) so scout for beneficials before you spray.

Woolly apple aphids on apples, pear, hawthorn, mountain ash and elm has also been found. These aphids produce a waxy substance and are often found clustered in pruning scars and wounds of branches. As populations increase, woolly apple aphids will move down the tree and feed on the roots. Root feeding by these aphids can cause significant damage on young trees.

Monitoring: Look for honeydew and sooty mold on foliage from aphids and the wax of woolly aphids.

Control: If present in the landscape, syrphid fly larvae, lady bird beetles and lacewing larvae are good predators of aphids. A parasitic wasp, Aphelinus mali, is a common predator of the woolly apple aphid. Insecticidal oil and horticultural soap can be used and have minimal impact on beneficial insects.

Photo of aphids on hellebore by Bill Miller in the current Maryland TPM/IPM report.

Information from the University of Delaware Ornamentals Hotline and the University of Maryland TPM/IPM Report.

Landscape - Hemlock Woolly Adelgid

The following is information on Hemlock Woolly Adelgid which has hatched at this time.

In most areas, Hemlock Woolly Adelgid (HWA) sistens have completed 100% egg hatch. Now is the time to control this pest with horticultural oil. 100% egg hatch has been recorded from 505-676 (Avg. 591) GDD. HWA crawlers appear as small black flecks along the needles, settling and feeding at needle bases. The white cottony sacks that were the adults will now fade away.

Very little growth and development of HWA occurs in the heat of the summer, and the pest often appears dead. With cool temperatures in September, the sistens nymphs resume feeding and swell up. You can manage adelgid populations successfully with sprays of horticultural oil at 1-2% (v:v). Soil-applied neonicotinoids like Merit (imidacloprid) or Safari (dinotefuran) are also used. Merit is typically soil injected in the fall, while Safari can be spring applied and found in the foliage in as little as three weeks. Remember only HWA is controlled--elongate hemlock scale is not generally affected by imidacloprid treatments.

Water mature hemlocks during the summer season. Do not fertilize infested hemlocks, as nitrogen will increase mite, scale, and adelgid populations. In fact, Spruce spider mite and hemlock rust mite populations have found to be stimulated by imidacloprid applications to hemlock. Most biological controls for HWA in forested situations have not established widely yet and are cost prohibitive for landscape use. Ironically, since it is a home-invader, nuisance pest, the multi-colored Asian ladybeetle (Harmonia axyridis) is an effective predator of HWA.

Information from Casey Sclar, IPM Coordinator, Longwood Gardens

Friday, May 22, 2009

Landcape - Current Diseases in the Landscape

The following is information on current diseases in the landscape from Bob Mulrooney, Extension Plant Pathologist, UD.

This is turning out to be an exciting year for plant pathologists--diseases springing up everywhere (pun intended). Look for scab, frog-eye leafspot and cedar-apple rust (bright orange lesions) on susceptible crabapple cultivars. Frogeye or Phyllosticta leafspot on red maple, silver maple and boxelder (irregular tan spots withred-brown margins--a minor disease rarely requiring control). Anthracnose, booming due to the cool wet weather can be found on sycamore, ash (same fungus causes anthracnose on Chinese fringe tree--look for curled, deformed leaves or leaflets and brown necrotic areas), even on oak leaves in the understory (producing large brown blotches and small irregularly shaped spots). Each host has its own specific anthracnose fungus. These diseases are usually not serious enough to warrant fungicide control.

Turf - Red Thread

Red thread disease in turf has been found recently. The following is more information.

Red thread has been diagnosed in a mixed turf of bluegrass and perennial ryegrass. The infected patch had a pink cast with red fungal threads easily seen upon close inspection. Although considered a disease of stressed turf, all turf can be infected under these ideal conditions. Red thread only infects the blades causing temporary damage. Infected turf will recover with time. Fungicides applied at the first signs of infection may help reduce damage but treatment is not usually warranted.

Red thread is a foliar disease that usually occurs on taller mown turfgrasses during spring and fall. The disease is often associated with malnourished, low quality, slow growing turf, but the effects of the disease are largely cosmetic. Red thread symptoms create an undesirable appearance, but crowns and roots are not infected, so plants are not killed and turf eventually will recover.

Red thread most commonly affects Kentucky bluegrass, perennial ryegrass, and tall fescue. Outbreaks usually occur in low maintenance turf stands such as residential lawns, golf course oughs, and some low budget athletic fields. Red thread development is most common where turfgrass nutrition is poor and there are other factors that promote slow growing turf.

The most important nonchemical (cultural) control option involves implementing an adequate nitrogen fertility program. A good fertility program implemented over two to three years will drastically reduce further red thread problems. Other cultural practices that promote healthy turf and vigorous growth also help suppress red thread. Outbreaks may be reduced further by avoiding irrigation practices that extend dew periods (such as watering in the late afternoon and early evening).

Photo from the Purdue University fact sheet BP-104-W on red thread disease of turf.

Information from Bob Mulrooney, Extension Plant Pathologist, UD and Purdue University fact sheet BP-104-W by Philip Harmon, Graduate Research Assistant and Richard Latin, Professor of Plant Pathology

Thursday, May 21, 2009

Turf and Landscape - Ground Nesting Bees

The following is a good article on ground nesting bees, a common issue you may find in turf and landscapes. These are often benefical pollinators and should not be controlled unless absolutely necessary.

Several bee species nest in the ground; they can be seen entering and leaving pencil- diameter holes in sunny areas of sandy or well-drained soils covered with a sparse grass stand. These entrances are often surrounded by small mounds of fine soil particles. Many of these bees live in individual tunnels where they raise their young but over time, sizeable communities can develop where conditions are favorable and nearby flowers are abundant. They can sting if handled or stepped on but do not aggressively defend their nests.

Control may be warranted on children's play areas or if excessive tunneling is creating bare spots. However, ground bees select and thrive in areas that meet their requirements. While insecticide applications may have some temporary effect, the factors that make the sites attractive remain unchanged.

Carbaryl or Sevin, applied to burrowed areas according to label directions for turf pests, can reduce ground bee activity. However, this approach is a temporary solution. The bees are nesting there because the site is attractive - well-drained or sandy soil with relatively a sparse grass stand. Site alteration is needed to provide a long-term solution. Over-seeding bare areas, adequate fertilization, and watering should improve turf stand make areas less attractive to these bees. Raising the mowing height may help, also.

Most ground bees are 3/8 to ½" long and vary in color from solid black to brightly metallic and have "hairy bodies". These "wild" bees are important pollinators and should be left alone if they are not causing a problem.

There are many important pollinating bees in addition to the familiar honey bee. These small, hairy bees tunnel into well-drained soils where grass cover is thin. Females may share entrances but dig separate tunnels with side branches for brood rearing. These bees collect pollen and nectar and bring them back to the nest to feed their larvae. They do not harm the turf. Ground bees can sting but generally are not aggressive and do not defend their nest area like honey bees. However, they pose a potential problem in children's play areas. In these cases, Sevin dust or other insecticides labeled for turf can be used to treat the entrances.

Reprinted from "Ground-Nesting Bees" By Lee Townsend in the current edition of the Kentucky Pest News

Landscape - Bacterial Leaf Scorch in Oaks

The following is a good article on bacterial leaf scorch in oaks and its management using antibiotic injections.

Bacterial leaf scorch, caused by Xylella fastidiosa, affects many landscape trees including oaks (pin, red, scarlet, shingle, and white) maples (Norway, red, silver, and sugar), planes (American sycamore and London plane) sweetgum, hackberry, elm and mulberry. Oaks are widely planted in Delaware and the disease is most common in them. Leaves of infected trees typically show marginal necrosis (scorch) late in the summer followed by premature defoliation. Infected trees re-foliate normally in spring and the process of late summer scorch and premature defoliation is repeated. The disease begins on one or a few branches and over several years gradually spreads throughout the tree. After many years, dead twigs, then dead branches and limbs begin to appear in the tree and the condition continues to worsen over the years until the tree needs to be removed. Bacterial leaf scorch is a very problematic plant disease in Delaware.

In Kentucky research in 2006, they were able to show in replicated pin oak plots that root flare injection of oxytetracycline antibiotic in late spring delayed the appearance of scorch symptoms by about 2-3 weeks. In 2007, they determined that the best results were obtained when injections were made about 3 weeks after the first emerging leaves were fully expanded. Arborists with clients who want their trees injected with antibiotic may wish to concentrate their efforts for sometime in the next 2 weeks.

In the Kentucky work, they used Bacastat®, a commercial injectable form of oxytetracycline. This antibiotic is used for management of bacterial diseases in agricultural crops and is active against gram negative bacteria such as Xylella. Mycoject® is also an injectable formulation of oxytetracycline, but our results indicated that the more viscous formulation of this product was not as effective.

Although the time of appearance of scorch symptoms was delayed as a result of these treatments, none of the treatments prevented disease or cured trees with bacterial leaf scorch. When bacterial leaf scorch symptoms are delayed with antibiotic treatments, it is not known if this will prolong the life or vitality of the treated trees, but it might. Nevertheless, if clients are demanding a treatment, certified arborists trained in micro-injection techniques will want to make the injections in late May to provide the greatest effect. It appears that the effect of antibiotic injection lasts only one year, so annual injections may be needed. More research is needed to determine these long-term needs and effects.

Adapted from "It Is Near Time for Injecting Oaks for Bacterial Leaf Scorch" By John Hartman in the current edition of the Kentucky Pest News

Wednesday, May 20, 2009

Turf and Landscape - Apply First Bermudagrass Controls Soon

The following is a repost of an article on bermudagrass or wiregrass control.

Bermudagrass control in cool season turf can be a challenge. There are some herbicide tools available but you need to start early. First herbicide applications should go on soon. The following are some recommendations.

Bermudagrass suppression has been achieved by applications of Acclaim extra (fexoxaprop-p-ethyl) applied at 0.46 fl. oz. per 1000 sq. ft. every 4-5 weeks (maximum of 6 applications) starting at bermudagrass first greenup in May. Acclaim extra mixed in combination with Prograss (ethofumisate) or Turflon Ester (triclopyr) has given better bermudagrass control (do not use Prograss on fine fescues) and fewer applications may be needed. Both Prograss and Turflon Ester both have some bermudagrass activity when used alone.

This program based on Acclaim Extra will be the best option for light to moderate infestations. For heavy infestations a complete renovation will be needed. Kill the bermudagrass with glyphosate applications (2 applications, 3 weeks apart) in mid summer and reseed around Labor Day.

In landscape beds, fexoxaprop-p-ethyl can also be used as a post emergence spray around and over top of many plants. Other options include sethoxydim, clethodim, and fluazifop-p-butyl. Check the labels for specific landcape species these products can be used around. Spot applications of glyphosate are also very effective (must not touch landscape plants).

Gordon Johnson, Extension Horticulture Agent, UD, Kent County

Landscape - Insect Pests to Watch For Coming Up in June

The following are insect pests to watch for in the landscape coming up in June.

June Pests. Click on table for a larger version in a new window.

Information from Rutgers University.

Tuesday, May 19, 2009

Greenhouse - Shorefly and Fungus Gnat Control

The following is information on shore fly and fungus gnat control in the greenhouse.

Shorefly and Fungus Gnats

The populations of shoreflies and fungus gnats will be exploding after the extended cloud cover and rainy periods. Fungus gnats are best controlled in the larval stage by applying drenches or heavy sprays. Biorational products applied as soil drenches include azadirachtin (Azatin), Bacillus thuringiensis H-14 (Gnatrol), cyromazine (Citation), fenoxycarb (Precision), kinoprene (Enstar II) and diflubenzuron (Adept). Biological controls are insect-attacking nematodes (mostly Steinernema feltiae) and predatory mites in the genus Hypoaspis. The insect growth regulators Citation, Precision and Adept) are registered for larval control of shore fly, but results may be inconsistent. This is probably because shore flies live in very wet areas and do not feed on plant roots. Insecticidal soap will give knockdown of adult shoreflies. Cultural and physical controls will help, but in wet seasons like the spring of 2009 this is nearly impossible. Avoid potting mixes that promote the growth of algae and keep plants on the dry side. Clean algae from benches, walls and floors. Avoid letting areas stay permanently wet in the greenhouse. Some growers have applied hydrated lime under the benches to discourage growth of algae. If you are growing on the floor you are out of luck with this practice.

Reprinted from the May 15, 2009 edition of the Greenhouse TPM/IPM Bi-Weekly Report from the University of Maryland Cooperative Extension, Central Maryland Research and Education Center

Landscape - Ambrosia Beetles Becoming a Problem in the Region

Ambrosia beetles are becoming a problem in the region. The following is more information from the University of Maryland.

Two invasive species of Ambrosia beetles very active in Maryland this season. These two non-native invasive species of ambrosia beetles are Xylosandrus germanus and Xylosandrus crassiusculus. Over the last 2 weeks the Univeristy of Maryland has received samples from nursery owners and landscape managers with damage from the ambrosia beetle, Xylosandrus germanus and Xylosandrus crassiusculus. We have recorded this beetle damaging honeylocust (Gledistia triacanthos), London plane tree, Zelkova, river birch, American holly (Ilex opaca), sweet bay magnolia (Magnolia virginiana), Chinese dogwood (Cornus kousa), yellowwood, and Styrax. A fruit orchard that is also a fruit nursery supplier sent in samples of Oriental persimmon, Asian pears, English walnut and chestnuts that were infested with Xylosandrus germanus. They lost all of their grafted 1 year old trees to an infestation of X.germanus.

Xylosandrus crassiusculus adult ambrosia beetle. Photo by J.R. Baker & S.B. Bambara, North Carolina State University,

Eggs and larvae of ambrosia beetle in wood. Photo by Will Hudson, University of Georgia,

Frass expelled in long "toothpick" from ambrosia beetle. Photo by J.R. Baker & S.B. Bambara, North Carolina State University,

Monday, May 18, 2009

Landscape - Frogeye Leaf Spot on Crabapple

The following is information on frogeye leaf spot of crabapple, a disease now appearing in the landscape.

Frogeye leaf spot on apple and crabapple is showing symptoms now in the landscape: circular spots on young leaves with indefinite purple margins. Later they will turn brown and if they regrow, they become lobed giving the frogeye pattern. Sometimes susceptible crabapples can be defoliated prematurely in wet seasons. Under most conditions, control is not necessary, but the same fungicides applied for scab will control frogeye.

Host plants:

Frogeye (Sphaeropsis) leaf spot occurs on apple and crabapple. There are frogeye leaf spots on leaves of other trees and shrubs. The appearance of the leaf spot is similar, but fungi other than Sphaeropsis cause these infections.


The concentric pattern of light brown to tan center portions of the leaf spot ringed by darker purple margins is the origin the name “frogeye leaf spot.” Young leaves exhibit circular spots with indistinct purple edges about 2 weeks after petal fall. Many of the spots develop no further and a well-defined circular brown spot is present by summer. However, in other spots, there is secondary enlargement during the summer and the brown spots develop irregular discolored lobes. Tiny black fruiting structures often develop in the center of the leaf spots. Extensive spotting of leaves initially causes chlorosis followed by early leaf loss.

Disease cycle:

Fruiting structures develop in black rot cankers on apple and crabapple branches and twigs in the spring and they release spores via wind and rain splash. If spores land on wet unfolding leaves, they germinate and penetrate the leaves through stomata. Later that season fruiting structures develop in the spots and these can serve as an inoculum source for black rot canker infections on nearby apple and crabapple branches with wounds or cracks in the bark.

Management strategies:

Usually, frogeye leaf spot alone does not threaten the health of apple and crabapple trees. However, it can be an important source of spores for black rot canker infections that cause extensive branch dieback. Remove and dispose of cankered branches when conditions are dry to reduce inoculum available to initiate frogeye leaf spot and well as cankers. Use fungicide treatments to prevent infections of fruit in orchard situations if sanitation does not sufficiently suppress fruit spot infections.

Information from Bob Mulrooney, Extension Plant Pathologist, UD and Daniel H. Gillman, Plant Pathologist, UMass Extension Landscape, Nursery & Urban Forestry Program

Landscape - Anthracnose of Shade Trees

The following is a good article from Rutgers on anthracnose of shade trees. This is a common disease in Delaware. Photos of sycamore anthracnose are shown in the previous post.

Anthracnose of Shade Trees

Anthracnose is a common disease of many shade tree species, particularly sycamore, ash, oak, maple, and walnut. This disease affects foliage as a scorch along leaf margins and veins, and also causes dieback and cankers to form on twigs.

Anthracnose begins its annual cycle in the spring. Small fruiting structures situated on small twigs infected the previous year produce spores. Spores are splashed and carried by wind to infect developing leaves. These diseased leaves develop lesions along veins and leaf margins, causing the tissue to appear “scorched.” In severe cases, leaves soon completely blight and fall from the tree. In some species such as sycamore, trees promptly refoliate in the drier, early summer months. These new leaves are not usually affected by the disease; anthracnose is more severe when temperatures during leaf expansion remain between 55 and 60 F, and when moisture remains on leaf surfaces for long periods of time.

In the twig blight phase of the disease, infected twigs may die back 6 to 8 inches from the tips, and larger cankers may form if infection is severe or if the tree is in poor health. Repeated tip dieback results in clusters of dead twigs called “witches’ brooms,” which are readily apparent as you look at the silhouette of the tree.

To manage anthracnose, improve plant vigor, prune cankers and dead branches, and avoid planting highly sensitive plants. Irrigate in the early morning hours and avoid over-head watering to prevent excessive moisture from remaining on foliage. Since anthracnose does not usually cause serious damage to healthy trees, application of fungicides is recommended only when it is necessary to keep trees as blemish-free as possible.

If desired, some control of this disease can be obtained with foliar applications of fungicides which include Armada, Bacillus subtilis, chlorothalonil, ConSyst, copper, (Badge, hydroxide, oxychloride, salts, sulfate), Junction, mancozeb, neem oil, phosphate (trunk injection), Quali-Pro TM/C WDG, Spectro, SysStar, thiabendazole (trunk injection), thiophanate-methyl, TwoSome (no commercial uses), trifloxystroban, or Zyban.

Information from "Foliar Diseases in the Landscape" by Ann B. Gould, Ph.D., Specialist in Plant Pathology, Rutgers Univerisity in the April 30, 2009 edition of the Plant and Pest Advisory newsletter, Landscape, Nursery, and Turf Edition from Rutgers University. Go to for the full article.

Sunday, May 17, 2009

Landscape - Sycamore Anthracnose

Sycamore anthracnose is finally evident on our native sycamores and susceptible London plane trees after last week’s rain. Look for the large brown blotches that follow the veins on the older leaves. No control is needed since the trees put out new leaves and seem to be unaffected by the damage. The following are some pictures.

Sycamore anthracnose closeup. Photo from Clemson University - USDA Cooperative Extension Slide Series,

Sycamore anthracnose. Photo by William Jacobi, Colorado State University,

Landscape - Hawthorn Leaf Spot

The following is information on Hawthorn leaf spot, a disease now present in the landscape.

Hawthorn leaf spot is present on susceptible hawthorns. Look for small round to angular spots. They can become numerous and can cause leaf loss on susceptible English hawthorn. This disease is caused by the fungus Entomosporium mespili, which causes Photinia leafspot.

Cause: Diplocarpon mespili (asexual: Entomosporium mespili), a fungus. Other names include Fabraea scald, leaf blight, or fruit spot. Host range is wide. The fungus overwinters on dead leaves and young twigs. Cool, wet weather favors disease development. English hawthorn (Crataegus laevigata) is very susceptible including the cultivars 'Paulii' and 'Crimson Cloud'. Most other commercial hawthorns appear resistant.

Symptoms: Small reddish brown spots on upper and lower leaf surfaces, numerous and severe after a wet spring. Later, the tissue between leaf spots turns yellow. The area bordering the leaf lesions may remain green, creating a green island effect. Raised bumps (acervuli) appear in the centers of lesions. When spots are numerous, defoliation often occurs. Repeated annual defoliation can reduce growth and weaken trees.

Cultural control:

Rake and destroy leaves in fall.
Grow other, more resistant species of Crataegus.

Chemical control:

Begin foliar applications at budbreak and repeat at 10- to 14-day intervals until dry weather arrives.

a. Daconil Weather Stik at 1.4 pints/100 gal water. Daconil (12.5%) can be used in home gardens. 12-hr reentry.
b. Eagle 20 EW at 6 to 12 fl oz/100 gal water. 24-hr reentry.
c. Bonide Fung-onil Multi-purpose Fungicide at 2.25 teaspoons/gal water.
d. Spectracide Immunox at 1 fl oz/gal water.
e. Mancozeb-based products. 24-hr reentry.
-Fore 80 WP at 1.5 lb/100 gal water plus a spreader-sticker.
-Pentathlon DF at 1 to 2 lb/A or per 100 gal water.
-Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker.
f. Spectro 90 WDG (chlorothalonil plus thiophanate methyl) at 1 to 2 lb/100 gal water. 12-hr reentry.
g. Thiophanate-methyl-based products. 12-hr reentry.
-AllBan Flo at 10 to 14.5 fl oz/100 gal water.
-Cleary’s 3336 WP at 12 to 16 oz/100 gal water.
-Ferti-Lome Halt at 2.5 tsp/gal water is registered for home use.
-OHP 6672 4.5 F at 10 to 14.5 fl oz/100 gal water.

Tebuject is registered for tree injection. Trees are to be injected as a preventative treatment. Do not inject trees less than 2 inches in diameter or those that are suffering from various stresses.

Hawthorn leafspot. Photo from the Oregon State University Online Guide to Plant Disease Control.

Information from Bob Mulrooney, Extension Plant Pathologist, UD and the Oregon State University Online Guide to Plant Disease Control. For more information go to:

Saturday, May 16, 2009

Landscape - Lace Bugs

Start looking for lace bugs in the landscape at this time. The following is information on lace bugs, plants attacked, damage done, and controls.

Lace bug activity has begun in Delaware and a great way to minimize the damage they cause is to control first generation nymphs or the overwintered adults as they resume feeding. Hawthorn lace bugs feed on hawthorn, cotoneaster, quince, crabapple, mountain ash, and pyracantha. Azalea lace bugs tend to feed on evergreen ornamental shrubs and oak lace bugs feed on different species of oak trees. The first generation of azalea lace bugs nymphs is active from 240 561 [318 peak] GDD and the 50 peak of adults is between 2802 3418 GDD . Overwintering 50 hawthorn lace bug adults begin feeding in the spring at 196 472 [349 peak] GDD or when Lagerstroemia indica is at the leaf bud 50 break phenological stage. Oak, sycamore, and azalea lace bugs may have two to three generations a year.

Lace bugs are usually found on the underside of leaves and they suck out plant juices with piercing mouthparts. Their feeding also kills nearby cells causing yellowish flecks on the upper leaf surface which coalesce into large bronze-colored patches. High populations may damage plants enough to cause premature leaf drop. Small lacelike adults may be difficult to see; an easier method to verify the presence of this pest is the fecal matter, which appears as shiny black spots called tar or resin spots. Lace bug nymphs are not lacelike, but are spiny and usually dark brown to black.

Horticultural oil or insecticidal soap applications must contact the insects; thus spray the underside of leaves. Both of these products have low impact on the natural enemies attacking lace bugs. Heavy infestations may require the use of products such as acephate, carbaryl, cyfluthrin, imidacloprid and pyrethrin. Plants with a history of mite problems should not use imidacloprid as a treatment.

Azalea lace bug adult. Photo from Pest and Diseases Image Library,

Lace bug damage on azalea. Photo by Whitney Cranshaw, Colorado State University,

Information from Brian Kunkel, Ornamental IPM Specialist, UD

Greenhouse and Nursery - Managing High Media pH

The following is a good article on dealing with high pH media problems in greenhouses and nurseries.

High media pH can lead to yellowing and stunting of petunias, calibrachoas, and gerberas as well as many other greenhouse and nursery crops. A desirable pH range for these, and many other “acid-loving” plants, is 5.4 to 5.8. When the pH is higher, iron in the root zone is relatively unavailable to these plants. There are two actions that can be taken to gradually lower the media pH: acidify your water or use an acid fertilizer.

Acidify your water

If the alkalinity of your water is too high (greater than 150 ppm), inject an acid into the water to neutralize the alkalinity down to around 100 ppm. If you are already injecting acid, consider increasing the amount. Remember that the water’s alkalinity, not its pH, is what drives the pH of a media up or down (along with other factors). If the media pH is above 7.0, consider using more acid so that the water alkalinity is down to zero. Once the media pH returns to a desirable level, scale back on the acid. Be careful because if too much acid is added, phytotoxicity is likely.

Use an acid feed

Use a fertilizer that has an acidic reaction. Fertilizers that contain a moderate or high percentage of ammonium can drive down the pH over time (a few weeks). Some common fertilizers with a moderately acidic reaction and other desirable attributes (similar amounts of nitrogen and potassium and lower amounts of phosphorus) are 20-10-20, 21-8-18, 20-2-20, and 21-5-20.

For a quick fix, drench with iron-EDDHAIf you don’t have a few weeks to correct the media pH, one option is to add iron that is soluble at a high pH. The most effective form of iron as a drench at a high pH is iron-EDDHA, which is sold as Sequestrene 138 or Sprint 138. A suggested application rate of iron-EDDHA is 10 ounces per 100 gallons of water, which provides 45 ppm of iron. This solution should be applied as a drench with generous leaching, followed immediately by rinsing off the foliage to avoid leaf burn.

Information from "What to do if your media pH is too high" by Erik Runkle, Horticulture, in the Michigan State University Greenhouse Crop Advisory Team Alert website:

Friday, May 15, 2009

Nursery - Spacing Container Plants

The following is a short article on spacing container plants in nurseries and garden centers.

Spacing Container Plants

Proper spacing is important to produce high quality plants. Adequate exposure to sunlight is necessary for trees to photosynthesize at the maximum rate, supporting the maximum growth possible. Leaves are shed if they do not produce more food than is required to maintain them. The leaves most prone are those in heavy shade on the lower trunk. Leaves and small stems along the stem are critical to developing caliper. Caliper development is crucial to developing a strong trunk that doesn't need to be staked and for growing a plant to the desired size. In addition, plants that are too close often look great as a block but when individual plants are pulled they have one-sided or sparse canopies. During production plants should not be closely spaced for any longer than is necessary. As a general guideline no more than 3 weeks to prevent canopy problems and less, especially if rainy or humid, to avoid the disease problems. Additional benefits are ease of spraying, pruning, and training leaders.

How much space is adequate? Check your plants several times throughout the day to see the shade pattern and adjust your space accordingly. Plants intended to grow in full sun (not under a shade structure) will do best with full sun or at least 6 hours of sunlight. During the hottest part of summer some midday shade can be beneficial but that is not the type of shade created when plants are too closely spaced. Consider that 15 gallon pot-in-pot socket pots are typically spaced on 5' centers and 25 gallons at 6' centers.

Source: Spacing and Pruning Trees in Field Nurseries. UT Pub. PB 1458.

Landscape and Nursery - Powdery Mildew on Dogwood

Powdery mildew on flowering dogwood is back again. The following is more information.

Flowering dogwood trees near Townsend Hall on the University of Delaware campus were observed with powdery mildew symptoms on May 13, which is very early. Now is the time to apply a fungicide to valuable susceptible trees. Look for the white talcum-like growth on the leaves in the center of the tree or on water sprouts. When powdery mildew shows up early on dogwood I recommend that infected trees be sprayed to control this potentially debilitating disease. Homeowner labelled fungicides include, Immunox, Infuse, Bayer Advanced Tree, Shrub and Flower Disease Control, and others. I have had very good success with applications of 1% solutions of Sunspray horticultural oil, neem oil (Triact), and potassium carbonate, (Kaligreen, Remedy). Commercial applicators can use Eagle, Cleary's 3336, Spectro, Banner MAXX, Heritage, Compass and others. Apply when first signs appear and reapply every 2-3 weeks until early August. If you use horticultural oil, neem oil or potassium bicarbonate time those sprays to cover new flushes of growth during the season for the best protection.

Powdery mildew on dogwood in a nursery. Photo from the University of Kentucky,
Information from Bob Mulrooney, Extension Plant Pathologist, UD.

Thursday, May 14, 2009

Greenhouse and Landscape - Phyllosticta Leaf Spot on Impatiens

The following is information on Phyllosticta leaf spot of impatiens, a disease you may find in greenhouses and landscape plantings in Delaware.

Phyllosticta leaf spot is identified on impatiens as spots that are tan and have concentric rings within them, indicating that small spots grew and grew. At the center of the spots, you may see (with a hand lens) a scattering of round dark bodies that are spore cases (pycnidia) for the fungus. This disease is found on New Guinea impatiens and Impatiens wallerana. Very little is known about this disease on impatiens, but restricting the leaf wetness periods and using standard anti-leaf spot fungicides should be effective for control, when coupled with roguing out the plants obviously diseased. Most leaf spot-countering fungicides will help against Phyllosticta, including the thiophanate-methyls, chlorothalonil, iprodione and coppers. Keeping foliage dry is an important control tactic.

Information from "What Can Go Wrong With Impatiens (Impatiens wallerana) Leaves" by Margery Daughtrey, Cornell University

Landscape - Weed Control in Liriope Beds

The following is information on weed control in Liriope beds.

Liriope is one of the most common ground covers used in landscape plantings due to its durability and ease of care. As with all ground covers, weed management begins with planting in a weed free bed. If there are problem perennial weeds in the area to be established, two applications of glyphosate herbicide should be applied 3-4 weeks apart prior to planting. Once weeds have died, the area should then be tilled, planted and mulched.

In established Liriope beds, mulch should be replenished after mowing over the beds in late winter or early spring. Preemergence herbicides can be applied to Liriope beds in the late summer or early spring to prevent annual weeds from germinating. Materials labeled for one or more Liriope species (check labels) include include prodiamine, dithiopyr, isoxaben, pendamethalin, metolachlor, trifluralin, oryzalin, and benefin as well as combinations. For grass weed escapes in Lirope beds, fenoxaprop, clethodim, fluazifop-P-butyl, and sethoxydim are labeled for postemergence use for one or more species. Imazaquin can be used on Liriope muscari “Evergreen Giant” and “Silvery Sunproof” for control of some broadleaf and grass weeds as well as sedges and wild garlic pre and postemergence. It is strong on winter annuals and sedges. Bentazon is labeled for over the top postemergence control of certain broadleaf weeds and yellow nutsedge.

Spot treatments of gyphosate, glufosinate, or pelargonic acid can be made to weeds between liriope plants but care must be taken not to touch Lirope plants with the materials. In some cases the only option will be hand weeding.

Gordon Johnson, Extension Horticulture Agent, UD, Kent County.

Wednesday, May 13, 2009

Landscape - Birch Leafminer

The following is information on Birch Leafminer, an insect pest active at this time.

Birch Leafminer

The insect that causes the splotch mine that shows up on birch in June is a sawfly larva that feeds between the leaf surfaces. The insect has been overwintering in the soil in the pupal stage. The adults start to emerge around 190 degree days – about when redbud is in full bloom. In Delaware we are beyond this point. The adult females will oviposit in new foliage of birch trees. The damage will show up as brown leaf blotches which will be very evident in June.

Control: If your customer is tolerant of a little foliar injury then I would do nothing for this pest. The plants are not really damaged unless the infestation is excessive. If control is needed then a soil application of imidacloprid or dinotefuran would control leafminers. This application would also take care of aphids that will feed on birch this summer.

Birch leafminer damage. Photo by Brian Kunkel, University of Delaware,

Information from the TPM/IPM Weekly Report for Arborists, Landscape Managers & Nursery Managers from the University of Maryland Cooperative Extension

Tuesday, May 12, 2009

Landscape - European Pine Sawfly

The following is information on the European Pin Sawfly.

European pine sawfly should be active at this time. The European pine sawfly is a pest of mugo Japanese black, red, and scotch pines. Larvae are dark green with a black head and closely align themselves along the needles so are very difficult to detect. European pine sawfly feed on last year's growth. They can defoliate needles rapidly as they mature. Hosts look sickly, growth is reduced and they have a "bottle brush" or "poodle tail" appearance due to removal of needles behind the new season's growth especially in the early instars. Small larvae feed on the surface of needles, causing them to turn brown and wilt. Larger larvae eat entire needles but do not feed on new growth. They usually occur in small clusters, if enough are present, they can consume most of the needles on the plant. Mature larvae will drop to the ground and pupate in brown paper-like cocoons that are blunt at each end. There is one generation each year. Plan to scout now--it is hard to see the 1st and 2nd instar larvae but they are easier to control and early control can reduce host damage. Control options include a host of materials such as sevin and the pyrethroid insecticides. Spot spraying works if you only have a few trees, but scout carefully to detect each colony. Remember sawflies are not caterpillars (although they resemble them) so B.t. will not provide control. Unfortunately, infestations often are not noticed until most of the larval feeding is finished.

European Pine Sawfly. Photo by Steven Katovich, USDA Forest Service,

Information from the University of Delaware and University of Kentucky.

Landscape and Greenhouse - Slug Season

This past week has been ideal for slugs. The following is a good article on the subject.

Slugs are almost universal pests in vegetable gardens, shade gardens, and shaded landscape areas. Their soft, unsegmented bodies, exude a slimy, mucous-like substance that leaves characteristically shiny trails as they move from hiding to feeding spots. Once on a plant, slugs use their rasping mouthparts to scrape away at the leaf tissue. Immature slugs tend to feed on surface tissue while larger individuals eat rounded holes completely through the leaf. Slugs usually feed at night and hide in moist, dark areas during the day. They may eat several times their own body weight each night so serious damage can occur in a very short time. Disappearance of seedlings or newly set transplants is often blamed on cutworms but slime trails are a key clue in incriminating slugs.

Slugs prefer temperatures in the low 60's but can lay eggs and develop normally down to about 40 F. They can survive slight freezing but tend to hide in cracks and crevices when cold weather threatens them. Usually, warm temperatures are the concern. Slugs try to avoid temperatures above 70. Rising temperatures spur them to crawl down to their hiding places to rest and absorb water through their skin. As temperatures start to fall, slugs actively begin foraging, again. Slugs are so sensitive to temperature that they can detect changes as gradual as 2 F per hour!

Slugs are very sensitive to air currents. Gentle breezes cause them to turn toward the source and extend their antennae. As the breeze becomes stronger, they turn away from the source, evidently to escape dehydration. Improved ventilation of a trouble spot may make it drafty and force slugs to move. Good sanitation, including removal of extraneous vegetation, excess mulch, or other materials that might offer food or shelter, will aid in the overall control program.

Slug baits containing metaldehyde or iron phosphate may be used for control. Best results are usually obtained if the baits are applied in the afternoon watering is delayed until the next day. Slugs feed intermittently so several applications of bait may be needed for control. Baits may attract slugs from up to 3 feet away. Beer-baited traps will lure in many slugs but is it important to check and empty the traps regularly. Pieces of wood, cardboard, or other objects can be placed on the ground in infested areas to provide hiding sites for foraging slugs. Regular visits to the slug accumulators will allow you to collect and discard the resting slugs.

Barriers can provide some relief if the slugs are moving in from outside the area that is being protected. Wood ash or fine lime can be used but both lose their effectiveness when wet and too much wood ash is not good for the soil. Slugs do not like to cross copper. A copper barrier tape (about 1" wide) can be used along borders or around the legs of greenhouse tables to deter slugs. There are wider copper barriers that can be set in the soil as fences but the expense makes this most suitable for small areas.

Information from Lee Townsend, University of Kentucky.

Monday, May 11, 2009

Landscape - Ants, Honeydew Producing Insects, and Insect Predators

The following is a good article on honeydew producing insects, the ants that protect them, and the predators that feed on these insects and the interactions of all three.

ANTS & HONEYDEW PRODUCERS vs. PREDATORS: Various pests such as aphids, soft scales, mealybugs, and whiteflies are plant feeders that insert their piercing-sucking mouthparts into vascular tissue (phloem) to remove plant sap from leaves or stems. Since phloem sap is not nutrient rich in proteins, plant pests must withdraw large quantities to maintain growth and reproduction. As a result, these insects must also expel copious amounts of unwanted waste called honeydew. The predigested honeydew still contains a lot of sugary carbohydrates and is valued by ants, wasps, bees and other vespids as a food source. The honeydew is often easily observed as a clear, shiny and sticky material on foliage. The honeydew usually darkens over time as a black sooty mold fungus grows on the liquid droppings.

Numerous predators and parasitoids including ladybeetles, lacewings, flower flies and wasp parasites typically attack and consume honeydew-producing pests. Carpenter ants and other colony ant species have waged vicious wars for “eons” against predators of honeydew producers. Certain ant species will expend a lot of energy and effort to protect honeydew producers and prevent effective biological control. As a result, to help restore the predator vs. prey balance in the landscape, it may be necessary for the pest manager to intervene and seek out ant colony locations to apply controls.

Ant protecting aphid colony. Photographer - Kent Loeffler © Cornell University, Dept. of Plant Pathology, 2005

Information from Steven K. Rettke, Ornamental IPM Program Associate, Rutgers University

Sunday, May 10, 2009

Landscape - Spot Anthracnose on Dogwood.

The following is information on spot anthracnose of Dogwood. You may see this disease on dogwoods in flower at this time.

SPOT ANTHRACNOSE on the petals (bracts) of flowering dogwood was identified on a sample from Sussex County. This fungus produces very small (1/8 in.) spots with purple red borders. Spots can be numerous and during wet weather spread to leaves. This disease is mostly cosmetic but can be controlled with Daconil (chlorothalonil), myclobutanil (Eagle, Immunox), Heritage, Cleary's 3336 (thiophanate-methyl) and other labeled fungicides.

Spot anthracnose on dogwood flower petals. Photo from the Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services,

Information from Bob Mulrooney, Extension Plant Pathologist, UD

Saturday, May 9, 2009

Landscape - Cedar-Quince Rust

The following is information on Cedar Quince Rust, a common disease in Delaware that can be observed at this time.

CEDAR-QUINCE RUST has been observed on ground cover juniper in Delaware at this time. This rust fungus produces spindle shaped orange-red gelatinous swelling in the infected twigs but not a round gall. They can be pruned out or left alone. They will not hurt the juniper but produce spores that can cause symptoms on serviceberry and hawthorn. Cedar-quince rust on those hosts infects the fruit and twigs causing malformations with tiny white finger-like projections on the fruit surface.

Fruiting Bodies of cedar quince rust on juniper. Photo by Edward L. Barnard, Florida Department of Agriculture and Consumer Services,

Aecial formation on Hawthorn fruit from Cedar-Quince rust. Photo by Ethel Dutky, University of Maryland,

Information from Bob Mulrooney, Extension Plant Pathologist, UD.

Friday, May 8, 2009

Landscape - Elongate Hemlock Scale

The following is information on the Elongate Hemlock Scale, a difficult to control pest in this area.


In our area, no scale insect is more frustrating than elongate hemlock scale (EHS). A major threat to conifers, damage from scale feeding causes eventual needle drop and branch dieback. There is no honeydew produced.

Breaking all the rules this scale has no set generational times in our climate and overwinters in the egg, nymph, or adult stage. Development progresses with warm weather in the early spring. Brown, 1.0 mm long oval shells house the females; males are slightly shorter, white and oystershell-shaped. Eggs hatch within the female shell cover and crawl out through a one-way flap at its rear. The orange crawlers quickly settle, molt, and develop into males or females. Adult females are completely protected within their hard shell; only their mouthparts protrude through its bottom to feed. These shells remain on the plant after the females have died, so scouting to ensure that infestations are active is very important.

Biological control does not provide meaningful suppression of EHS. The use of growing degree days or plant phenologies to predict crawler emergence patterns is futile. Several different researchers investigated EHS management, and have come up with variable results. Studies in Central PA favored spring applications of Tristar (acetamprid), a foliar-applied neonicotinoid. Safari (dinotefuran) drenches showed promise in studies by the Univ. of CT and would appear to be the most mobile neonicotinoid compound best suited for armored scale control. The Univ. of MD saw suppression of EHS using spring applications of horticultural oil, Merit (imidacloprid) soil drenches, and Distance (pyriproxifen). Remember that some neonicotinoid applications may lead to mite outbreaks. Our work at Longwood had great results with October applications of 2% v:v horticultural oil, while Merit soil drenches and Distance sprays were ineffective.

Information from Casey Sclar, IPM Coordinator, Longwood Gardens

Landscape - Elongate Hemlock Scale Pictures

The following are pictures of the Elongate Hemlock Scale.

Heavy Elongate Hemlock Scale infestation. Photo by Eric R. Day, Virginia Polytechnic Institute and State University,

Elongate Hemlock Scale. Photo by Eric R. Day, Virginia Polytechnic Institute and State University,

Thursday, May 7, 2009

Landscape and Nursery - Cedar-Apple Rust

The follwing is information and pictures of cedar apple rust on eastern red cedar.


The round woody galls on twigs and branches of eastern red cedar have been observed in Delaware. During wet weather these woody galls produce orange-red gelatinous spore horns with spores that infect apple and crabapple leaves. The best control on cedar is to prune out the galls to the extent possible.

Cedar apple rust gall on Eastern red cedar. Photo by Daniel H. Brown, USDA Forest Service,

Telial-stage horns of the cedar-apple rust pathogen. Photo by Joseph O'Brien, USDA Forest Service,

Information from Bob Mulrooney, Extension Plant Pathologist, UD.

Greenhouse - Ethylene Injury from Heaters

The following is an article on ethylene injury to plants from heaters that are not functioning properly.

Ethylene (C2H4) occurs in trace amounts in gasoline and natural gas and is produced when these substances are burned. It also is present in wood and tobacco smoke. Ethylene is a plant hormone produced by plants during their growth and development. However, ethyl­ene produced through defective heating equipment can be detrimental to greenhouse crops, because it is pro­duced in greater quantities. Ethylene pollution influences the activities of plant hormones and growth regulators, which affect developing tissues and normal organ development, many times without causing leaf-tissue damage. Injury to broad-leaf plants occurs as a downward curling of the leaves and shoots (epinasty), followed by a stunting of growth. Other symptoms of excess ethylene exposure include the abscission of flower buds, petals or leaves; water-soaking of older leaves; chlorosis; and wilting of flowers. Crops vary in their sensitivity and response to ethylene toxicity. The degree to which a crop is affected depends on the variety, temperature, ethylene concentration, and the duration of exposure. High temperatures and high light levels will increase the severity of ethylene damage. Symptoms of ethylene damage can be very subtle, especially if there are no plants grown in clean air avail­able for comparison.

Proper heating system installation and maintenance are the best ways to prevent problems. A maintenance plan should include cleaning the unit heater and fuel orifice twice a year. Propane flames should have a small yellow tip when properly adjusted and natural gas flames should be a soft blue with a well-defined inner cone. To ensure proper combustion, heater units should have a clean air intake and should be vented to the outside with a stack that has the cap above the ridge of the house, which keeps exhaust gas from being drawn back into the greenhouse through the ventilation system.

Information from Jerry Brust, IPM Vegetable Specialist, University of Maryland