Landscape - Phytophthora Root and Crown Rot

Phytophthora root and crown rots are very common in landscapes this year. The following is more information.

Phytophthora root, crown, and collar rots are common and destructive diseases of trees throughout the world. Trees declining from Phytophthora root and crown rots are frequently diagnosed as suffering from"wet feet" (mistakenly assumed to be root asphyxiation or "drowning"), and sometimes are confused with those suffering from winter injury.

Diseased trees are most likely to be found in heavy, wet soils or areas where water collects or is slow to drain . Above-ground symptoms are variable among tree species and locations, but include poor growth with sparse off-color foliage, wilt, and collapse. Infected trees may decline over more than one season, and gradually-declining trees often show abnormal or premature coloration of the foliage in early autumn. In other cases, previously-healthy trees may suddenly collapse and die shortly after resuming growth in the spring, especially if the previous autumn was excessively wet. Similarly, previously-healthy trees may suddenly collapse during the latter part of the growing season following a very wet spring.

A diagnostic reddish brown discoloration of the inner bark can be seen by removing several inches of soil around the base of declining trees and cutting away the outer bark layer on the exposed crowns; often, it's possible to see a sharp contrast between the infected and healthy (white) crown tissues. The inner bark of larger infected roots often shows a similar discoloration. These symptoms distinguish Phytophthora root and crown rots from other common causes of decline and collapse.


Red coloration under the bark on a Phytophthora infected tree.

Information adapted from Kearneysville KTFREC - Fruit Disease Focus - Phytophthora Root, Crown, and Collar Rots, West Virginia University

Landscape - Black Spot on Roses

The following is a good article on black spot on roses from Rutgers University

Black spot, caused by the fungus Diplocarpon rosae (the imperfect stage of this fungus is Marssonina rosae) is the most commonly recognized disease of roses. The disease can cause damage all season long in temperate climates where leaf tissue remains wet for extended periods. Plants chronically affected by black spot become unthrifty and are prone to winter injury.

Black spot is most troublesome early in the growing season. In the spring, fungal spores are produced and disseminated from lesions on canes and leaves infected the previous year. These spores infect young leaves (6- to 14-days old) when a 7-hour period of continuous leaf wetness occurs. Disease development is greatest at temperatures of 75 to 85oF with greater than 85% relative humidity. Symptoms appear as black leaf spots (0.1- to 0.5-inch) on the upper leaf surface within 3 to 16 days following infection. These spots have feathery edges and are accompanied by yellow “halos” of leaf tissue. Spores produced in these spots continue to infect newly expanding leaves and canes throughout the summer. Black spots may also form on the lower leaf surface about a month following infection. On first-year canes, irregular, raised, red-purple blotches appear that become blackened and blistered. Diplocarpon produces a toxin that causes affected leaves to turn yellow and defoliate prematurely. Indeed, heavily infected plants lose much of their carbohydrate reserves, and as mentioned above, grow poorly as a result and become more susceptible to winter injury and other stresses.

Since the fungus overwinters on diseased leaves and canes, rake old leaves and prune diseased and damaged canes before spring. Avoid overhead watering and excessive shade, and when planting, space plants to avoid excessive humidity. Disease management before the growing season begins is critical; control is difficult once black spot is established in a planting. Resistance to black spot varies among the different types of roses. Floribunda, shrub, and climbing roses tend to be more tolerant to this disease, whereas hybrid tea, grandiflora, and miniature roses are more susceptible.

For best results, spray fungicides after budbreak (mid-May) and repeat at intervals specified on the label. Compounds labeled for black spot control include Armada, Bacillus subtilis, calcium polysulfide (dormant) captan, chlorothalonil, Concert (outdoors only), ConSyst, copper (Badge, hydroxide, metallic, salts, sulfate), ferbam, Junction, mancozeb, maneb, myclobutanil, neem oil, paraffinic oil, propiconazole (outdoor use only), Spectro, Sporan, sulfur (dusting, elemental, flowable, wettable), SysStar, thiophanate-methyl, trifloxystrobin, ziram, and Zyban. Use a surfactant to enhance fungicide coverage if this practice is listed on the fungicide label, and rotate classes of chemicals to reduce the likelihood that fungal resistance to compounds will develop. Pay close attention to spray practices during wet periods, especially when caring for roses that are highly susceptible roses to this disease.

Black spot on rose leaves with feathery purple/black spots having no definite margin. Photo by Paul Bachi, University of Kentucky Research & Education Center, Bugwood.org

Information from Ann B. Gould, Ph.D., Specialist in Plant Pathology, Rutgers University. See the full article including other rose diseases at http://njaes.rutgers.edu/pubs/plantandpestadvisory/2009/ln082009.pdf

Nursery - Forage Radish Cover Crop For Improving Growth of Trees in Nurseries

The following is a good article on using forage radish as a cover crop in nurseries from the University of Maryland.

Forage Radish: For improving growth of trees in nurseries

Forage radish, also called tillage radishes, is from Daikon radish, which is a traditional Japanese radish. Daikon radishes have been grown for human consumption for a very long time but are being used more and more for natural weed control. The tillage radish is extremely competitive and will outgrow most other weeds. The seed rate is 1 lb per 4000 ft2 and is seeded in September or October. The seed germinates very quickly and light green foliage will expand to cover about 12 – 18” of soil surface. The radish that is produced is huge. It is several inches in diameter and will grow several feet into the soil profile. I (Stanton) have been playing with forage radish at my farm for the last two years. I plant it at the base of fruit trees and blueberry plants where I usually have problems controlling weeds. So far it is working fairly well. It competes with most weeds except Canadian thistle which still manages to thrive even in thick plant of forage radish. In December the plants die down and the root will die over the winter. As the large root dies it leaves an excellent column of organic material in the soil and adds nitrogen back to the soil as it decomposes. If you attend the October 2 Sustainable Nursery Field Day at D.R. Snell Nursery, Inc. you can learn more about the trials the University of Maryland is conducting on the tillage radish in nursery plantings. Do a web search for Daikon radish or tillage radish and you will find seed sources. I bought my seed from Groff seed in Holtwood, PA


Information from Stanton Gill, Extension Specialist, IPM for Nursery, Greenhouse and Managed Landscapes, University of Maryland

Greenhouse - Scouting for Insects and Mites

The following is a good article on scouting for insects and mites in the greenhouse from Rutgers University.

Scouting Options and Methods

There are essentially three options available when scouting your greenhouse crops for insect/mite pests. 1- No scouting performed with pesticides being applied on a calendar timetable. 2- Simply scouting for pest occurrence with pesticides applied when presence is observed. 3- Scouting crop and making pesticide application decisions based on pest counts and action thresholds. The third option is part of an integrated pest management (IPM) approach that has been promoted throughout the green industry the past few decades. Greenhouse pest populations are measured by trapping or direct plant inspection and both involve determining pest numbers.

Counting pests and using action thresholds requires time and knowledge, but results in less pesticide use and can improve plant quality. It is important to remember that trapping (e.g. yellow or blue sticky cards) improves the efficiency when scouting your greenhouse, but does not replace the actual inspection of individual crop plants. This is particularly the case when scouting for aphids and mites. Benefits of Counting Pests The scouting and counting of insects/mites helps to detect when they are first present. Therefore treatments are made before large populations build up, but not before it becomes necessary.

Tracking pest numbers over a period of time allows for the use of action thresholds, or when pest density levels threaten crop salability and economic loss. When pest densities and damage are low, it is not efficient to spend 95% of your time controlling the last 5% of the pest.

The use of biological controls (e.g., beneficial insect/mite augmentation) is most effective when pest numbers are low, and scouting helps to know their density and location so that natural enemy release can be targeted. When using biological controls, pest count estimates are required in order to determine how many beneficials to release per target management area. Finally, instead of guessing, scouting and estimating pest counts makes it possible to evaluate the effectiveness of pest control interventions after they are applied.

Using Sticky Cards to Trap Adults

Generally one (1) sticky card is placed within each 1,000 sq. ft. area and also near greenhouse vent and door openings. Ideally the card should be placed at the level of the crop canopy or slightly below to effectively trap many of the major adult pests found in the greenhouse. Each of the sticky cards should be examined at least once per week. Using stakes and double clothespins to support the traps is effective. Also, be certain to number and date each trap card to a specific location. When pest counts are low it is acceptable to re-use the trap card for additional weeks.

Yellow sticky card

Information from "Pest Counts and Action Thresholds in the Greenhouse" by Steven K. Rettke, Ornamental IPM Program Associate, Rutgers University in the August 20, 2009 edition of the Plant & Pest Advisory, Landscape, Nursery & Turf Edition; A Rutgers Cooperative Extension Publication

Greenhouse - Monitoring for Spider Mites

The following is information on scouting and monitoring for spider mites in the greenhouse.

Monitoring for Two Spotted Spider Mites

Obviously, since spider mites are unable to fly during any life stage they will not be observed on sticky traps. Hence, when scouting for mites it is necessary to inspect individual plants within the crop. Looking for symptoms and signs such as leaf stippling and webbing help to indicate which plants to inspect more closely with a 15x magnifying hand-lens.

Some specific thresholds of two-spotted spider mites on ivy geraniums have been determined through research. It was shown that action thresholds of 7 mites per leaf are reached on plants greater than 5 weeks in production. Alternatively, action thresholds of only 2 mites per leaf are reached on plants less than 5 weeks in production. Estimated pest mite counts are required when releasing beneficial predatory mites (e.g., Phytoseiulus persimilis). Release one (1) predatory mite for every 4 to 10 twospotted mites counted

Two spotted spider mites. Photo by Frank Peairs, Colorado State University, Bugwood.org


Information from "Pest Counts and Action Thresholds in the Greenhouse" by Steven K. Rettke, Ornamental IPM Program Associate, Rutgers University in the August 20, 2009 edition of the Plant & Pest Advisory, Landscape, Nursery & Turf Edition; A Rutgers Cooperative Extension Publication

Greenhouse - Monitoring for Aphids

The following is information on scouting and monitoring for aphids in the greenhouse.

Monitoring Aphids

It is probably not possible to use action thresholds to manage aphid populations. If winged aphids are found on sticky cards, then populations are usually already high. As a result, plant inspections are the only reliable way to scout for aphids. To simplify scouting efforts attempt to group aphid-susceptible plant species together. (e.g., chrysanthemum, sunflower, gazania, portulaca, pepper, and others).

The distribution pattern of aphids in the greenhouse is typically spotty, with clumped populations (e.g., Melon aphids). On the other hand, Green Peach aphid species have a greater tendency to sometimes move throughout the crop. This behavior forces scouting to be more widespread. Look for plant symptoms such as distorted, discolored terminal tissue and for various aphid signs such as honeydew, sooty mold, cast skins and the actual aphids themselves.

Aphid damage to pepper plant. Photo from the University of Connecticut.

Information from "Pest Counts and Action Thresholds in the Greenhouse" by Steven K. Rettke, Ornamental IPM Program Associate, Rutgers University in the August 20, 2009 edition of the Plant & Pest Advisory, Landscape, Nursery & Turf Edition; A Rutgers Cooperative Extension Publication

Landscape - Fewer Japanese Beetles This Year

There were few Japanese beetles this year in most of Delaware. The following are some reasons why.

Many people in Delaware were very happy about the reduced numbers of Japanese beetles that they saw this summer. So what did happen? Most likely, we are seeing fewer Japanese beetles in areas where the soil was dry last year in July-August. Remember that we had a very dry period (5 weeks without rain) in 2008 during mid summer. Japanese beetle grubs do not survive well in dry soils. If it was very dry last July and August, the adult beetles would try to avoid laying eggs in the dry turf and soil, and if it was moist when they layed eggs, then became very dry later, the grubs did not survive. If most turf areas were dry last year, then few beetles would have emerged this summer.

Another thing that happened this summer is the cool weather during July. At cool temperatures, beetles are not as active as during warm temperatures. So, even if we had the same number of beetles, you would see less activity during a cool summer.

Because Japanese beetle grubs survive best in moist soil, it should mean that they will survive well this summer and fall, so more beetles will probably emerge next year than what we saw this summer.

Adapted for Delaware from an article by Dave Smitley in the Michigan Landscape Crop Advisory Team Alert website http://ipmnews.msu.edu/landscape/

Greenhouse - Monitoring for White Flies

The following is information on scouting and monitoring for whiteflies in the greenhouse.

Monitoring Whiteflies

Although the use of yellow sticky traps can improve scouting efficiency, when scouting for whitefly it is especially important to also inspect crop foliage. It is critical to start scouting early so whitefly populations are not allowed to build-up. High populations of whiteflies are one of the more difficult pests to suppress in the greenhouse.

Typically on infested plant foliage a consistent top to bottom distribution of whitefly growth stages can be observed. For example, adults will usually be found on the undersides of the upper canopy leaves. When inspecting for eggs, concentrate on the undersides of lower adjacent leaves just below the upper canopy. Smaller scales (1st /2nd instar nymphs) are then found on the undersides of foliage below the leaves containing eggs. Larger scales (3rd/4th instar nymphs) are found on the undersides of the next level of lower/older foliage. Finally, whitefly adults will be emerging from pupae found on the lowest/ oldest leaves closest to the soil media.

Similar to aphids, whiteflies often produce sticky honeydew with the corresponding growth of the black sooty mold fungus. If this becomes readily visible, then it is certain that high whitefly infestations are already present within the crop.

When using biological controls (e.g., Encarsia formosa (parasitic wasps)) it is necessary to estimate counts of whitefly scales (nymphs) within a pest management unit in order to determine how many beneficials to release. It has been determined a release ratio of 30:1 (scale to wasp) will prevent a population build-up of whiteflies. An even smaller release ratio of 150:1 (scale to wasp) will only be required if most of the scale nymph counts are early 1st/2nd instars. When using any kind of biological control tactic, it is crucial to start releases early before high pest levels are reached.

Greenhouse whitefly nymphs. Photo by David Riley, University of Georgia, Bugwood.org

Information from "Pest Counts and Action Thresholds in the Greenhouse" by Steven K. Rettke, Ornamental IPM Program Associate, Rutgers University in the August 20, 2009 edition of the Plant & Pest Advisory, Landscape, Nursery & Turf Edition; A Rutgers Cooperative Extension Publication

Greenhouse and Nursery - Calibrating Your Fertilizer Injector by the EC Method

The following is information on how to calibrate your fertilizer injector by the electrical conductivity method.

Electrical Conductivity Method

Items Needed:

1 Electrical Conductivity Meter
1 Standard Solution for Meter Calibration
1 Plastic Measuring Cup

Calibrate the EC Meter according to the directions included with the meter before use.

1) Run the irrigation water for at least 5 minutes without any injected fertilizer, this can be done before the fertilizer injector, or after the injector with the injector turned off. Collect a sample of this in the plastic measuring cup. Using the calibrated meter, take the EC reading from this sample.

2) Collect a sample of fertilizer solution at the output end of the hose after allowing the injector to run for at least 5 minutes in the cleaned and dried plastic measuring cup. Subtract the EC reading for the clear water from the EC reading for the fertilizer solution.

Note this number: _____ = EC of the Fertilizer Solution

Many fertilizer companies list the Electrical Conductivity for various dilutions on the bag or publish this information in literature available from the manufacturer. Compare your EC reading of the Fertilizer Solution with that provided by the manufacturer of the material.

Information by Chuck Schuster int the September 4, 2009 edition of the Greenhouse TPM/IPM Bi-Weekly Report from the University of Maryland Cooperative Extension Central Maryland Research and Education Center

Greenhouse - Monitoring for Fungus Gnats

The following is information on scouting and monitoring for fungus gnats in the greenhouse from Rutgers University.

Monitoring for Fungus Gnats

When using yellow sticky traps to capture adult fungus gnats it is most effective to place traps horizontally (flat) near the root medium. Sticky traps placed in this position typically increases catch by 50% over traps set-up in the traditional vertical position at canopy level. Adult fungus gnats are weak flyers and generally will not be found in high numbers around the tops of crop canopies. Yellow traps should also be placed under benches if the floor is not cement.

Potato disks or wedges placed within the medium to attract fungus gnat larvae can determine density counts. The disks are typically 1 to 2 inches in diameter and are pressed ½ inch into the root medium. The wedges (French fry shape) are approximately ½ inch square and 1.5 to 2 inches long. The disks are best used in propagation areas while the wedges are best used with more established, deeper-rooted crops. Place the disks every 100 sq. ft. in propagation areas and the wedges every 1000 sq. ft. in production areas. Count fungus gnat larvae feeding on potato 48 hours after placement in media. It has been shown that after 72 hours the potato pieces may dry-out and lose their drawing capabilities. Or worse yet, the pieces may begin to rot, promoting a breeding ground for the larvae.

Some action thresholds have been determined for fungus gnat larvae when using the potato disks. Within propagation areas as few as 3-5 larvae per disk (after 48 hours) can cause significant damage to the small, shallow root systems. Alternatively, when using the potato wedges in a 6-inch pot, it may require as many as 15-20 larvae per disk (after 48 hours) before any meaningful root damage occurs.

Fungus gnat larvae. Photo by Whitney Cranshaw, Colorado State University, Bugwood.org

Information from "Pest Counts and Action Thresholds in the Greenhouse" by Steven K. Rettke, Ornamental IPM Program Associate, Rutgers University in the August 20, 2009 edition of the Plant & Pest Advisory, Landscape, Nursery & Turf Edition; A Rutgers Cooperative Extension Publication

Landscape - Iris Borers Lay Eggs in Late Summer

Iris borer moths lay eggs in the late summer. The following is more information on this pest.

Most of the time, the evidence of iris borer damage to rhizomes is discovered when people dig the rhizomes to transplant them during the summer. The iris borer is a caterpillar in the same family as the corn earworm and cabbage looper. The moths emerge in late summer to mate and lay eggs on the oldest, roughest, dead and bleached out iris leaves or on plants nearby. A single female may lay more than 1,000 eggs, usually in crevices or in folds of the leaves. The eggs hatch the following spring. The tiny caterpillars first feed on the new foliage and sometimes cause the margins of the leaves to be ragged. The holes caused by the young caterpillars bleed causing deposits of sap on the leaves. The caterpillars then mine in the leaves for a while before working downward toward the rhizomes. Narrow, watersoaked slits appear where the external feeding and mining have injured the leaves. As the caterpillars grow, they excrete slimy frass in which grow bacteria and fungi causing an unpleasant odor. The caterpillars are about half grown by the time they reach the rhizome. There they feed on the edge or on the underside of the rhizome sometimes boring right in. Often a single caterpillar may completely devour the insides of a rhizome.

To control the iris borer, it is important to remove all old iris leaves and other plant rubbish from the beds in fall or early spring before new growth emerges. If the borers are discovered later in the spring, it may be possible to crush the caterpillars with the thumb and finger inside the leaf. Imidacloprid (Merit) is a systemic and effective. Orthene is another product. Either could be applied in the spring and would be taken up into the plant reasonably quickly. Studies at the University of Maryland show that entomomopathogenic nematodes, Steinernema carpocapsae and Heterorhabditis bacteriophora, were as effective as chemicals against iris borer when applied correctly. For more information, see the Purdue University link at http://www.entm.purdue.edu/Entomology/research/cs/mg/mg.html

Pink iris borer caterpillar is exposed when heavily damaged leaf is split. Photo from Purdue University.

Information from Steve Bambara, Extension Entomologist, in the September 4, 2009 edition of the North Carolina Pest News http://ipm.ncsu.edu/current_ipm/pest_news.html

Greenhouse - Monitoring for Western Flower Thrips

The following is information on monitoring for western flower thrips in the greenhouse.

Western Flower Thrips

There are no universally accepted thresholds for the western flower thrips (WFT) because of numerous variables that cause the threshold number to change. A general guideline to start with might be 15 thrips per yellow sticky card per week per 1000 sq. ft. This arbitrary number is only a suggested starting point and it may often be necessary to refine your own action thresholds with experience.

If releasing predatory mites for biological controls it may be necessary to begin when as few as 2 thrips/ysc/ wk/1000sqft are observed. Plants that are sensitive to thrips damage such as African violet and streptocarpus crops may have a threshold of less than 10 adult thrips captured on sticky traps per week per 1000 sq. ft. Alternatively, moderately sensitive plants such as impatiens, rose, gerbera, mum, and gloxinia crops may have action thresholds ranging as high as between 18 to 30 thrips/ trap/wk/1000sqft. (If tospoviruses (INSV or TSSV) are present within a crop, then thrips thresholds are essentially one (1)). A poinsettia crop has a low sensitivity to thrips damage and can have an action threshold of 40 or more adults captured per trap/wk/1000sqft.

When these various threshold guidelines are reached it should be a signal to begin examining individual crop plants more closely, especially those plants closest to the sticky traps. However, the distribution pattern of the Western Flower Thrips in the greenhouse is random. Therefore, the thrips could potentially be found anywhere throughout the greenhouse. Some methods to scout for thrips on plants include the following: 1- Tapping the plant (especially flowers) over a piece of white paper to dislodge the thrips. 2- Exhaling carbon dioxide on the flowers in order to agitate the thrips and coerce them to leave their cryptic hiding places. 3- Pullingback and closely examining the nectar producing flower organs with a hand lens to detect thrips presence.

Western flower thrips adult and nymph. Photo by Jack T. Reed, Mississippi State University, Bugwood.org

Information from "Pest Counts and Action Thresholds in the Greenhouse" by Steven K. Rettke, Ornamental IPM Program Associate, Rutgers University in the August 20, 2009 edition of the Plant & Pest Advisory, Landscape, Nursery & Turf Edition; A Rutgers Cooperative Extension Publication

Landscape - Watch for Redheaded Pine Sawfly

Redheaded pine sawfly is now active on pines in the region. Watch for this pest that can cause significant damage in a small period of time.

Redheaded Pine Sawfly

We have received several reports of redheaded pine sawfly activity this week. The larvae feed gregariously. This group feeding of larvae can defoliate whole sections of a pine very rapidly in late August to early September.

Physical control: Prune off the tip growth while the larvae are small.

Chemical control: Horticultural oil sprayed onto the larvae will give control. Neem products can also be used to control early instar larvae. Spinosad (Conserve) will also give control.

Redheaded pine sawfly. Photo by Herbert A. "Joe" Pase III, Texas Forest Service, Bugwood.org

Information from the September 4, 2009 edition of the TPM/IPM Weekly Report for Arborists, Landscape Managers & Nursery Managers from the University of Maryland Cooperative Extension http://www.ipmnet.umd.edu/09Sep04L.pdf

Greenhouse - Eriophyid Mites

Eriophyid mites can cause distortions in flowers and other plant parts. The following is information on this pest of greenhouses and nurseries.

Eriophyid mites are extremely tiny (0.3 mm in length), microscopic, spindle-shaped mites with elongated bodies. They resemble sausages with the head and legs located on one end of the body. Eriophyid mites only have 4 legs, which is a unique characteristic among mites. All other mites have 8 legs as adults.

These mites are a specialized group of plant feeders. In general, many eriophyid mites feed on a few closely related species or genera of plants. Eriophyid mites feed deep within the plant tissues sucking out plant juices with their stylet-like mouthparts and transferring a substance, which causes deformation of plant growth. Eriophyid mites live and reproduce within the folds of plant tissues. The eggs are spherical and generally laid in groups. They hatch in less than two weeks into young mites that may take approximately two weeks to a month to mature into adults. Several generations may occur throughout the growing season.

Eriophyid mites can easily come in on plant material from a supplier. If you are a grower examine your plants for eriophyid mites in September and make sure you are not selling customers infested plants. Once damage is evident, it is too late because the mites are already established within the plant. The number of miticides for controlling eriophyid mites is limited. Pest control materials with translaminar properties are your best choices for "managing" eriophyid mites. These would include abamectin (Avid) and chlorfenapyr (Pylon) which can be used in greenhouses only. Additional pest control materials that may work on eriophyid mites, if you can make contact, are pyridaben (Sanmite), fenpyroximate (Akari), and endosulfan (Thiodan).



Reprinted in part from the September 4, 2009 edition of the Greenhouse TPM/IPM Bi-Weekly Report from the University of Maryland Cooperative Extension Central Maryland Research and Education Center http://www.ipmnet.umd.edu/09Sep04G.pdf

Landscape - Current Pests

The following are some current pest problems in Delaware landscapes.

Septoria leafspot is one of several common diseases showing up now on flowering dogwood (Cornus florida) and silky dogwood (Cornus amomum). Some trees have numerous small angular spots on the lower branches that look like small dogwood anthracnose spots. It is too late for any chemical control.

This time of year we often see an increase of anthracnose on oak, maple and walnut. On oak and maple, look for large brown spots that follow the veins and some round spots as well. This late in the season no control is necessary. On walnut, the spots are irregular in shape, numerous and can cause premature defoliation. Again it is too late in the season for any control and the fungus does little to harm the health of the trees.

Puss caterpillars and other stinging caterpillars are actively feeding. Puss caterpillars have been found on Ilex and Acer.

Ground nesting wasps, yellowjackets, and hornets are active and becoming more of a nuisance as we approach fall.

Slime molds have been appearing on lawns especially after recent rains. Slime molds produce a gray growth over the blades of turf that give it a dark appearance from a distance. What you see is the reproductive stage of this primitive fungus. It is not harmful to turf and can be removed by cutting the grass. These are related to the slime molds that appear in mulched beds as white, pinkish red, and yellow blobs often referred to as the “dog vomit fungus”.

Information from the current issue of the Ornamentals Hotline newsletter from the University of Delaware Cooperative Extension.

Landscape - Managing Cool Season Mites

The following is information on managing cool season mites in the landscape. These pests are now active in Delaware.

Cool Season Mites.

This year has been unusually cool, so cool season mites may become active sooner than previous years. Cool season mites such as spruce spider mites and southern red mites become more active as temperature are consistently in the 60's and 70's. Shake a branch or small portion of the plant against a clipboard with a white sheet of paper to monitor mite populations. Mites will begin to move a few moments after shaking and will appear as dots the size of periods. Predatory mites usually move quicker than herbivorous mites and a hand lens will be helpful to recognize the pests. Predatory mites and small lady beetles are common predators of pest mites. Miticides available for controlling these mites include: hexythiazox (Hexygon, Savy), bifenazate (Floramite), abamectin (Avid) and others. Research has shown bifenthrin (Talstar) to cause mite resurgences because it also kills many of the beneficial arthropods helping to keep populations low.

Information from Brian Kunkel, Ornamental IPM Specialist, UD

Landscape - Spruce Spider Mites

Spruce spider mites can build up during cooler weather in late summer. The following is more information.

Spruce spider mites feed on fir, arborvitae, spruce, and other conifers. This mite feeds on older foliage first and damaged foliage has a yellow to bronze coloration. Spruce spider mites begin to feed about 2301- 3957 [3094 peak] GDD base 50 and usually continue until a hard frost. The mite is dark green to dark red after initial feeding and overwinters as a reddish colored egg. The
damage found during the summer on plants is the result of heavy feeding by this mite the previous fall and spring.

Spruce spider mite infestation with webbing. Photo from the USDA Forest Service - Northeastern Area Archive, USDA Forest Service, Bugwood.org

Information from Brian Kunkel, Ornamental IPM Specialist, UD

Landscape - More on Botrytis Blight in the Landscape

The following is more information on botrytis blight (gray mold) in the landscape.

As the weather cools and more dew forms in the evenings, conditions become ideal for the development of Botrytis blight or gray mold. To reduce this fuzzy, gray fungus, keep rose gardens and flowers beds dead-headed and spray with Daconil or Fungonil (chlorothalonil), Cleary's 3336 (thiophanatemethyl) or other labeled fungicide. Other fungicides for commercial use include Chipco 26019 (iprodione) and Decree (fenheximide) or other labeled fungicides. Often the fungus causes a stem canker when infected flowers fall into the plant canopy. Black or caramel-colored, sunken and elongated lesions, with a definite outline, frequently appear on succulent stems or stalks of such ornamentals as begonia, geranium, annual vinca, peony, rose, snapdragon and many other annuals and perennials. Infection also may spread through the stem causing it to be weakened, girdled, and collapsed at the point of infection followed by wilting of the foliage above the lesion.

Information from Bob Mulrooney, extension plant pathologist, UD.

Landscape - Southern Red Mites

Watch for increased southern red mite activity as cooler weather continues. The following is more information.

Southern red mite adults and nymphs are active from 1913 -3518 [2933 peak] and 240 -3584 [3034 peak] GDD base 50 respectively. This mite feeds azaleas, camellias, hollies, photinia, and many others. Southern red mites generally feed on the underside of leaves causing them to turn brownish to grayish and damaged leaves may drop prematurely. This mite is dark red to brownish and has a pale stripe. Eggs are brownish to reddish and have a fine hair coming off the center.

Southern red mite highly magnified. Photo by Jim Baker, North Carolina State University, Bugwood.org

Information from Brian Kunkel, Ornamental IPM Specialist, UD

Landscape and Nursery - More on Japanese Maple Scale

The following is more information on Japanese Maple Scale from the University of Maryland. This pest is on the increase in the region.

Japanese Maple Scale

We are finding 2nd generation crawlers of the Japanese maple scale active this week. The crawlers are purple and if you flip over the female covers you will see the purple colored females and the purple eggs she lays (as hown in photo). If you plan to make an application of Distance or Talus now it is the time to do it.

We are conducting trials at two Maryland nurseries for control of Japanese maple scale. Back in June these nurseries applied the insect growth regulator Talus and horticultural oil at the 1% rate for control of Japanese maple scale crawlers and early instars. The material worked well in killing newly settled crawlers and 2nd instars for about 3 weeks. The interesting thing is that the first generation females continued to lay eggs past this 3 week period. What we are seeing at the sites where Talus was used is that the 2nd generation crawlers are not present yet. We suspect that since we wiped out the early developing scale this took out the population that is producing crawlers at other locations. We plan to delay the next application at these two sites until crawlers start to show up.

Reprinted in part from the August 28, 2009 edition of the TPM/IPM Weekly Report for Arborists, Landscape Managers & Nursery Managers from University of Maryland Cooperative Extension

Landscape - Botrytis Blight

Watch for Botrytis blight in annual and perennial beds. The following is more information.

Botrytis flower blight and stem canker is often present this time of year on annuals and perennials. The cooler weather and prolonged dews will favor Botrytis. Remove spent infected blossoms to prevent the fungus from moving from the flowers to leaves or stems. Stem cankers can develop on roses if old flowers are not pruned and the fungus proceeds to the stems. Look for the tan to gray fluffy fungal growth on the flowers or stems. Fungicide applications of Daconil, or thiophanate-methyl can be helpful in controlling Botrytis in the landscape along with sanitation measures.

Information from Bob Mulrooney, Extension Plant Pathologist, UD.

Landscape - Azalea Caterpillars

Azalea caterpillars can be active this time of year. The following is more information.

The female Azalea caterpillar moth lays clusters of eggs on the underside of leaves, and caterpillars feed gregariously. Early instars appear red with four white to yellowish longitudinal lines down each side. Older larvae have read heads, red legs, and black bodies with white to yellowish 'broken' longitudinal lines down each side. This gives older larvae a spotted appearance. Young caterpillars skeletonize leaves, and as larvae age, they consume entire leaves. Caterpillars will raise both ends off of leaves when disturbed, thus displaying a C shape. Control options when larvae are small include Bacillus thuringiensis (kurstaki), Conserve SC, Sevin, or pyrethroid insecticides.

Azalea caterpillars in mass. Photo by Arnold T. Drooz, USDA Forest Service, Bugwood.org

Information from a past issue of the UD Ornamentals Hotline Newsletter.

Landscape - European Hornets Out Now

European hornets are now active in Delaware landscapes feeding on ripe fruits. The following is more information on this insect.

The European hornet is a large wasp resembling a yellow jacketsbut much larger. The European hornet is about 35 mm (1.5 inches) long and is brown with yellow markings. Nests are rarely constructed in open areas and are more likely to be found in protected areas such as tree cavities, bird houses, barns, or sheds. During the summer, these hornets feed on large insects such as caterpillars, grasshoppers, flies, and bees. European hornets damage a number of ornamental trees and shrubs including, lilacs, rhododendrons, birch, ash, and dogwood. The hornet gains nourishment from the plant sap and the bark may be used as nesting material. Workers expand the nest throughout the summer, and in the fall the next season's queens mate with newly emerged male hornets. European hornets feed on substances high in carbohydrates in the fall. These food sources include overripe fruits, tree sap, soft drinks, juices, and possibly honeydew produced by insects such as aphids or scales. This hornet is also known to attack small fruits such as grapes and consume the sugars. European hornets do not reuse nests and populations die off with the onset of cold weather. The only effective method of control is nest removal. A pressurized wasp and hornet spray with a range of 10 15 feet is desirable. Treatments should be made at dusk or after dark to ensure most of the hornets are in the nest. Caution should be used when treating hornet nests since hornets guard the nest, can sting repeatedly, and can fly at night.

European Hornet. Photo by Jessica Lawrence, NC State Entomology Department, Bugwood.org

Information from Brian Kunkel, Ornamental IPM Specialist, UD

Greenhouse and Nursery - Pythium Rot on Mums

We often see Pythium problems on mums in Delaware. The following is an article on this disease that is a problem this year in many areas of the Northeast due to the wet weather.

The 2009 growing season for fall mums has presented real challenges for the growers. The cool and wet weather of June and early July were less than ideal conditions for growing fall mums. As the summer progressed many growers pushed the mums with fertilizer trying to keep the mums in a vegetative state. Now in late August the varied weather has brought on diseases common to fall mums. A Pythium species, most likely Pythium aphanidermatum, was observed in roots and stems of the specimens from several growers. Symptoms of Pythium attack vary with temperature, moisture, and the species of Pythium involved. The first symptom is often a wet, black basal rot which extends several inches from soil surface. Affected plants wilt and collapse rapidly. Often the fungus invades leaves touching the soil and progresses into the stem at the node, causing a black lesion. In such cases, plants may not exhibit root and basal stem rot. Root rots are also common in Delaware.

Pythium is favored by high fertility and high moisture; avoid overwatering and overfertilizing. Pythium is a natural inhabitant of the soil and can survive there indefinitely as well as in dirt and debris in the greenhouse. Use soilless growing media media. Keep hose ends off the floor and avoid contaminating growth medium with soiled hands, tools, or flats. Fungicides for controlling Pythium include Aliette, Alude, Banol, Banrot 40 WP, Subdue Maxx, Stature DM (drench) Terrazole 35 WP, and Truban 30 WP. Many greenhouse isolates of Pythium are resistant to Subdue. Recommend a drench with a systemic chemical, followed by a sprench to target lesions above soil line. Avoid consecutive applications of fungicides within the same chemical class: rotate among different active ingredients' mode of action for best results.

Stem rot on mum caused by Pythium. We also see root rots caused by Pythium in Delaware. Photo by P. Lopes, University of Massachusetts.

Information from M.Bess Dicklow, Extension Plant Diagnostic Clinic and Paul Lopes, Floriculture and Greenhouse Crops Program in the New England Greenhouse Update http://www.negreenhouseupdate.info/index.php/august/508-chrysanthemum-garden-pythium-stalk-rot

Landscape - Orangestriped oakworms

The following is information on Orangestriped Oakworms from North Carolina State University. This is an occasional pest in Delaware.

Orangestriped oakworms are sometimes very abundant on oaks in summer. They occasionally feed on other hardwoods as well. The moth is brown in color with a white spot and a dark stripe on each forewing. The moths emerge in June and July and deposit their eggs in clusters of several hundred on the underside of oak leaves. The eggs hatch in about a week. The tiny, green caterpillars eventually grow into attractive black caterpillars with yellow or orange stripes running lengthwise along their bodies. Young caterpillars feed in groups whereas older caterpillars tend to be solitary, although there may be thousands of caterpillars on a single tree. Small trees are sometimes defoliated completely by midsummer.

As the caterpillars mature, they are often seen crawling along sidewalks, driveways and yards. These caterpillars may wander for a considerable distance while searching for a place to pupate. You can step on these without fear, as long as you have on shoes. They dig into the soil three or four inches and pupate there. There is usually one generation per year, and the caterpillars overwinter as pupae in the soil. Control is complicated by the size of many of the infested trees. Most people do not have sprayers that can reach very high into shade trees, and by the time the caterpillars descend and crawl about on the soil they are extremely resistant to pesticides. Fortunately, late summer defoliations are much less damaging to the health of trees than early spring defoliations. In most cases it is probably better to rely on birds, diseases and parasites to lower the population next year.

For more information, see http://www.ces.ncsu.edu/depts/ent/notes/O&T/trees/note139/note139.html. If you would like to consider boosting the paper wasp predator population with nest boxes in the spring, see http://www.ces.ncsu.edu/depts/ent/notes/Other/note121/note121.html.

Orangedstriped oakworm. Photo by David Cappaert, Michigan State University, Bugwood.org.

Information from Steve Bambara, Extension Entomologist in the August 28, 2009 edition of North Carolina Pest News http://ipm.ncsu.edu/current_ipm/09PestNews/09News20/pestnews.pdf

Landscape - Powdery Mildew Showing Up on Crape Myrtles This Year

Powdery mildew has been showing up on crape mrytles this year, even in resistant varieties. The following is more information.

Powdery mildew on crape myrtle has not been a problem for many years since the introduction of new cold tolerant varieties (devl. at the National Arboretum and other places) that also happen to have powdery mildew resistance. But, this season has been so favorable for powdery mildew (especially the last several weeks) that we have seen powdery mildew on flower trusses of some of these cultivars. Remember resistance is not immunity. While levels have been low, homeowners have probably never seen powdery mildew on their crape myrtles before. While infection doesn't affect overall plant health, it may be severe enough to prevent flower buds from opening.

Information from Bob Mulrooney, Extension Plant Pathologist, UD

Landscape - Leopard Moth Caterpillar Damage

The following is information on damage from Leopard moth caterpillars, a pest you may see in Delaware.

At 2-3” long, the leopard moth (Zeuzera pyrina) is a large moth, introduced from Europe/N. Africa and found May-September in Delaware. Adults have black and white spots on their wings. Early symptoms of damage from Leopard mothe caterpillars are girdled or broken twigs and branches with wilted/yellow foliage. Monitor trees for branch and limb dieback, which may be mistaken for squirrel activity. Scout dead limbs for exit holes (possibly with silk coverings and resin flow) at the end of broken stems. Fine white frass pellets and possibly pupal skins may be left in bark crevices and inside these galleries.

Larvae damage over 125 tree species incl. oaks, maples, lilacs and apples. They have an unusual life cycle (2 years or longer). Several yellow eggs are laid in small clusters usually in bark crevices. After 10 days, newly hatched larvae crawl some distance before burrowing into a young branch and tunneling into the heartwood to begin feeding. When a branch is too small, the caterpillar exits the branch, migrates along the outside, and tunnels into a larger branch to complete its next caterpillar stage. At the end of the first year, caterpillars are 1” long, yellow with dark spots. At maturity (2”), tree branches up to 3.5 inches and tree trunks may have been fed upon. Pupation occurs in its final gallery.

Leopard moth seems to strike only individual trees and does not spread rapidly. Female moths are not strong fliers. Spread may be through infested nursery stock. Control by pruning out affected limbs/branches. Woodpeckers, other birds and squirrels are important biological controls. As with all borers, growing a healthy tree is the best defense against injury. Chemical control is not practical because of the lengthy flight time. Note that this species shouldn't be confused with the Great/Giant Leopard Moth (Hypercompe scribonia) a native woolly bear caterpillar.

Leopard moth. Photo by James Solomon, USDA Forest Service, Bugwood.org

Leopard moth caterpillar tunnelling in wood. Photo by James Solomon, USDA Forest Service, Bugwood.org

Information from Casey Sclar, IPM Coordinator, Longwood Gardens and Emma Seniuk, Professional Gardener Student, Longwood Gardens

Landscape - Diplodia Tip Blight in Pines

This time of year, tip blight in some pines is very evident. The following is more information:

Austrian and Mugo pines growing in landscapes are showing the effects of infections by the Diplodia tip blight fungus, Diplodia pinea. The disease is noticeable in landscape pines now. Austrian, Mugo, and Scots pines are often planted in landscapes because of their dense, green foliage and symmetrical shape. When healthy, a grouping of Austrian pines can form an attractive year-round screen. Diplodia tip blight, also known as pine tip blight, or Sphaeropsis tip blight, is a devastating disease worldwide, but especially here on exotic two-needle pines such as Austrian pine (Pinus nigra), Mugo pine (P. mugo) and Scots pine (P. sylvestris) in landscape settings and Christmas tree plantations.

Tip blight symptoms on Austrian pines first appear on the newly elongating candles (shoots) in late April to early May. As its name indicates, the shoot tips are killed very quickly and by late May, the diseased tips are noticeably necrotic and stunted. Needles, even before they are out of the needle sheaths, start to turn a straw brown color and droplets of resin can be seen exuding from these dead needles. Some of the diseased needles may begin to break out of their sheaths, but often their growth is halted resulting in stunted, dead needles. Symptoms on Austrian pines are most characterized as progressing from the shoot tip inward. Over a few days to a week all of the needles on infected candles will turn brown and die and shoots will appear brown through late summer. The candle as a whole will be stunted, necrotic, and eventually brittle from resin exudation. The necrotic shoot and needles can sometimes give these dead tips a gray color.

As the fungus progresses from the tip back towards the trunk, older needles will turn straw color and die. This generally happens later in the year or the following year. Progression of the fungus can lead to branch dieback and eventually death of the tree. These symptoms typically start in lower branches of the tree and progress toward higher branches year after year until the tree dies or is so damaged it needs to be removed. On landscape Austrian pines disease symptoms generally begin to appear after trees reach cone-bearing age, typically 12-13 years old. Close examination of infected shoots will often reveal the presence of tiny black dots (pycnidia) on the base of infected needles. Pycnidia are black fungal structures embedded in and protruding through the host tissue, and in D. pinea are only produced on dead host tissue, such as cone scales and dead needles. Pycnidia are tiny but can be seen with the naked eye, resembling black pepper sprinkled on the dead cones and needles. It is not uncommon to see dead cones and needles from infected trees covered with pycnidia. The pycnidia release spores in warm, rainy spring and summer weather which we have had in abundance this year. These spores are dispersed by rain splash and windblown rain.

Pines are most susceptible to D. pinea infection in spring when shoots are just elongating and not yet lignified. As the fungus colonizes the host, it kills the host cells resulting in necrotic symptoms and sometimes resin production. An additional field symptom, canker disease, also is often accompanied by excess resin. After the fungus has killed the host tissue, it can produce pycnidia which can overwinter and be a source of inoculum the following spring.

Information from "Diplodia Tip Blight Is Causing Dead Shoots on Pines" By John Hartman in the current edition of the Kentucky Pest News. For the full article with pictures go to http://www.uky.edu/Ag/kpn/kpn_09/pn_090825.html#Landscape

Landscape - Current Pests

The following are pests you should be on the watch for now in Delaware landscapes.

Clearwing borer populations (Lilac/Ash, Dogwood, and others) are prevalent. Protect trees as needed with pyrethroids like permethrin or bifenthrin.

Watch for building whitefly populations on annuals and select perennials. Parasites may move in and turn the normally yellowish nymphs black or other management strategies may be required.

The USDA has initiated a citizen survey for the Asian longhorned beetle (not yet ID’d in DE). Interested persons may receive a letter and identification sheet, along with a card to return to report findings. Call the PLSC office (302-831-2534) for materials.

Japanese maple scales have been found in egg & crawler stage in Kent County.

Puss caterpillars were found feeding on Ilex & Acer. This caterpillar has a nasty sting associated with its hairs, so be careful moving plant material. Feeding damage is not severe on plants so treatment is not often warranted.

Tuliptree & magnolia scale crawlers are approaching peak crawler activity. Horticultural oil, Insecticidal soap, Distance are good products for crawler control.

Information from the "What's Hot" section of the Ornamentals Hotline Newsletter from the UD Cooperative Extension Ornamentals Group.

Turf and Landscape - Weed Seed Bank

With the ample moisture provided by recent rains, I see many turf areas and landscapes with weeds going to seed at this time. This will add to the weed seed bank and make weed management more challenging in the future. The following is more information.

Weed Seed Bank is a term used to describe the reservoir of viable weed seeds on the surface or in the soil profile. One major weed management goal in turf and landscapes should be to reduce the weed seed bank. Late summer is a major challenge because many weeds such as crabgrass are going to seed, especially in low maintenance areas. This adds to the weed seed bank and will make future weed control more challenging. It takes several years with no additions to the seed bank to reduce weed pressure. This is because of dormancy mechanisms allowing some weed seeds to remain viable for years.

The key to managing the weed seed bank is to not let weeds go to seed. For crabgrass, to get a 75% reduction in the seed bank, it will take 3 years of active control measures making sure there is little seed head production. To reduce weed seed head production in turf, mow more frequently using very sharp blades. This is especially critical in late summer. One challenge is low growing weeds that produce seed heads below the height of mowing. Herbicides will be your best option in that case (for large multi-tillered crabgrass use quinclorac – Drive herbicide). There are also some growth regulators registered for seed head suppression in specific weeds such as annual bluegrass.

Gordon Johnson, Extension Agriculture Agent, UD, Kent County