Greenhouse - Downy Mildew and Its control

Downy mildew is a relatively new disease for greenhouse growers to contend with. The following is some information on this disease and its management.

Downy mildew is a water mold and related to the well-known Pythium and Phytophthora pests. Impatiens, rose, snapdragon, alyssum, pansy and salvia are susceptible to downy mildew and often suffer from the disease. Other crops such as cineraria, lisianthus, ranunculus, coleus and anemone may also become infected by a downy mildew pathogen although the disease problems are less frequent. Snapdragons, roses, impatiens and other crops susceptible to downy mildew each have a unique downy mildew pathogen. While the disease may look similar on the different crops, they are quite different. The downy mildew on snapdragons cannot blight roses, nor can the downy mildew on impatiens spread to coleus.

Downy mildew recommendations

Don’t forget to look under the leaves. Downy mildew may be restricted within the plant without causing severe injury. For instance, leaf spots are called “local infections” and are considered mild symptoms because the downy mildew is limited within the plant. However, if downy mildew advances and invades the internal or vascular part of the plant, the disease becomes “systemic” and is more destructive. When the infection is systemic, it affects the internal mechanism of the plant and hampers its ability to grow. Plants become stunted and yellowed with distorted leaves. When young plants and seedlings are infected, they generally do not survive. Downy mildew produces purplish, gray fuzz on the underside of the leaves. This can go unnoticed because growers are not accustomed to turning over the leaves to look for plant problems. Other than an especially severe case of Botrytis, no other disease causes gray or purplish fuzz on the underside of the leaf.

Look for the disease.

Downy mildew is often explosive and early detection is critical. The downy mildew pathogen produces plenty of spores called sporangia that are spread via air currents to nearby healthy plants. Turn the leaves over to look for gray or purplish fuzz. Susceptible crops should be scouted weekly. Don’t forget to check the susceptible crops when you receive them and continue to check them once they’re potted especially if they’re in baskets that are hard to monitor.
Keep the production area clean. If you had downy mildew last year, this pest may persist in soil and growing media and mats via a thick-walled spore. The downy mildew pest can also reside in compost or cull piles where volunteer plants are likely. Once these volunteer plants become infected, spore production ramps up and the disease is off and running.

Downy mildew likes water.

Limit this disease by venting, reducing the time that leaves are wet, and keeping relative humidity to a minimum. Water plants at a time of day that allows the foliage to dry quickly. Downy mildew is a water mold because it needs water to grow and develop. Any strategy that reduces water, leaf wetness, and relative humidity in a greenhouse will help limit downy mildew.
Apply effective fungicides preventively.

Fungicides should be used for plants prone to downy mildew when the weather is favorable for an outbreak but before disease develops. A protectant fungicide such as mancozeb acts as a barrier to the downy mildew pathogen but is not absorbed by the plant so the spray program must begin prior to a disease outbreak. At MSU, downy mildew studies with snapdragons and vegetable crops have shown that weekly sprays of mancozeb effectively limit downy mildew if applications are made early and repeated frequently. Mancozeb sprays can serve as a relatively low cost, effective foundation for downy mildew protection. Systemic fungicides can be added to the fungicide program as needed. Systemic fungicides can be especially helpful in managing downy mildew because these products are absorbed by the plant in a limited way and can fight the pathogen from the inside out. Systemic fungicides include mefenoxam (example: Subdue MAXX), which is labeled as a soil drench only. Mefenoxam 2 applied to the soil performed well in most of our downy mildew trials with snapdragon. Stature and Fenstop are also downy mildew fungicides. Cyazofamid is currently an unregistered product that provided exceptional control in two trials. Other products that appeared helpful but did not always perform as well as Stature include Compass, zoxamide + mancozeb (not registered), Echo, Aliette, and cymoxanil (not registered).

Downy mildew has a tendency to change and become resistant to the systemic fungicides (Subdue MAXX is an example.). Since Subdue MAXX is especially at risk, it should only be used once in a production program and must be applied as a drench only. Using mancozeb is not likely to cause the pathogen to change and become resistant so using multiple applications of this fungicide is considered OK. Fungicides such as the strobilurins (Compass is an example.) and Aliette should be used only in rotation with other fungicides that have a different mode of action to ensure that they remain effective and reliable tools.

Reprinted from "Downy mildew update" by Mary Hausbeck and Blair Harlan, Plant Pathology, in the February 2009 edition of the Greenhouse Alert newsletter from Michigan State University.

Landscape and Nursery - Plants for Delaware Landscapes Featured at the 2009 UDBG Spring Plant Sale #9

This year, the University of Delaware Botanic Garden spring benefit plant sale features those plants that add to the biodiversity of the landscape and offer food and habitat for wildlife, especially insects and the birds that eat them. Many native plants are featured. This is the ninth in a series on plants being offered at the UDBG spring plant sale that are recommended for Delaware landscapes.


Cornus alternifolia, Pagoda Dogwood 15-25', sun to part shade, moist soil conditions. A much underrated native shrub with white flowers in April to May, blue-black fruit borne on red stems in late summer, and rich burgundy foliage in the fall. Very horizontal habit. Native plant. Photo from the Dow Gardens Archive, Dow Gardens, Bugwood.org.


Cornus racemosa,Grey Dogwood, 10-15', 2-3', sun to part shade, dry to wet soil conditions. The common name is derived from the winter stem color. Plants produce abundant white flowers in the spring and white fruit are borne on showy red stems in the late summer. Fruit is a delicacy, sought by more than 100 species of birds. Native plant. Photo by Richard Webb, Self-employed horticulurist, Bugwood.org.


Corylus americana, Filbert 4-6', full sun to full shade conditions, moist to wet soil conditions. A frequent component of our native woodlands, this shrub typically grows as an understory plant but becomes denser in habit, fruits more heavily, and exhibits intense fall color when grown in full sun. Wildlife love the nuts. Native plant. Photo by Richard Webb, Self-employed horticulurist, Bugwood.org.

For more information on the 2009 UDBG Spring Plant Sale go to http://ag.udel.edu/udbg/events/annualsale.html

Nursery and Lanscape - UDBG Guided Walk of Plant Sale Highlights

The following is information on the guide walk planned to highlight plants being offered at the spring plant sale for the University of Delaware Botanic Gardens.

Guided Walk of Plant Sale Highlights

Date: Thursday
Time: March 26, 4 – 5:30 pm
Meeting place: Fischer Greenhouse entrance
Cost: Free to members; $10 non-members
Registration: Call (302) 831-2531 to register

John Frett will take you on a guided walk to show you UDBG landscape-size plants that will be offered in the plant sale. Maximum 35 people; registration required.

Landscape and Nursery - Plants for Delaware Landscapes Featured at the 2009 UDBG Spring Plant Sale VIII

This year, the University of Delaware Botanic Garden spring benefit plant sale features those plants that add to the biodiversity of the landscape and offer food and habitat for wildlife, especially insects and the birds that eat them. Many native plants are featured. This is the eighth in a series on plants being offered at the UDBG spring plant sale that are recommended for Delaware landscapes.


Aronia arbutifolia, Chokeberry, 6-10', full sun to part shade, moist to wet soil conditions. Despite the common name, this plant has many appealing attributes that make it a very popular shrub: Abundant white flowers April-May; excellent red fall foliage color; and abundant red fruit in the fall, that is until they’re devoured by birds. Native plant. Photo from The Dow Gardens Archive, Dow Gardens, Bugwood.org.


Aronia melanocarpa, Chokeberry, 3-4', full sun to part shade, moist to wet soil conditions. Culturally adaptable, A. melanocarpa is a compact plant that suckers, creating attractive masses. Clear white flowers in spring are followed by abundant black fruits that are often eaten by wildlife. Glossy foliage turns red to wine color in fall. Native plant. Photo from http://commons.wikimedia.org/wiki/File:Aronia_melanocarpa_HabitusFruitsLeaves_BotGardBln0906b.JPG


Cephalanthus occidentalis ‘Sputnik, Buttonbush, 3-6', full sun to part shade, moist to wet soil conditions. Naturally occurring in wetlands, buttonbush shows wide adaptability in the landscape. The round cluster of white flowers appears in June and July and serves as a source of food for many pollinators. Native plant. Photo by John D. Byrd, Mississippi State University, Bugwood.org.


For more information on the 2009 UDBG Spring Plant Sale go to http://ag.udel.edu/udbg/events/annualsale.html

Greenhouse and Nursery - Water Alkality and Growing Media

High alkalinity in irrigation water used in greenhouses and nurseries can lead to media related pH problems. The following is some information on the topic from the University of Maryland.
The pH of a soil-less growing medium is primarily influenced by the alkalinity of the irrigation water.

What is Alkalinity?

• A measure of the water’s ability to neutralize acid.
• Composed of:
- Bicarbonates - HCO3- - Primary Component (Ca, Mg, or Na)
- Carbonates - CO3= (only at pH > 8)
- Hydroxyls – OH- (small influence)

Hard Water

• Hardness refers to cations of calcium and magnesium
• Alkalinity is a measure of bicarbonate and carbonate anions.
• High alkalinity is not necessarily hard water.
• A water high in sodium bicarbonate has high alkalinity, but is not hard.
• Water softeners are not the answer!!

Effect of Alkalinity on Growing Medium pH

• Waters with high alkalinity will cause the pH of the growing medium to rise over time.
• These effects are most dramatic in small containers, e.g. plug trays.


Reprinted from the March 14, 2008 edition of the Greenhouse TPM/IPM Weekly Report from the University of Maryland Cooperative Extension, Central Maryland Research and Education Center http://www.ipmnet.umd.edu/08Mar14G.pdf

Greenhouse and Nursery - Problems Associated with High Alkalinity Water or Acid Water

Alkalinity or acidity levels in water used in greenhouses and nurseries can lead to media related pH problems, nutrient deficiencies, or toxicities. The following is some information on the topic from the University of Maryland.

Problems Associated With High Alkalinity in Greenhouse or Nursery Water

• Rise in the pH of the growing medium.
• Micronutrient deficiencies as these elements become insoluble.
• Possible magnesium deficiencies due to calcium imbalance.
• Possible high sodium levels.

Managing High Alkalinity

• Utilize acidic fertilizers.
– Formulations with active acidity
– Formulations with high potential acidities
• Practice constant liquid feeding.
• Consider acid injection.
• Modify the growing media to start at a lower pH.
• Monitor sodium levels.

Acid Use Calculator for Correcting High Alkalinity in Water
• This tool is available from North Carolina State University. Go to www.pourthruinfo.com
- go to floriculture
- click floriculture software
- click alkalinity calculator

In all cases you should send your water sample to a lab that test water for greenhouse or nursery operations each year to check alkalinity levels.

Problems Associated With Acidic Waters

• Drop in the pH of the growing medium.
• Possible micronutrient toxicities as these elements become highly soluble.
• Deficiency of calcium and magnesium.

Managing Acidic Water

• Select fertilizers that are neutral or have a low potential acidity.
• Supply Ca & Mg via fertilizer or growing media additions.
• Monitor pH - make sure it is stable.
• Consider K bicarbonate injection.
• Monitor nutrient contents of media.

Reprinted from the March 14, 2008 edition of the Greenhouse TPM/IPM Weekly Report from the University of Maryland Cooperative Extension, Central Maryland Research and Education Center http://www.ipmnet.umd.edu/08Mar14G.pdf

Greenhouse - Growth Regulators and Growing Media Interactions with Drenches

The following is information on the effect of growth media on the effectiveness of plant growth regulators when used as drenches in the greenhouse.

Growing medium composition directly affects the efficacy of drench applications of certain PGRs. The effectiveness of A-Rest® (ancymidol), Bonzi® (paclobutrazol), and Concise® and Sumagic® (uniconazole) decreases as the pine bark component of a medium increases. In general, as organic matter content of a growing medium increases, the effectiveness of a PGR drench decreases. As the inorganic content of the medium increases (for example, the amount of sand, soil, rockwool, or perlite), the effectiveness of a PGR drench increases. Growing medium composition may indirectly influence plant response to PGRs by affecting plant vigor. Plants growing in media that reduce, retard or stunt growth (i.e., cause stress) are especially sensitive to PGRs. A slow growing plant is most sensitive to a PGR application, and takes a longer time to resume normal growth. Uniform application of a PGR drench is critical for uniform height control when multiple cuttings are growing in a single container such as a basket or pot. If most of the PGR is applied to only one side of the pot, then the plants on that side will be more affected than the plants on the opposite side.

Reprinted from the 2009-2010 New England Greenhouse Floriculture Guide http://www.umass.edu/umext/floriculture/pest_management/ne_pest_manage_guide.html

Greenhouse - Chemical Control of Thrips

Thrips are a major insect pest in greenhouses and are notorious for transmitting viruses such as INSV. The following are some guidelines for controlling thrips with insecticides.

For growers using pesticides to manage thrips, plan to treat in the early evening. Thrips have two mass flights per day, so sprays in the early evening may contact more thrips. Small droplet sprays, repeated applications (two to three sprays about 5 days apart) and treating before you see a peak in adult numbers on yellow sticky cards are critical. Adult thrips numbers on cards tend to peak every two to three weeks. Apply insecticides before this peak, so adults will be killed before they lay eggs. A mass aggregretion pheromone or thrips lure is also available to be placed into sticky cards to aid in early detection of thrips.

To manage thrips, shorten spray intervals to 4-5 days and rotate pesticides with different modes of action. Some options for management (based upon grower feedback) include Avid (abamectin-group 6) tank mixed with Azatin (azadirachtin- Group 18B), Mesurol (methiocarb-group 1A), Pedestal (novaluron-group 15) tank mix with Pylon (chlorfenaphyr- group 13), Safari (dinotefuran Group 4A) and Conserve (spinosad-group 5). Overture (pyridalyl) (unknown mode of action) has contact, translaminar and some ingestion activity and can be added into your rotation program. It is labeled for thrips and caterpillars but may take from 7 to 14 days before you see control.

Horticultural oil (Pure Spray Green, Saf-T-Side, or Ultra fine oil) may also be an option provided label cautions regarding plant safety are followed. Note that Mesurol has a 24 hour REI plus it may leave an unsightly residue and Pedestal is an IGR labeled for immature stages. In addition, TriStar (acetamiprid - group 4A) or Aria (flonicamid - Group 9C) may help suppress thrips.
Growers often ask about adding sugar to their spray for thrips management. Recent research by Raymond Cloyd, Kansas State University showed that the addition of brown sugar and other sweeteners to lure thrips from hiding does not work and in some cases can cause the growth of black sooty mold.

Reprinted from "Reviewing Thrips Management" by Leanne Punt, University of Connecticut and Tina Smith, University of Massachusetts in a February 27, 2009 post on the New England Greenhouse Update website http://www.negreenhouseupdate.info/greenhouse_update/?p=2552

Landscape and Nursery - Plants for Delaware Landscapes Featured at the 2009 UDBG Spring Plant Sale VII

This year, the University of Delaware Botanic Garden spring benefit plant sale features those plants that add to the biodiversity of the landscape and offer food and habitat for wildlife, especially insects and the birds that eat them. Many native plants are featured. This is the seventh in a series on plants being offered at the UDBG spring plant sale that are recommended for Delaware landscapes.


Pinus rigida, Pitch Pine, 40-60', full sun, dry to moist soil conditions. This pine is common in the serpentine barrens, as well as the Pine Barrens of New Jersey, thriving in the most inhospitable situations. It is quite salt tolerant – great possibilities for beach planting. Native plant. Photo of Lake Atsion in the New Jersey Pine Barrens with Pinus rigida forest http://commons.wikimedia.org/wiki/File:Lake_Atsion_3.jpg

Taxodium ascendens‘Morris’, Debonair® Pond Cypress, 50-70', sun to shade, dry to moist soil conditions. Named for the narrow upright habit, the ferny foliage is distinctly elegant. The leaves turn a rusty orange color in the fall prior to dropping. Small branches gracefully droop, then turn up at the ends, creating a slight weeping habit. Native plant.


Thuja occidentalis ‘Filiformis’, Eastern Arborvitae, 4-8', full sun, moist soil conditions. The broad-pyramidal habit is softened by the thread-like foliage that drops gracefully at the ends of the branches. Native plant.


Thuja orientalis ‘Beverly Hills’, Oriental Arborvitae, 8-10', full sun, dry to moist soil conditions. More heat tolerant than our eastern arborvitae, the bright yellow green winter color foliage is a sure eye catcher. Plants stay relatively small with a consistent, conical habit.


For more information on the 2009 UDBG Spring Plant Sale go to http://ag.udel.edu/udbg/events/annualsale.html

Landscape and Nursery - Plants for Delaware Landscapes Featured at the 2009 UDBG Spring Plant Sale VI

This year, the University of Delaware Botanic Garden spring benefit plant sale features those plants that add to the biodiversity of the landscape and offer food and habitat for wildlife, especially insects and the birds that eat them. Many native plants are featured. This is the sixth in a series on plants being offered at the UDBG spring plant sale that are recommended for Delaware landscapes.

Chamaecyparis thyoides, Atlantic White Cedar, 40-50', full sun, moist to wet soils. Native from Maine to Florida, this plant has great adaptability. The typically narrow form makes this a good choice for a screen: Dense enough to break your view but open enough to see what lies beyond. Native plant. Photo by James Henderson, Gulf South Research Corporation, Bugwood.org


Juniperus virginiana, ‘Grey Owl’ Eastern Redcedar, 3-4', full sun, dry to moist soils. This is a shrubby version of the species with distinctive blue foliage. Mature plants are 3 feet tall and 6 feet wide. This is a female clone. Native plant.


Pinus banksiana, Jack Pine, 35-50', full sun, dry to moist soils. A great pioneer species for sandy soils, this is a very tough pine that flourishes in poor, dry soils. Native plant. Photo by Keith Kanoti, Maine Forest Service, USA.


Pinus echinata, Shortleaf Pine, 60-80', full sun, dry to moist soils. Another tough native pine with great adaptability. Plants can be used to provide filtered shade for shrubs planted beneath. Mature plants develop an attractive scaly, reddish brown bark. Native plant. Photo from Missouri State University.


For more information on the 2009 UDBG Spring Plant Sale go to http://ag.udel.edu/udbg/events/annualsale.html

Ornamentals Hotline Back Issues and Photos Online

Back issues of the Ornamentals Hotline newsletter along with associated pictures are available now on-line. The following is more information:

To view pictures of pests described in Hotline articles, visit this website:
http://ornamentaldiagnostics.blogspot.com
There is no longer a password required to get to this website.

The pictures include images of different life stages of insects, diseases and weeds. The site has pictures of the pests covered in last two year's Ornamental Hotline articles archived by insect, disease or weeds, time of year, and year the pest was found. Archived Hotline issues from 2008 and 2007 are also posted on the website.

Ornamentals Hotline Resubscription 2009

It is time to subscribe or resubscribe to Ornamentals Hotline. This one-page newsletter will tell you what you need to know about pests, diseases, weeds and cultural problems in the landscape. It is published weekly during the growing season. Contributors scout the landscape and monitor Cooperative Extension calls. Reading Ornamentals Hotline will keep you in tune with your customers and their landscape problems. Learn when to scout for pests and diseases.

Subscription form. Click on image for larger version to print.

Nursery, Greenhouse, and Landscape - Late Winter Notes

The following are some late winter notes for nurseries, greenhouses, and landscape companies.

CANKER - Early spring is a good time to look around your yard for signs of winter damage, breakage of limbs, and cankers that may not be noticeable once trees and shrubs leaf out. Cankers caused by Botryosphaeria or other fungal opportunists will often appear as sunken, target-shaped or oval areas on branches. Trim back behind the canker before new growth begins.

Botryosphaeria canker. Photo by Theodor D. Leininger, USDA Forest Service, Bugwood.org.

ROOT ROT - The Diagnostic Clinic has received samples of pansies with poor growth and blackened roots. These plants are infected with the black root rot fungus, Thielaviopsis. Once established in your garden soil, this fungus can persist and cause problems on other annuals such as petunia and vinca. Check your new plants before planting to be sure root systems look light in color and healthy.
Black root rot causing pansy decline.

INSECTS and TEMPERATURE. Spring is quickly approaching and some arthropod pests we may find active in early spring are eastern tent caterpillars, white pine sheath mites, spruce spider mites, and juniper webworms. Did our colder winter have an impact on insect populations? Insect species are affected by cold temperatures differently, so some arthropod populations may decrease while others are unaffected. When your customers ask you to predict pest problems based on the type of winter we’ve had, there really is no simple answer.
Spruce spider mites. Photo by Petr Kapitola, State Phytosanitary Administration, Bugwood.org

Information from the resubscription notice of the 2009 Ornamentals Hotline newsletter from the University of Delaware Cooperative Extension.

Turf - Crabgrass Germination and Temperatures

The following is information on soil temperatures and crabgrass germination.

Once the first warm days arrive, the topic of discussion becomes crabgrass. Crabgrass emergence is well correlated with soil temperatures and degree day accumulations. Mike Fidanza and Peter Dernoeden at the University of Maryland proposed the following from their research (Fidanza, M.A., P.H. Dernoeden, and M. Zhang. 1996. Degree-days for predicting smooth crabgrass emergence in cool-season turfgrasses. Crop Science 36:990-996.)

Ave. Min. soil temp. at which initial appearance is observed =54 F
Ave. mean soil temp. at wich initial appearance is observed = 60 to 64F
Ave. Min. soil temp. at which major emergence occurs = 60 to 70F
Ave. mean soil temp. at which major emergence occurs = 73 to 75 F

Soil temperature at a 1 inch depth is used for these measurements. Measuring soil temperatures first thing every morning is the best way to get this number.

Now regarding crabgrass germination and preemergent herbicide applications, in Southern Delaware the window is generally March 1 to April 1, northern Delaware, March 15 to April 15,

Regarding soil temperatures, a rule of thumb is 3 consecutive night soil temperatures above 50 F. When soil temperatures consistantly stay above 50 F, pre-emergent herbercides, if they are to be applied, should be down or going down.

Degree days can also be used. Degree days for crabgrass germination using a base of 53.6 F are as follows:

Turf - Great Weed ID Site

The following is a link to a great interactive weed identification site from Michigan State University. Most of the weeds on this site are also found in Delaware.

MSU Turf Weeds.net.

This site is intended to help you learn the key identification characteristics of common and not-so-common turfgrass weeds found in Michigan and the midwest (most also are found in Delaware). Correct identification is the first step to proper management.

They have created biography pages for each weed to help you better understand why weeds invade. The biography pages include information on habitat, alternative common names (AKA), look-a-likes, management practices and chemical controls.

Give the site a try at http://www.msuturfweeds.net/

Greebouse and Nursery - Alternatives for Plastic Pots 5

The following is information from a Chinese company that produces biodegradable pots from bamboo fiber.

EnviroArc biodegradable pot's material is totally derived from natural sources which are biodegradable by nature. They were the first company in the world to perfect bamboo pulp for the use in the manufacturing of biodegradable pots. Because bamboo pulp is the main raw material it is 100% organic with no contaminants and they have an uninterrupted supply of raw material to allow high volume production. Bamboo grows naturally easily and quickly (without the need of fertilisers). The bamboo uses is sourced from their own bamboo farms ensuring that none of China's natural bamboo forests (that the panda's rely on for a food source) are destroyed.

With their technology, the materials used are easily moulded into a variety of shapes and forms, with a large range of textures, colors and shapes to choose from. As with all biodegradable products, their pot's organic biodegradable composite means that in nature it will naturally break down safely, relatively quickly and biologically.

If stored as stated, EnviroArc pots have a shelf life of 18-24 months and once disposed of into the earth will be fully biodegradable in under 6 months.


Example of one of their pots.

See their website at http://www.enviroarc.net/index.php

Landscape and Nursery - Plants for Delaware Landscapes Featured at the 2009 UDBG Spring Plant Sale V

This year, the University of Delaware Botanic Garden spring benefit plant sale features those plants that add to the biodiversity of the landscape and offer food and habitat for wildlife, especially insects and the birds that eat them. Many native plants are featured. This is the fifth in a series on plants being offered at the UDBG spring plant sale that are recommended for Delaware landscapes.

Amelanchier × grandiflora ‘Robin Hill’, Apple Serviceberry, 20-30', full sun to shade, moist soil conditions. What’s not to love about this small tree: Deep pink buds opening to white flowers in April; sweet edible fruit in June; and yellow to red fall color. Add to this the smooth grey stems in the winter and you have four seasons of outstanding display! Native plant. Photo by Burncoose Nurseries, UK.


Amelanchier laevis, Allegheny Serviceberry, 15-25', full sun to shade, moist soil conditions. Allegheny serviceberry is more tree-like in habit with fewer suckering stems. The new foliage emerges bronze before changing to green in summer and orange-red in fall. The leaves and 4-6 inch long clusters of white flowers in April are covered with soft hairs, separating it from other serviceberries. The sweet black fruits are delicious to humans and wildlife. Native plant. Photo from the Dow Gardens Archive, Dow Gardens, Bugwood.org.


Arctostaphylos uva-ursi, Bearberry, 1', full sun to shade, dry to moist soil conditions. Evergreen groundcovers are so valuable to the landscape and this is one of the best. The white flowers tinged with pink appear in late April to May, followed by showy red fruit in fall. Plants thrive in poor sandy soils and show good salt tolerance. Native plant. Photo by Dave Powell, USDA Forest Service, Bugwood.org.

For more information on the 2009 UDBG Spring Plant Sale go to http://ag.udel.edu/udbg/events/annualsale.html

Greebouse and Nursery - Alternatives for Plastic Pots 4

There are many alternatives to plastic pots being offered for the greenhouse and nursery trade. The following is the fourth in a series of posts on this subject (information from the University of Maryland).

Plastic pots benefited the horticulture business for many years, enabling growers to sell product at just about anytime of the year in an attractive and inexpensive package. Plastic pots are not gone just yet but consumers are interested in products that are environmentally friendly. Plastic is not conceived as environmentally friendly or sustainable material. Limited oil reserves and concern about using anything that is not renewable has changed many of our notions about plastic pots and trays.

This is an important enough topic that we decided to have it as subject matter and discussion point at the 2009 Chesapeake Green Conference in February. Greg Trabka of Ball Horticulture Company laid out several interesting alternatives to plastic pots at the Chesapeake Green Conference. The alternatives vary from pots made from Coir (coconut fiber) and peat moss, wheat based compostable pots, potato flour pots that are biodegradable, and rice hull pots that are biodegradable.

One thing to keep in mind is that the largest pot that can be made so far that has the stiffness or integrity to stand up is a 1 gallon container. None of the alternative pots presently on the market hold up well when growing crops outdoors for several moths or longer. It would be great to have mum pots that held up outdoors and pots that perennial growers could use in their multi-month production of plants in outdoor growing conditions. Alternative pots are still evolving and there are some problems to work out before growers adopt them widely for use in greenhouse floriculture.

Grower concerns include how to make these alternative pots last through the production stage and still be an attractive package for the consumer. Another thing to consider is how well the pots will hold up at the garden centers and how the consumer will get the plants home without making a mess. How to keep the rootballs from imploding before making it to the planting site is the main concern.

Several growers pointed out that many consumers take plants home and let them sit around for a couple of days before they are planted. They are concerned that customers will let roots growing through pots dry out before getting them into the ground. This last problem can be solved with educational literature to let customers know to get plants into the ground quickly.

What is a little confusing for the public is that there are home compostable pots and industrial compostable pots. Home compostable pots can be thrown on the home compost pile and will bread down with little effort. Industrial compostable pots have to be placed in windrow compost piles and turned regularly to get them to break down. The compostable pots appear to be better suited to mechanical planting systems and can be handled in a lot of ways like the familiar plastic pot. Bio-degradable pots break down when planted in the landscape or garden. These biodegradable pots are probably the best system but the trick is have the pots hold up in the production greenhouses with varying length of growing times and growing conditions.

Information from the February 20, 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/09Feb20G.pdf.

Landscape and Nursery - Plants for Delaware Landscapes Featured at the 2009 UDBG Spring Plant Sale IV

This year, the University of Delaware Botanic Garden spring benefit plant sale features those plants that add to the biodiversity of the landscape and offer food and habitat for wildlife, especially insects and the birds that eat them. Many native plants are featured. This is the fourth in a series on plants being offered at the UDBG spring plant sale that are recommended for Delaware landscapes.

Aesculus parviflora, Bottlebrush Buckeye, 8-12', Full sun to shade, moist conditions, Multi-stemmed and wide spreading, this shrub is well suited for massing, and does best in shade conditions. A handsome specimen, pollinators will be lured to the candelabra-like white flowers in June, and then in the fall, the nuts will be coveted by wildlife. Native plant. Photo by David Stephens, Bugwood.org


Aesculus pavia ‘Humilis’, Red Buckeye, 15', Full sun to part shade, moist soil conditions. This adaptable plant can be grown as a large shrub. The pure red flowers appear in late spring and contrast well against the deep green foliage. While leaves do not have any significant fall color, they are free from disease. The nuts, produced in the fall, are a good food source for many animals. Native plant. Photo by Dan Tenaglia, Missouriplants.com, Bugwood.org


Amelanchier canadensis, Shadblow Serviceberry, 6-20', full sun to shade, moist to wet soil conditions. The suckering stems produce dense shrubs that often occur in wetlands in their native habitat. Numerous white flowers in early April entice early pollinators. Sweet, edible black fruit mature in June. Fall color typically golden yellow with red or orange tints. Native plant. Photo by the Dow Gardens Archive, Dow Gardens, Bugwood.org


For more information on the 2009 UDBG Spring Plant Sale go to http://ag.udel.edu/udbg/events/annualsale.html

Greenhouse and Nursery - Alternatives for Plastic Pots 4

There are many alternatives to plastic pots being offered for the greenhouse and nursery trade. The following is the third in a series of posts on this subject (information from the University of Maryland).

ITML has coir fiber plantable pots which are biodegradable and sustainable. The coir pots are not stiff by any measurement but they are reported to hold up in greenhouse growing conditions. The coir, a waste product from coconut production, is considered a sustainable product. Once it is planted roots will penetrate through the walls easily. There is also a pot made from potato flour by Dillon Company and this pot is considered biodegradable.

Coir Pot

Information from the February 20, 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/09Feb20G.pdf.

Greenhouse and Nursery - Alternatives for Plastic Pots 3

There are many alternatives to plastic pots being offered for the greenhouse and nursery trade. The following is the third in a series of posts on this subject (information from the University of Maryland).

Ball has a pot called the OP-47 which is thermoformed and looks like a lot like a standard thin plastic pot (green colored). This OP-47 pot is made from wheat and is rated for industrial composting. This pot is being tried out by a couple of Maryland operations in 2009. It will be interesting to see the public reaction to these compostable pots. Ball has printed compostable on the side of the rim of the pot so the public is aware this pot is different. The tray to hold the pots is yellow and is called PLA and is made from corn based plastic. These trays are industrial compostable.


Information from the February 20, 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/09Feb20G.pdf.

Landscape and Nursery - Plants for Delaware Landscapes Featured at the 2009 UDBG Spring Plant Sale III

This year, the Univeristy of Delaware Botanic Garden spring benefit plant sale features those plants that add to the biodiversity of the landscape and offer food and habitat for wildlife, especially insects and the birds that eat them. Many native plants are featured. This is the third in a series on plants being offered at the UDBG spring plant sale that are recommended for Delaware landscapes.

Morus alba, ‘Chaparral’ Weeping Mulberry, 10-20', full sun to part shade, dry to moist soils. The distinctive architecture of the twisted, weeping branches is best appreciated during the winter months but this weeping form, covered with glossy green leaves, makes a striking specimen throughout the year. Fall foliage is bright yellow. Don’t worry, this is a fruitless form. Photo from Garden State Nursery.

Nyssa sylvatica, ‘Wildfire’ Black Tupelo, 30-50', full sun to part shade, dry to moist soils. The brilliant red fall color is vivid and consistent on this selection of black tupelo. Containerized plants establish reliably, since the root system is completely intact. Native plant. Photo by Richard Webb, Self-employed horticulurist, Bugwood.org


Oxydendrum arboreum, Sourwood, 25-30', full sun to part shade, moist soils. An elegant understory tree, sourwood produces clusters of pendulous white flowers in the early summer that attract numerous pollinators. The developing fruits turn upright and contrast with the brilliant red autumn foliage to make it seem as though the plant is still in flower in the fall. Native plant. Photo by Wendy VanDyk Evans, Bugwood.org


Persea palustris, Swamp Redbay, 15-20', full sun to part shade, moist to wet soils. The broadleaf evergreen foliage offers a real treat during the bleak winter months and can serve as a screen or a backdrop for heavily fruited shrubs. Photo by Chris Evans, River to River CWMA, Bugwood.org


For more information on the 2009 UDBG Spring Plant Sale go to http://ag.udel.edu/udbg/events/annualsale.html

Greenhouse and Nursery - Alternatives for Plastic Pots 2

There are many alternatives to plastic pots being offered for the greenhouse and nursery trade. The following is the second in a series of posts on this subject (information from the University of Maryland).

Fertilpots are a biodegradable wood fiber pot composed primarily of spruce fibers. Fertilpots are biodegradable and are intended to be planted directly in the ground. Water, air, and roots penetrate the walls of the fertilpot so there is supposedly no need for drainage holes. Fertilpots do not require a composting situation to degrade and are planted directly into the ground by the consumer. Fertilpots has come up with a tray for handling of biodegradable containers. Developed jointly by Fertil International and Desch Plantpak, the Dioni tray encourages airflow around the pots for better root formation. The design of the Dioni tray provides an air space which promotes air pruning of the root tips emerging from the porous walls of fetilpots.

Fertilpot

Dioni tray.


Information from the February 20, 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/09Feb20G.pdf.

Greenhouse and Nursery - Alternatives for Plastic Pots 1

There are many alternatives to plastic pots being offered for the greenhouse and nursery trade. The following is the first in a series of posts on this subject (information from the University of Maryland).

Ball Horticultural Company and Summit Plastic Company are partnering to make biodegradable, compostable pots for the Ball Circle of Life sustainable horticulture program. Circle of Life pots, made of rice hulls, are available in six sizes: 3.5 in. (9 cm), 4 in. (10 cm), 4.5in. (11 cm), 5 in. (13 cm), 6 in. (15 cm) and trade gallon. The pots are made from waste rice hulls from China. It would be nice if the pots were made from rice hulls from America but evidently the Chinese are the ones with the patent on this process. The rice hulls are mixed with glue to stiffen them. The pots look a lot like plastic but some are compostable and others can be planted right into the ground and bio-degrade. Ball has come out with an interesting biodegradable pot with slits in the slide of the pot. The whole pot is planted into the ground and the roots grow into the surrounding ground. The pot is supposed to breakdown during the growing season – at least the part of the pot that is placed in the soil.



Rice Hull Pots.

Information from the February 20, 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/09Feb20G.pdf.

Greenhouse - Iron Deficiency and Rot Rot on Pansy

Pansies have been a profitable crop for greenhouse growers over the years and are one of the first sales items to offer in the spring planting season. The following are some notes on growing problems you may see in pansies.

Pansies are fairly easy to grow but are susceptible to iron deficiencies in the media pH goes higher than 5.8. When checking pansies showing yellowing, also look for healthy roots. Yellowing may be due to Thielaviopsis root rot (also known as black root rot). Black root rot can also be kept in check by keeping the media pH below 5.6.

Thielaviopsis Root Rot on pansy. Plants are stunted due to black root rot. Photo by Jay W. Pscheidt, 2002, Oregon State University Extension.

Intervienal chlorosis on pansy with a pH level of 6.3. Photo from the University of Maryland http://www.ipmnet.umd.edu/09Feb20G.pdf

Gordon Johnson, Extension Horticulture Agent, UD, Kent County

Turf - Avoid Foot Traffic on Frost or Ice Covered Turf

The following is information on the effects of foot traffic on frost or ice covered turf.

Trafficking frost or ice-covered turf usually results in extensive physical “breaking” of the leaves. The xylem and phloem tissues that are involved in moving water, nutrients, and carbohydrates around in the plant are usually severed when traffic is applied to ice-covered foliage. The damaged turf leaves don’t fall away completely from the stem, but instead slowly turn brown and die. You will likely see visible damage from the traffic (in the form of footprints, paw prints from pets or wild animals, etc.) within a few days and the evidence of the trafficked turf will remain for several weeks until new leaves form later in the spring. For cool-season grasses that can mean living with the damage well into April or May. The good news is that the damage is primarily cosmetic and does not impact the overall survival of a lawn.


Information extracted from "My Turf’s On Ice" by Mike Goatley, Extension Turf Specialist & Associate Professor, Crop & Soil Environmental Sciences, Virginia Tech.

Greenhouse - Edema

Edema is a common winter and early spring problem on Ivy Leaf geranium. It can also occur on other greenhouse crops. The following is more information on this disorder.

Edema (oedema) is not a disease like a bacterium, or a virus and it is not transmittable from one plant to another. Edema is a physiological problem occurring mainly on ivy geraniums but is also found on sweet potato vine (ipomoea), begonias, cacti, ferns, palms, pansy, cleome and cole crop vegetables like broccoli, cabbage and cauliflower. Some fleshy ­leaved plants such as jade and peperomia are particularly sensitive to conditions which lead to the development of edema although almost any broadleaved plant may be affected.

Edema on leaf. Photo by Joseph LaForest, University of Georgia, Bugwood.org.


Edema, is a bursting of the cell walls on the underside of the leaf. Symptoms of edema appear as bumps or blisters initially on the undersides of lower or older leaves on a plant. They may then turn brownish or tan and become corky. Severely affected leaves will often turn yellow and fall off the plant. The corky spots sometimes resemble spider mite or thrips damage. To rule out pest damage, use a handlens and check carefully on the undersides of leaves along midveins for spider mites and in growing points for thrips. Mildly affected plants often recover from edema, putting out symptomless new growth, with the arrival of more favorable growing conditions in late spring and early summer. Some plants however are severely affected, have dropped significant numbers of leaves and have badly distorted remaining leaves. These plants are probably not worth saving as they will not recover in time.

Edema is caused by maintaining a greenhouse environment that is not ideal for growing susceptible plants such as ivy geraniums, often combined with over watering. Edema occurs when the growing media remains moist and the greenhouse air is cool and moist. The plant roots absorb water at a faster rate than is transpired through leaf cells causing the leaf cells to rupture. This rupturing of the leaf epidermis and the inner cells causes the raised, crusty appearance on the underside of the leaf.

There are several cultural practices that contribute to edema. First, most growers grow their ivy geraniums in baskets hung above the benches where the air is most humid and with poor air circulation that reduces the transpiration rate. Secondly, many growers are now using saucerless hanging baskets for their ivy geraniums. This type of container retains water after each irrigation including periods of cloudy and overcast weather which results in overwatering. Third, hanging baskets are often on automatic watering systems, all watered at the same time. However, not all hanging baskets dry out at the same rate and therefore, some plants are overwatered. Lastly, during cool, cloudy weather, humidity is high in the greenhouse and plant transpiration rates are low. These factors combine to create the perfect conditions for edema to occur.

What can growers do to prevent edema on susceptible plants? The main method is to carefully manage the greenhouse environment. Begin by using a well drained growing media. Increase light intensity by spacing plants farther apart. Avoid over-fertilizing plants, especially when the plants are growing slowly and avoid growing cultivars that are highly susceptible. Do not over water, and keep plants on the "dry side" during extended periods of low light and cool temperature. Water when air temperature is rising or humidity is low.

Anything a grower can do to improve drainage and air circulation around plants will help prevent edema. Reduce humidity by venting the greenhouse first thing in the morning, even if that means turning up the heat. Make sure there is adequate air flow, whether from fan jets or horizontal air flow fans. Air movement is important 24 hours a day. Do not use saucerless hanging baskets. Instead, use containers that have snap-on saucers, but do not put the saucer on until the crop is nearly finished, or if possible, until point of sale. This will ensure maximum drainage of each basket. When using an automatic watering system, place varieties with similar growth vigor on each line or section, again to eliminate over watering. Lastly, properly manage media pH and soil fertility. Make sure media pH for ivy geraniums is 5.5. Fertilize once every three feedings with calcium and potassium nitrate. Calcium will thicken up the cell walls, making ivy geraniums more resistant to edema.

Reprinted from "Tips for Managing Edema on Spring Crops" by Tina Smith, University of Massachusetts, Extension Floriculture Program http://www.umass.edu/umext/floriculture/fact_sheets/greenhouse_management/edema.htm

Greenhouse - Monitor Your Media pH

The following is a short article on pH issues with greenhouse media and plant deficiencies.

Media pH

Most plants have an optimal pH range in which they perform best. Some plants may prefer slightly acidic media while other plants can tolerate a much lower or higher pH. The pH of the media influences the uptake and availability of all nutrients. Growing greenhouse plants in media with a pH lower than the optimal range can result in poor uptake of macronutrients (in particular Calcium, Magnesium, and Phosphorus) and increased uptake of some micronutrients (e.g. iron toxicity). On the flipside, micronutrient deficiencies generally occur on plants growing in media with a pH higher than the optimal range (e.g., iron or manganese deficiencies).

Iron Toxicity in Marigold probably due to low media pH. Photo by Tina Smith, UMass.

Iron deficiency in petunia probably due to a high media pH. Photo by Tina Smith, UMass.


Written information from the Michigan State University Greenhouse Alert Newsletter March 4, 2008.

Greenhouse - High Soluble Salts

High soluble salt levels in greenhouse media can cause plant performance problems or if severe, plant failure. High salt levels usually occur from over fertilization in liquid feeds or excessive release of fertilizer salts from slow release fertilizers. The following is a short article on the subject.

The soluble salt content of the media and irrigation water should be tested frequently throughout the growing process. All soluble nutrients, such as nitrate, ammonium, potassium, calcium, magnesium, chloride, sodium and sulfate, contribute to the soluble salt content of the media. A soluble salts test will alert growers if the salt level starts to creep upward and can also provide an indication of the nutrient status available for plant uptake.

Greenhouse plants vary in their tolerance to salt levels and this tolerance is often dependent upon the growth stage of the plant. Excessive soluble salts can result in reduced growth and loss of vigor, root death, chlorosis and necrosis of leaves, wilting and marginal leaf burn. Excessive soluble salts are generally a result of too much fertilizer present in the soil solution in relation to the plant’s needs. High salts may occur from miscalculation of fertilizer dilutions, poorly calibrated or malfunctioning fertilizer injectors or over-application of fertilizers. Other causes of excessive salt buildup may be inadequate leaching and poor drainage. Excessive soluble salts may be reduced in the media by leaching several times with clear water.

Total soluble salt content is determined with a solu-bridge conductivity meter and is expressed as millisiemen (mS) or millimho (mmho). Millisiemen is the preferred unit for expressing soluble salt measurements. Regardless of the unit, the value is the same. Growers often determine soluble salt content by using one part media to two parts distilled water, allowing the solution to sit idle for up to one hour before taking a reading. Many testing labs determine soluble salt content on the saturation extract.

Soluble salt levels by various test and plant reactions.

Information from "Diagnosing plant problems – don’t forget about pH and soluble salt content" by Steven Gower and Jan Byrne, MSU Diagnostic Services, in the Michigan State University Greenhouse Alert Newsletter, March 4, 2008.

Landscape and Nursery - Plants for Delaware Landscapes Featured at the 2009 UDBG Spring Plant Sale II

This year, the Univeristy of Delaware Botanic Garden spring benefit plant sale features those plants that add to the biodiversity of the landscape and offer food and habitat for wildlife, especially insects and the birds that eat them. Many native plants are featured. This is the second in a series on plants being offered at the UDBG spring plant sale that are recommended for Delaware landscapes.

Cladrastis kentukea, American Yellowwood, 30-50', full sun to part shade, moist soil conditions. A true star in the garden with a heavenly fragrance. The nearly 12-inch long terminal white clusters provide quite a display in mid May. A great small to medium sized tree for residential landscapes with clear yellow fall foliage. Native plant. Photo from The Dow Gardens Archive, Dow Gardens, Bugwood.org.


Crataegus crus-galli, Cockspur Hawthorn 20-30', full sun, dry to moist soil conditions. How can you resist — white spring flowers loved by pollinators, deep red fruits eaten by birds, and bronze red to purple red fall foliage. These large shrubs also offer great cover for birds due to their long 2-3 inch spines. Native plant. Photo by Richard Webb, Self-employed horticulurist, Bugwood.org.

Diospyros virginiana, Common Persimmon, 35-60', full sun, dry to moist soil conditions. The small white flowers in early summer are prized by pollinators and produce 1-2 inch apricot colored fruit. The fall foliage often turns purplish-red about the time the fruit is being savored by wildlife. Native plant. Photo by John D. Byrd, Mississippi State University, Bugwood.org.


Magnolia virginiana, ‘Henry Hicks’, Sweetbay Magnolia, 25', sun to part shade, moist to wet soil conditions. Difficulty propagating this outstanding magnolia has greatly limited its availability in the nursery trade. This cultivar retains its foliage as well as or better than all other sweetbays. The upright habit, white flowers, and stunning fragrance make this an ideal choice for nearly all gardens. Native plant. Photo by The Dow Gardens Archive, Dow Gardens, Bugwood.org.

For more information on the 2009 UDBG Spring Plant Sale go to http://ag.udel.edu/udbg/events/annualsale.html