Greenhouse TPM/IPM Bi-Weekly Report Central Maryland Research and Education Center Ellicott City, Maryland June 8, 2012 From: Stanton Gill, Extension Specialist IPM for Greenhouse and Nurseries, Central Maryland Research and Education Center, University of Maryland Extension Karen Rane, Extension Specialist, Director of the Plant Diagnostic Clinic, University of Maryland Extension Andrew Ristvey, Extension Specialist, Wye Research and Education Center, University of Maryland Extension Suzanne Klick, Technician, CMREC, University of Maryland Extension Spittlebugs We found some spittlebugs on field grown cut flowers this week. Look for white, frothy spittle on plant stems and foliage on a wide range of herbaceous plants. There is also a species that is found on pine, fir and spruce. The nymphs feed on plant sap from under frothy, spittle-like foam which protects them from predators, parasites and dry weather. If you examine the spittle closely, you will find the nymphs within. Control: Usually not necessary for this pest. This pest has a wide range of natural enemies. Powdery Mildew on Dahlias Powdery mildew is active on greenhouse crops such as dahlia this week. We continue to have favorable weather conditions (bright sunny days and cool nights) for the development of this disease. Some fungi of powdery mildew are very host specific while others can infect a wide range of plants. Look for the whitish fungal growth on the surfaces of leaves and stems. Management: Reduce humidity by increasing plant spacing and air circulation. Scout plants regularly for the first signs of powdery mildew, as this disease can spread very quickly throughout the crop. Fungicide options include strobilurins (Heritage, Cease, Rhapsody, Cyngus, Compass-O), Bacillus subtillis, chloronitriles (Daconil, Echo, Chlorothalonil and others), coppers (Champ, Junction, Camelot, Phyton 27), and benzimidazoles (Cleary s 3336).
Impatiens Downy Mildew We first wrote about an outbreak of impatiens downy mildew in the Greenhouse IPM Report back in February, and this week we received our first sample with the disease in the UMD Plant Diagnostic Lab. Impatiens downy mildew, caused by the fungus-like microorganism Plasmopara obducens, is favored by cool, moist conditions. The disease affects both seed and cutting propagated Impatiens walleriana, but New Guinea impatiens are resistant or tolerant. Symptoms can be very subtle, starting as a slight light green mottling or stippling on one or a few leaves. Infected leaves may curl downward. If you look at the undersides of these leaves, the white fuzzy growth of the pathogen is visible. As the disease progresses, infected plants will be stunted, and leaves and flowers fall leaving bare, leafless green stems. The disease can cause severe losses in both greenhouse production and landscape plantings. Thick-walled oospores produced in infected leaves and stems can overwinter in soil and be a source of the disease in following years. Slight mottle and leaf curl symptoms of downy mildew on impatiens Underside of leaf, note white fuzzy sporulation There are several fungicides that can protect plants from downy mildew infection, but they must be applied preventatively. Unfortunately, fungicides do not cure infected plants, so all symptomatic plants must be bagged and discarded. It is very important to scout impatiens regularly for symptoms, making sure to check the undersides of leaves. In the landscape, remove infected plants and all plant debris, and plant other annuals in the beds. We really would like to know the extent of this disease in our region. If you think you have impatiens downy mildew in greenhouse or landscape plantings, please contact me (Karen Rane) at the UMD Plant Diagnostic Lab (phone 301-405-1611, email rane@umd.edu) so we can arrange to get samples. Check out the American Floral Endowment website listed below for an excellent collection of articles, fact sheets and fungicide recommendations for both greenhouse growers and landscapers. http://www.endowment.org/afe-news/press-releases/221-controlling-downy-mildew-on-impatiens.html 2 Close-up of sporulation of Plasmopara obduscens on the underside of an impatiens leaf Thrips Thrips populations continue to increase in greenhouses with the hot weather. More damage is being reported on plants this month. Look for white streaks on flowers and speckling on foliage for thrips damage. Do a tap test of flowers and foliage onto white paper to see if thrips are present. Materials for control include: Abamectin (Avid), Acetamiprid (TriStar 70 WSP), Azadirachtin (Azatin XL, Neemix 4.5), Befenthrin (Talstar, Attain TR), Chlorfenapyr (Pylon), Dinotefuran (Sarfari), Flonicamid (Aria), Imidacloprid (Marathon), Kinoprene (EnstarII), insecticidal soap, horticultural oil, and Spinosad (Conserve SC).
Beneficial Insect Activity In cut flower fields, landscapes and outdoor nurseries, a variety of beneficial insects are active which include: Soldier beetles: A soldier beetle, called goldenrod or Pennsylvania leatherwing, was found around cut flowers this week and can also be found on outdoor nursery plants. Margined soldier beetle is another species found in Maryland. These beetles are both pollinators and predators. Adult soldier beetles are reported to feed on nectar, pollen, honeydew, and small insects. Soldier beetle larvae feed on insect eggs, small caterpillars, fly larvae (maggots) and other soft-bodied insects. Lady bird beetles: Lady bird beetles have been active throughout the spring. Adults and larvae feed on a variety of small insects including aphids, scale, mealybug, and caterpillar eggs. Look for various stages on plants including the orange, ridged and spindle-shaped eggs. The convergent lady bird beetle, Hippodamia convergens, is found naturally in Maryland and is also a species that is available commercially for release in greenhouses. Lacewings: Lacewings are another general predator found in greenhouses, nurseries and landscapes. Look for the small white eggs that are laid singly on top of a silk strand to prevent them from eating each other when they hatch. Lacewings rarely reproduce in the greenhouse, but can come in from outside and lay eggs on plants. The larvae are the predaceous stage and are most often the stage released in greenhouses. Adults feed on nectar, pollen and aphid honeydew. A Pennsylvania leatherwing, Chauliognathus pennsylvanicus A ladybird beetle larva A convergent ladybird beetle adult Lacewing eggs on fennel A lacewing larva A lacewing adult 3
v c i Twice-stabbed Stink Bug (Cosmopepla lintneriana) Twice-stabbed stink bugs are active outside this week. Look for this bug on both landscape plants and cut flowers. This stink bug has a wide host range. In recent years in Maryland, we have had reports of it feeding on various plants that include cleome, snapdragon, physostegia and salvia. Damage includes aborted flower buds and distorted growth. This stink bug overwinters in the adult stage among dead leaves on the ground. Control: If necessary, options include Talstar (bifenthrin) and Orthene (acephate). Fourlined Plant Bug Fourlined plant bugs adults are still active on boneset, mints, and other plants in the landscape this week. This bug can damage around 250 herbaceous and woody plant species. There is only one generation a year so activity will finish up soon. Damage occurs early and plants grow out of it through the season. Monitoring: Look for white to dark colored spots on the foliage with damage concentrated on the upper foliage of the plant. The fourlined plant bug is a sucking insect that injects a toxin that discolors the foliage. Eventually the dead tissue drops out of the leaf making the foliage looked tattered. Control: If necessary, this pest is easily controlled by insecticidal soap or neem products. Acephate (Orthene) is also effective. Aphids The aphid explosion continuesd in greenhouses with the long stretch of warm weather. This week has been cooler so hopefully activity has been a bit suppressed and control measures more effective. 4
Upcoming Programs: ASCFG Mid-Atlantic Regional Meeting June 18, 2012 Roost Flowers and Design Location: Virginia Beach, Virginia ascfg.org 2012 Perennial Plant Symposium July 4-10, 2012 Location: Boston, Massachusetts perennialplant.org OFA Short Course July 14-17, 2012 Location: Columbus, Ohio ofa.org Cut Flower Tour August 6, 2012 Location: 2 sites in Montgomery County OFA Perennial Production Conference September 10-12, 2012 Location: Grand Rapids, Michigan ofa.org ASCFG National Conference November 12-14, 2012 Location: Tacoma, Washington ascfg.org The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by University of Maryland Extension is implied. Read labels carefully before applying any pesticides. Photographs are by Suzanne Klick, Shannon Wilhelm and Stanton Gill unless stated otherwise. University of Maryland Extension programs are open to all citizens without regard to race, color, gender, disability, religion, age, sexual orientation, marital or parental status, or national origin. 5