Greenhouse Update - July 23, 2005
Leanne Pundt, Extension Educator, University of Connecticut
The hot, humid weather was favorable for many different diseases including powdery mildew, downy mildew, erwinia, web blights, etc. Continued high temperatures were favorable for mites and thrips on various crops, however, high temperatures made it difficult to spray.
Downy Mildew
Downy mildews symptoms appear very rapidly and tend to be much more difficult to control than powdery mildew. Conditions that promote leaf wetness, such as high relative humidity, overhead irrigation and close spacing, favor downy mildews. With a hand lens, closely examine the bloom of sporangia (microscopic stalks bearing spores) on the underside of the oldest leaves. (They will look like many tiny branched trees, each bearing tiny lemons). This can help you distinguish downy mildew from powdery mildew. Aster, Artemisia, Centaurea, Geranium, Lupinus, Potentilla, Rudbeckia and Viola are susceptible to down mildew. (See photo).
 Downy Mildew on Rudbeckia. Note white fungal sporulation on underside of leaves. Photo by: Leanne Pundt, University of Connecticut click for a larger image |
If you've had a history of problems with downy mildew on certain crops, start a preventive spray program during favorable environmental conditions. Some labeled fungicides include Aliette, Alude, Compass, Champion, Heritage, Junction, Kocide, Protect, Stature, Stature DM and Zyban. (Consult and follow product labels for registered uses, some fungicides may only be labeled for greenhouse use, others outdoor use, some may have geographic restrictions). |
Bacterial soft rot
Bacterial soft rot is a mushy soft rot with a distinct, foul, fishy odor caused by different types of Erwinia. Leaves or stems appear water soaked and collapse (See photo). The bacteria are easily spread from plant to plant by overhead irrigation and enter plants via wounds. Erwinia can survive in infected plant debris and in the soil and has even been recovered from irrigation water in nurseries. Iris may also become infected with soft rot (especially after being wounded by iris borer). Delphinium, calla and other ornamentals may also become infected.
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Bacterial soft rot is best managed by strict sanitation. Discard infected plants; disinfect hands, and propagation tools. Avoid wounding, stressing or freezing plants to avoid introducing the bacterium. Phyton 27 is labeled for certain crops (see label for registered uses and precautions) and may help reduce spread. Poinsettia cuttings can also become infected with erwinia soft rot. If you see cuttings with a soft, mushy rot, dispose of them immediately. Erwinia is prevalent during excessive growing temperatures. Strict sanitation is needed to reduce losses both during and immediately after propagation. |
 Bacterial soft rot on sedum. Photo by Leanne Pundt, University of Connecticut click for a larger image |
Inspect incoming rooted poinsettia cuttings as soon as you receive them. Check roots to see that they are white and healthy with no signs of root rot. Blunt root tips can be an indicator of fungus gnat feeding. (See photo). Insect growth regulators such as Distance, Citation, Enstar, Azatin, Ornazin, and Aza-Direct may be options for use against fungus gnat larvae. The systemic neonictotindoid Safari is also labeled as a drench for fungus gnat larvae as well as whiteflies.
 Fungus gnat feeding injury to poinsettia cutting. Photo by Leanne Pundt, University of Connecticut click for a larger image. |
New England Greenhouse Update now online. University Extension Specialists in New England, in conjunction with USDA's Northeast Sustainable Agriculture Research and Education, contribute information to this new website. Timely updates are provided for commercial growers of greenhouse crops and flowers in Massachusetts, Connecticut and Rhode Island. You can use this additional resource for more information about current observations and recommendations on environmentally safe production practices.
| Topics posted July 2005 |
| July 1--Slugs |
| July 5 -- Daylily Rust |
| July 15 -- Anthracnose on Sedum |
| July 15 -- Angular Leaf Spot on Zinnia |
| July 22 - Downy Mildews |
| July 22 - Bacterial Leaf Spot on Garden Mums |
| GREENHOUSE IPM COORDINATOR (commercial interests and growers) |
LEANNE PUNDT | 860-626-6240 |
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