Greenhouse Update -
April 4, 2008
Leanne Pundt, Extension Educator, University of Connecticut
Thrips – feeding damage is being noted by growers on some of their favorite hosts including double impatiens, verbena, Ipomoea, lobelia, ivy geraniums. If only a few plants, such as heliotrope are flowering, it is helpful to remove the flowers which are a source of pollen, contributing to thrips egg laying and reproduction. It is also extremely important to remove weeds, such as galinsoga and chickweed, especially if they are flowering to remove potential sources of virus infected thrips.
Thrips
feeding damage (silvery scars) on an impatiens
Leanne Pundt photo
click on image to see a larger view
Many growers are mentioning that Conserve is not working for them as well as in the past. This may be due to pesticide resistance (first reported in the literature in 2005) but inadequate spray coverage or other factors can also be to blame. Unfortunately, there are few new materials are available for thrips to add to your rotation schedule.
Some growers have mentioned that the miticide Pylon (chlorfenapyr – Group 13), which is one of the few new materials labeled for thrips, is working well for them. Or Botanigard tank mixed with an IGR such as Ornazin (azadirachtin – Group 18B) may be helpful to suppress thrips. Many of the Group 4A materials also help suppress thrips and are safe on open blooms. If you are using beneficial nematodes for fungus gnat control, they will also help against thrips pupae in the soil (as will Adept (diflubenzuron –Group 15).
To manage thrips, shorten spray intervals to 4-5 days and rotate pesticides with different modes of action. A rotation program for thrips might include Mesurol (methiocarb-group 1A); (Avid (abamectin-group 6) with Ornazin (azadirachtin- group 18B); Novaluron (novaluron-group 15). Mesurol has a 24 hour REI and the residue may be of concern. Both Pedestal and Ornazin are IGR’s for immature stages.
Botrytis Blight was evident during the cloudy, overcast weather especially starting near wounded tissue or spent flowers in tightly closed plastic houses. Reduce condensation levels in the greenhouse by using HAF fans; heating & venting 2 or 3 times in the evening after sunset and in the morning at sunrise. Keep trash cans covered so spores do not release into the crop. Water early in the day. Some options for control include: Decree (fenhexamid – Group 17), Daconil (chlorothalonil – Group M5) Compass (trifloxystrobin – Group 11).
Growing Cooler results in cooler growing media which then influences nutrient uptake. One may see more signs of phosphorus deficiency (purpling of stems, or leaves) or iron deficiency symptoms (interveinal chlorosis) because the roots are not functioning as well.
Be careful of potential ammonium toxicity. Keep in mind that ammonium forms of nitrogen (NH4) convert to nitrate nitrogen (NO3) by the action of soil microorganisms, which tend to be low in artificial growing mixes. The action of these beneficial microbes can be inhibited by cool, wet and poorly aerated media.
Ammonium is both directly toxic to plants, lowers the pH and may interfere with the uptake of calcium. Some symptoms of ammonium toxicity include reduced growth, interveinal chlorosis, and foliar marginal chlorosis. Ammonium is extremely difficult to leach from the growing media.
Use fertilizers low in ammonium and higher in nitrate nitrogen such as Dark Weather Feed and closely monitor your nutrient levels.
| March 24, 2008 |
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| January 8, 2008 |
| 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. |
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GREENHOUSE IPM COORDINATOR (commercial interests and growers) |
LEANNE PUNDT | 860-626-6240 |
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