Saturday, August 2, 2008

Greenhouse - What to Do if you Detect Herbicide Damage in Greenhouses

Herbicides can be drawn into greenhouses from outside applications through the vents. Growers have also misapplied residual herbicides not labelled for greenhouse use. The following are some remedies if you suspect herbicide damage in greenhouse crops.

If you detect herbicide injury on greenhouse plants, several things can be done to save plants and get the greenhouse back into production. First, determine where the herbicide injury is coming from. Herbicides or herbicide vapors may be coming from treated plants brought into the greenhouse, from previous herbicide contamination in the greenhouse, or from herbicide vapors drawn into the greenhouse by circulation fans. If you can determine the source of the herbicide injury, you can do several things to eliminate the source of contamination and possibly save damaged plants.

If someone makes herbicide applications near the greenhouse, there's a good possibility that, at the time of that application, circulation fans brought herbicide vapors into the greenhouse. Try to contact the person who applied the herbicide, and ask them to stop herbicide applications close to the greenhouse. If the applications cannot be stopped, consider turning off fans when these herbicides are being applied.

If plants are continually injured when placed into a contaminated greenhouse, herbicide vapors probably are coming from within the greenhouse. You can employ certain measures to decontaminate the greenhouse.

First, remove the desirable plants from the greenhouse. Water wash the entire greenhouse interior with a high pressure sprayer. Avoid any motors, electrical panels and other mechanical devices when water washing. There is unpublished information that indicates that a strong base (e.g., household bleach and ammonia) included in the wash mix (1:10 base to water) helps neutralize herbicides. If this wash is performed, make sure you follow it with a pure water wash. Depending on the herbicide and amount of herbicide that entered the house, you may want to use activated charcoal to help neutralize the herbicide. Before washing, coat the greenhouse floor with a 1- to 2-inch layer of activated charcoal. Allow the charcoal to remain for 1 to 2 weeks, and then remove it. Follow this with a high pressure water wash.

The possibility of herbicide injured plants recovering depends on the sensitivity of the plant or plants to the contaminating herbicide(s) and the dose of herbicide(s) the plant received. Determining the herbicide that contaminated the greenhouse can be done by certain laboratory techniques, but this will do little to help the herbicide injured plants recover. You may try to save injured plants by pruning out as much of the injured plant material as possible. This will produce new growth. By producing new growth, the plant can further dilute the herbicide from its system. Pruning may or may not save the herbicide injured plants, and your only option may be to discard the injured plants.

Information from "Weed Control in Greenhouses" by Mark A. Czarnota, Extension Horticulturist, University of Georgia.

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