Greenhouse - Weed Control and Herbicide Use in Greenhouses

Summer sales are ending and poinsettia planting season has not started in greenhouses. Now is the time to perform maintenance in empty greenhouses. Remove all plant materials, do not keep a few plants in an otherwise empty house. By shutting down fans for a few days, you can solarize a house and kill many insects and other pests with the high temperatures that develop. Remove all weeds before they go to seed. Apply control measures to weeds growing on greenhouse floors and walkways. This includes certain non-selective herbicides with limited residuals. The following are your options:

Herbicides labeled for use in greenhouses. These herbicides are intended for use under greenhouse benches and walkways and not for use in pots.

1) Diquate (Reward and others), 0.75 oz (22 ml) per gallon of water, Controls all emerged vegetation to which solution is applied. Need to add surfactant to spray solution.

2) Glufosinate (Finale) 3-4 oz (89-118 ml) per gallon of water, Controls all emerged vegetation to which solution is applied. Make sure that circulation fans are turned off during application. When making application, be sure to use low pressure nozzles that produce larger droplets. Do not use in greenhouses with food-producing crops.

3) Glyphosate (Roundup Pro and others), 2.5-6.5 oz (75-190 ml) per gallon of water. Make sure to use a glyphosate product that contains 42% or greater active ingredient. Controls all emerged vegetation to which solution is applied. If used in the greenhouse, fans must be off and all desirable vegetation must be removed from the greenhouse.

4) Pelargonic acid (Scythe), potassium salts of fatty acids, 1.3-13 oz (38-384 ml)per gallon of water. Controls all emerged vegetation solution comes in contact with. Avoid contact with desirable plant material. When making application, be sure to use low pressure nozzles that produce larger droplets.

*1 oz = 30 milliliters (ml).

Do not use any other herbicides in greenhouses unless labeled. Many residual herbicides will volatilize in a greenhouse environment leading to injury on subsequent greenhouse crops. This could potentially render greenhouses unusable for a period of time.

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