Controlling arthropod pests in greenhouses can be a challenge since these protected environments provide ideal conditions for development of some common plant pests. Additionally, the structure itself excludes natural enemies from attacking these pests, allowing their populations to develop more quickly. With this in mind, there are a few steps we should take to get crops off to a clean start.
Eliminate all weeds
Eliminate weeds both inside structures as well as 10 to 20 feet around the outsides. Gravel around the outside of greenhouses can be used to reduce weed growth. These weeds can serve as sources of arthropod pests, as well as harbor inoculum that some insects can vector to plants, resulting in disease. The same is true for ‘pet’ plants in greenhouses.
Consider using insect screening on ventilation openings. High tunnels with drop walls can be fitted with permanent screening inside drop walls.
If possible, keep annual vegetable production separate from ornamental production. This is best done by using separate greenhouses or high tunnels. Pests on ornamental plants can rapidly colonize vegetables and the plant protection chemicals may be very different between these production systems.
Reduce clutter and clean the structure
Avoid storage within structures; these areas can provide shelter for some pests. Residues from previous crops must be removed and those areas cleaned thoroughly.
Begin monitoring for pests
Use weekly plant inspection and yellow sticky cards. Keep records; write down what you find and where you find it! Generally, in a standard high tunnel, I examine five areas containing three plants that are scattered in the planting and representative of the house. Find a magnifying lens, hand lens, or microscope to identify pests. UK Extension publication, An IPM Scouting Guide for Common Problems of High Tunnel and Greenhouse Vegetable Crops in Kentucky (ID-235), will help you identify common pests and diseases.
Get ready to spray
Check the pesticide sprayer to be sure it operates well. The start of the crop is often the time to recalibrate equipment. Make certain that thorough coverage can be obtained with your equipment when plants are large and dense. Inspect your chemicals to make certain they are sufficient and in good condition. Be sure you have the personal protective equipment supplies you will need for the crop cycle.
Consider an early-season systemic for recurring pests
Pre-harvest intervals often prevent the use of systemic insecticide applications later in the crop cycle.
Understand biocontrol options
Common pests in greenhouses can be managed using commercially available natural enemies. Pests that can be controlled this way include spider mites, whiteflies, thrips, aphids, and mealybugs. Many common greenhouse insecticides may not be compatible with these natural enemies of pollinators.
By Ric Bessin, Extension Entomologist