Insect and mite control options for plants grown in greenhouses
June 6, 2013
Whether you grow fruit and vegetables in a traditional garden space or in a protected space such as a greenhouse, low tunnel, hoop house, and/or high tunnel, you will eventually have insect or mite problems.
Structures not only protect the plants from the elements but also provide optimal growing conditions for pests.
Scouting, correct identification, and understanding the feeding damage and reproductive methods of these pests are critical to any good defensive strategy.
It is important to understand control options available and have a plan in place to quickly implement tactics that work best for your production strategy.
If you choose to use biorational or conventional pesticides as control methods it is important to know that the Wyoming Department of Agriculture classifies hoop houses and high tunnels as greenhouses.
This is important to note as all Worker Protection Standard regulations for greenhouse workers must be followed.
There are many control options available to you and the best management plan utilizes Integrated Pest Management Strategies (IPM).
IPM can be defined as: A sustainable approach to managing pests by combining biological, cultural, physical, and chemical tools in a way that minimizes economic, health, and environmental risks.
In other words it is the understanding of all possible controls and utilizing the best combination of tactics to manage the problem — consider IPM as a "toolbox" full of control options. Pest Detection by Traps
In order to implement a proper control plan you must first identify the insects present and one way to do this is by trapping what is there.
Commercially available yellow sticky traps in high tunnels will catch winged insects including aphids, leafminers, thrips, whiteflies, fungus gnats, and shore flies.
Blue traps are sometimes better at detecting western flower thrips.
Attach sticky traps to a wooden stake and place the stake vertically in or near a plant at or just above the top of the foliage.
Other pests can be trapped by placing the sticky trap just above the soil surface.
Be sure to place some traps near vents, doors, and other areas where pests may be found. Some growers place traps outside of a high tunnel to help detect insects moving in from outside. The number of traps to use will depend upon your objectives and ability to inspect them.
A minimum number should be two to three per structure, but more will be better, especially if using traps to monitor whitefly population trends.
A good rule of thumb in large structures is to use 1 trap per 1,000 square feet of farmable or production space.
Traps should be visually inspected weekly.
Captured insects should be identified and counted to determine the infestation level.
Estimates of pest population densities are usually sufficient to determine if control measures are needed.
Some people prefer to deploy traps for shorter periods; for example, a few hours or a day, to get a better picture of insect activity at that moment.
Number the traps and create a map for reference so all traps can be monitored.
Pest Detection by Plant Inspection
Sticky traps will not replace plant inspection as a pest detection method. Whiteflies occur in localized infestations that traps may not detect.
Non‐winged aphids and spider mites are not caught on traps.
Therefore, plant inspection is a very important part of a pest management program. Inspect plants in all areas of the high tunnel, looking underneath leaves near the top, middle, and lower parts of plants.
A 10‐30X hand lens can aide in detecting plant pests. It is important to identify what is there and take appropriate control measures when necessary.
The most common greenhouse pests include: whiteflies, aphids, mealybugs, scale insects, thrips, flies, leafminers, "caterpillars", and spider mites.
A little knowledge of insect biology particularly the types of mouthparts and feeding damage they inflict can assist you in the identification of these and other insect pests.
Some control strategies can be implemented ahead of time to mitigate a potential problem. Other control strategies must be implemented immediately once you have identified the pest.
Regardless, you must have a control strategy that can be best implemented to suit your needs.
Destroy crop residues promptly after harvest.
The longer these plants remain, the greater the chances for pest problems.
It is recommended not to compost plant residue in a high tunnel as it can become a pest harborage.
Also, do not place the crop residues immediately outside of the high tunnel; the flying adults from many insect species will simply move back inside.
Vegetable gardens planted adjacent to a high tunnel can also become sources for recurring infestations.
If an infestation is isolated to a few plants remove them or the affected tissue and discard away from the area of production
Screens can be useful in reducing the movement of some insects into a high tunnel.
Whiteflies, leafminers, Lepidoptera (moths), and winged aphids can be excluded relatively easily.
Thrips are very difficult to exclude because of the small screen mesh size required.
The use of screens will require increasing the screen surface area over openings in a high tunnel to compensate for reduced air flow.
The calculations for surface area increase can be made in cooperation with the screen supplier.
High tunnels with mechanical ventilation can be screened more easily than high tunnels with natural ventilation.
Colored plastic mulches have been shown to have some repellency of some of the pest insects. ❖