Pest Management in High Tunnels
Tomatoes, field greens, berries, and more can be grown under high tunnels in Utah to get produce early in the season. Pests on high tunnel-grown plants are similar to those on plants in field production, but conditions inside tunnels are often warmer and more humid, resulting in greater pest pressure. Following preventive practices throughout the growing season can avert future problems.
Every high tunnel grower should implement a regular scouting program. Early warnings of pest problems will enable the grower to avoid an outbreak. Typically, at least 10% of the plants should be inspected weekly. Over time and with practice, diseases and pest insects will become easier to locate and identify. Don’t rely on visual inspection alone; yellow and blue sticky traps are an inexpensive way to determine the presence of whiteflies, aphids, fungus gnats, and thrips.
Diseases typically are not a problem in well managed high tunnels. Problems arise when air does not flow inside the tunnel, plants are crowded together, or the plants are over-watered. These types of scenarios increase humidity, promote spread of pathogens from plant to plant, and create an environment conducive to plant diseases such as gray mold, phytophthora root rot, and powdery mildew.
To prevent diseases:
- Space plants properly to avoid excessive shading and to enhance air circulation.
- For larger tunnels, add ventilation (gable-end vents, etc.) and fans.
- Select disease-resistant varieties. The seed packet or plant label will specify the resistance such as V for verticillium wilt, F or FW for fusarium wilt, N for nematodes, A for alternaria or EB for early blight. There are several disease-resistant tomato varieties with good yields and taste qualities.
- Practice good sanitation by removing all diseased plants from the tunnel quickly and carefully (to prevent further spread), removing crop residues each year, maintaining a weed-free tunnel, and using only clean mulch.
- Test the soil for nutrients at least every other year and provide the necessary amendments and water necessary for optimal crop growth.
- Utilize a good crop rotation scheme, such as rotating plants in the cabbage family (kale, radish), beet family (chard, spinach), or carrot family, with lettuce.
- In winter, open the high tunnel to kill tender overwintering pest insects or fungal spores.
Botrytis (left) is a disease that can be prevented by proper plant spacing and reducing humidity in high tunnels, and verticillium wilt (right) is a soil borne pathogen that can be eliminated with proper crop rotation.
Like diseases, insects are typically not a problem, especially early in the season when the tunnel prevents immigration of aphids and other early season insects. But as temperatures rise and the tunnel remains open, pests with a broad host range like spider mites, thrips, aphids, and sometimes whiteflies, or even ants, can be a problem. In addition, insect pests that successfully overwinter inside the tunnel will emerge earlier than outside the tunnel.
Insect management without pesticides is ideal because application of chemicals in tunnels is more hazardous than in the open field due to the closed environment. Other options for insect pest management are:
- Trap crops. Some plants are highly attractive to certain pests, like thrips on ‘New Guinea’ impatiens, and can be used to draw the pest away from the desired crop. Trap crops are then destroyed.
- Beneficial insects. Purchasing and releasing beneficial insects is not practical when crops are grown outdoors, but in high tunnels, which are partially enclosed, beneficials may remain in the area to reduce insect pests. Parasitic wasps such as Aphidius colemani can be bought to control aphids and Encarsia formosa can be released to control whitefly. Suppliers of beneficials provide instructions on their release and management.
- Floating row covers can be effective at preventing certain pests like flea beetles, leaf hoppers, and leaf miners from reaching the crop. They must be put in place and sealed immediately before opening up the high tunnel.
- Insect repellents such as hot pepper, garlic, or kaolin clay may provide some control of certain insects.
- Entomopathogenic nematodes applied to the soil can help combat certain root-feeding or soil-overwintering pests like root weevils, flea beetles, cucumber beetles, and others. Beneficial nematodes require moist soil to be effective, and for this reason, are typically not used in field-grown crops in Utah. But in a high tunnel with a shade cloth and irrigation, the soil may remain moist enough for the nematodes to work.
There are a few low toxicity insecticides to choose from when a treatment is necessary:
- Horticultural oil (0.5-1% in water) and insecticidal soap target soft-bodied insects like aphids, whiteflies, thrips, and spider mites.
- Pyrethrin is mildly effective on most other pests.
If a stronger insecticide such as a pyrethroid or carbamate is necessary, determine if the material is registered for greenhouse use, and if so, follow the directions on the label and always wear appropriate protective equipment.
USU Extension specialists Dan Drost (vegetables), Brent Black (fruit), and their graduate students have created a series of fact sheets on building high tunnels and how to grow crops inside them. They can be accessed from their Production Horticulture website.
-Marion Murray, IPM Project Leader