By Nathan Jackson
The Pest: Thrips (multiple species)
First Signs: Leaf surfaces finely speckled with yellow spots. A silvery metallic looking sheen may cover leaf surfaces. Black specks (thrips fecal material) dotting the leaf surface.
Identification: Thrips are a common pest in southern Oregon. They are small, about 1/16”, but larger than a spider mite. They are long, thin, and move very quickly. Many gardeners report thrips as a small “worm with legs.. Larvae and adults look similar, but adults have wings and can fly a short distance. They feed by scraping and rasping at tender leaf surfaces. Thrips are a vector for diseases such as tomato wilt virus. In a bad infestation the leaves can become twisted and distorted, and eventually the plants can die.
Life Cycle: Thrips overwinter in the soil. In the spring, they emerge from the soil and reproduce. Females lay eggs into the tissues of flowers, leaves or stems. Each one can produce up to 80 eggs, which hatch within a few days in warm weather. The larvae do not have wings, and they feed on the plant tissue. After several nymph stages, most thrips drop to the soil to pupate. They emerge as winged adults ready to feed on plants and reproduce. There can be multiple generations per year.
Control: Predator nematodes can be applied to the soil in spring and throughout the growing season to disrupt the thrips’ life cycle. The nematodes will attack the thrips pupae before they emerge from the soil. They are a very important predator to use to help prevent and control thrips.
Getting rid of thrips is very difficult without treating the soil stage. Hypoaspis mites (a small mite) can also provide some soil control, although predator nematodes are more effective.
In heavy outbreaks, it is also important to use predators for above-soil control. Green Lacewings (Chrysopa rufilabris) are very good general feeders and will handle a variety of environmental conditions.
The pirate bug Orius insidiosis is extremely effective against thrips, but it requires at least 15 hours of light per day to reproduce. Adults can fly, which allows them to quickly go from plant to plant.
Thrips predator mites (Amblyseius cucumeris) are affordable little mites that eat thrips and russet mites. They do best in a high humidity environment above 70%.
Amblyseius swirskii is another russet mite predator that can also help control thrips. It is related to Amblyseius cucumeris but does not require the high humidity. Thrips are attracted to the color blue, so Blue Sticky Traps can be used to help monitor and reduce their population.
Thrips are not difficult to find in nearly every garden in southern Oregon, whether cannabis or veggies are growing. A few here or there are not a serious problem, but in large populations they can be very serious pests.
You can discourage thrips by keeping weeds and grass mowed down around your garden. Provide a healthy population of beneficial insects around your garden before you find any pests, and be sure to regularly check your leaves for any signs of trouble.
An ounce of prevention is worth a pound of the medicine.
Nathan Jackson is the owner of Nature’s Control and Ladybug Indoor Gardens. Located in Phoenix, Oregon, Nature’s Control has supplied growers with beneficial insects for over 35 years. He can be reached at (541) 245-6033 or firstname.lastname@example.org.
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