Thrips

Marijuana Horticulture

by Jorge Cervantes

Identify

More common in greenhouses than indoors. These tiny, winged, fast moving little critters are hard to see but not hard to spot. From 0.04-0.05 inch long, thrips can be different colors, including white, gray, and dark colors, often with petite stripes. Check for them under leaves by shaking parts of the plant. If there are many thrips present, they choose to jump and run rather than fly to safety. But often you will see them as a herd of specs thundering across foliage. Females make holes in soft plant tissue where they deposit eggs that are virtually invisible to the naked eye. Winged thrips easily migrate from infested plants to the entire garden.

Damage

Thrips scrape tissue from leaves and buds, afterward sucking out the plant juices for food. Stipples – whitish-yellowish specks – appear on top of leaves; chlorophyll production diminishes and leaves become brittle. You will also see black specks of thrip feces and little thrips. Many times thrips feed inside flower buds or wrap-up and distort leaves.

Cultural and physical control

Cleanliness! Blue or pink sticky traps, misting plants with water impairs travel. Manual removal works okay if only a few thrips are present, but they are hard to catch. Thrips can be very vexing t control once they get established.

Biological

Predatory mites, parasitic wasps, pirate bugs, fungus, Verticillium lecani, is effective.

Sprays

Homemade sprays such as tobacco-nicotine base; commercial pyrethrum, synthetic pyrethrum, insecticidal soap. Apply two to four times at five to ten day intervals.