Thrips are a nasty pest that nearly every gardener will face at one time or another. The first sign of thrips is usually yellow specks all over the leaf surface. Tiny black dots of thrips fecal matter might be scattered on the leaf. With some thrips varieties a silver sheen almost like a tiny snail trail might appear on the leaves as a result of the way thrips feed. Some thrips can cause plant leaves to curl. If you look closely tiny 1/16” long, thin, fast moving bugs can be seen scurrying about.

Most thrips reproduce by laying their eggs inside plant tissue with the eggs hatching in about 6 days, although this can vary a great deal depending on temperature. After the eggs hatch, there are 2 larval stages that feed on plants and cause much of the visible damage. After a few weeks of feeding the larva then drops into the soil for the pre-pupa and pupa stages. They do not feed while pupating. They will then emerge from the pupal stages as a winged adult who is ready to feed on plants and make more thrips.

So now that you know what you’re up against, you should know how to get rid of them. Predator Nematodes applied to the soil will disrupt the thrips pupal stage and reduce the number of adult thrips emerging to reproduce. In light infestations this can be an adequate defense and will eventually wipe out the problem. In heavier infestations, it is best to release some sort of above-soil control in conjunction with the Nematodes. Thrips Predator Mites (Amblyseius cucumeris) are a predatory mite that eats onion and flower thrips (probably the most common variety). They require a high humidity of 75-90% to reproduce and can also supplement their diet with some species of mites.

If your humidity is not high enough for the Thrips Predators, then you might want to consider Pirate Bugs (Orius insidiosis). Pirate Bugs are general feeders that attack thrips, mites, whiteflies, aphids, and many more soft bodied pests. They fly around your plants looking for a meal, and when they find it they use their “piercing-sucking beak” to pierce the insect and suck its juices out. Pirate Bugs prefer thrips larvae, although they will eat adults as well. Pirate Bugs tolerate a wide range of environmental conditions; however they need 15 hours of light or more per day to reproduce.

Green Lacewings are another great general feeder that attacks many of the same insects as Pirate Bugs. They do not fly in their predatory larval stage; however they tolerate conditions that might not be suitable for thrips predators and pirate bugs. They tolerate a wide humidity range and they don’t have a minimum light requirement.

Lacewings are voracious predators that attack almost any prey they can grab, using pincer-like jaws. After injecting paralyzing venom, they suck the body fluids from their helpless victim. Green Lacewings are only predatory for the first 3 weeks of their life, so they might need to be reapplied every 2-4 weeks.

Thrips are attracted to the color blue, so blue sticky traps can be useful tool to catch some of the adults and help you monitor the thrips population. Try to avoid getting thrips by using insect netting over ventilation intakes, check new plants thoroughly for bugs, and every few months use nematodes for prevention. If you do get an infestation, take care of it quickly before it gets out of hand. Thrips can be hard to eradicate, but if you are diligent your plants will come out on top.

Nathan Jackson is the owner of Nature’s Control and Ladybug Indoor Gardens. You can send your specific bug questions to nathan@naturescontrol.com. For more information, to request a catalog, or to find a local distributor, check out www.naturescontrol.com or call (541) 245-6033.

This article was originally published in Garden & Greenhouse Magazine. Garden & Greenhouse is written for small commercial growers, hobby greenhouse owners and indoor/outdoor gardeners and is free to qualified readers. For more information visit http://www.GardenAndGreenhouse.net.

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