Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
Thrips are tiny insects that literally suck the life out of your plants, resulting in pale leaves and twisted, discolored plants. One of the best ways to get rid of them is by enlisting the help of their mortal enemies.
What are Thrips?
Thrips (Thysanoptera spp.) are so tiny that without a magnifying glass, they just look like threads on your plants. But despite their size, they are very destructive. They are classified as sucking insects because they feed on the sap of your plants by sucking it out of the plants. They are a scourge in both the vegetable garden and the flower garden.
In addition to sucking all the sap out of plants, they also transmit disease much like mosquitoes transmit malaria when they suck your blood. This dual danger of loss of sap plus disease transmission is what makes thrips so dangerous,
Thrips overwinter in the soil of your garden in both the adult form and as larvae. When the soil warms in the spring, the adults emerge. The females fly to your plants, make slits in the stems and leaves, and lay up to 80 eggs at a time. They do not need to mate to produce eggs. The eggs hatch within a few days or weeks depending on the temperature, and the larvae begin to feed on the plants' sap. Within two weeks, they drop to the soil to pupate into adults.
Because their lifecycle is so short, there can be a dozen or more generations within one growing season.
Use Beneficial Insects
Beneficial insects are insects that eat pests in your garden. They are the best defense against thrips. The Amblyseius cucumeris is a predatory mite that you can purchase via mail order to release into your garden where it will eat both the larvae and eggs of thrips.
Pirate bugs, lady bugs and lacewings are also available by mail order and all love dining on thrips, as well as other pests that they find in your garden.
Be aware that once the beneficial insects have consumed all of the thrips in your garden, they will leave in search of more food. They won't wait around for the next generation to hatch.
Use Insecticidal Soaps
Spraying with insecticidal soaps such as neem oil can be effective in killing thrips. They work by covering the insects and smothering them. Soaps and neem oil coat the insects blocking the pores through which they breathe.
When spraying, make sure that you coat the entire plant. Don't forget the undersides of the leaves and where the leaves attach to the stems. Both are places where thrips love to hide.
Use Insecticides Containing Pyrethrum
Insecticidal sprays are effective in killing thrips, but they also kill all other insects. Insecticides make no distinctions between "good" bugs such as pollinators and "bad" bugs that destroy your plants.
Sprays containing pyrethrum are good choice if you are overwhelmed with thrips and must spray. Pyrethrum is potent but loses its toxicity within a few days, so beneficial insects can safely move back into your garden.
Since pyrethrum is toxic for honey bees, use it early in the morning or at dusk when they are not active. The spray should be dried by the time the honey bees come looking for nectar.
Once you have cleared your garden of thrips using a spray, release predatory insects to prevent the thrips from infesting your plants again. Remember, there are larvae pupating into adults in the soil which will emerge after you have sprayed.
Remove Infected Leaves or Whole Plants
Check your garden daily for signs of thrips. Cut off and discard any damaged leaves that you see.
If the insects have infested most of the plant, remove the entire plant and discard it. Make sure that you throw away your plants in the garbage and not in your composter. If you discard infected plant material into your composter, you risk infecting your compost with thrips which will then be spread all over your garden when you add compost to it.
Remove All Plant Waste From Your Garden
Remove all plant waste from your garden, such as onion tops, weeds, and grass where thrips like to hide.
Use dry mulch like wood chips, because thrips don't like the dryness. They prefer green mulches and plant waste which are moist.
A colony of thrips can decimate your garden. Keep them under control using a mixture of beneficial insects, sprays and sanitary practices.
Questions & Answers
Question: I have for the 3rd year running had a thrip problem in my wooden beam above my bed...they appear in June throughout sept. I've tried everything on the market..sprays, powders ect.. if I can't get rid of them I'm going to have to replace the beams. Any suggestions?
Answer: As far as I know, thrips only eat/infest plants. They can infest indoor plants but not beams. Thrips do not eat wood. I don't think that you have thrips in your beam. Your best bet is to contact an exterminator who can tell you exactly what kind of insect you have and how to get rid of it.
Question: Is there a plant food to kill thrips ?
Answer: No, there are no "baits" or poisons consumed in the form of food for thrips. Insect baits are customarily used for insects that live in colonies. The idea is rather killing individual insects, the baits are carried back to the nests to be consumed by the entire colony resulting in the deaths of all the insects.
Question: I developed thrips on my gladioli which seems to have reduced. Should I remove them and change the soil for new plants?
Answer: You should remove any infected plants. You can try removing the soil in that area in the fall, but you may not be able to get rid of all of the hibernating insects because some may be in the soil in surrounding areas. Your best bet is to purchase the predatory mites that I mentioned which will eat the larvae and eggs. You should also be spraying your plants with neem oil which smothers the thrips.
© 2014 Caren White
Caren White (author) on September 07, 2014:
Thank goodness that there are also a lot of critters who like to eat the bad guys, Flourish. Thank you for reading and commenting.
FlourishAnyway from USA on September 07, 2014:
I've never seen or heard of these. So many garden critters competing for our crops!
Caren White (author) on August 22, 2014:
Thanks, Jackie! Glad you found it helpful. Thank you for reading and commenting.
Jackie Lynnley from the beautiful south on August 22, 2014:
Helpful advice; thank you.
Caren White (author) on August 21, 2014:
Sorry to hear that your vegetable garden didn't do well. Weather has a big effect on how well a garden does. Temperature (too high, too low) and rainfall (too much, too little) are the two big ones. Thanks for reading and commenting.
ologsinquito from USA on August 21, 2014:
I've never heard of thrips. Maybe I had them because my one attempt at starting a vegetable garden was dismal. Even the weather didn't cooperate that year.
Caren White (author) on August 19, 2014:
I totally agree! It may be true because we've had a rainier than usual summer. Thanks for reading and commenting.
Kaili Bisson from Canada on August 19, 2014:
So many nasty bugs in the garden this year...must be the weather.