In 2015, dreaded chili thrips arrived in California from Texas and Florida. Originally from Southeast Asia or India, this pest first hit North America in 1991 and is expected to be a permanent part of our gardening experience from here on out.
Let’s see what we’re up against.
Before we do that, however, let’s get one thing clear. Whether you are talking about many thrips, or just one (and there is never just one), they are both referred to as “thrips”, with the “s” on the end. I know, it’s strange, but there it is. It comes from an 18th century word meaning “woodworm”, which is even more strange since these pests are disease-carrying sap-suckers.
So, what does a thrips look like?
Chili thrips description
Like other thrips, chili thrips (Scirtothrips dorsalis Hood) are really tiny - often less than 1/20” long. That works out to 8 or 9 thrips, standing nose-to-tail, across the head of a dime. Their pale bodies are thin and they have dark wings, but you may never get that close. What you may see is light-colored flecks of movement as you walk past a plant. That’s your first clue there is a problem.
Plants vulnerable to chili thrips
Your habaneros and Scotch bonnets are not the only plants susceptible to these pests. In fact, over 100 species [no, make that 200 species], from 40 different plant families [rather, 70 families], have been identified. Host plants include fruit trees, such as apples, bananas, cashews, citrus, figs, lychee, mango, pears, and even the beloved cocoa bean. Other garden favorites include asparagus, basil, beans, blueberries, buckwheat, corn, eggplant, grapes, peanuts, sweet peppers, soybeans, strawberries, and tomatoes, as well as many popular ornamentals, including chrysanthemums, coleus, camellia, Gerber daisies, poinsettias, pyracantha, roses, snapdragons, and zinnia.
Damage caused by chili thrips
Symptoms of chili thrips infestation are first seen as damage to the upper surfaces of leaves, creating yellowish-green or brown angular spots on the upper surface and a grey sheen on the under surface. Leaves may become thickened or start curling. As nutrients and water are pulled from the plant, stunting, bronzing, distorted or elongated leaves, and flower bud scarring are also seen. Severe infestation can lead to the complete defoliation of a plant and these pests can carry tomato spotted wilt virus, peanut necrosis virus, peanut chlorotic fan virus, and tobacco streak virus.
Compounding the problem, chili thrips damage looks a lot like chemical overspray, aphid feeding, and micronutrient deficiencies.
Chili thrips lifecycle
Female chili thrips insert eggs into leaves, petioles, fruits, leaf axils, in curled leaves, and in leaf litter. In other words, they can be anywhere. Those eggs hatch in about one week and go through two larval stages in the second week. A single adult female can lay 60 to 200 eggs in her lifetime. That works out to a lot of sap sucking, disease-carrying insects.
Controlling chili thrips
Fast moving, highly prolific, and devastating to many of our garden plants, chili thrips have already developed resistance to insecticides containing asbifenthrin, cyfluthrin, and permethrin, so don’t bother. As of 2016, chili thrips had not yet developed resistance to insecticides containing acephate, imidacloprid, and orspinosad, but that window of opportunity may already have passed, and who wants those chemicals on their food anyway? Spinosad is actually more effective and less damaging to the environment. Sticky barriers may be used to monitor for chili thrips, but they won’t control the problem.
Your best defense against chili thrips is to encourage beneficial insects, such as green lacewings and minute pirate bugs. Certain predatory mites and thrips and parasitic wasps will also help in the battle against chili thrips. These garden helpers are all attracted to gardens with a wide variety of plants and flowers, a clean water supply, and the absence of broad spectrum pesticides. Sadly, releasing purchased predators into the garden rarely works out. If conditions are good, they will come to you. If conditions are not good, it doesn’t matter how many times you buy and release beneficial insects. They will simply leave or die.
Dusty conditions should also be avoided. Give susceptible plants an occasional quick shower with the garden hose in the morning to make life more difficult for thrips of all sorts. Also, stressed plants are more susceptible to infestation than healthy plants. This is yet another reason for selecting resistant cultivars that are suited to your microclimate, putting them into quarantine until proven healthy, feeding and watering them when they need it, and then giving them a helping hand with row covers as they become hardened off to your garden. Since shearing cuts off the ends of all twigs, it should be avoided if thrips are suspected. It is simply too stressful for the plant. Reflective mulch may disrupt thrips flight, if you want to try that.
Infested foliage should be removed, bagged, and taken to your local County Extension Office for identification. If you don’t have time for that trip, please throw the bag in the trash. Do not compost plant material infested with even one chili thrips.
You can grow a surprising amount of food in your own yard. Ask me how!