Thrips can enter greenhouses through migration, or via contaminated cuttings or seedlings.Photos ©Frank Peairs, Colorado State University, Bugwood.org
Chilli thrips (Scirtothrips dorsalis ) attack plants with new foliage growth, and deform and at times discolor foliage. Chilli thrips are much smaller than western flower thrips, so they are extremely hard to see when you’re scouting.
Brett Alldredge, former pest management supervisor at Greenleaf Nursery in Texas, handled pest and disease control for 450 acres of ornamental crops. In Texas, Alldredge says chilli thrips start in April and continue to be a problem through October, peaking in the hot summer months.
“Those are a real challenge because they fly in waves, and they attack anything that flushes,” he says.
Matt McClellan is editor of sister publication Nursery Management. Contact him at mmcclellan@gie.net .
THE FACTS ABOUT CHILLI THRIPS DESCRIPTION: Chilli thrips are extremely small and difficult to distinguish from other thrips species without the aid of a good hand lens or compound microscope. Adults are pale with dark wings and less than 1 millimeter in length. Immature chilli thrips are also pale in color and resemble the immature stages of many other thrips species.
Symptoms: Silvering of the leaf surface Linear thickenings of the leaf lamina Brown frass markings on the leaves and fruits Gray to black markings on fruits often forming a conspicuous ring of scarred tissue around the apex Fruit distortion and early senescence of leaves Management: Treating the soil of infested plants is not effective. Therefore, systemic insecticides should be applied as a foliar spray. Pyrethroid insecticides are not effective against chilli thrips and should not be used, since they are toxic to natural enemies. Soft products, such as insecticidal soaps, appear to suppress chilli thrips populations. To be effective, these products need to be applied on a regular basis. Thrips populations have been shown to increase dramatically once applications have stopped. To prevent insecticide resistance from developing, it is important to rotate insecticides between chemical classes with different modes of action. Predators such as the minute pirate bug, predatory mites and even predatory thrips have shown potential to control chilli thrips.
Chemical control: No insecticide will provide complete control of thrips. It is important to detect and start management strategies before thrips populations have a chance to increase to moderate or high levels. Use the shortest labeled interval when pest pressure is high and temperatures are warm. Insecticides should be rotated by changing modes of action with each treatment or at most with each generation of thrips, unless the label indicates otherwise.
Biological control: Biological control programs should begin at the first sign of thrips. Sticky traps may help to detect thrips up to a month before they are seen on plants. Yellow sticky cards or ribbons should be hung just at the tops of plants and examined weekly. Blue sticky cards will sometimes, but not always, catch more thrips than yellow sticky cards. Thrips are the tiniest insects you will find in any numbers on sticky traps. Thrips are found with wings folded, so they appear like tiny brown flecks of peat moss. Some specimens will show hairs on edges of wings when viewed with a hand lens; often their stocky antennae stick out at the front in a V-shape.
Sources: University of Florida IFAS , Texas AgriLife Extension
