Unless you have a magnifying glass, you probably won't see these tiny pests on your plants, but you may notice signs of their presence, including black, shiny speckles (droppings), silvery stippling (masses of tiny discolored scars on plant parts), or, in severe cases, deformed growth.
Magnification shows thrips to be shiny, elongated blackish or yellowish insects. Adults have feathery, fringed wings, and nymphs lack wings. There are many generations per year. Thrips prefer to feed on new, rapidly growing plant tissue where it is easy to hide. Most feeding by thrips causes only slight damage, but high populations can be quite destructive. Feeding thrips can prevent rose buds from opening, and results in deformed petals. Certain species spread viruses to tomatoes and impatiens. Thrips also attack asparagus, cabbage, lettuce, onions, peas, flowers, and fruit and shade trees.
Natural enemies generally keep thrips populations below damaging levels. Conserve natural enemies by reducing or eliminating pesticide use. Locate garden plants away from weedy, grassy borders where thrips live. Keep plants well watered, and fertilize judiciously to prevent overly lush growth. Dormant oil is a useful control on fruit trees.
Photography by Alton N. Sparks, Jr., University of Georgia, Bugwood.org