Did you know that thrips are the only insects that don't have claws? Their "foot", the last segment of the leg, is hoof-like in shape and contains a sticky bladder that helps the thrips to climb on slippery plant surfaces. Thrips are also unique in that 'thrips' ends with an 's' both in its singular and the plural forms. This makes sense... for you will never see a single thrips on your roses - where there is one, you can be sure there are hundreds.
Thrips belong to the order 'Thysanoptera' which includes approximately 4,000 species. Common species include, Banded Greenhouse, Greenhouse, Bean, Blueberry, Camphor, Chrysanthemum, Citrus, Composite, Dracaena, Gladiolus, Grape, Grass, Hollyhock, Iris, Lily Bulb, Onion, Pear, Privet, Tobacco and Flower Thrips. The latter, Flower Thrips, are the bane of rosarians everywhere, from coast to US coast and worldwide. The Flower Thrips is an omnivorous feeder on grasses, weeds (they especially love dandelions), flowers, field, forage & truck crops, fruit & shade trees, berries, vines, etc; but has a preference for grasses, legumes, peonies and ROSES.
The tiny thrips do not so much fly, as get blown around by the wind. Their mouth parts are so small that they can pierce a single pollen grain or fungus spore, and suck out the contents. Without the aid of a magnifying glass, thrips are very difficult to see - they resemble tiny dark threads. Young thrips are lemon yellow, adults amber or brownish yellow with an orange thorax, 1/20 inch long. Some are wingless, but others have two pairs of short wings fringed with hairs. The head is prolonged with a cone-shaped protuberance housing needle-like mouthparts that rasp the surface of a leaf or petal to form a slurry that the thrips sucks up through its cone-shaped snout. The result of this hearty appetite is rosebuds and blooms that turn brown and either ball, petals staying stuck together, or open part way to crippled, distorted blooms with brown edges and/or streaks of brown on the petals, causing the bud or bloom to wither prematurely. Rose leaves can become twisted, distorted and scarred.
The thrips can be seen deep inside the blooms, usually near the base. They have a preference for the lighter colored roses and are most injurious with the June bloom. However, thrips damage to roses is always worse during a dry season - after a wet spring, their is seldom a serious infestation of thrips in June.
Thrips are difficult to control because they are continuously arriving on the rosebuds from from nearby weed, grass and tree flowers. Good rose hygiene is important in the control of thrips. Before thrips become adults, the larvae lives for a short period of time in the ground, usually among the decaying vegetation in the rose beds (leaves, petals, canes, etc), so cleaning up the rose beds regularly will help in controlling the population. Dead-heading is also essential: cut off and destroy spent and infested blooms with the thrips still inside. Some rosarians find chemical controls helpful, but in order to be efficient, the chemical must get deep inside the petals where the majority of the thrips are and also soak the ground around the rose as well. Chemicals used to control thrips include: Malathion, Diazinon (soon to be banned), Orthene and Mavrik.
Sources:
The Handy Bug Answer Book, pages 99, 100
The Gardener's Bug Book, pages 383-5
Rodale's Color Handbook of Garden Insects, page 193
10,000 Garden Questions, page 1273
