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Field and Forage Crops |
We are in need of significant rainfall across most areas of North Carolina. In general, thrips levels are on the high side at present, as was the case in both 2000 and 2001.
Increased moisture will both help cotton seedlings grow more quickly and also enhance insecticide uptake. Initial field checks for thrips should begin around the expanded cotyledon stage. These checks can be done along with walking fields for stand and weed checks. For the most part, if new plants look healthy when examined close up, thrips are not likely a problem at that time, and closer scouting is not needed. These preliminary inspections can be carried out rather quickly. Of course, healthy-looking plants can change rapidly if insecticide uptake diminishes, or if thrips levels increase suddenly. If plants from the cotyledon stage through about 5 true leaves look ragged, have small silvery spots on the cotyledons, show dull, cupped or deformed leaves, or have damaged buds, thrips may be the problem. Here, closer observations are required to determine the possible presence of a live damaging thrips population.
If prioritizing fields for potential thrips establishment is necessary, consider scouting the seed treatments Gaucho and Cruiser first, followed by Di-Syston and Thimet and the 3.0 pound rate of Temik, and finally the 5.0 pound rate of Temik. If thrips levels and hot, dry weather conditions continue (or resume), a foliar insecticide treatment may be needed with any of the above options.
A sample of at least 10 seedlings selected randomly from throughout the field is suggested for finding live thrips. Both the various-colored larger adult thrips and the yellow, very small immatures may be present; the adults are more common earlier in the season. Magnification with a hand lens may be helpful to see the small immature thrips. A treatment threshold of approximately 25 percent or more plants showing significant injury to new leaves (with an average of about one thrips per expanded cotyledon or first true leaf plant, or an average of two or more thrips per 2 to 5-leaf plants) is suggested.
Expect thrips flights to be heavier in hot, dry weather. Even under conditions favorable for good at-planting insecticide uptake, seed treatments will probably only control thrips for about 3 weeks after planting. Finally, in Roundup Ready cotton, a single combination thrips insecticide plus glyphosate application timed for the 3 to 5-leaf cotton stage may be too late for minimizing thrips damage, particularly with seed treatments.
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Last modified on May 6, 2002 by Stephen J. Toth, Jr.