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NC State Extension

Thrips

Injury and damage. Various thrips species feed and reproduce on the leaves and buds of soybean seedlings. Their feeding creates bleached-out lesions along the leaf veins and gives a silvery/bronzed appearance to the leaf surface when damage is severe. Often, injured plants will have numerous black and white cross-striped adult thrips and yellow immature thrips on the leaves; these insects are very small (less than 1/10 inch) and are torpedo shaped. While thrips always occur on soybean seedlings, it is only during outbreak years that they cause concern. In particular, during dry weather and on earlier planted full-season soybeans, thrips populations can soar when plants are growing slowly. Under these circumstances thrips injury can occasionally kill seedlings, although this is rare. Other stressors, such as herbicide injury, can add to thrips damage and cause plant loss.

Insecticide Management. Multiple research trials have indicated that, although plants may look very poor, thrips seldom justify foliar insecticide treatment. Furthermore, in multiple research trials, yields have never been show to benefit from any insecticidal seed treatment. Although many of these products reduce thrips abundance and may produce a healthier looking seedling, soybean plants are thought to compensate for this early injury. Finally, research has found that severe thrips injury may increase damage from post emergence herbicides that cause leaf burn. This may be a concern in fields planted to conventional soybeans, due to glyphosate weed resistance.