The following is an advisory from Ames Herbert.
Thrips species captured on sticky cards at the Tidewater AREC in Suffolk, VA, are increasing, and we expect these counts to rise for several more weeks. The adult thrips are migrating into fields from adjacent winter hosts. Counts of adult thrips have risen from about 20 per card during the second week of April to an average of 90 per card for the first week of May. The species complex consists of tobacco (mostly), eastern flower, onion, soybean, and an occasional western flower thrips (based on a subsample of 30 thrips per card). For more details on sticky card thrips captures, please see the attached graph. Sticky cards will catch all thrips species, not just the pests of cotton, therefore we also sample what is present on the cotton plant itself using soapy water thrips samples. Soapy water samples involve cutting cotton plants, submerging them in soapy water (to dislodge the thrips), vacuum filtering the sample, and counting all adult and immature thrips under a stereoscope. Soapy samples were taken on May 9 and 10 from cotton fields planted around April 20 near Boykins and Ivor, VA (cotton plants were at the 1-2 true leaf stage). Additionally, samples were taken from research plots at the Tidewater AREC that were at the 1st true leaf bud stage. In all samples, only adult thrips were present. This is important because foliar insecticide applications should target the thrips larvae which do most of the damage to seedlings. Historically, we have recommended foliar applications when the first true leaf is just expanded (1/4 inch or so). This usually coincides with the onset of larval activity. Cotton planted around April 20 is at or beyond that stage. Cotton planted a week later has not yet reached that stage (bud, only). Each year is different of course, but the many consecutive cool nights are slowing the progress of cotton and slowing the development of thrips. This may be a year to wait a few more days before making a foliar application, wait until a few more larvae are present on the plants. Thanks to my graduate student, Jessica Samler, and my assistant, Sean Malone, for taking the data used to develop this advisory and preparing the draft. Additional information: advisory-thrips-graph-docx