Much was made earlier in the spring about heavier than usual flights of thrips moths.
So far Virginia Tech Entomologist Ames Herbert says this hasn’t prevented researchers from being able to manage thrips in test fields with a combination of seed treatments and a number of foliar-applied insecticides.
In his latest Virginia Pest Advisory, Herbert says, “Cotton in our 11 research trials is in the first true leaf stage. We are rating these each week for injury (visual ratings) and numbers of adult and immature thrips (soapy water samples, 5 plants per plot).
“Numbers of immature thrips have more than doubled since last week, from a high of 40 immatures per five cotton seedlings last week to a high of 148 per five seedlings this week.”
Herbert says such high thrips counts are providing a measuring tool as to how effective various treatment methods are working. The 148 count, he says, means thrips seem to be waiting in line to feed on the leaf cells. He cautions that one true leaf isn’t enough plant material to allow accurate visual injury ratings.
“Overall, foliar sprays alone (no seed treatment) of several products are providing some decent levels for control of immature, but not at the levels we think are needed to achieve cotton yield potential,” Herbert says.
One cautions, he warns, “As in the last few years, data show that we should avoid using pyrethroids.”
The treatments with the fewest number of immatures are the seed treatments followed by a foliar application.
Several product combinations are working well. For example, in one trial the numbers of immatures in the better treatments range from seven or less per five seedlings compared, with 85 per five seedlings in the untreated control, Herbert says.
What are the recommendations?
“I think, based on the high numbers of immatures we are seeing this week, we may be at or near the peak. This is the best time to make that foliar application to minimize seedling injury.
“The results of that application will not be visible for 4-5 days, until the next leaf emerges, which should look normal, healthy, not crinkled or worse, blackened,” the Virginia Tech Entomologist concludes.