The cotton in our eleven research trials is in the 1st 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 5 cotton seedlings last week to a high of 148 per 5 seedlings this week. These high counts are in the untreated plots and by comparison give us a good indication of how well the many treatments we are testing are working. Breaking it down a bit, the 148 count means that each 1st true leaf seeding has about 30 immatures feeding on the small bud. They must be standing in line to feed on the leaf cells. In general, the seedlings are still growing slowly so it is difficult to do accurate visual injury ratings—with only one true leaf to rate, just not enough plant material. So this week, we think the thrips counts give a better picture of how products are working, with the idea that by next week as plants push into the 2nd and 3rd leaf stages, treatment differences in levels of plant injury will begin to express.
Overall, foliar sprays alone (no seed treatment) of several products are providing some decent levels for control of immatures but not at the levels we think are needed to achieve cotton yield potential. We will provide more specific results soon, but one caution, 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 7 or less per 5 seedlings compared with 85 per 5 seedlings in the untreated control.
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.
Peanuts are a different story. Over the last several years we have seen a trend where thrips numbers and injury to seedlings lags behind cotton by a week to 10 days. That is what we are seeing with untreated peanuts only showing the beginnings of the injury, at most a 3.5 on the 0-10 injury rating scale. This is compared to years when the injury can exceed 6 to 8 at the peak. Where cotton should be treated soon, peanut treatments could be delayed until the middle to end of next week.