Forget everything I predicted last week. Most of it was wrong. I had a mentor early on in my career who very wisely said, “If you try to predict insects, they’ll make a liar out of you every time.” So true he was. Last week I suggested that we might have a relatively light thrips year; that based on the excellent soil moisture and warm growing conditions up to that point, cotton might grow so quickly as to not need extra foliar sprays. Two major things have changed. One, the weather took a dramatic turn to the cool side. Since May 11, we have had five nights in the 40s&not good cotton weather. We have continued to get rain, heavy in some spots, with up to 3 to 6 inches in single events. Most of our cotton is germinated, in the 1st to 2nd true leaf stage, but the cold weather has it ‘sitting still’. To make matters worse, thrips populations are increasing. As I said in last week’s email, we are using yellow sticky cards to monitor thrips populations in five locations across our cotton region. We check and replace the cards two times each week, on Mondays and Thursdays. The counts are up (see the attached line graph with sticky card data counts from the 5 locations), and based on what we know from sampling over the past few years, the peak has not occurred. When cotton is growing so slowly, plants are very vulnerable to thrips feeding. Thrips concentrate their feeding on the tiny seedling bud, or growing point. Just a few days of intensive feeding can have dramatic effects by stunting plants, greatly slowing maturity, or in really bad cases, will even kill the seedling. And in our experience, when plants are ‘sitting still’ it does not take many thrips per plant to cause significant damage.
So what should growers do? Scout fields and consider a foliar treatment if more than 10% of plants have noticeable damage to the bud. Damaged buds will be deformed and blackened. Bud damage indicates that whatever was applied at planting, seed or in-furrow treatment, is no longer doing the job. Fields that had heavy or continued rains will be at the highest risk as any planting time insecticides will most likely be washed out of the system. I have been asked about what to spray and how much. To date, our best foliar control has been obtained with acephate (e.g., Orthene). Pyrethroids do a good job, but never quite as good as acephate. Each year we do a lot of cotton thrips trials and we have yet to see an Orthene failure. But, it has happened on a few growers’ fields where western flower thrips have become the primary pest species. Orthene does an excellent job of controlling tobacco thrips, still our primary pest species, but does a poor job on western flower thrips. Pyrethroids are no better, even worse in some cases. To date, we have only seen ‘westerns’ as the primary pest species in a very few fields. The great majority are still infested with tobacco thrips, which means they can be protected with 4 to 6 oz of Orthene per acre. We recommend that broadcast sprays go out with enough volume to achieve good coverage of the seedlings. I tell folks that good coverage means seedlings should be completely wet after the sprayer passes over. Higher rates of Orthene are not needed for tobacco thrips, and higher rates are not more effective on ‘westerns’. Last year we found that the best product for controlling ‘westerns’ was Radiant SC (a Dow AgroSciences product). This would be a costly choice and only warranted if a good thrips sample and identification by a lab verified the problem. Let’s hope ‘westerns’ are not a big issue this year. Based on what we know today, we are still recommending the ‘old standards’. Additional information: stickycards-mar21-09-ppt