This is Jack Bacheler Extension Entomologist at NCSU with the first Cotton Insect Hotline tape of 2009. Today is Wednesday, April 29.
As if cotton producers needed a reminder, the North Carolina and Virginia area has the dubious distinction of having the highest levels of thrips and potential damage in the Cotton Belt. It’s probably no coincidence that our states probably also have the highest ratio of surrounding host vegetation to small average cotton field size. To make matters worse, our often cool spring conditions limit plant growth, leaving the tender seedlings in the very susceptible cotyledon to two or three true leaf stage for extended periods. Thrips damage at this growth stage can result in significant yield losses and maturity delays
Unfortunately, our often cool wet seedling grow-off conditions, coupled with the very high ratio of thrips host acreage to small average cotton field size and resulting high thrips levels, often seem to create a ‘perfect storm’ of thrips headaches, especially on early planed cotton – but that’s probably no surprise to anyone who’s listening.
So, what do we do? For starters, cotton producers should plan on using either the 5 lb. rate of Temik 15G, or one of the seed treatments (Cruiser, Gaucho Grande, Avicta, or Aeris). For cotton planted in April or during the first 3 weeks of May, plan on a foliar application for thrips following a seed treatment, often best timed at the 1st true leaf stage, or at three weeks following planting when the seed treatment activity runs out. In the case of Temik, this application, if needed, should be based on scouting for the tiny immatures on the new leaves or in the bud area with the aid of a hand lens. Still, in the past three years over 80% our producers used a foliar treatment following Temik and over 98% following a seed treatment. Although expensive, approx. 6% of our producers used a combination of a seed treatment plus 5 lb. of Temik. Only 34% of those acres needed a follow-up treatment for thrips with a foliar insecticide.
If needed, any additional foliar applications for thrips should also be based on inspections of the bud area for live immature thrips. In this case, don’t be fooled by crinkled older leaves – they’re not going to straighten out.
On a positive note, with cotton planted on or after May 20-25, we’ve had pretty good luck with a seed treatment or the 3-4 lb. rate of Temik without a follow-up foliar treatment for thrips, though scouting is still highly recommended.
An old myth about “late” planted cotton has persisted in North Carolina for many years. That is, cotton planted after about the first week in May was thought to loose approximately 10 lb. of lint per acre on average for each day past this date. This “finding” was largely based on drawing a straight line on a graph from high yields in early May to low yields in June planed cotton. More recent information has revealed that this relationship was quadratic, not linear (a straight line). This finding translated into essentially no yield loss for cotton planted here in mid to late May. We have long known that cotton planted later in May his far less subject to thrips damage than cotton planted in late April to early May, primarily due to the shorter “window” of seedling vulnerability under warmer grow-off temperatures.
In 2006, North Carolina producers planted 860,000 acres of cotton. For the past two years, our cotton acreage has dropped by approximately 50%, significantly shortening the time to plant. This may be good time for cotton producers here to consider planting dates between May 10 to 25. Planting dates in this range could well present a combination of good yield prospects coupled with far fewer headaches.
In essentially all of our research trials, when the cotton plants have an average of approximately 5-6 true leaves with adequate moisture levels and reasonably warm weather, thrips control was no longer needed. Let’s keep our fingers crossed for warm moist conditions conducive to rapid seedling growoff and few thrips headaches in 2009 – and perhaps more mid-May cotton planting dates. We’re due a break.