This is Jack Bacheler, extension entomologist at NCSU with the Thursday Cotton Insect Update. Today is Thursday May 1.
As is often the case with many other damaging insect pests of cotton, one might assume that cotton in the Midsouth, Texas, or even Arizona would take the crown for the highest thrips levels, right? Wrong. As North Carolina and Virginia cotton producers know from experience, and tests confirm, this region has the dubious distinction of having the highest levels of thrips and potential damage in the cotton belt.
To make matters worse, our often cool spring conditions limit plant growth, leaving the tender seedlings in the very susceptible cotyledon to two true leaf stage for extended periods.
As we mentioned last week, May 20-25 often avoids these cool conditions, and the quick seedling growoff greatly reduces the thrips damage window. Additionally, approximately three weeks after these late plantings, levels of adult migrating thrips are often declining.
Seed treatments are hard to beat for convenience and safety, and this technology now represents about half of our cotton acreage. However, growers should be aware that the odds of having to treat for cotton aphids or spider mites increases dramatically following seed treatments compared to Temik. In a series of large scale surveys of our independent crop consultants in 2004-2005 and in 2007, foliar applications were 2.5 to 10 times higher for cotton aphids and 9.5 to 12 times higher for spider mites following seed treatments than behind Temik. Fortunately, even following seed treatments, the amount cotton acreage sprayed for either pest was here still on the low side – at least for now. But if you were one of the producers who had to deal with treatable levels one or both of these pests, they can be a headache. If the status of these pests increases in North Carolina, the impact of increased spraying could well be a factor in choosing an at-planting insecticide approach.
In some years, especially following extended hot dry weather, western flower thrips occur at high enough levels to result in significant control problems. Although tobacco thrips are far and away our most common species on cotton and can be very damaging in their own right, in most cases they can be reasonably well controlled. Cotton producer-supported research conducted here the past two years has shown:
1. Control of western flower thrips with a “normal” rate of acephate (most often Orthene in the past at 0.25 lb active/acre) is at best very limited and often no better than the check plots. Producer and consultant experience has suggested that very high rates of acephate or Monitor (0.5 to 1.0 lb. active/acre) provide some control of “westerns”, and that other organophosphates and pyrethroids fare worse.
2. In another test, Temik 15G at 5 lb. product/acre controlled about 60% of the western flower thrips adults while a seed treatment followed by a foliar spray only control 30% of the western flower thrips. In this same test control of our more common tobacco thrips exceeded 95% with both approaches.
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 few thrips headaches in 2008. We’re due a break.