Georgia peanuts: thrips raise concern about TSWV

Thrips are on the increase in Georgia peanuts this spring, and that leads to concern about tomato spotted wilt virus (TSWV), which is linked to thrips activity. The insects act as vectors, spreading the virus in young stands. They are particularly troubling in weak or uneven stands because relatively small numbers concentrate on the first plants up and heavily implant the virus.

One way to minimize thrips activity has been to follow the TSWV risk index, which lays out a set of guidelines. The more index points a grower follows, the lower his likely risk of seeing intense TSWV. A key element is later planting, and May 15 has been seen as an optimum date for starting. While earliness has been emphasized with every other field crop in the last 10 years, planting peanuts later became a logical part of a disease management program.

The idea is that peanuts planted in that period have a better likelihood of making a quick, even stand and diluting thrips pressure. There are other points to the index – planting on twin rows, for example, and using planting-time systemic insecticides – but of all the factors the index takes into account, the later planting date was at least a key element. A grower could do everything else right, but an early planting date still put him at great risk, research showed.

The later planting date has been a widely accepted idea, practiced by farmers as far west as central and south Texas. And with the exception of large-acreage growers who must start early, it’s hard to find many farmers in the lower Southeast who begin planting peanuts much before mid May.

Here’s the problem: TSWV rates dropped dramatically as more growers began following the index guidelines. But in 2004 TSWV pressure blipped up. It was worse in 2005, and so were thrips. Yield loss in Georgia to TSWV went from 1% in 2003 to 4% in 2004 to as much about 7% in 2005, based on Extension estimates.

This year’s influx of thrips in Georgia do not portend well for 2006 being a light TSWV season. John Beasley, Extension Peanut Specialist, said this week that it’s too early to say that heavy thrips activity will automatically lead to increased TSWV. But Beasley added that his “gut instinct” tells him it could be a season with problems. He and Extension Entomologist Steve Brown have been comparing notes, Beasley said, and their consensus is that 2006 is shaping up to be the worst thrips year since 1997.

Why are thrips worse?

That’s a question that Brown and other entomologists will be pondering well after harvest. The first assumption is that the weather has somehow triggered an upward population trend. In some areas wheat is coming off early, for example, due to warmer conditions in April, and maybe that flushed more thrips into outlying areas.

Consultants and Extension entomologists already are reporting heavier-than-normal pest pressure in other crops, like sweet corn, may indicate that this will be a challenging insect season, anyway. Thrips have been active in cotton, too, catching stands that were slowed down by adverse growing conditions.

See this weekend’s PeanutFax for more comments.