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Black drop cloths get edge in sampling for plant bugs

If you’ve been using a white drop cloth to sample for plant bugs in cotton, you may want to change your strategy — black may be better.

And if this year’s anything like 2005, when the insect was a problem over much of the Mississippi Delta, sampling is a necessity for staying on top of the situation.

“Plant bug pressure was heavy last year,” says Angus Catchot, entomologist with the Mississippi State University Extension Service. “With a threshold based on 5 plant bugs per row foot, we were seeing 40 to 46 per row foot in the unsprayed check.”

With such heavy infestations, he says, one spray application likely won’t provide adequate control. “It’ll take two applications, five to seven days apart, and in some cases, maybe three.”

Catchot, who met with growers in the northwest Delta recently, said Gordon Snodgrass, research entomologist with USDA’s Southern Insect Management Unit at Stoneville, Miss., has been monitoring the pest for several years and “we’re seeing some alarming developments” in its resistance to pesticides.

“We’ve had plant bug resistance to pyrethroids in the Delta for a long time, but in many of our test locations last year we were seeing resistance levels that would have resulted in control failures with any of the materials in our organophosphate arsenal. As scary as that is, it’s even more so that we don’t have many new materials in the pipeline.”

An ongoing problem with plant bugs, Catchot says, is that many growers and consultants don’t have a lot of confidence in established threshold levels for the pest. “I wish I had a dollar for every time someone has told me our thresholds aren’t right.”

The sticking point, he notes, is that “there’s no consistency” between the visual sampling methods.

To that end, a multi-state project (Mississippi, Arkansas, Tennessee, and Louisiana) is under way to evaluate threshold levels and sampling methods.

“It’s not that what everyone is doing now is wrong, it’s just that in many cases they’re not doing it the way the program is designed. These inconsistencies can lead to different conclusions as to when to treat. If one person’s sample is below the actual threshold level, he’ll end up spraying too much; if it’s above, he won’t spray enough.”

The project last year involved 10 commercial fields, with four sites in each field, and five sampling methods. Among the conclusions, Catchot says: sweep nets and drop cloths are more efficient than whole plant sampling or the “dirty bloom” method. The latter, he says, is not very practical because it indicates what existed seven to 10 days previous.

“I like the drop cloth, because it catches more nymphs, and one of the things we found is that color can make a huge difference. Black is much better than white — on black, the insects really pop out and glow.”

Catchot said some companies are considering black drop cloths as a giveaway. “I challenge you to give it a try this season — I think you’ll find black works much better.”


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