Insects cost Mississippi cotton growers nearly $70 million last year, says Angus Catchot, with tarnished plant bugs responsible for more than half that amount — almost $40 million.

A distant second was the bollworm/budworm complex, at $14 million, and spider mites third at almost $8 million.

Fewer cotton acres in recent years have been a factor, Catchot says, concentrating insects that would otherwise be diluted across much larger acreages.

“Cotton doesn’t produce a lot of insects that move into other crops,” the Mississippi State University associate Extension professor of entomology and plant pathology said at the annual Delta Ag Expo at Cleveland, Miss. “Rather, cotton serves as a sink for most insects that move out of other crops and from field borders, ditch banks, etc.”Controlling insects early, particularly plant bugs, can pay, Catchot says.

“We have consistently seen a net return from Diamond insecticide the third week of squaring or first week of bloom. We’re seeing a yield increase by doing this early rather than later. Preliminary research in the lab shows that when adults are exposed to Diamond, it reduces egg lay, and a lot of the eggs that are laid don’t hatch.”

For subsequent applications, when nymphs get embedded in cotton plants, tightening intervals to 4 to 5 days will provide better control than 7 days.

Adding pyrethroid boosts effectiveness

As cotton begins blooming, he says, adding a pyrethroid to organophosphates provides better control, plus offering a safety net for control of escaped worm eggs.

Planting date can also be a factor in insect control, Catchot says.

“Growers have long been told that managing for earliness can help avoid late-season buildups of resistant worms. Now, we’re seeing the same situation with plant bugs — that early planting results in higher yields and fewer insecticide applications for tarnished plant bug.

“If you can plant in the April 15-May 1 window, it may save applications on the back side. In our trials, we’ve reduced applications as much as 60 percent just by planting early.”

Growers should also consider applying ULV malathion plus a pyrethroid in the end of July/August period, he says. “Using this mix in rotation with other materials late season can, we feel, make a difference in plant bug control and offer another option not currently being utilized for control of the pest.”

Although 80 percent of insecticide applications on cotton are made by air, Catchot says, “we’ve seen some eye-opening differences in control for ground application, and in many cases probably could have made one less application. It will be important to focus on water volume and tip selection, particularly late in the season when cotton gets rank.

No changes in insect susceptibility to Bt

Last year, he says, there were more instances of worm breakthroughs in Bollgard II and Widestrike cotton.

“We saw a very extended period of moths in traps, and high numbers, and we had questions from growers as to whether the technology was working.

“While we’re aware of grower concerns, none of the data to date have shown any changes in the insects compared to previous years in terms of susceptibility to the Bt toxins. Rather, the difference has been the result of increased and sustained worm pressure. We’re continuing to evaluate the situation.”

A new insecticide from Dow, Transform WG, has been evaluated in trials the last three years, Catchot says, and application has been made to the Environmental Protection Agency for a Section 18 permit for 2011. If approved, its availability is expected to be limited.

“Last year, under very heavy plant bug pressure, this product looked as good as the best materials now available, and in some cases better. It also has very good activity on cotton aphids, so when it becomes available, we’ll have another good product for both plant bugs and aphids.”

We have also been testing Belay, a new Valent neonicotinoid product, which has also performed well in our testing program, he says.