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New pests emerging in Bt cotton

If this year's cotton crop is anything like the 2000 crop, growers can expect to find some out-of-the-ordinary early-season pests in their cotton fields.

Entomologist Blake Layton at Mississippi State University in Starkville, Miss., says cotton growers last year saw an “unusual number of unusual early-season cotton pests” populating their crop fields.

Some experts are attributing the increase in non-traditional cotton pests to the rapid adoption of Bt cotton varieties, as well as the expansion in both conservation tillage acreage and areas included in the boll weevil eradication program. Although some of these “unusual” pests may have existed in cotton fields in the past, they are becoming more prominent now that Bt varieties are controlling tobacco budworm and bollworm infestations and the eradication program is steadily wiping out the boll weevil.

According to Layton, a number of non-caterpillar pests are emerging as problem pests, specifically in Bt cotton. Among the insects threatening to reduce Delta lint yields are stink bugs, false chinch bugs, sugarcane beetles, and three-cornered alfalfa hoppers.

Stink bugs: Three different stink bug species, including the green stink bug, the brown stink bug, and the Southern green stink bug, are being reported in Delta cotton fields.

Although all three of these species are shield-shaped and possess the same identifying odor, the green species (Acrosternum hilare) and the Southern species (Nezara viridula) are bright green. A narrow, orange-yellow line also borders the body of the green stink bug. The brown stink bug (Euschistus servus) is slightly smaller and brownish in color.

While the brown stink bug is a little more tolerant to pyrethroids, none of three species is difficult to control with insecticides, Layton says.

Stink bugs overwinter as adults and are highly mobile as they feed on the fruits and seeds of the cotton plant.

According to Layton, stink bug infestations should be treated when the populations of adults or nymphs greater than one-quarter inch in size exceed one bug per 6 row feet, or five bugs per 100 plants.

Treatment options suggested by Layton include the insecticides Orthene, Bidrin, methyl parathion, Baythroid, Karate, and Scout X-tra.

False chinch bug: About one-tenth of an inch long, false chinch bugs are gray or brown in color with long, narrow bodies.

According to the University of California's pest management guidelines, false chinch bugs often hide under plants or dirt clods during the heat of the day.

“False chinch bugs migrate to cotton when cruciferous weed hosts dry up or are destroyed by cultivation.

“Therefore, early-season control of weed hosts well before planting will eliminate the probability of this pest occurring in cotton,” the guidelines state. “False chinch bugs are fairly difficult to control,” says Layton. “A treatment of Bidrin at a rate of 0.4 to 0.5 pound per acre seems to work the most consistently, but it is currently under review by the EPA.”

Sugarcane beetle: Primarily an infrequent corn pest, the sugarcane beetle (Euetheola rugiceps) is a black, hard-shelled beetle that is domed-shaped with faint ribbed lines on its back. Layton says he saw sugarcane beetle populations in cotton for the first time in 2000 in a clean conventional tillage field. “It looks like a firecracker blew up the root system of the cotton plant,” he says. “High populations of sugarcane beetles may seem particularly bad, but the good news is that it doesn't seem to do a large amount of damage in most cases.”

For control of the sugarcane beetle, Layton recommends applying a pyrethroid, banded, at the full labeled rate.

Three-cornered alfalfa hopper: Sometimes called the beaver of the crop world, the three-cornered alfalfa hopper (Spissistilus festinus) is another odd early-season cotton pest.

“The three-cornered alfalfa hopper nymph, which resembles a beaver, often shows up more in the edges of a field,” Layton says. Adult insects are green, wedge-shaped, and range in length from 6.0 to 6.5 millimeters.

Three-cornered alfalfa hoppers pull up plant stems and cause large, knot-like swelling areas on the stems.

According to North Carolina State University's insect control guidelines, “Three-cornered alfalfa hopper girdle stems by their feeding and egg-laying activities. Nymphs and adults weaken the lower stem by piercing it with their needle-like mouths to extract plant juices. As a result, lodging and breaking usually occur weeks after attack.”

“This insect can mow over a crop if it is not controlled. But, to catch populations in time to treat, you will have to scout heavily and early. Often, when damage by this pest is noticeable it is too late to make control applications.”

Layton said pesticides that have been shown to offer control of the three-cornered alfalfa hopper include Orthene at a rate of 0.75 to 1 pound per acre and pyrethroids at a mid-range labeled rate.

Two other unusual cotton pests Layton observed in 2000 are negro bugs and snails, neither of which seems to cause substantial economic damage to Delta cotton. “As best as I can tell, negro bugs do not seem to do any damage. They simply use the cotton plant for shelter in no-till situations,” he says. “Snails, which also appear to be more prevalent in no-till cotton fields, don't seem to feed on the seedling cotton even when high populations are present in a field.”


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