Insects play havoc with cotton on the Texas High Plains every year, an estimated $150 million in yield losses in 2007. To add insult to injury, producers had to pay out $190 million to keep the losses from being higher.
“The average annual cost to producers to control cotton insects is approximately $64 per acre,” says David Kerns, associate professor and AgriLife Extension entomologist-cotton at Lubbock. “Most of this is spent on approximately 2 million irrigated acres; the rest is spent on about 780,000 dryland acres.”
“An effective scouting program is an absolute first step in minimizing these monetary losses,” Kerns said. “Depending on the pest under consideration, producers should check their fields at least every three to five days.
“Naturally, the next step is to 'know your enemy.' Producers need to know what the pests look like and when they are likely to appear. Armed with this information, they can make timely decisions about control measures.”
Thrips are the first harmful insects that usually appear after cotton emergence. They are slender, straw colored, 1/15-inch long with rasping and sucking mouthparts. They attack the young, tender leaves and leaf buds of newly emerged cotton. Significant damage stunts the plants and may delay fruiting and maturity. They are most damaging during cool, wet periods when small cotton is growing slowly.
“Even though producers spent an average of $12.50 per acre to control this pest, bale losses were estimated still to be around 57,000 in 2007,” Kerns said.
Cotton fleahoppers are the next likely insect to cause early problems. These pests are pale green, about 1/8-inch long, and move very rapidly when disturbed. They feed on the small squares, causing them to drop off the plant. The cotton plant can compensate for these lost squares given time, but the compensated fruit may be lower in quality.
“Last year cotton yields were reduced about 1.6 percent by this insect, and approximately 430,000 acres on the High Plains were treated for cotton fleahoppers at a cost of $7.80 per acre,” Kerns said.
Lygus may appear at the onset of squaring, but are more prevalent after bloom and late in the season. These pests are 1/4-inch long, have a triangle in the center of their back, have wings, and vary in color from pale green to yellowish brown with reddish brown to black markings.
Lygus feeding results in shed squares and small bolls and may cause stained lint and boll deformation. They can move in and out of a cotton field in a very short time.
“In 2007 producers lost about 10,000 bales to lygus. Chemical control for this pest runs $8.75 per acre,” Kerns said.
Cotton bollworms may appear in very low numbers before blooming begins but are most prevalent from August on. Full-grown larvae are about 1 to 1.5 inches long and vary in color from pale green, pink or brownish to black, with longitudinal stripes on the back.
“Since Bollgard, Bollgard II and WideStrike varieties became available, losses from these pests have declined sharply. However, under heavy insect pressure, we have observed incidences where these worms still required control measures on Bollgard varieties, but I have yet to see a case where Bollgard II or WideStrike varieties required treatment,” Kerns said.
“There were no reported losses in 2007 from these pests in fields of Bollgard, Bollgard II and WideStrike varieties in the Texas High Plains. However, 27,000 bales were reported lost from varieties not containing Bt genes. Also, an estimated 25,000 acres of non-Bt cotton were treated for these pests at a cost of about $10.00 per acre.”
Cotton aphids are about the size of pencil lead, ranging in color from light yellow to dark green to almost black. Infestations can occur from plant emergence to open bolls, with the highest populations occurring post bloom.
Heavy and prolonged infestations can cause leaves to curl downward, older leaves to turn yellow and shed, square and small bolls to shed, and bolls to be reduced in size, resulting in stunting and incomplete fiber development.
“A major problem with this pest comes from the honeydew excreted by aphids and dropped onto fibers of open bolls because of the stickiness and the black, sooty fungus that may develop,” Kerns said. “This results in fiber that is stained, sticky, of lower quality, and difficult to harvest, gin, and spin into yarn.
“In 2007, 1.25 million acres were treated for this pest at a cost of about $12.00 per acre. A lot of acres avoided chemical control due to the presence of large populations of lady beetles, a parasitic wasp and a fungus that kills the aphids. However, yield reduction was still estimated at 1.4 percent or about 56,000 bales. In 2007, there were no incidences where lint was downgraded because of sticky cotton.”
Boll weevil adults emerge from hibernation very early in the cotton-growing season. They are about 1/4-inch long and tan-brown in color. They puncture squares and small bolls, which usually fall off. Larger bolls remain on the plant but will contain damaged lint.
“Boll weevils are generally not a problem on the High Plains due to the effectiveness of the Texas Boll Weevil Eradication program. But if producers determine they are in their fields, we want to know immediately. Growers should contact their local Texas Boll Weevil Eradication Foundation or the state Foundation at (325) 672-2800,” Kerns said.
Other potential problem pests on the High Plains include pink bollworm, grasshoppers, stink bugs, cabbage loopers, spider mites, fall armyworms, beet armyworms, yellow-striped armyworms, salt-marsh caterpillars, cotton square borers, and cutworms.
“Fortunately, we also have many beneficials,” Kerns said. “Among these are assassin bugs, big-eyed bugs, damsel bugs, green lacewings, lady beetles, spiders, syrphid flies, aphid parasites, and ichneumon wasps.
“Populations of beneficials at the right time can (preclude) the need for chemical controls. So before the decision to spray is finalized, producers should consider that the beneficial population might reduce the pest infestation to tolerable levels,” Kerns said.
Identification photos and additional information on cotton insects and control measures are available at http://lubbock.tamu.edu/.