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SW Crops Conference: Pest targets changing for High Plains cotton growers

Thrips now lay claim to the dubious honor as the Southern Plains most damaging cotton insect.

“Year in and year out, thrips are our most important pest and cause more annual yield reductions, than anything else,” said Jim Leser, Texas Extension entomologist at the Agricultural Research and Extension Center in Lubbock.

Leser discussed the region's changing insect pest landscape during the recent Southwest Crops Production Conference and Expo in Lubbock.

He recommends preventive treatments for thrips in irrigated acreage. He said the added expense in dryland situations could be risky. Leser said a relatively new seed treatment, Cruiser, shows considerable promise as an alternative to Temik.

“Temik still holds thrips for 21 days.” But Leser said cotton farmers might want to increase Temik rates from the 2 to 2.5 pound rate to 3 to 3.5 pounds.

“Something has changed in the field,” he said. “There is a possibility the soil microbes are breaking down the Temik and reducing residual activity.

Foliar applications on top of a Temik in-furrow treatment might help extend control under protracted thrips infestations.

“Foliar applications over Cruiser increased net profits by $30 dollars,” he said. Leser said that the same results would probably occur with Temik.

Timely application makes a significant difference in control with foliar insecticides. Leser recommends using economic thresholds based on the number of thrips and the plant growth stage. “Initial foliar treatments are justified when thrips numbers per plant average or exceed the number of true leaves present at the time of field scouting”, he said. “After the initial foliar application or preventive treatment, additional foliar application recommendations include 30 percent immatures in addition to the number of thrips per plant.

Leser recommends a foliar insecticide application to control thrips in narrow row cotton.

Controlling insects early pays off with early maturity, Leser said. “Growers can gain from nine to ten days if they manage insects early.”

Leser added a caveat about being too aggressive with insecticide applications after squares are present but before flowers appear. He's conducted tests that show cotton will recover from significant square loss. “Removing all first position squares resulted in no yield losses during the three year study near Lamesa,” he said. “Irrigated cotton increases retention of second and third position bolls to compensate.”

Excessive early square loss can delay maturity, however. “Removing 100 percent of all squares (21) delayed maturity by 37 days. Delay from a 40 percent or less square loss proved insignificant. In many cases, we probably manage early-season insects too aggressively,” Leser said.

He also discussed progress of the Texas Boll Weevil Eradication Program. “We've recommended that the remaining seven West Texas eradication zones be moved into the suppressed category for 2004,” Leser said. “That classification lifts the quarantine and also reduces trapping density.”

He said as the zones phase into a maintenance program costs go way down. “Farmers will be able to pay their loans off more quickly.”

Leser said a zone reaches suppressed status when trap catches number no more than 25 weevils per 1000 trap inspections. The Texas Department of Agriculture will declare a zone functionally eradicated when no weevil reproduction is detected and no more than 1 weevil per 1000 trap inspections is found.

Leser said some zones experienced setbacks in 2003. Northern Glasscock County, for instance, does not participate in a 35-year voluntary producer diapause program with the rest of the St. Lawrence Zone and weevils migrated from that area into adjacent zones in active eradication. Leser said so far the resulting treatments have added $8 million to program costs for 2003.

Leser said Texas Panhandle growers will vote in a March 16 referendum to establish a zone and will start at the maintenance phase. Cotton acreage is expanding from the south, where eradication has already reduced weevil populations and infestation pressure is virtually nonexistent.

“We're also finalizing plans for a program in the Lower Rio Grande Valley,” Leser said. A referendum could be scheduled for a 2005 start.

Leser addressed the possibility of pyrethroid-resistant bollworms creating control problems for Southern Plains cotton growers. He said instead of a typical 95 percent control result, some reports indicate a reduction in control to 85 percent or less. He said tolerance appears to be seasonal, with low levels of tolerance early and building later in the season.

“Resistance also has been low in the High Plains compared to areas farther south. But they spray more often to the South.”

Leser said three factors could contribute to field control problems: resistance, poor coverage or poor application timing.

“We may have some localized worm populations with pyrethroid resistance,” he said, “but in the Plains pyrethroids are working well as a whole.”

He said resistance also could underscore the importance of Bt cotton varieties. “Currently, Texas cotton farmers plant less than 18 percent of their crops in Bt cotton, less than 9 percent in the Southern Plains.”

He said farmers economic evaluations of the technology often determine the cost is not justified. That may change with Bollgard II, Leser said.

He said in test plots with Bollgard II he could not find caterpillars. “We found some minor damage but the toxin is so powerful it takes them out quickly. Very little feeding is required on Bollgard II to kill the worms.”

He said even Bollgard looked good in tests. “Bollgard II looked much better.”

Leser said the control spectrum for Bollgard II also makes it a better economic fit. “It controls bollworm, armyworms, loopers and is a killer against pink bollworms.”

The pink bollworm has not been on the radar screen for High Plains cotton farmers until recently. “We've seen some localized infestations to the Southwest of Lubbock in Gaines, Terry and Yoakum Counties,” Leser said. “It's an emerging pest, coming out of New Mexico.”

He said extremely dry conditions last summer provided an ideal environment for pink bollworms, which can cause severe injury. “Late season damage can be devastating,” Leser said. “Some growers sprayed six times last summer and still had a 20 percent yield loss. This pest is worse than the boll weevil. We don't want it.”

Leser doesn't expect the pink bollworm to move rapidly north but says several factors may prompt infestation expansion. “Low insecticide use for other pests may be a factor,” he said. “A long growing season also may allow pinkies to establish.”

He said insecticide applications work best when made late in the evening, when it's almost dark. “We go after the moths,” he said.

“Once the pink bollworm is a problem, we switch to Bt cotton.”

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