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Volunteer cotton provides food and reproduction site for weevils

Volunteer cotton can be a lot bigger problem than a nuisance weed, as if that’s not bad enough. Left untreated, volunteer cotton stalks become ideal havens for boll weevil reproduction.

Noel Troxclair, Texas A&M assistant professor and Extension entomologist at Uvalde, says volunteer cotton often may appear in rotation crops, where growth and fruiting may be limited because of competition, but also in non-crop areas—fence lines, drainage ways, railroad rights-of-way, ranches or feedlots where cottonseed is fed to livestock. Also, volunteer cotton may emerge in places where cottonseed is used in deer feeders, often in remote areas.

“In open areas, where cotton has little or no competition, plants may grow quite large,” Troxclair says.

Eliminating these volunteer cotton stalks is critical to improve success of the Boll Weevil Eradication Program.

“With each passing year in the Texas Boll Weevil Eradication Program, limiting reproduction becomes ever more critical in attaining the goal of no weevil,” he says. “This is particularly true regarding volunteer cotton that often goes undetected and untreated.”

He says such cotton may produce a lot of fruit that “boll weevils use for food and, more importantly, for reproduction.”

He says the amount of fruit detected on cotton growing in a fence line shows that volunteer cotton may be a greater threat to the success of boll weevil eradication than previously suspected.

“As a follow-up, we harvested volunteer cotton plants from several designated sites, counted fruit, recorded associated boll weevil feeding and egg-laying damage and reared weevils from the fruit with egg-laying punctures,” Troxclair says.

The cotton was evaluated to determine how much fruit cotton growing in more open areas might produce, and thus serve as a source for reproduction and food for overwintering boll weevils.

The initial site included 66 plants from which he stripped fruit. He examined all fruit for boll weevil feeding, egg laying or emergence and recorded the data.

“I held no fruit for weevil emergence since there was no evidence of recent egg-laying in any of the fruit,” Troxclair says.

At a second site, Alpha, he harvested two plants and recovered fruit shed on the ground.

“The fruit were stripped from each of the two plants and we recorded the number of squares, small, large and open bolls from each plant,” Troxclair says. “Each of 900 fruits from the Alpha site was examined for feeding, egg-laying or weevil emergence and the status of each fruit was recorded. Fruit with egg-laying punctures were placed in a rearing chamber (a five-gallon bucket with screen covering the portion of the lid that was cut out) and held until adult boll weevil emergence ceased. Adult boll weevil numbers were recorded.”

In Sites 1 through 5, he used the same methods employed at the Alpha site except fruit from each plant were not counted separately by plant, but were combined for a total of 3,911 fruit from twelve plants. Also, all fruits from the five sites that had egg-laying punctures were combined and held in a rearing chamber for adult emergence.

“Toward the end of the period that the fruit was held in the rearing chamber, a light misting with water and subsequent thorough mixing seemed to encourage adult emergence. Stirring the mass of cotton fruit once a day also seemed to stimulate adult emergence.”

Troxclair says 19 weevils emerged in the field from the fruit examined from the 66 plants at the initial site. At the Alpha site, 153 boll weevils emerged from fruit collected from the two plants on Oct. 4 and 16. With the 153 weevils that emerged in the lab, plus the 96 that had already emerged in the field, a minimum of 249 weevils were produced on two plants at the Alpha site. In sites 1 through 5, 176 boll weevils emerged from the fruit collected on October 16 from the 12 plants.

“With these 176 weevils, plus the 117 that had emerged in the field, a minimum of 293 weevils came from these 12 plants. At least 561 weevils emerged from the volunteer cotton I examined from this farm,” Troxclair says.

“I did not examine another dozen or so large plants that a Texas Boll Weevil Eradication Foundation employee removed after growers left the plants for two weeks following being informed the plants needed to be destroyed.”

He says with a 50:50 sex ratio, and 100 percent survival of well-fed weevils in a mild winter climate and an average of 150 eggs per female, weevils that emerged from this one farm represent the potential for over 42,000 eggs in 2008.

“When multiplied many times over by all of the volunteer cotton in the South Texas-Winter Garden Zone, it becomes apparent that volunteer cotton must not be ignored. The potential consequences for boll weevil eradication are too great.”

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