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Scientists looking for new weapons to fight cotton-damaging insect

Cotton has made a rebound over the last few years, but growers still face challenges. One of those is damage from insects.

However, new research shows potential for offering new strategies to limit tarnished plant bug damage in cotton, though sure options already exist.

Mississippi State University scientists and Extension specialists have compiled decades of research to create a comprehensive recommendation for dealing with tarnished plant bugs in cotton.

Angus Catchot, MSU Extension row-crops entomologist, said tarnished plant bugs have been a problem for years, and their resistance to insecticides has increased over time. These insects are direct pests of cotton and feed on the flower bud, called a square, causing it to drop from the plant. Yield losses can be very high under heavy pressure.

Mississippi producers have moved away from planting cotton in favor of grains in recent years. Catchot said this decrease in acres makes the problem worse because plant bugs typically develop on other hosts and move into cotton.

“When cotton acres are low, you have the same numbers developing and moving into fewer acres, which can intensify the problems,” Catchot said. “We’ve developed a multi-tactical approach designed to break the tarnished plant bug’s reproductive cycle, decrease damage, and better manage cotton crops based on scientific experiments and what we’ve seen work over the years.”

Earliness …

Planting the cotton crop earlier is Catchot’s first recommendation.

“As planting dates get later, tarnished plant bug populations increase and develop tolerance for the pesticide chemistries,” he said. “Variety selection, in terms of early-maturing varieties, helps manage for earliness and increases yields.”

Location …

Cotton producers should also consider the crops that are planted around cotton fields. Producers can keep insect numbers down by blocking cotton away from other crops, especially corn, to discourage migration into cotton.

Mixtures …

Catchot said MSU researchers found that currently available foliar-applied pesticides produce marginal results. Only a limited number of pesticides are effective at all, so using recommended tank mixtures is important in managing tarnished plant bug populations.

Growth regulation …

“We recommend earlier use of Diamond insecticide, during the third week of squaring,” he said. “Diamond is an insect growth regulator and has activity only on nymphs. The third week of squaring is generally the time we start seeing the first nymphs in cotton. When Diamond is applied at this stage, eggs hatch into the residual insecticide, and nymphs are controlled at their most susceptible state, first instars.”

Host management …

The insects overwinter as adults outside the field and quickly invade broadleaf plants before migrating into cotton fields in early spring. Catchot recommended timely ditch and field bank management to eliminate the wild hosts on which insects develop before they invade cotton.

“Keep the field margins mowed early and keep them from flowering to discourage large populations of tarnished plant bugs,” he said.

Pesticide application frequency …

During times of heavy pressure, Catchot recommended decreasing the time between sprays to help break the pest’s reproductive cycle.

“Two back-to-back applications, even at lower rates, is always better than a single application during heavy pressure times of the season,” he said.

Variety selection …

Jeff Gore, entomologist with the Mississippi Agricultural and Forestry Experiment Station at the Delta Research and Extension Center in Stoneville, said scientists have found that leaf hairiness may affect tarnished plant bug populations.

In initial experiments, smooth-leaf varieties lost squares, while hairy leaf varieties did not have as much damage, Gore said.

“Interestingly, we found more bugs in the hairy leaf varieties, but bug numbers can be deceiving,” he said. “The evidence in the field was almost shocking to see, in terms of bolls evident in the hairy-leaf varieties compared to the low numbers of bolls in the smooth-leaf varieties.”

Gore said that the expense of the chemicals used to control tarnished plant bugs is not sustainable.

“We want to tie together all of these different management practices into a solid recommendation to reduce management costs for the producers, but also to reduce the amount of chemicals used,” Gore said. “But to get cotton acres back in the Delta, we need a different type of technology.”

Historically, genetically modified cotton has successfully reduced the impact of targeted insect pests. For example, Bollgard cotton produces a toxin specific to caterpillar pests, such as the boll worm or tobacco budworm.

“Tobacco budworm was resistant to all insecticides, and we had a huge outbreak in 1995 that resulted in a lot of money spent on foliar insecticides,” Gore said. “Bollgard cotton came out in 1996, and we have not had to spray a single Bollgard field since that time for tobacco budworm. Now we’re at that stage with tarnished plant bugs.

“We need a technology similar to Bollgard cotton that controls tarnished plant bugs to provide enough incentive for growers to start planting more cotton in the Mississippi Delta,” he said.



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