Sunday, September 26, 2021

Alabama Extension recaps 2020 insect season

Cotton Boll Damaged by Stinkbugs
Cotton boll damaged by stink bugs

Life in 2020 was dominated by COVID-19, however, the work continued for cotton producers. While the Alabama cotton industry had an unusual weather season, no one cotton pest dominated the growing season.

Alabama Cooperative Extension System entomologists Scott Graham and Ron Smith said while there were notable pests, no single species required extra effort to control.

“The beginning of a new year is always a time when producers begin thinking about seed orders and making budgets for inputs and variables throughout the growing season,” said Smith, who has served Alabama Extension as a cotton entomologist for 48 years.

“Thankfully there is not a single pest that we are struggling to control in the field, so we want to focus on helping farmers manage their crops and plan for the upcoming year,” Graham said.

Traditional cotton pests

Producers are no strangers to dealing with a wide array of crops pests—from grasshoppers to plant bugs and bollworms. The most damaging cotton pest for Alabama producers is the stink bug complex which includes Southern green stink bugs, brown stink bugs and brown marmorated stink bugs.

As planning for 2021 begins, Graham and Smith want producers to include pest control applications in their crop budgets.

Grasshoppers

“Most of the time early in the season, entomologists expect calls about thrips damage,” Graham said. “In 2020, the winter was drier and warmer than usual. These conditions were right for grasshopper overwintering and subsequent damage.”

Graham said if conditions in 2021 are similar to 2020, grasshopper control should be first and foremost on the pest control radar.

“Some years grasshoppers decimate a large area of a field; other years they don’t touch cotton plants,” Smith said.

Graham said growers should manage preventatively, targeting emerging immatures, as adults are more difficult to control. Smith said it appears grasshoppers consistently affect the same fields year after year. With this knowledge, cotton producers can make targeted applications based on the field history.

Thrips

thrips
Thrips — photo by David Kerns

Once cotton stands are established, thrips are the next pest producers encounter during the growing season. Both entomologists encourage producers to use the thrips predictor model developed by researchers at North Carolina State University.

This can be an excellent tool, especially for large-scale producers, when it is time to map out applications. The model can help producers predict which fields will likely need foliar applications to supplement at-plant insecticides.

Minimal and no-till situations generally reduce thrips damage. However, additional old crop residue increases the likelihood of sporadic early-season pests like slugs, snails, spidermites, grasshoppers and armyworms.

Although many farmers are aware, it is important to remember that multiple foliar applications of certain chemistries can aggravate spidermite populations. For this reason, it is best to rotate chemistries when making multiple applications in a short amount of time.

Cotton producers have something to look forward to as a new thrips-controlling seed technology will move into the large-scale testing phase in 2021. Graham hopes this technology will be available for on-farm use in 2022.

Plant bugs

plant bugs
Plant bug

Plant bugs become an issue when cotton plant begins putting on pinhead squares. Unfortunately, Graham and Smith agree pyrethroids are not as effective now as in the past.

“When producers use pyrethroids, such as bifenthrin, to control plant bugs, they should follow-up carefully to be sure they are getting adequate control,” Smith said.

Stink bugs

Stink bugs inhabit much of the farmscape, including row crops and other vegetative growth.

“There is typically one large migration from corn to cotton, but peanuts seem to feed populations of stinkbugs into cotton throughout the season,” Graham said. “There is also a movement of stinkbugs from pecans as the shells begin to harden.”

Smith said stink bugs are the most common cotton pest—as well as the most damaging—because they target developing bolls, when there is not much time for the plant to compensate for damage. These pests generally have a heavy presence on field borders, first 40 to 50 feet of the field.

“The larger the field, the less likely you are to see damage throughout,” Smith said.

Spidermites and silverleaf whiteflies

Both spidermites and silverleaf whiteflies cause issues in areas of Alabama. Spidermites are closely associated with extended dry periods. Hotter, drier weather makes populations more pronounced.

Silverleaf whiteflies were devastating in 2017 and are another hot, dry-weather pest. These pests migrate into cotton from cold crops and vegetables produced during the winter and spring months.

Graham and Smith recommend that growers in the Wiregrass budget for potential pesticide applications, as these pests can be costly to control. Their damage can be devastating, especially if infestations build on late maturing cotton.

Alabama Cooperative Extension contributed this article.

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