Plant bug battle lasts all season in cotton

The tarnished plant bug is Mississippi's No. 1 most economically damaging insect in cotton, costing an estimated $42 million in yield losses plus millions more spent to control the pest.

Whitney Crow, entomologist with the Mississippi State University Extension Service, said these insects also can be found in corn and soybeans, but they are the most economically important pests in cotton. Yield losses to tarnished plant bugs can happen even with the proper use of pesticides.

“Losses can range from 400 pounds to 1,000 pounds an acre depending on the year,” Crow said. “The biggest issue in cotton is that they like the squares -- the flower buds -in cotton's earlier stages. When they feed on those squares, they have the potential to fall off, causing direct yield loss to that plant.”

The boll weevil was once the most economically important cotton pest in the state. Boll weevil eradication efforts that sprayed broad-spectrum insecticides on a scheduled basis also controlled tarnished plant bugs.

“When we eradicated the boll weevil, it left the opportunity open for another insect to fill that void and become the most problematic,” Crow said.

The tarnished plant bug is native to

North America and found throughout the U.S., parts of Canada and into Mexico. It is a true bug, with piercing, sucking mouth parts that include an almost straw-like proboscis that is used to inject enzymes to break down plant material.

Plant bugs feed on the nutrients and plant sugars in the flowering structures of their hosts. There are more than 500 documented host plants for tarnished plant bugs.

Crow said adults are small, only about 5-6 millimeters long, and are a brownish color with a light-colored V-shape behind their heads and two light-colored patches near the end of their wings.

The immature nymphs vary in size and are generally yellow-green to bright green. The nymphs go through as many as five developmental stages, known as instars, and they have different markings in these stages.

Managing these pests requires more than applying chemical control at the appropriate times.

“It is important to utilize various integrated pest management tactics throughout the season so we're not completely reliant on chemical control for plant bug management,” she said.

This is important as there are limited insecticide options available to control the pest because it has become resistant to a number of classes of chemicals.

“That resistance has developed over the last 10 to 20 years,” Crow said.

Cultural control is important for these pests. Planting cotton early is one way to limit plant bug problems.

“Early-planted cotton allows for higher yield potential, and it allows you to avoid increased insecticide ap

Tarnished plant bugs such as these nymphs feed on cotton flowers, or squares. This damage can cause the bud to fall off, resulting in direct yield loss. (Submitted photo by Ben Thrash)

plications common with later planted cotton or cotton with delayed maturity,” she said.

Another insect management tactic is to try to grow cotton in adjoining fields and away from corn, which helps limit migration of the pests from corn into cotton.

Don Cook, an entomologist at the MSU Delta Research and Extension Center in Stoneville, said that, before boll weevil eradication and the introduction of genetically modified Bt cotton varieties, tarnished plant bugs were considered secondary pests in many areas.

“It was primarily considered a pest prior to flowering,” Cook said. “After flowering had begun, insecticide applications for boll weevil and bollworm/tobacco budworm provided management of plant bugs.”

When boll weevil eradication was complete and Bt cotton was introduced, growers needed fewer insecticide applications. These factors contributed to plant bugs becoming a season-long pest.

“This change in habits, along with development of resistance to several insecticide classes, has helped elevate the status of tarnished plant bugs as a pest of cotton in the Midsouth,” Cook said.

Find up-to-date information about cotton pests and other row crop topics at https://www.mississippicrops.com.