Cotton Links


Expect The Unexpected With Stinkbugs

By Amanda Huber
Southeast Editor

While stinkbugs rank sixth on the list of top insect pests for the past 10 years across the Cotton Belt, they have risen to first or second in the Southeast.

A combination of events has created the situation in a low-spray environment: boll-weevil eradication, Bt cotton and “second generation” Bt cotton, selective insecticide chemistry and “soft” foliar insecticides.

As Jeremy Greene, Extension entomologist at Clemson University, explained in his presentation at the Beltwide Cotton Conference in January, this has led to reduced broad-spectrum insecticide use, from nearly 16 sprays per season down to two and has allowed stinkbugs to avoid “coincidental” control.

The rise in stinkbug prominence has caused researchers to look more closely at the pest to learn more about it. Items such as feeding habits, distribution patterns, sampling techniques and treatment thresholds represent just a few of the subject areas of research projects conducted over the past few years – all geared toward gaining a better understanding of this insect.

In the Southeast, producers are generally dealing with green stinkbugs, Southern green stinkbugs and brown stinkbugs. All stinkbugs have piercing, sucking mouthparts and cause damage to cotton by feeding on the seeds of developing bolls.

According to the University of Georgia’s 2008 Cotton Production Guide, stinkbugs feed by piercing the boll wall with their beaks and injecting a digestive enzyme into the boll near the seed to soften or dissolve plant tissues so the bug can remove them.

Boll damage from stinkbugs on the outside wall may show a shrunken, purple spot. However, previous research has shown that internal symptoms of injury are a much better indicator of stinkbug feeding.

The use of internal feeding sites has become standard practice in scouting to determine if the treatment threshold was reached. The current recommendation is 20 percent of medium-sized bolls with at least one internal feeding symptom per boll and bugs present in the field and/or one bug per six row feet (38-inch rows) using ground cloth.

Refining Treatment Thresholds

During 2007, research on this treatment threshold for stinkbugs in the Southeast was conducted, and this was the data presented by Greene at Beltwide. Last year proved to be one of lower stinkbug pre-ssure than in previous years, and it provided limited insight into refining threshold levels.

“It does seem that our current threshold recommendations are still sound, and there will be no change in recommendations in South Carolina,” Greene says. “Twenty percent will be the recommendation, but depending upon week of bloom, it does appear you can get a little more aggressive during weeks three, four and five of bloom, possibly lowering that to 10 percent.”

Looking At Distribution Patterns

Another presentation focused on the distribution and dispersal of stinkbugs and their natural enemies within and between crops, particularly between peanuts and cotton.

This information, presented by Glynn Tillman, USDA-ARS entomologist, found that stinkbugs do develop in peanuts, travel into cotton, and the distance they travel depends on the availability of food.

“In the laboratory, our question was, ‘Do these stinkbugs feed on peanuts,’ says Tillman, “and if they do, what exactly do they feed on?

“We found that the first instars exclusively feed on the leaflets, mainly, we think, to get water. The second instars feed on petioles, and the third, fourth and fifth instars and adults feed mainly on stems.”

Tillman says they observed that in mid-July, the stinkbugs moved into peanuts and the females started laying eggs.

“But, in mid-August, we saw a drop in peanuts because, at this time, they were beginning to disperse into cotton,” he adds.

In what sounds like an arduous task at best, Tillman and her research assistants painted the stinkbug nymphs and adults to track all of their movements.

What they found is that not only do adult stinkbugs move from peanuts to cotton – their preferred food source – but the nymphs can move from crop to crop as well.

While research on many aspects of stinkbug management continue, researchers advise that producers not become complacent in their scouting and management of this important pest. A year of intense stinkbug pressure could be around the corner.

Contact Amanda Huber at (352) 486-7006 or ahuber@onegrower.com.


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