AgriLife Extension entomologist: Monitor and treat early for cotton thrips

Writer: Kay Ledbetter, 806-677-5608, skledbetter@ag.tamu.edu
Contact: Dr. Ed Bynum, 806-677-5600, ebynum@ag.tamu.edu

AMARILLO – With cotton planting underway across the High Plains, a Texas A&M AgriLife Extension Service entomologist is warning producers to be on the lookout for thrips and be prepared to treat.

The most critical time for controlling thrips is the first two weeks after plant emergence, said Dr. Ed Bynum, AgriLife Extension entomologist in Amarillo.

“It is important to control thrips before there is significant damage,” Bynum said. “Research has shown that if you use foliar insecticides and wait until you see damage or until you make an herbicide spray, the damage from thrips has already been done.”

With thrips, feeding generally occurs in the new terminal growth and on the underside of leaves, causing stunted plants, deformed crinkled leaves that curl upward, and terminal loss, he said.

Bynum said on the High Plains, the predominant thrips species are the western flower thrips, Frankliniella occidentalis; the onion thrips, Thrips tabaci; and less numerous, the tobacco thrips, Frankliniella fusca.

“With the cold fronts moving through our area every so often this spring, we may need a reminder about thrips control in seedling cotton,” Bynum said. “Damage by the thrips occurs from seedling emergence up to the fifth true leaf stage. But, the most critical period for control is the first two weeks post emergence.

“Their damage is often more severe during periods of cool, wet conditions when seedling growth is slowed down and when huge numbers migrate out of senescing wheat.”

Generally, when there are warm growing conditions, the insecticide residual activity is usually sufficient to protect cotton from germination to the fifth true leaf growth stage, he said.

For making foliar application decisions when daily maximum temperatures are above 83 degrees, use the following action threshold: one true leaf, one thrips per plant; two true leaves, two thrips per plant; three true leaves, three thrips per plant; four true leaves, four thrips per plant. If it has reached five to seven leaves or squaring initiation, treatment is rarely justified.

But when there are cold fronts with daily maximum temperatures below 83 degrees for four to five days, thrips may be able to cause significant damage. Under these conditions, a follow-up foliar insecticide may be required and should be applied based on a modified action threshold by dividing each true leaf threshold in half.

He said insecticide seed treatments from Aeris, Avicta, Acceleron, Poncho/Votivo or Cruiser packages are probably the best option for protection from thrips because the control lasts from 18-21 days after planting. Research trials have shown Gaucho Grande and Acephate seed treatments last at most seven days after planting.

Foliar applications of Orthene/Acephate and Bidrin provides about five days of protection and Dimethoate about four days of control. This could require multiple foliar applications to prevent severe damage.

A sign that control is declining and no longer effective is when immature thrips are found surviving on the cotton leaves, Bynum said. When 30 percent of the thrips are immatures then a foliar application is needed if numbers reach the action threshold.

Severe early season damage to the young cotton plants can reduce plant stands and prevent early fruiting and maturity, Bynum said. The delaying of maturity can be critical to having sufficient heat units for boll development and prevention of yield loss, particularly on the Northern High Plains.

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