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Early season pests mean trouble for stressed crops

Spider mites and thrips are the primary early targets in cotton. Use tactics that protect beneficials insects. Climate-stressed cotton can’t afford pest injury.  

Texas AgriLife Extension IPM agents in West Texas caution growers to watch for early-season insects that could cause significant damage, especially to plants already suffering from environmental stresses.

Spider mites and thrips are the primary targets.

Monti Vandiver, IPM agent for the Northwest Plains, has observedspider mites in corn and sorghum, particularly on field margins. “Now would be a good time to start developing a spider mite management plan,” he says “Primary strategies are threshold based curative methods or a preventive approach.”

He recommends tactics that protect beneficials insects. “When considering a preventive miticide application, remember current products are not systemic and will only protect the leaves that are sprayed—any subsequent growth will not be protected. Applications to small corn or sorghum are also less cost effective when considering that less miticide is intercepted by the plant versus an application made to larger crop near canopy closure.”

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An extra application could pay off, he says. “The additional cost of a ‘dedicated’ preventive miticide application would likely be a good trade for the added protection offered by more crop coverage.”

He’s also seeing increased pressure from thrips in cotton. “I have observed immature thrips in some cotton that had a seed treatment insecticide applied. If immature thrips are present following seed treatments, the treatment has lost or is losing its effectiveness. Treatment thresholds for thrips in cotton are dynamic; under good growing conditions a foliar treatment should be considered when one thrips per true leaf is present, but in cotton growing slowly due to poor environmental conditions or other stress, the threshold should be reduced by half.”

Cotton stressed by recent storms should be watched closely. “It cannot afford additional loss of leaf tissue,” Vandiver says. “The lack of leaf surface area will make application coverage even more important. I cannot stress enough the need make timely insecticide applications for thrips. Insecticide applications based on visual plant symptoms are late and will not provide the economic benefit of a timely application and are what I like to call a ‘revenge’ treatment.”

Gaines County

Gaines County IPM agent Manda Anderson is also seeing thrips pressure on cotton.

“Thrips numbers have been below threshold levels in the IPM scouting program fields,” so far, she says. “However, we have seen a few fields in which the threshold should be lowered because the plants are already suffering from environmental damage, such as wind and blowing sand. In these cases, producers may consider lowering their thresholds to one-halfthrips per true-leaf if they are seeing immature thrips in the already damaged fields.” She says typical treatment threshold is one thrips per true leaf through the fifth true-leaf stage.

Anderson says presence of immature thrips indicate that thrips are reproducing in the field. She agrees that cotton farmers can’t afford the damage. “Thrips’ feeding damage, along with the environmental damage, will set the plants back and slow growth and development.”

Farmers should monitor fields. “Weekly scouting will help you to accurately monitor thrips populations and help determine whether leaf damage is being caused by thrips feeding, wind or blowing sand, or a combination of the two. Never make a treatment based solely on leaf damage; only treat if thrips are still present and the population has reached the economic threshold.”

She says thrips are out and looking for an attractive crop.

She’s also found evidence of Kurtomathrips but says growers should not panic. “Earlier this week I found an adult Kurtomathrips on a cotton plant at the cotyledon stage, so we could see Kurtomathrips earlier this year, and a large Kurtomathrips population would likely be devastating on young cotton plants.

“Seed treatments would likely control this pest until the treatment starts wearing off. In 2011, we conducted three insecticide trials in Gaines County. Our data suggest that Trimax Pro (imidacloprid), Orthene (acephate), Intruder (acetamaprid), and Centric (thiamethoxam) all have excellent activity on Kurtomathrips.”

Vandiver says farmers should continue to be vigilant for herbicide resistant weeds. “I have received several reports of potential glyphosate resistant pigweed,” he says. “We need to be diligent in managing weeds using multiple and timely tactics.”



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