Friday, August 6, 2010

Threshold Levels of Bollworms Found in Conventional Cotton

From Ames Herbert, Virginia Extension Entomologist

We are finding threshold levels of bollworms (eggs and live worms) in conventional cotton (no Bollgard2 or Widestrike). Those fields should be managed using the old system (treat at egg threshold and retreat in 5-7 days). The best approach for Bollgard2 and Widestrike cotton is the treat one time 5-7 days after the egg threshold, which targets any escaped worms. Not treating Bollgard2 or Widestrike cotton could be a mistake. For the past 2 years, we have seen as much as 2-3% boll damage in some Bollgard2 varieties, and as much as 10% damage in one Phytogen variety. A single pyrethroid application (highest labeled rate) cleaned up the problem.

One cautionary note, we have gotten reports of worms escaping pyrethroid treatments in cotton.

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