Starting Bollworm Management Plans in Cotton
Bollworm (aka: corn earworm) poses a significant threat to cotton and soybean – particularly late planted soybean that are still flowering when the flight arrives.
Below are some thoughts on managing for this troubling pest in cotton.
Our primary concern for economically damaging infestations will be in the two-gene Bt cottons (and of course any non-Bt cotton). For Tennessee, this means almost exclusively Bollgard II, and we know treatment for bollworm is sometimes necessary on Bollgard II varieties. This article from last year discusses treatment options, but the diamide insecticides such as Prevathon and Besiege are the go-to treatments.
I would not expect treatment to be needed on WideStrike 3, Bollgard III, or TwinLink Plus technologies, except under unusual circumstances. Having said that, you most definitely should scout these technologies for bollworm infestations. For one thing, mistakes are made, and I’ve been in fields that were supposedly one variety and turned out to be another.
However, I would scout the 3-gene technologies differently, paying more attention almost exclusively to square and boll injury to make treatment decisions. Look specifically at one-third to one-half grown squares and small to medium sized bolls. Thresholds are based on injury, but a quick overview of treatment thresholds shows that Bt cotton should be treated when:
- Four or more surviving larvae (> 1/4 inch or longer) are visible per 100 plants – or a combination of square and boll sampling shows 6% or more injury (or anytime 3% or more boll injury is observed).
- Applications to Bollgard II should be considered when high numbers of eggs are present (> 20% or more of plants with eggs).
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