Bollworm Management in Early Bloom Cotton

There are reports of bollworm eggs starting to show up and in some areas are at or above egg threshold. In a normal year, the bollworm flight generally begins around July 4th and peaks about the 15th.  That timeline would follow are normal trend; however, in some areas of Mississippi cotton was planted later than normal due to the high amounts of rainfall. In these situations, it is possible to hit an egg threshold when cotton is just now starting to bloom.

It is important to reminder when talking about the egg threshold it is only for cotton that does not have VIP3a or is 3-genne cotton. This egg threshold would be applied to non-Bt, Widestike, Bollguard II, and Twinlink. Below is a management strategy based on blooming cotton. If you are in a situation where you don’t have 3-gene cotton, have hit an egg threshold, and are at the beginning of bloom, I would consider making an insecticide application. The proper timing of insecticide applications in regards to spraying on eggs can have a huge impact on effective control. Last year, Angus did a spray study in Glendora, MS on 100% egg lay where he sprayed early and compared it to a late application. The early had 94% larvae control with 98% control on squares, and 88% control on bolls. While the late application provided 63% control of larvae with 80% control on squares and 55% on bolls.

So what should you consider when deciding on a management strategy:

When to treat cotton?

• Technology: 3-gene cotton (Bollgard 3, Widestrike 3, Twinlink Plus) vs. 2-gene cotton (Bollgard 2, Widestrike, Twinlink). The 3-gene cotton varieties are going to provide better control of bollworm than 2-gene cotton. This does not mean that foliar insecticide applications will not be needed at some point in the future on 3-gene cotton.
• Resistance: In recent years, there have been numerous escapes in 2-gene cotton due to resistance to the Bt cry proteins. 3-gene cotton has the addition of Bt Vip, which currently has shown no issues.
• Thresholds: The threshold that is recommended is dependent on the technology. ONLY USE the egg threshold on non-bt or 2-gene cotton.
  • The threshold for 2-gene cotton is 20% of plants with at least one egg anywhere on plants. Plant terminals can be scouted for eggs, but the threshold for eggs in the terminal should be lowered to around 10% of plants if you are only looking at terminals. You can also utilize the damage threshold, if that’s what triggers first.
  • The threshold for 3-gene cotton is 4% larvae (>1/8 inch) or 6% damaged fruit (squares and bolls).