Most of our cotton is wrapping up around here, there’s open bolls scattered around, and the corn and milo is getting harvested. Cutout occurs when cotton is 5 Nodes Above White Flower (NAWF), and at 350 degree days (DD60) past cutout we can stop worrying about plant bugs and bollworms. We can stop worrying about stink bugs at 450 DD60 past cutout, so keep that in mind while scouting and if you are considering treatment.
Most of the cotton in the Wharton, Jackson, and Matagorda area is past concern for pest pressure. The bolls they are feeding on past this point are bolls that will not reach maturity by harvest anyway, as the ones that are going to be harvested have grown too hard for them to feed on.
If you’re still under 450 DD60 since cutout and are looking for stink bugs, pull 10 to 20 bolls about an inch in diameter from four places in the field. Check the inside of the bolls for warts, lesions, and stained lint. The economic threshold for stink bugs is 20% or more of the bolls with internal damage and stink bugs present. Some of the brown stink bug populations in our area have also been shown to have some resistance to pyrethroids.
If your cotton is still under 350 DD60 since cutout and susceptible, bollworms are caterpillars that feed on multiple crops and vegetables. In cotton they feed on squares and bolls, causing fruit loss. The last few years we had high numbers of this insect in our Bt cotton as well. The eggs of this insect are small and white, turning brown as they get closer to hatching. The caterpillars are also highly cannibalistic, the eggs are normally laid singly, but if you find a couple or more on the same leaf, count it as one.
To scout for cotton bollworms I use the terminal and square inspection method. I make about four stops in a field, more if the field is larger than 100 acres. At each stop, I look at 25 plant terminals, checking at least the upper third of the plant for caterpillars and eggs. I also pull 25 half grown or larger green squares to bolls and look for bollworm damage. This season the egg lay has been in oddball places.
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We have been finding eggs in the lower 1/3 of the plant, as well as in bloom tags and bracts on fruit. When documenting egg lay, if I find more than one on a leaf, I only count it as one. This caterpillar is highly cannibalistic, and generally only one caterpillar will result from eggs too near each other. The economic threshold for bollworms is 6% damaged bolls with live caterpillars present.
In areas like ours on the upper gulf coast with documented Bt failures, the threshold for eggs on single and dual gene cotton is 20% (20 plants out of 100 with at least one egg). If you’re finding bollworms in cotton, especially in viptera fields, please give me a call.
The current A&M recommendation is to use pyrethroids with caution. In areas needing residual control Prevathon at 18-20 fl oz or Besiege at 9-10 fl oz works well. If you don’t need residual control you can get by with Prevathon at 14 fl oz or Besiege at 7-8 fl oz. I’ve seen a few places where folks have gone out with imidacloprid and bifenthrin, but this combination does not work well to kill bollworm eggs in the field or moths.