Open Cotton and Late Season Pests

Howdy,

This week some of yall have started harvesting sorghum and corn. I'm glad to see our crops finishing out. The cotton is moving along nicely as well, most of the fields I look at are past cutout and in a couple places beginning to open. In the fields that are at or past cut out, or 4-5 NAWF, the carbohydrate supply is equal to the demand, and vegetative growth stops, so no more harvestable fruit will be set. That means that the squares on the plant at that time are the last ones with potential to develop into bolls.

This week we are seeing bollworm eggs, larvae, and damage in the following fields that are still susceptible:

Wharton County 

Cry1Ac + Cry2Ab near Crescent
20% bollworm eggs
18% bollworm larvae
18% bollworm damage

Cry1Ac + Cry2Ab + Vip3A near Crescent
10% bollworm eggs
0% bollworm larvae
4% bollworm damage

Jackson County

Cry1Ac + Cry2Ab near El Toro
7% bollworm eggs
3% bollworm larvae
5% bollworm damage

Cry1Ac + Cry1F + Vip3A near La Salle
20% bollworm eggs
0% bollworm larvae
10% bollworm damage

Matagorda County

Cry1Ac + Cry2Ab + Vip3A near Tidehaven
10% bollworm eggs
3% bollworm larvae
10% bollworm damage

Cry1Ac + Cry1F + Vip3A near Tidehaven
7% bollworm eggs
0% bollworm larvae
3% bollworm damage

 Bollworms, Helicoverpa zea, are caterpillars that feed on multiple crops and vegetables. In cotton they feed on squares and bolls, causing fruit loss. These past few years we have had high numbers of this insect in our Bt cotton as well.

H. zea caterpillar in cotton square
Kate Harrell

  To scout for cotton bollworms I use the terminal and square inspection method, as well as making some full plant checks, as they can lay eggs anywhere on the plant. 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 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. When documenting egg lay, if I find more than one on a leaf, I only count it as one. 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.

Cotton Insect Guide

 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.

Cotton Insect Guide

 This week we found 3 brown stink bugs in a field near Tidehaven, and one green stink bug nymph in a field near El Toro. It is still buggy out there, but we are finishing out in most places. To scout 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. Texas 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. Once cotton reaches 450 heat units past cutout, we should be past the window for damage since the bolls on the plant that will reach maturity will be too large for stink bug feeding.

Green Stink Bug adult
Kate Harrell

Carpal Wall Warts from Stink Bug feeding damage
Kate Harrell

  Below I have included information for stink bug thresholds from a South Carolina guide with good images of what damage looks like in bolls. Our cotton does not bloom as long as theirs, so the week of bloom threshold information will not line up exactly the same for our fields. 

  

Heat unit accumulation for July 12th to 18th:

Wharton (Wharton): 169.5

Jackson (El Toro): 180

Matagorda (Palacios): 155

  I hope everyone has a good weekend. If you're not sure what kind of insect or issue you have, feel free to drop by the Wharton county office or give us a call.

Sincerely,

Kate Harrell

Looking for more information? Check out the Cotton Insect Guide

Looking for more information? Check out the Cotton Growth and Development Guide

Need help with weed control? Check out the Weed Management Guide

Information on cotton bollworm resistance problems