Texas Upper Coast Cotton: Bollworms and Stink Bugs

Bollworm eggs on cotton leaf.

I am still seeing a few different plant bug species around, in cotton as well as other crops, but we should be able to stop worrying about damage from these plant bugs in cotton soon. Once bolls get larger and we reach 350 degree days (DD60) past 5 Nodes Above White Flower (NAWF), we can stop scouting for plant bugs. Most of the cotton in my scouting program is between 9 and 5 NAWF.

The threshold for verde plant bugs is 20-25 insects per 100 plants with using a beat bucket. Verdes can feed on fruit up to bolls about an inch in diameter.

Lygus bugs will also feed on cotton squares, flowers, and small bolls. Feeding can cause damage to blooms (dirty blooms and damaged anthers, or puckered petals), deformed bolls, stunted growth, fruit shed, and small lesions on bolls.

I have seen few stink bugs in cotton this year, but damage is picking up. 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.

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.

We’ve picked up a few eggs and bollworms in fields this week. In Wharton county we picked up 0% eggs and 8% damaged squares in a field near the fairgrounds, 8% eggs with 6% small worms and 10% damaged squares, 6% eggs and 8% damaged squares, and 21% eggs and 4% damaged squares in another.

In the blue creek area we found 15% eggs with 3% damaged squares, 9% eggs with 1% small worms and 4% damaged squares, and 0% eggs with 4% damaged squares in another. Near Danavang we found 4% eggs and 3% small worms with 8% damage.

Near Elm Grove we picked up 11% eggs with 3% small worms and 7% damage, near Egypt we found 6% eggs with 2% small worms and 4% damaged squares. There were 20% eggs, 4% small worms, and 8% damaged squares in a field near the airport.

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In Jackson county we found 2% eggs in a field near El Toro with 2% damaged squares, 6% eggs with 2% small worms and 6% damaged squares near Vanderbilt, and 22% eggs with 6% damaged squares near La Salle.

In one field near the county line off 35 we picked up 3% eggs with 1% fruit damage, and 3% stink bug damage. In the other field near there we found 5% eggs and 4% damaged squares and 3% stink bug damage.

In Matagorda county we found 3% eggs with 4% small worms and 13% damaged fruit at Tin Top, 7% eggs with 4% small worms and 7% damaged squares near Tidehaven, and 4% eggs with 1% small worms and 3% damaged fruit near Palacios.

These 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 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 week there were a few moths flying around in a couple of the fields in Matagorda county, and in one near Palacios we found two eggs laid. 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 or in corn, 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.

This week I was able to make a few checks in sorghum. We found moderate numbers of rice stink bugs and a few headworms in the field, as well as a slight increase in sugarcane aphid numbers from last week.

None of the insects were over threshold in the fields I looked at, but in places headworm and stink bug numbers have been high. If you’ve got high numbers of sugarcane aphids, give me a call.




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