Bollworms and Stink Bugs

Howdy,

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This week most of our cotton is blooming. We are nearing the end of fleahoppers in cotton in all but the later replanted fields, and will very rarely need to treat for them once fields are blooming. I've seen a lot of sprayers going out since we've been dry. How the crops look is pretty directly tied to how well that location drained. In places with good drainage, it's looking pretty good, and in the low ends where water sat it looks like the photo below.

Low Edge of Cotton Field
Kate Crumley

Everything I scout is past concern for cotton fleahoppers, but I know some of the later replanted fields are still susceptible. We are currently looking for bollworms and stink bugs in cotton. The bollworm egg lay this week was very light early on, but started to pick up a bit toward the end of the week. What we found scouting is below.

Fleahopper feeding will cause squares to drop. Plant can recover for and compensate for some square loss, but the threshold for fleahoppers is 15-25 per 100 plants. I check for fleahoppers by inspecting the plant terminals once they start squaring. I look at 25 plants per stop in the field, usually checking 100 plants total in an 80-100 acre field, more if the field is larger. Fleahopper nymphs can be close to the size of aphids, but look like smaller versions of the adults without wings, and are much more mobile than aphids.

Cotton Fleahopper Adult

Kate Crumley

The chart below contains insecticide suggestions from cottonbugs.tamu.edu for reference if you have fleahoppers at the action threshold.

The threshold for cotton aphids is 50 aphids per leaf, and if you see aphid mummies in the field (tan or black dry and unmoving aphids), that's a good thing. Parasitoid wasps lay eggs in the aphids, and the aphid forms a mummy while the wasp larvae is pupating inside. These wasps, lady beetles, and lacewings can knock back aphid populations. Treatment for aphids is rarely justified, but if you do decide to treat for aphids, do not use a pyrethroid. Pyrethroids kill beneficial insects as well as your target insect, but pests like aphids bounce back much quicker than their predators do. Their high reproductive rate will allow their numbers to soar after a broad spectrum insecticide application kills all their predators.

Lady Beetle on Cotton (aphid predator)

Kate Crumley

Aphid Mummies on Cotton

Kate Crumley

Helicoverpa zea is our cotton bollworm and corn earworm. 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. They are already in the corn, below is a photo of a caterpillar I pulled from dual gene corn. As the corn matures, the next generation of bollworm eggs will be laid in cotton. I start looking for bollworm eggs in cotton when that field starts blooming.

H. zea Larvae
Kate Crumley

Our scouting guide recommends checking in the top 1/3 of the plant, but it's important to also pull bolls and flowers from lower to check as well. Egg lay has been occurring low in the plant as well, and it's not uncommon to find small larvae or eggs in flowers and bloom tags.

H. zea Larvae in a Cotton Bloom
Ben Crumley

Our Bt traits overlap across corn and cotton. If the caterpillars survive the traits on corn then as adults fly to cotton to lay eggs, it's likely their offspring will survive the same traits on cotton. Below is a chart showing the overlap of Bt traits between crops and technologies.

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. 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).

H. zea Eggs on Cotton
Kate Crumley

I have seen few stink bugs in cotton yet, but I've heard of a few consultants finding bolls with carpal warts. 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.

Green Stink Bug adult
Photo: Kate Crumley

Carpal Wall Warts from Stink Bug feeding damage
Photo: Kate Crumley

My scouts and I have also seen a lot of predatory stink bugs on the move lately. I have photos of the spined soldier bug below, which we've seen in a few locations. They are predatory, and while they look similar to the brown stink bug, they aren't causing damage.

Spined Soldier Bug Nymph
Kate Crumley

Spined Soldier Bugs
Kate Crumley

Most of our corn has been sprayed once if not twice for southern rust. If you'd like more information on that, please check out this publication by our plant pathologist, Dr. Tom Isakeit.

We have had fairly high populations of sorghum midge in our fields as well. Sorghum is susceptible to midge damage during bloom. Since spraying for midge involves the use of pyrethroids, it can flare sugarcane aphids. Our sugarcane aphid numbers have been relatively low, but dry weather and a pyrethroid application could cause their numbers to rise. I've not seen high headworm populations yet, but we do need to be scouting for them. For more information on scouting sorghum and insect pests, check out this publication. If you need economic calculators for sorghum pests, those can be found here for midge, headworm, and rice stinkbug.

Check out our weekly IPM Audio Updates, the link is below. As always, if you have any questions feel free to contact me either by email or calling the office. Have a good weekend everyone!

Check out our weekly IPM Audio Updates

How Waterlogged Soils Impact Cotton Growth and Management Decisions

PGR Management Considerations

Plant Growth Regulators as Tools for Challenges

Cotton Insect Management Guide

Development and Growth Monitoring of the Cotton Plant