Plant Bugs and Bollworms

Howdy,

This week has been fairly dry aside from a few popup showers. Our cotton is mostly blooming and we are finding thumb sized bolls in the biggest cotton. There are some places still squaring. Our sorghum is coloring, and some of the later planted is still blooming.

In sorghum we need to be scouting for sugarcane aphid, those are building with the drier weather. I've picked it up in sorghum in all three counties, and there are fields that reached threshold for it already. If it's blooming, we need to look for sorghum midge. Here are some links for just sugarcane aphid, and a more recently updated guide for sorghum insect management. Here are links to the threshold calculators for sorghum midge, rice stink bug, and sorghum headworm. I am picking up low numbers of headworm and rice stink bug right now.

Sugarcane Aphids in Sorghum
Kate Crumley

Aphids are still in the cotton, and have been fairly heavy depending on the location. We are still picking up fleahoppers, and need to be scouting anything with squares carefully for those. This week we started picking up bollworm eggs and very light damage on some of our smaller fruit, but no live worms. We will be shifting from looking for fleahoppers to looking for bollworms as the fields start to bloom. Below is my scouting information for the week of 6/3/2022. On fields that just started blooming this week, we did still look a bit for fleahoppers in fields that just started to flower, but we are not worried about them causing damage after bloom.

Cotton Aphid
Kate Crumley

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 I have seen some cotton at threshold this year. If you do decide to treat for aphids, do not use a pyrethroid. Pyrethroids and organophosphates are broad spectrum, and 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.

Aphid Mummies on Cotton
Kate Crumley

Cotton Fleahopper Adult
Kate Crumley

Fleahopper feeding will cause squares to drop. Plants 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.

The chart below contains insecticide suggestions from cottonbugs.tamu.edu (also a good resource) for reference if you have fleahoppers at the action threshold in the upcoming weeks.

We started picking up bollworm eggs in cotton this week. We found very few, and I've had low moth numbers in our traps as well. 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 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 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 check lower down the plant, and count eggs while making fruit counts. 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

We've started seeing a few stink bugs, as well as Lygus and Verde plant bugs (Creontiades). The threshold for verde plant bugs (Creontides) is 20-25 insects per 100 plants, but have not found verde plant bugs or lygus to reach threshold on their own anywhere, so if cotton is squaring I count them as two fleahoppers, and if its after bloom is going, I count them as either one or half a stink bug depending on the boll size. Verdes can feed on bolls up to an inch in diameter. Below are the action thresholds for both as well as photos of the insects.

Verde Plant Bug
Ben Crumley

Lygus Bug Adult

Lygus Bug Nymph
Kate Crumley

Evidence of Sucking Insect Damage on Cotton Boll
Kate Crumley

Check the inside of the bolls for warts, lesions, and stained lint. Above is a photo of a boll with potential stink bug feeding damage from the outside, note the slightly raised look of the dark spots. Be sure to open the bolls to confirm it is damaged, other sucking plant bugs may be unable to get through the carpal walls, and the inside will be clean. The economic threshold can be found below, depending on how long the field has been blooming. It is based on the percent damaged bolls with live bugs present. This year we've mostly seen brown stink bugs in cotton so far, and some of the brown stink bug populations in our area have 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

I'd also like to let everyone know that there is an Agricultural Pesticide Waste Collection event happening on Wednesday, June 29th from 8:00 am to 12:00 pm at the Victoria County Pct #4 Yard at 226 Beck Road East, Inez, TX 77968. The flyer for that event is below. For any additional questions on this event, please contact the Victoria County Extension Office at (361)-575-4581.

Please check out our weekly IPM Audio Updates, the website to sign up to receive those is listed below. If you have any questions feel free to contact me either by email or calling the office. Have a good weekend, everyone!

Sincerely,

Kate Crumley

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Cotton Insect Management Guide

Development and Growth Monitoring of the Cotton Plant