Rain and Fleahoppers


This week we’ve been dodging rain while scouting, all of our crops could use a little drier weather. Our cotton is exhibiting some nitrogen deficiency symptoms since it’s been so wet, and the waterlogged conditions have delayed plant maturity. I have received a few questions on PGR considerations with our recent rainfall as well. The best approach with our current conditions would be to apply a conservative rate when making insecticide applications. We want to avoid applying a high rate on fields that have experienced the stress of saturated conditions, but decisions should be made on a field by field basis. If you need more information on making PGR decisions and on waterlogged symptoms, check out the links at the bottom of this article.

We started counting the first position squares in our cotton to check square retention. Everything we looked at this week had square retention between 75 and 85%, except one location with 95% retention. The loss looks to be a mix of fleahopper feeding and weather related stress. I found my first cotton bloom in Matagorda county this week as well, and Jackson county is also beginning to flower.

Cotton Flower in Matagorda County
Kate Crumley

We picked up a few fleahoppers this week, but their numbers have been relatively low. They are still out there, and there are a mix of adults and nymphs around. Cotton fleahoppers can cause yield reduction and need to be scouted for carefully and regularly. I saw a few aphids in cotton as well, their numbers were spotty and far below threshold. Below are the scouting results for this past week. The fields we didn’t scout this week were due to rain, road closures, or aerial pesticide applications.

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.

Aphid Mummies on Cotton
Kate Crumley

I have not seen any bollworms, Helicoverpa zea, or eggs in fields yet this year, but I anticipate we will need to start checking for them in the next couple of weeks as our cotton starts flowering. 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.

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 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

Check out our weekly IPM Audio Updates, the link is below. 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

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