Howdy,
This week most of our cotton is blooming. We are nearing the end of fleahoppers in cotton, and will very rarely need to treat for them once fields are blooming. I've seen a lot of sprayers going out as our fields dry out. The drier weather is a good opportunity to make herbicide applications.
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| Cotton Flower in Matagorda County Kate Crumley |
Our cotton fleahopper numbers have been relatively low this week. We were still picking them up, but most were adults. 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.
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| 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.
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| Lady Beetle on Cotton (aphid predator) Kate Crumley |
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| Aphid Mummies on Cotton Kate Crumley |
We started picking up bollworm eggs in cotton this week. We found very few, and I've had very 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. 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.
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| 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).
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| H. zea Eggs on Cotton Kate Crumley |
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
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