Squaring Cotton and Fleahoppers

Howdy,

This week was drier than last, with scattered showers. A lot of our waterlogged cotton from last week has started growing out of it, and is looking healthier.

I have seen an increase in thrips numbers this week, but only 4 of the fields I look at have fewer than 5 true leaves and are still susceptible to thrips damage. If you are still looking for thrips in smaller cotton, those populations are increasing. Cotton fleahopper numbers are also increasing, they can cause yield reduction and need to be scouted for carefully and regularly. This week they were a little more difficult to find, and I was finding almost exclusively nymphs. The cooler weather slowed the nymphs down and made them more difficult to spot in the terminals, but populations were high in several fields. Below are charts with my scouting information for this past week, the week of 5/14/2021.

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.

Cotton Fleahopper Adult
Kate Crumley

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.

Thrips are a small (about 1/15") light tan, straw, to brown or black colored insect with a punch and suck type mouthpart and asymmetrical mandibles. They punch a hole with one side, then siphon the juice out with the other. They typically feed on one plant cell at a time, and march along punching and sucking as they go. The adults are winged, and can travel short distances on their own, or be carried by a breeze for a fair distance. Larvae hide on the underside of the leaves, often close to the leaf veins, as well as in the terminal of the plant. This week I found most hiding in the rolled up true leaf in the terminal. Feeding damage for this insect causes cotton leaves to crinkle and curl, and often looks silvery when examined. Thrips feeding can cause delays in plant maturity, which can lead to yield reduction.

Western Flower Thrips
Kate Crumley

Tobacco Thrips
Kate Crumley

Thrips are visible to the naked eye and scouting can be done by examining the plant, but it is easy to miss some of the smaller larvae. Smacking a cotton plant around on the inside of a cup will knock them off and can make them easier to count. Cotton with a neonicotinoid seed treatment is usually safe from thrips for about 2-3 weeks after planting, depending on weather and soil types. Seedlings in sandier soil will typically lose the effect of seed treatments more quickly than those in heavier clay soils. Heavy rainfall can also reduce the amount of time a treatment is effective, while not enough water can impact the plant's uptake of the treatment and also cause a reduction in efficacy.

Thrips Damage
Kate Crumley

The economic threshold for thrips is 1 thrips per true leaf until the 5th true leaf stage. Once the plant reaches this stage, treatment for thrips is rarely justified.

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 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

Spider mite populations rarely get high enough to treat, as they thrive in drier climates and we tend to be fairly humid. Treatment is justified when spider mites are causing visible defoliation.

Spider Mites on Cotton
Kate Crumley

Please check out our weekly IPM Audio Updates, the audio file this week can be found here on soundcloud. 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

Plant Population Evaluation

Making Replant Decisions in Cotton

Cotton Insect Management Guide

Development and Growth Monitoring of the Cotton Plant