We've been off to a relatively cool and very windy start, and nearly everywhere still needs rain, but most of our cotton is up, and the earliest planted will probably be squaring as early as next week. The corn and milo is looking a little dry and we are seeing some aphids, corn leaf and yellow sugarcane, both in low numbers, and a few folks have started watering. I am seeing some sorghum downy mildew around still, if you are looking for more information on that check out this publication. I have been looking for sorghum aphids (renamed from sugarcane aphids) a bit in some of the johnson grass on the edges of fields, but I have not picked any up yet in the spots I've looked. With the weather we've had lately, it's also possible we could start to see chinch bugs in corn or sorghum. If you are concerned about those, check out this publication.
Cotton stands can be impacted by some of the weather we've had recently, but stands as low as 13,000 to 26,000 plants per acre can still be viable as long as the plants are fairly evenly spaced out, with at least 1 plant per foot of row.
Thrips numbers in cotton have dropped this week compared to last week, and I didn't see any spider mites this week. Aphid numbers have decreased as well. I did see one location with false chinch bugs in the end of a field in Matagorda county, but it was a localized problem in that field. Below are charts with my scouting information for this past week, the week of 4/30/2021. I have two locations we didn't check this week due to pesticide applications or delayed planting.
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|
The insects are visible to the naked eye and scouting can be done by examining the plant, 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.
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.
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|
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|
|Cotton Fleahopper Adult|
I've seen a few fleahoppers this week, but not in squaring cotton yet. Next week I plan to start checking for fleahoppers in fields with squares.
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.
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!
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