Texas Upper Coast Cotton: Early Season Pest Thresholds

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    We’ve been off to a chilly and windy start, and nearly everywhere needs rain, but most of our cotton is in the ground now, and soybeans are currently being planted. The corn and milo is looking a little dry, but good otherwise. I have been looking for 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.

    I have seen very few thrips this year, only two in all the fields I looked at this week. There have been light aphid numbers in all of the fields I looked at, with at least a couple of winged aphids in each 25 plant check. There are also a few spider mites in most fields I looked at in Jackson and Matagorda counties, but all at levels far below the economic threshold.

    Thrips are a small (about 1/15″) light tan, straw, or brown 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 mach along unching 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.

    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.

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    While 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.

    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 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 pyrethroid application kills all their predators.

    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.

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