South Carolina Cotton: Time to Scout for Plant Bugs

    Tarnished plant bug. Photo: University of Georgia

    As some of our crop is now squaring and growing rapidly, we will start to see populations of plant bugs increase. Plant bugs will include several species, such as the tarnished plant bug, Lygus lineolaris, the clouded plant bug, Neurocolpus nubilus, and the cotton fleahopper, Pseudatomoscelis seriatus.

    The plant bug species of most concern in the Coastal Plain of SC is the tarnished plant bug. Most of the clouded plant bugs I have observed were in the Upstate area of SC, as I have not observed many in cotton in the Coastal Plain counties. Cotton fleahoppers are widely distributed but rarely an issue, unless large populations develop on a wild host, such as cutleaf evening primrose, and move into young cotton nearby.

    These three species comprise a complex of bugs that can feed on pre-floral buds (squares), blooms, and small bolls. Some photos of these species are on the bottom of the next page.

    Treatment thresholds are as follows:

    Plant-bug injury to squares infrequently cause problems in SC, but an economic problem could develop if an early-maturing variety was planted late, an average of 3 plant bugs per 6 rowft is detected using a beat cloth or beat pan, an average of 1 plant bug per 10 sweeps is found, and/or 25% or more of pinhead squares have been lost due to plant bug injury.

    Cotton in SC is most susceptible to plant bugs around the time of first bloom (a couple of weeks on each side of first bloom). Pyrethroid insecticides can provide suppression of plant bugs when applied at stink bug/bollworm control rates. Avoid treating Bt cotton for plant bugs unless absolutely necessary in June and July as subsequent reductions in beneficial populations often trigger problems with bollworm or fall armyworm.

    Plant bugs can also injure small bolls like stink bugs. For combinations of plant and stink bugs feeding on small bolls, use boll-injury treatment thresholds for stink bugs. Insecticides recommended for control of plant bugs are listed below, but some are better than others. For example, Belay is a great product for control of TPB, but it cannot be used after pinhead square.

    AgFax Weed Solutions

    Diamond works only on immature plant bugs and not on adults, so it needs to be mixed with a material that controls adults. Imidacloprid can be weak on TPB, and acephate and Bidrin will kill many beneficials.

    Any aphids that build in cotton are the cotton or melon aphid, Aphis gossypii, as other species rarely colonize cotton. This species can transmit the Cotton Leafroll Dwarf Virus (CLRDV) that we have been following. So far, this disease has not caused widespread problems in the Southeast, and only isolated issues have been identified.

    We will continue to follow this vector/virus combination and let you know if data indicate we have more to be concerned about – you have enough to worry about now, so don’t worry about this one.

    Continue to watch aphids, and only spray to control them, if the stress is just too much on the plant (i.e. you have young, infested plants that will undoubtedly be stunted if aphids are not controlled; or, you have a drought-stressed crop that is hurting, and you can control a large population of aphids and remove one of the stressors, etc.).

    We have good insecticides for aphids, but the big question is whether or not we need to spray for them. Aphids are good prey items for beneficial arthropods to eat and build up populations of the “good guys” in the field. Regularly, we get a naturally occurring fungal organism, Neozygites fresenii, that wipes out aphids in days, leaving a robust army of natural enemies ready to take on bollworm eggs and larvae.

    So, manage the insects in your field wisely. Some of the subeconomic pests we can tolerate and benefit from later in the season.

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