COTTON
Alabama Extension entomologist Dr. Ron Smith and I along with my summer worker Ben Tankersley scouted several cotton fields in Cherokee County this Tuesday (July 12) as part of a research project involving ThryvOn and non-ThryvOn varieties.
No adult tarnished plant bugs were found as they have mostly cycled out. Also, growers did an excellent job controlling the high numbers of plant bugs from the previous weeks. Unfortunately, we started to pick up very young nymphs (just hatched) that was just below threshold. The threshold is 3 nymphs per 5 row feet.
It is necessary to use a black shake cloth to see these very small nymphs. We can wait until next week, as more plant bugs hatch out, to apply an insecticide if threshold is met. Unfortunately, very few growers use a shake cloth to scout for plant bug nymphs as it is very time-consuming.
An insecticide (Bidrin at 5.33 ounces per acre or bifenthrin at 6.4 ounces per acre) to control both plant bugs and stink bugs is advisable if threshold is met for either. Orthene (acephate) should be avoided to prevent flaring spider mites.
We started to find more stink bugs (mostly brown) in cotton. The brown stink bug is more cold tolerance than the green or southern green stink bug, so it is usually the dominant species coming out of wheat. Stink bugs have traditionally been our most damaging insect in cotton, so a good scouting program is critical to minimize yield losses.
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Bolls about the size of a quarter should be examined for damage from stink bugs. Ten percent damage is the threshold during weeks 3-6 of bloom. Twenty percent in weeks 2 and 6, and 30% during weeks 7+ of bloom when fewer susceptible bolls are present. Alabama Extension entomologists Dr. Scott Graham and Dr. Ron Smith have an excellent stink bug scouting video, see it below.
Aphid populations are beginning to crash in South Alabama due to the aphid fungus. We generally see the aphid fungus shown up in NE Alabama about 7-14 days later. An addition of 1.5 ounces per acre of imidacloprid would be an economical choice if a spray application is necessary and there are high aphid numbers suppressing the cotton plant’s growth.
I have been getting reports of whiteflies in cotton in Cherokee County, but these are phantom midges. Phantom midges are not harmful to cotton. The phantom midge larva, called glassworms, develop in the muck at the bottom of lakes. The closer your cotton field is to Lake Weiss, the more likely you are to see these white swarms in your field.
SOYBEANS
We are beginning to pick up more stink bugs (brown, southern green, and brown marmorated) in our April planted soybeans, especially on the border of the fields, along with increased numbers of kudzu bugs. Japanese beetles are doing most of the foliage feeding along with bean leaf beetles. I suspect we will soon have to spray for stink bugs on our April planted soybeans.
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Now that soybeans have produced most of their foliage, if any insecticide sprays need to be made, adding two ounces per acre of Dimilin 2L would be a wise and economical choice. The Dimilin 2L will give season-long control of green cloverworms and, more importantly, velvetbean caterpillars on foliage that the Dimilin comes in contact with.
Velvetbean caterpillars are an occasional but potentially devastating pest in N Alabama if not caught early. They a voracious foliage feeders and can quickly strip a soybean plant as many growers found out two years ago.
