Tennessee Soybeans: In Late Fields, Don’t Make Matters Worse

    Soybean looper on leaf. Photo: University of Tennessee

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    We’re seeing various caterpillars but not in high numbers. I’m not finding a high number of loopers yet, but keep an eye out because people to our south report a pretty good flurry, and those tend to move up on us.

    They traditionally develop in late August and early September, so our later-planted fields will be the most susceptible.

    A little spraying has been going on for stinkbugs in soybeans, and that’s very common. Stinkbugs have a way of blowing up at about R5 and often at R6 and R7. In places, various kinds of stinkbugs are are pushing threshold.

    Let The Beans Tell You When To Quit

    It’s very important to understand the difference between R5 and R6. At R6, we recommend doubling the threshold from 9 per 25 sweeps to 18 per 25. In 7 to 10 days after you hit R6, we would rarely recomment treating stinkbugs. An exception might be where you’re growing soybeans for seed.

    When soybeans reach R7, you will see brown pods at the bottom of the plant. At that point, we typically recommend not treating for insects because the seeds have reached full size and any spraying won’t affect yield.

    At that stage, plants start fully defoliating themselves. The only thing stinkbugs would affect then is seed quality, and it would take very high numbers to cause concern. But in later maturing fields, we still may be dealing with a flurry of bollworm.

    Those would be fields sitting at R2 to R3, and are still be flowering. Those same fields will more likely be infested later with loopers. Keep that in mind when making insecticide applications. Don’t make an unjustified pyrethroid application prior to a looper flight.

    Try To Avoid Hitting Beneficials

    If you have to spray, you have to spray. But understand that treating will take out beneficial insects you will need later to hold loopers in place. We don’t see loopers often in Tennessee. But they are consistent enough that if you apply a pyrethroid, looper populations will build 2 to 3 weeks later.

    Often, people don’t link those two things together, but it happesn. If you do have to spray something like corn earworms, you have want to with a softer option.

    AgFax Weed Solutions

    If you’re dealing with a green cloverworm outbreak, for example, you could apply Intrepid or the generic version. Or, you could use a low rate of the diamide or Intrepid Edge and save your beneficials. If you opt for a diamide, go with Prevathon if your goal is to save beneficials. Besiege contains lambda-cyhalothrinin, which is a pyrethroid, and it will reduce beneficial numbers.

    People are sending me photos of moths that are all over their window screens. Without exception, these have been green clover worms (GCW). We’ve had a pretty fair infestation in our later beans. Those caterpillars matured and pupated, and now they’re emerging as moths.

    Often, though, that doesn’t translate into field infestations. GCW are a funny creature. Sometimes you’ll see little population spikes, then they disappear. Diseases tend to take out populations.

    This isn’t anything to get you too excited, but those moths do indicate past CCW pressure.

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