Sorghum Heading – Scouting For Insects

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Our early planted sorghum is heading now and is past flowering stage. We are looking at a few different insect pest I want to write about. Some fields have sprayed 3 times now for sugarcane aphids. At this point, we want to watch for aphids in the grain heads. Also we are seeing caterpillars in grain heads. Last week, we were checking for midge.

Midge

Midge can be more difficult to scout for. Once grain heads come out, we need to be looking for midge. Once flowering is complete, midge is not an issue. One way to scout is take a paper plate, and slap the head in the plate. Dr. Angus Catchot, entomologist in Mississippi, shows on Scouting For Sorghum Midge With Confidence, a method of putting a gollon ziplock bag over the grain head and thumping it. The midges fly to the top of the bad, and you don’t have to close the bag.

Scouting for midge

Scouting for midge

UGA Extension Entomologist Dr. David Buntin says we need to avoid pyrethroids and insecticides that would flare aphid populations. Do not do automatic sprays for this reason.

Sorghum Midge - Photo by Ben Thrash

Sorghum Midge – Photo by Ben Thrash

Caterpillars

We are also seeing caterpillars on the grain heads. Most of the caterpillars we are seeing are corn earworms. We were also seeing armyworms. Our threshold is to treat when an average of 1 or more (1/2 inch or larger) of any of these worms are found per grain head. Below is a photo of corn earworms on this head. Flowering is complete here, and they blend in to the grain.

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Sugarcane Aphids

One of the four fields we checked yesterday is at dough stage of development. Dr. Buntin says when we get to dough stage, we do not have the concern for sugarcane aphids. We still need to check for aphids in the grain heads, because of issues with harvest equipment from aphid honeydew. Here is a photo of some aphids in the grain head. This field is in the dough stage and past flowering, so pre harvest intervals are more difficult as we move to heading.

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Some milo fields have been sprayed three times for sugarcane aphids. It is difficult to assess thresholds following a devastating 2014 season where aphids hurt us before we knew what was going on. However, Dr. Buntin believes we should be able to get SCA with two sprays during the season. We have learned to scout by not only checking aphids on a plant, but walking fields and looking for honeydew. It is easier to see honeydew on the leaves from a distance and you can check more than one row at a time. Where honeydew exists, this indicates a high aphid population – one that is treatable. Below is a photo of sooty mold on leaves. Sooty mold grows on the honeydew left from aphids. This is another indicator, however, I have not seen sooty mold show up until now. This is not an issue for the plants, just sign of aphids.

Sooty Mold

Sooty Mold

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