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Soybean Insect Update
Author: Gus Lorenz, Extension Entomologist

Insects are beginning to show up in soybean fields across the state right now, and you should be scouting beans very closely.  Don’t think because the beans are small that they are not in danger. In most cases, beans are too small for sweepnet or shake sheet sampling, but just walking the field and observing will let you know if you have a problem.  The picture below, courtesy of Rick Thompson, is a field hit by YSAW (Yellowstriped Armyworm) and bollworm/corn earworm. It’s not hard to see the damage.

Yellowstriped Armyworm damage in field

Field damaged by YSAW and bollworm/corn earworm

YSAW larvae

Yellowstriped Armyworm larvae

Yellowstriped Armyworm on soybean

Picture taken last week courtesy of Rick Thompson in Poinsett Co.

Yellowstriped Armyworm.

We are seeing quite a few of these pests around. I thought last year was bad, but I think they may be worse this year. We have received reports and observed populations all across the soybean growing region of the state, from Clay Co. through Poinsett Co. and Arkansas Co. down into SE Arkansas. They are foliage feeders, but also, they will bore into the stalk around the terminal sometimes. Since they don’t feed on fruit, don’t get real excited about them unless defoliation reaches damaging levels 35-40%. Pyrethroids should do the job if treatment becomes necessary.

Bollworms and Tobacco Budworm

We had a big moth flight last week and saw a fairly heavy egg lay toward the end of the week. The bollworm flight has finally subsided but has resulted in many fields with bollworm larvae in the field this week, and I suspect that many will find these worms in the next few days. I have received many phone calls in the last two days about finding worms in fields across the state. The moths laid eggs in late planted beans that are about V2-V5. Pyrethroid applications appear to be giving good control. Remember, in soybeans, we use a much lower use rate compared to cotton, as larvae are much easier to control. Consult the MP-144 for use rates. Consider the fact that we have a long way to go with this crop, and we don’t want to spend up the insecticide budget too early. I strongly encourage everyone to watch fields closely for developing populations. At this point, we base the decision to spray on defoliation, same as other defoliator pests the threshold is 40% defoliation prebloom and 25% after bloom. The big threat from bollworm/corn earworm is when the plants begin to bloom and set pods. For now, stick with pyrethroids, don’t let anyone convince you to use more expensive products.  Trust me, there will be plenty of opportunity for that later in the season…..unfortunately.

Bollworm larvae (green phase)

Green color phase of bollworm larvae

Brown color phase of bollworm larvae

Brown color phase of bollworm larvae

Blister Beetles are showing up in several fields across the state. Adult blister beetles have broad heads and narrow necks. Several species are recognized. Two of the most common include the margined and striped blister beetles. The margined blister beetle is black, gray, or a mixture of the two colors. Striped blister beetles are yellowish-orange with brown stripes. They are usually spotty in fields and cause severe defoliation in small areas of the field. When you see one you will see thousands as they like to stay together. Believe it or not, blister beetles are also considered beneficial because the larval stage eats grasshopper eggs. Pyrethroids such as Baythroid, Karate, and Mustang Max, are all effective for spot treatment control. Check the MP-144 for rates.

Adult blister beetle

Adult blister beetle

Blister beetles

Blister beetles on soybean






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