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Soybean podworms can strip field quicklyPosted Monday, August 22, 2011, at 4:57 PM
Soybean podworms have been reported in some parts of the state. This pest is known as the corn earworm in corn or the soybean podworm in soybeans. University of Missouri Extension specialists recommend scouting fields now to prevent damage to the crop. According to Wayne Bailey, MU Extension entomologist, if podworms are high enough in number they will take off all the pods in a field.
In 2010 in Chillicothe, podworms came in and defoliated for awhile and then moved to the pods and cut them off. Sometimes they will feed on the bean within the pod first before cutting pods off, then once they defoliate most of the plant they will eat the pods off the ground. Some fields experienced a 100 percent loss.
With many soybean fields either in flowering or pod-fill stages, especially with late planting, it is critical to scout now. The worms occasionally feed on flowers but prefer soybean pods and foliage. Holes in the side of a pod can indicate a podworm has been enjoying a tasty meal.
The worms come in all colors, from brown with yellow spots to white with black spots and green. Bailey says that there are more green soybean podworms this year. To distinguish podworms from worms like green cloverworm, farmers should look at their legs. The soybean podworm has four pair of large abdominal prolegs right in the center of the body, while cloverworm only has three pairs.
Soybean podworm got a foothold in soybeans throughout Missouri in 2010. A natural fungal pathogen normally keeps late-soybean podworm in check in most of the state. The pathogen uses green cloverworm as a host. Low numbers of cloverworm has drastically reduced the presence of the pathogen and that combined with increasing populations of corn earworm for the last five years has allowed the soybean podworm population to explode.
Bailey recommends treating fields if you find the insect present and pods are being fed upon by the larvae. It only takes one larvae per plant to take all the beans out of the pods. Even small podworms, not just the ones that are 1 to 1.5 inches long, are economical to treat because of how much damage they can do in such a short time. There are many foliar insecticides labeled for soybean podworm control. Use enough water to get good coverage. Spray quickly after you find soybean podworm, because they can do a lot of damage in short order.
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As our local University of Missouri Agronomy Extension Specialist, Crook has been writing a column for the print edition Agriculture page for the past three years and we will now be sharing it on our web version. Crook has a bachelor and masters degree in agronomy from University of Missouri and received his doctorate in Agronomy from Kansas State University. He was in soybean variety development research for 22 years for various seed companies and has been Saline County's agronomy specialist for 10 years.