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Agronomy Today |
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This article was written by Rod King, Regional Agronomist Soybean Insects and Diseases – Keep WatchingThe next couple of weeks are critical times to be walking your soybean fields. Here are a couple of soybean pests to watch for. Frogeye leaf spot – I found frogeye in two locations late last week –Wabash and Pulaski Counties in Indiana. It is being reported in other areas as well. Neither infestation I saw was severe, but the presence of the disease at this stage is a concern. Frogeye leaf spot shows up mostly on upper leaves of soybeans (relatively easy to scout for) as round to slightly angular lesions, tan in the center with a narrow rim of dark brown-red. Lesions are normally about 1/8 inch in diameter. If you use a hand lens you might see some dark gray/black matter more or less in the center of the lesion – these are the sporulating bodies. Frogeye likes leaf surface wetness and warmth, and can spread rapidly if conditions are right. Spores travel easily on air currents. This disease can “explode” and can cause significant yield reduction. Most of the fungicides we use on soybeans are effective in preventing or stopping the spread of the disease. If you have applied a fungicide in the past week or two, you should be protected (about three weeks of protection from the time of application, except that new leaves are generally vulnerable). If you find a few lesions, watch that field carefully and be prepared to apply fungicide up until R5 if the disease becomes prevalent Soybean aphid – I found low numbers of soybean aphids last week – Kendallville (LaGrange County, IN). They were of no concern at the levels we saw, but this insect can multiply rapidly and its presence means we need to monitor fields for infestations. The threshold for insecticide treatment is a minimum of 250 aphids per plant (perhaps a higher threshold level is appropriate for the current growth stage of the bean crop). Remember to look on the underside of leaves and on stems for this insect. Other insects: Bean leaf beetle and various other leaf feeders can be found, but are rarely of economic significance at this stage. If you see what appears to be significant leaf feeding and/or alarming numbers of leaf feeding insects, call us to discuss.
If you have any questions or concerns please contact:
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