By Jeremy Ross, Extension Soybean Agronomist
Starting last Thursday, I have been getting more and more reports from around the state about pod splitting and/or seed sprouting in the pod. So far, no commodity has escaped this sprouting problem since I have seen or heard about sprouting in rice, corn, grain sorghum, cotton, and soybean. Pod splitting is most common when pods develop and seed begin to expand (R4 to R6 growth stages) during stressful conditions and seed finish filling under very wet conditions. Seed sprouting is usually caused by extremely wet conditions after a crop is mature and seed moisture has dropped below 50%. However, many of the calls I have been receiving are sprouting of seed around the R6.0 growth stage.
Many are asking the questions, “What is causing the pod to split?” The reason is not clear but definitely is related to the wet conditions we have had over the last two weeks. These weather conditions are very similar to those seen late during the 2009 growing season, the last time I observed these symptoms in soybean fields. Soybean plants determine how many and how large pods will be early in the season. If the soybean plant experiences stressful conditions during this developmental period, the soybean plant responds to these conditions by having smaller and possibly more pods. We did experience some very hot and dry conditions during June and July that could have caused some stress to the soybean plants. With the wet conditions we have had over the last two week, seed have expanded to the point where the pods split along the sutures exposing the seed.
Usually, the number of split pods and the sprouting seed is low and yield and seed quality effects are minimal. After a week of drying conditions, the sprouting seed will dry up and may fall out of the pods. At the worst, there could be some lower test weight and seed could contain more foreign material (from the dried up sprouts). However, the light seed will likely be blown out the back of the combine. Adjustments to the combine should be done to remove the light, sprouted seed at harvest.
Can a foliar fungicide reduce splitting pods and sprouting soybean? No, as these developments are not caused by fungal pathogens. There are several fungi associated with pod rot like anthracnose, which is a common late-season disease that is easily identified with a hand lens. Look for dark “mini-spines” (setae) in concentric rings on pods. In addition to anthracnose, other opportunistic, saprophytic fungi are often found on these brown, discolored pods. These are more common on mature plants during conditions of prolonged wet, cloudy weather, which we have experienced over the past few weeks. Finally, and most importantly, university research trials show no positive benefit from a fungicide to protect seed/pod quality at late-reproductive stages of growth (R5+) and there is no evidence of any benefit from a fungicide at R6.