We are seeing immature soybean once again sprouting in the pods in Suffolk and Gloucester County, and I heard of this happening in other states. This seems to occur every 3-6 years somewhere. Although I don’t have a great explanation for why this occurs, it usually happens when there are good growing conditions early followed by 2-4 weeks of drought stress during pod formation, and then excellent conditions return for seed fill. Typically, it happens in big-canopied soybean (lots of leaf area) with lots of yield potential, but not enough pods (or big enough pods) to fulfill that potential. I think that the seeds enlarge so much that the pod splits.
Keep in mind that I’m talking about immature seeds and pods. This can also occur after the crop matures (R7 to R8) when we get excessive rainfall after the seed in question has dried down. But, I have not seen that yet this year.
There is little that you can do about it. Those sprouted seed will usually dry up on the plant and be blown out the back of the combine.
Although there has to be some yield loss, I’ve not seen it to be very great. And, I suspect that if you did not notice the sprouted seed, you probably would not know that you had a loss.
For more information, see previous blogs on this subject.
One of the most disturbing late-season issues can be pod splitting and/or seed sprouting in the pod. Pod splitting is most common when pods develop and seed begin to grown (R4 to R6 stages) during dry conditions and seed finish filling under wet conditions. Sound familiar. This is more-or-less what we experienced this year. Seed sprouting is usually caused by extremely wet conditions after the crop is mature and seed moisture has dropped below 50%.
What causes pod splitting? The reason is not clear, but here are my observations. Generally pod splitting happens when the crop is under severe stress, usually drought conditions up until the full-seed stage (R6). Pods are generally small due to the drought. Then rains set in between R6 (full seed) and R7 (physiological maturity). The seed grow and grow, and seem to outgrow the pods, causing them to split. Obviously, this splitting can then lead to seed quality issues. It can also open the plant up to seed sprouting,
Even if the crop does not experience the above conditions and pods do not split due to rapid seed enlargement, wet conditions after the crop is mature can lead to sprouting seed. Sprouting seed is not always directly related to the pod splitting; pods may not split until seed sprout. I’ve seen up to 30% of pods with sprouted seed when conditions are perfect for this. Although an unusual occurrence, seed sprouting can occur if soybean seed drop below 50% moisture, then increase to 50% or more moisture.
In addition, I have seen more sprouting in pods showing Cercospora blight (very dark pods). I do not understand why and could not definitively relate the sprouting to this disease. But, there appeared to be a relationship. Sprouting occurred primarily at the top of the plant where the dark pods were located. In contrast when pods were not dark, I have observed most sprouting at the bottom of the plant where the relative humidity is greater.
Usually, the number of split pods and sprouting seed is low and yield and seed quality effects are minimal. After a week of drying conditions, the sprouted 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. If you do observe the problem and it is severe, I suggest that the air on the combine be adjusted to remove those light, sprouted seed at harvest. Too many sprouted seed in the bin could lead to rejection by the buyer.