Heavy rain fell across much southern Minnesota on Sept. 22 and 23 and left large areas of Minnesota corn and soybean fields submerged. Floodwaters covered nearly 100,000 acres for several hours as rainwater moved from fields into creeks and rivers. Longer-term flooding of fields affected tens of thousands of acres of cropland. In most instances, drainage tile, where present, was unable to prevent ponded waters. In other cases, streams swollen by 4-12 in. of rain falling on fields, roads and cities came out of their banks and flooded fields.
Many factors will affect the quality of the corn and soybean crops following standing water. These include, but are not limited to: duration of the flooding, crop stage or maturity, depth of the water, movement of the water, and air and water temperatures. Fortunately, late-season rain events of this magnitude are relatively rare. Unfortunately, there is virtually no data to help estimate crop losses and conditions of corn and soybean crops.
Floodwaters are thought to affect soybeans more than corn. Potential flooding damage to soybean includes stem breakage and lodging, moisture-swelled seeds that can lead to pod splitting, seeds spouting or rotting and contamination with mud. We do know that short duration flooding events are gentler on the crop than floods that last several days or more. While little is known about crop stage effects on flooding damage, one can be sure that flooding of any duration on any soybean field in late September will cause damage to the crop. The extent of this damage is unknown.
Anecdotal information from flooding occurring in Mississippi in 2009 indicates that soybean fields that have reached full maturity (R8) at the time of flooding were found to have less damage than fields that were not yet fully mature (less than R7). Bruce Potter has, so far, noted little loss from fields that were at R8 at the time of flooding and where ponded water receded in a few days. Significant lodging and loss is present where heavy stream flooding occurred.
Management: The only management considerations that are open to producers at this very late date may be harvest timing and logistics. Rather than waiting for wet spots, harvesting the non-flooded portions of fields first will speed harvest, minimize wear and tear on equipment and keep water damaged soybeans separated from good quality grain.
Farmers should harvest and store soybeans from flooded areas separately from areas that were not flooded. Because damage levels are difficult to estimate and thresholds and allowances provided by grain elevators are unknown, it is critically important that producers not mix damaged soybeans with clean ones. Do not be tempted to blend off a few bushels of damaged soybeans with a whole bin of good ones. The risks are simply too great.
Another reason to harvest flooded areas separately is related to crop insurance. It is important that producers clearly document these flooded areas so that insurance or disaster relief assistance claims may be made a later date. Isolating these flooded areas is the best means to document losses from these heavy rains. Again, please harvest and store flooded soybean acres separately. This is the best means available to minimize your risks.