June 24, 2011
The scouting trips this week have left me fairly optimistic about soybean progress at this time. I know we have a lot of growing season to go but around the county most of the soybean stands look good. However, there are a few soybean stands around the county that appear to have some issues. There are several possibilities for the poor stands including diseases, insects, poor quality seed, or just poor growing conditions.
One of the hardest diagnosis to make is seedling disease in soybeans. To really make a accurate diagnosis, soybean seedling should be examined under a microscope to look for signs of the pathogen that are causing the problems. If you have seedlings that are in the process of dying, bring them into the office and we can send them to OSU’s state Plant Pathology specialist Dr. Anne Dorrance. She will be glad to check them. Dr. Dorrance use then seedling samples to help her decide the next direction for soybean management studies.
According to Dorrance, symptoms of many seedling diseases look the same. But there are a few that can be distinguished. Brick-red colored lesion on the base of the stem is indicative of Rhizoctonia. This pathogen is controlled by resistance and primarily the fungicide Maxim. Fuzzy, pink discoloration is indicative of, the same fungus that causes head scab of wheat and Gibberella stalk rot of corn. The watermolds, both Pythium and, symptoms are the same. The seedlings will appear light brown to dark brown, and soft. For all of these diseases, the stand loss will occur in patches or a few seedlings here and there scattered across the field.
The best management of seedling diseases is first to choose varieties that have resistance. The second is to work on drainage. For problem fields, improving soil drainage will go a long way to minimize stand losses in years like 2011 where it doesn’t seem to stop raining. Seed treatments can also play a role in protecting seeds and seedlings, but they only protect under moderate saturation levels. When soils are totally saturated for weeks, that is just too much to expect from the seed treatment. Finally, long-term no-till fields may also see more seedling pathogens as the inoculum will build up in the top few inches of soil.