Check soybean seedling stands for signs of disease

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.