Continued wet weather and concerns about the impact poor quality soybean seed in particular are on the minds of many. Last month I discussed the numerous factors that encourage fungal root rots. In disease conducive fields, a fungicide seed treatment can be a value to establish a good stand. But that is not the whole story.

Extension Plant Pathologist Carl Bradley recently addressed the issue of whether a fungicide seed treatment would help germination for out a poor quality seed lot. Bradley notes that soybean seed with lower than normal germination, especially in certain maturity groups, is very common this year. This low germination is apparently due to thin seed coats, which make seeds more prone to mechanical damage. So what effect will a fungicide seed treatment have on those lots? Bradley notes that fungicide seed treatments will not increase germination of poor-quality seeds when the poor quality is due to mechanical damage. However, if the poor quality is due to fungal infection, in the field or carried on the seed itself, fungicide seed treatments could increase germination.

Planting damaged seed can also actually lead to an increase in seedling blights. Carl explains this based on research conducted in the 1970s at Ohio State University. The studies indicated that the quality of soybean seedlings that emerged from seeds with cracked or scarified seed coats was poorer than of seedlings that emerged from seeds with intact seed coats. Exudation of nutrients from seed with damaged seed coats can be greater than from seed with intact seed coats. This nutrient exudation can stimulate Pythium, a soilborne root pathogen that can cause seedling blight of soybean. For this reason, treatment with a fungicide of seed with damaged seed coats could provide some protection against Pythium and other soilborne pathogens that can cause seedling blight.

Dr. Bradley recommends that if the decision is made to treat soybean seeds or to use a planter box treatment, it is important to use a product that contains either mefenoxam or metalaxyl, both of which provide specific protection against Pythium. In addition, the product should contain at least one other active ingredient (fludioxonil, trifloxystrobin, carboxin, and others) that will provide protection against other pathogens.

Planting date and field history of root rots are also major factors in deciding to make a fungicide seed treatment. You will realize the most benefit from a fungicide seed treatment in fields that are planted early in cool soils that have a history of rot. Reducing the need for replant is the most direct benefit from good disease free stand establishment. And that's nothing to shake a stick at given soaring fuel costs alone.