To treat or not to treat?  That is the question.  With each passing year there are more options for treating soybean seeds with a fungicide.  These options encompass both type of product and application time.  The desired outcome is to prevent seedling diseases from reducing stands to the point where yield value lost is greater than the cost of treating the seed.

Soybean seedling diseases are most problematic under conditions of early planting, high crop residue, wet soils, low seed quality, and when soybeans are grown frequently in crop rotation.  Not surprisingly, positive research results with soybean fungicide seed treatments vary with location and year.  View their use in the same manner that you purchase insurance and realize that there simply will not always be an economic advantage.  Know the conditions when seedling diseases are most likely to be a problem.

Particular disease pathogens predominate under different environments.  The most common seed and seedling pathogens in Wisconsiin are Pythium, Phytophthora, and Rhizoctonia.  Pythium and Phytophthora are water-loving organisms and infect seedlings when soil conditions are wet to saturated.   Rhizoctonia prefers moist but not saturated soils.  The disease pathogens also differ in their preference of optimum soil temperatures for infection.  Many species of Pythium prefer cool soil (50­60 degrees), although some species prefer warmer conditions.  Phytophthora prefers slightly warmer soils (60­76 degrees), and Rhizoctonia is most active in warm soils over 74 degrees.  The first pathogen that often causes problems after planting is Pythium.  The soft-rot, tan symptoms on roots and stems caused by Pythium and Phytophthora are very similar and cannot be distinguished without laboratory testing, while the reddish-brown, often sunken, lesions caused by Rhizoctonia are easier to recognize.

Types of seed treatments

        There are several seed treatment products on the market.  Some of these are characterized for disease control in Table 1.  On most of our medium to fine textured soils it is recommended to choose a product that has activity against Phytophthora, Pythium, and Rhizoctonia.  These products include Rival/Allegiance, ApronMaxx, Allegiance, and Apron XL.  The latter two products have no activity for Phomopsis.  SoyGard is a new fungicide for 2002 but probably is not strong enough on Phytophthora for widespread use in our area.

Compatibility with inoculants

        The compatibility of inoculants with seed applied fungicide treatments is also an important issue.  Most fungicide seed treatments have a degree of detrimental effect on the health of Rhizobia bacteria.  Some inoculant labels list their compatibility with popular fungicide treatments or growers can contact the individual companies for further information.  The following general rules apply for use of inoculants in conjunction with seed treatments:

·        Unless the inoculant label indicates strong compatibility, in-furrow application of inoculants will give the best result when seed treatments are used. 

·        When inoculants and seed treatments are used together, keep the exposure time to a minimum (less than 8-12 hours is best).  Re-apply inoculant if the seed has been treated over 12 hours and not planted yet.

·        If the chemical seed treatment is a liquid, apply it first, allow it to dry, and then apply the inoculant.  Some inoculants are labeled to be tank mixed and applied at the same time as the seed treatment, but check the label to make sure this is the case.

         Inoculation failure can be avoided by following label instructions and keeping the time between application and planting as short as possible.