Planting Soybeans Into Cold Ground? Think About Seed Treatments

 Phytophthora sojae

Phytophthora sojae is a limiting factor for soybean on poorly drained soils.  This is managed primarily by resistance genes, but In Ohio Rps1a is no longer effective in any field; Rps1c and Rps1k may provide protection in approximately 40% of the fields.  Partial resistance for P. sojae is now more important as a management tool in which under high disease pressure, some roots do become infected but that infection is limited and the plants produce good yields.  This is also known in the industry as field resistance or tolerance.  Seed should be treated with either  metalaxyl  or  mefenoxam, but the rates of both of these fungicides are different due to the amount of the primary active ingredient.  In addition, substantial infection can occur for both products at the low labeled rates. At the mid-rate some disease does develop, but at the high rates not any infection occurred in greenhouse inoculations.  We have also shown that in very high disease situations, the highest rate of both products protects stand and yield of highly susceptible and moderately susceptible varieties. 

There are now a a number of strobilurin compounds labeled for seed treatments.  These fungicides impact P. sojae by reducing the size of the colony growth on agar assays and there is also some protection against root infection but it is not a complete control.  Thus, these compounds provide limited efficacy toward P. sojae.