Soil temperatures from around the state are highly variable still on the cool side. From the weather stations at the branches, these are the soil temperatures at 2.5 inches, from April 20 were:
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Cool, wet soils promote the growth of one of the major seed and seedling pathogens of corn and soybean, Pythium. Some or the more than 25 different species of Pythium are particularly favored by these cooler temperatures. Since the soil is moist, oospores which overwinter, are germinating. When the soils become saturated, they will form a structure called a sporangium which forms the zoospores. What is unique about this group of pathogens compared to watermolds is that these spores will then swim to the roots, they are actually attracted to germinating seeds and growing roots. When seeds are planted into cool soils, and we have some low temperature nights, the seeds themselves can be injured. This then serves to attract more zoospores – quite a system all in favor of these cool, wet loving pathogens.
I think Peter Thomison said it best in last week’s article. Plant in as close to optimum conditions as possible. Don’t try to beat a major storm front – in Ohio that is a classic set up for replant conditions. Keep monitoring those soil temperatures to ensure the best jump start for this seed. If in doubt, go back and look at the receipt for that seed, this is a huge investment for the overall farming inputs. You only want to plant once.
Well drained soil, and seed treatments with one or more of the following: metalaxyl/mefenoxam, strobilurin, or the new fungicide ethaboxam will all protect young seeds/seedlings, but to a point. Too much cold, long periods below 50 F and extensive saturated soils can overwhelm the system. Resistance to Phytophthora sojae (warmer temperature oomycete) is well studies and well known for all of the varieties that you purchase. It is not known how resistant the varieties are to Pythium spp. There are just too many to test.