Pythium

​Recent cold and wet environment shortly after corn planting favored the fungal-like organism known as Pythium. Among the unique characteristics of these species and other Oomycetes are development of special thick-walled spores for dormancy during winter and dry environments and swimming spores released in moisture.  The latter are attracted to the carbohydrates and other chemicals released as seeds imbibe and germinate.  After attachment to the tissue, Pythium species form filaments (hyphae or mycelia) invading the plant tissue.   Primary roots and mesocotyl are the most frequent site of invasion.  Lower temperatures and water saturated soil favor the Pythium and disfavor the corn seedling growth.  If these conditions are present before the development of secondary roots in the young plant, while dependent upon nutrition from the seed endosperm, the plant will wilt.
 
It is reasonable to expect that Pythium will be among the causes of poor stands in some fields this spring as early May weather favored the invader and disfavored the corn planted in the last week of April.  Individual seed, already weakened by the internal damage after imbibition, having trouble recovering at the low temperatures, probably are most vulnerable to invasion by the organism favored the same environment.  Even if the soil temperature increases to above 50°F, allowing cellular respiration to increase in the young tissue, low oxygen levels in saturated soils will add to the difficulty of the seedling to produce new tissue ahead of the invading Pythium mycelia.
 
Analysis for causes of poor stands after the recent weather will be complex because of the interaction of seed quality differences among the seed, soil water holding capacity, time of planting, and presence of organisms such as Pythium.  Seed treatments selected to ward off Pythium species can be overcome by races of the fungus, further confusing the analysis.  In addition, several less pathogenic fungi will invade the damaged seed and seedling tissue making the analysis more confusing. 
 
I am not sure if most people outside of agriculture understand the complexities involved in growing a successful corn crop.  And those of us involved in some aspect of agriculture have difficulty understanding these complexities as each new bit of information seems to lead to more questions.