Pythium species (spp.) are one of the major pathogens known to cause seedling diseases in corn in Iowa. Fungicide seed treatments can help provide protection for a window of time. Not all fungicide seed treatment active ingredients are effective against Pythium. Active ingredients that specifically target Pythium include metalaxyl, mefenoxam, ethaboxam, and picarbutrazox. Trials were established in 2017 and 2018 to examine the effect environmental conditions at planting, seed treatments, and previous crop residues (corn (Zea mays L.), soybean (Glycine max L.), and winter rye (Secale cereal L.) have on early corn stand establishment, plant vigor (2018 only), seedling diseases caused by Pythium spp., stalk rot severity, final stand, barren plants (2018 only), and grain yield.

The trials demonstrated the impact previous crop residues and planting date have on plant stands, plant vigor, root rot severity, stalk rot severity, final stands, barren plants, and grain yield. In 2017, corn stands were the lowest in a previous crop residue of winter rye compared to stands in continuous corn or soybean residue. Corn stands were the greatest in soybean residue in 2018 compared to those in corn or winter rye residue. Earlier planted corn had lower stand counts compared to later planted corn in both years. Plants were more vigorous (taller) when planted into soybean residue compared to those planted into winter rye residue or corn residue. Additionally, the earlier planted corn was more vigorous than the later planted corn. Root rot severity observed on corn plants in the continuous corn plots in 2017 and soybean residue plots in 2018 was less than that observed on the other crop residue treatments evaluated. The later planted corn had less root rot than the earlier planted corn in 2017, but the opposite was observed in 2018. Stalk rot severity was the greatest in the continuous corn plots in 2017 and no effect of planting date on stalk rot severity was detected. Final stand counts were the greatest in corn planted into soybean residue in both years. The number of barren plants were the least in corn planted into soybean residue in 2018. Later planted corn had a greater final stand count than the earlier planted corn in 2017 but not in 2018. In both years, the corn in the soybean residue had the greatest yield. In 2017, the earlier planted corn yielded less than the later planted corn, and no planting date effect was detected on yield in 2018.

Seed treatment effects were detected across all trials on corn stand 14 days after planting (DAP) in 2017 (p = 0.050) and at 28 DAP in 2018 (p = 0.017) as well as on root rot severity in 2018 (p = 0.024). In general, seed treatments that contained active ingredients that specifically targeted Pythium spp. improved stand and reduced root rot severity. Additionally, preliminary research identifying the Pythium spp. present in the trials, suggested P. sylvaticum was the most prevalent species recovered from corn seedlings in these trials.

Results suggest that previous crop residue and environmental conditions around planting influence early corn stand establishment, plant vigor, seedling diseases caused by Pythium spp., stalk rot severity, final stand, barren plants, and grain yield. Additionally, these results suggest that the use of a seed treatment that contains an active ingredient(s) that specifically targets Pythium spp. is an important tool farmers can utilize in protecting corn seedlings from seedling diseases caused by Pythium spp.