Effects of pyraclostrobin foliar fungicide, corn hybrid, and harvest timing on stalk health of corn

The use of foliar-applied fungicides on corn (Zea mays) in the United States has been heralded as a way to improve stalk health. Our goal was to provide evidence whether the use of pyraclostrobin fungicide provided benefits beyond managing foliar diseases of corn, such as gray leaf spot (caused by Cercospora zeae-maydis). Field trials evaluating the response of four corn hybrids at two harvest times to the foliar application of pyraclostrobin fungicide applied at tassel stage were conducted near Champaign, IL in three consecutive years (2008-2010). The selected corn hybrids were either susceptible ('H-8838' and 'H-8939') or moderately resistant ('H-8852' and 'H-8953') to gray leaf spot. In addition, each set of hybrids represented "sister" lines, with H-8939 and H-8953 containing transgenic Bt traits for European corn borer (Ostrinia nubilalis) and corn rootworm (Diabrotica spp.) control. Plots were harvested at two different times when seed moisture concentration was approximately 25% or 3 to 4 weeks later. Stalk health was evaluated immediately prior to harvest by splitting the stalks open and visually rating stalk rot using a 0 to 5 severity scale. In general, corn hybrids that were susceptible to gray leaf spot had greater stalk rot severity than those that were moderately resistant to gray leaf spot. Within "sister" lines, no stalk rot differences were observed between Bt and non-Bt hybrids. Stalk rot severity generally was greater at the second harvest date compared with the first harvest date. In general, plots treated with pyraclostrobin had reduced stalk rot severity compared with non-treated plots.