Application and Timing Effects of Qoi and DMI Fungicides on Controlling Disease and Improving "Plant Health" in Corn.

The use of fungicides on corn has recently increased as a result of higher grain market prices, changes in cropping practices, and the availability and marketing claims of new fungicides. Some of the marketed potential “plant health” benefits include improved tolerance to drought and heat, improved N utilization, and increased stalk strength. Large-scale field experiments were conducted at three locations representing different soil types and growing conditions to study the effectiveness of application and timing (V5, VT, V5+VT) of two QoI fungicides and two fungicides containing both QoI and DMI active ingredients. Multiple measurements were conducted throughout the growing season to determine effectiveness of controlling disease and improving overall “plant health”. At the end of the growing season, grain yield and moisture content were estimated with a commercial combine and calibrated yield monitor. Inadequate rainfall during the 2012 growing season led to very low disease (<1% of leaf surface area) throughout the entire growing season resulting in a good opportunity to measure “plant health” benefits in the absence of disease pressure. No effects of early (V5) fungicide treatments on levels of disease were observed, but late (VT) fungicide treatments significantly decreased the amount of disease at two of three locations from about 0.5% to 0.06% of leaf area affected at one location and from about 0.7% to 0.55% of leaf area affected at the other location. However, these small differences in levels of disease were unlikely to have an effect on yield. Two active optical reflectance sensors and chlorophyll meter were used to evaluate the purported “greening effect” attributed to QoI fungicides. Little to no effects of fungicide treatments on biomass or chlorophyll content, were detected with the active optical reflectance sensors and chlorophyll meter. Small and inconsistent effects on the number of green leaves below the ear leaf were observed. Stalk strength (push test) was unaffected by the fungicide treatments. Fungicide treatments had no effect on yield, yield components, grain N concentration or grain N content. Based on the data collected from the 2012 growing season, application of fungicides did not prove to be a beneficial practice.