Efficacy and profitability of fungicide use to manage Curvularia leaf spot of maize

Maize leaf spot disease, caused by Curvularia lunata, significantly reduces maize yield. Maize growers in China have been continuously challenged with controlling this disease. Maize is a tall and densely planted crop, and the motivation of farmers to perform disease control is affected by various aspects, such as the timing of disease control, types of fungicides and application methods, the effectiveness of the fungicides, and profitability. This study used maize inoculated and not inoculated with the pathogen Curvularia lunata under three conditions: fungicide treatment applied post-inoculation, fungicide treatment applied pre-inoculation, and fungicide application without inoculation (natural field conditions). We selected maize plants at growth stage V12 and performed a single fungicide application, then compared the characteristics and profitability of six types of fungicides on maize leaf spot disease. Under these conditions, all fungicide treatments resulted in a significantly lower number of leaf spots and lower disease index than the control group (P < 0.05), and the grain yield of all fungicide treatments was higher than the control. Under a net return of $0/ha (D = $0/ha), the probability of profit was within the range of 0.470–1.00. In terms of yield increase and probability of profit for achieving a net return of $225/ha (D = $225/ha) under all conditions, we found that 18.7% propiconazole·azoxystrobin was effective in protecting, preventing, and improving plant health. However, it was less effective in treating the disease, indicating that it can be applied during the early growth stages to prevent subsequent leaf diseases. The characteristics observed using 250 g/L pyraclostrobin and 125 g/L epoxiconazole was similar to that of 18.7% propiconazole·azoxystrobin. However, because of the higher cost, the probability of profit of 250 g/L pyraclostrobin was lower than 0.695 (D = $225/ha), and the probability of profit of 125 g/L epoxiconazole was lower than 0.624 (D = $225/ha) because of the smaller improvement in yield. Seventy-five percent trifloxystrobin·tebuconazole showed great effect on disease treatment and plant health improvement but was less effective for crop protection and disease prevention, suggesting that this fungicide is suitable for later application. Seventeen percent pyraclostrobin·epoxiconazole was only efficient at disease prevention, whereas 23% kresoxim-methyl·epoxiconazole was effective in treating the disease; regardless, their probabilities of profit were all lower than 0.629 (D = $225/ha).