Comparison of fungicide application technology: Relationship between coverage and disease severity and the physiological impact of fungicides on grainfill

Abstract

Fungicide use in corn has increased since the mid-2000s. Researchers and chemical companies have long stressed the importance of coverage when making a foliar fungicide application. There is very limited information, however, about how important coverage is for disease management and yield response to fungicides. Farmers need more information regarding which application technique, aerial or a traditional ground sprayer, provides the best fungicide coverage. The effect of fungicide application methods on coverage, disease management, and yield were tested during 2017 and 2018 in Iowa. Four on-farm trials were conducted in Ames and Nevada in 2017, and Ames and Kelley in 2018. Also, five small plot trials were established in Ames, Kanawha, and Sutherland in 2017, and Kanawha and Sutherland in 2018. Three application methods were compared: aerial, traditional ground application, and a newly available 360 Yield Undercover. The latter is a ground unit that has three sprayer nozzles, one spraying directly up, and the other two spraying to the sides in a fan pattern. A premix of pyraclostrobin + metconazole was applied at 730 mL/ha to the corn canopy at the silking stage for all application methods. Fungicide coverage was measured using water sensitive spray cards and the tracer dye pyrenetetrasulfonic acid (PTSA). Foliar diseases data were collected from R4 to R6 as percent leaf area covered by disease lesions on lower canopy, ear leaf, and upper canopy leaves. PTSA dye results showed similar coverage for traditional and undercover applications in both on-farm and small plots trials. Both ground-based methods had greater coverage compared to aerial applications in on-farm trials. There were few significant differences between ground-based application methods for small plot and on-farm trials in coverage throughout the canopy. Major foliar diseases during 2017 and 2018 were anthracnose leaf blight, common rust, southern rust, gray leaf spot, and northern corn leaf blight. Disease management for all application methods was similar, with all methods having significantly less disease than the control in most locations. Despite this reduction in disease severity by the fungicides, yield was only positively impacted at one site-year, across all on-farm and small plot trials. Kernels were collected multiple times during grain filling to determine if fungicide treatment impacted the rate or duration of dry matter accumulation and the moisture percentage at physiological maturity (PM). The fungicide application did influence the effective fill period and moisture at physiological maturity at the Nevada 2017 location. Fungicide-treated plants had