Evaluation of Early Season Foliar Fungicide Applications to Support Non-Fungicidal ‘Plant Health’ Benefits

The recent labeling of a new fungicide and rumors of non-fungicidal ‘plant health’ benefits achieved through early-season foliar applications of certain fungicides have led to inquiries concerning the practice. The objective of this research was to determine the impact of an early-season fungicide application on early-season growth or end-of-season lint yields, turnout, and/or fiber quality when disease symptoms are not present. During the 2014-2016 growing seasons, a total of ten trials were established in Alexandria, LA; Starkville, MS; Fort Cobb, OK; Jackson, TN; and Snook, TX. Fungicide treatments included an untreated control, a foliar application of 0.11 kg ai ha-1 zoxystrobin, and a foliar application of 0.07 kg ai ha-1 fluxapyroxad + 0.15 kg ai ha-1 pyraclostrobin. All treatments targeted the two through four true leaf growth stage. A significant interaction between fungicide treatment and site-year was observed from node counts collected at 14 and 28 DAA. Site-year analysis indicated a significant reduction in node counts observed with the azoxystrobin treatment in one site-year in the 14 DAA data and one site-year in the 28 DAA data. Fungicide treatment did not impact plant height or vigor ratings collected at 14 or 28 DAA, chlorophyll meter readings, lint yield, turnout, or fiber quality parameters in any site-year. Failure of fungicide treatments to positively impact in-season growth measurements, yield, and yield parameters suggests the evaluated fungicides should not be applied early-season for the purpose of improving ‘plant health’ and should instead be reserved to target above-threshold levels of disease incidence/severity.