Location: Application Technology Research Unit
Title: Rainfastness of Prothioconazole+Tebuconazole for Fusarium head blight and Deoxynivalenol management in soft red winter wheat Authors
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 14, 2014
Publication Date: N/A
Interpretive Summary: In the US wheat production system, it is usually not economical to make multiple fungicide applications in order to control any possible secondary infections such as Fusarium graminearum. It is important for US growers to know whether a single anthesis application would be sufficient to control Fusarium graminearum. The retention of fungicide residue on or in wheat spikes after application has direct relevance for the control of secondary Fusarium graminearum infection, whether this is due to late infection of spikes on primary tillers or to infection of spikes on late-developing secondary tillers. A series of field and greenhouse experiments were set-up to evaluate the rainfastness of post-treatment residue levels to determine whether a single anthesis application would be sufficient to control late Fusarium graminearum infections. Three field experiments were conducted during 2012 and 2013 in Wooster, Ohio. Simulated rainfall of a fixed intensity and duration was applied to separate field plots at five different times after the fungicide treatment. A similar set of greenhouse experiments were conducted using six post-fungicide-application rainfall timing treatments. Spike samples were collected at 4-day intervals after fungicide application and assayed for fungicide residue. Test results showed that on average, fungicide residue levels decreased by 50% within 6-9 days (the half-life) after fungicide application, regardless of rainfall treatment. These findings demonstrated that grower applicatons of tebuconazole + prothioconazole (Prosaro 421 SC at 100 g of each a.i./ha) are fairly rainfast when applied with the surfactant InduceTM (0.125% v/v) with no substantial decrease in efficacy when a rainfall event occurs more than 15 minutes after fungicide application under dry and relatively uniform greenhouse conditions and 60 minutes under wetter and more variable field conditions. Following these guidelines, growers can produce higher yielding wheat with the expectation of less toxin in the grain over a wide range of post-application rainfall of similar duration evaluated in this study.
Technical Abstract: Fungicides are most warranted for control of Fusarium head blight (FHB), a disease of wheat caused by the fungal pathogen Fusarium graminearum, when wet, rainy conditions occurs during anthesis. However, it is unclear whether rainfall directly following application affects fungicide efficacy against FHB and its associated toxin, deoxynivalenol (DON). The objective of this study was to determine the rainfastness of the fungicide tebuconazole + prothioconazole and the residual life of tebuconazole when applied to wheat spikes at anthesis in combination with a non-ionic surfactant. Three field experiments were conducted during 2012 and 2013 in Wooster, Ohio. Simulated rainfall of a fixed intensity and duration was applied to separate plots at five different times after the fungicide treatment (0, 60, 105, 150, and 195 minutes). Spike samples were collected at 4-day intervals after fungicide application and assayed for tebuconazole residue. A similar set of greenhouse experiments were conducted using six post-fungicide-application rainfall timing treatments (0, 15, 30, 60, 120, and 180 minutes). All experiments were inoculated at anthesis with spores of Fusarium graminearum, and FHB index (IND) and DON were quantified. In four of the five experiments, all fungicide-treated experimental units had significantly lower mean IND and DON than the untreated check, regardless of rainfall treatment. Among rainfall treatments, experimental units that received the earliest rains after fungicide application tended to have the highest numerical mean IND and DON, but were generally not significantly different from experimental units that received later rain or fungicide without rain. In both years, fungicide residue on wheat spikes decreased rapidly with time after application, but the rate of reduction varied somewhat between years, with a half-life of 6-9 days. Rainfall treatment did not have a significant effect on the rate of residue reduction or the level of residue at a fixed sampling time after fungicide application. In this study, tebuconazole + prothioconazole mixed with a nonionic surfactant was fairly rainfast for a fixed set of rainfall characteristics, and tebuconazole residue did not persist very long after application on wheat spikes.