Efficacy of Fungicide Applications During and After Anthesis Against Fusarium Head Blight and Deoxynivalenol in Soft Red Winter Wheat

D’Angelo, D. L., Bradley, C. A., Ames, K. A., Willyerd, K. T., Madden, L. V., and Paul, P. A. 2014. Efficacy of fungicide applications during and after anthesis against Fusarium head blight and deoxynivalenol in soft red winter wheat. Plant Dis. 98:1387-1397. Seven field experiments were conducted in Ohio and Illinois between 2011 and 2013 to evaluate postanthesis applications of prothioconazole + tebuconazole and metconazole for Fusarium head blight and deoxynivalenol (DON) control in soft red winter wheat. Treatments consisted of an untreated check and fungicide applications made at early anthesis (A), 2 (A+2), 4 (A+4), 5 (A+5), or 6 (A+6) days after anthesis. Six of the seven experiments were augmented with artificial Fusarium graminearum inoculum, and the other was naturally infected. FHB index (IND), Fusarium damaged kernels (FDK), and DON concentration of grain were quantified. All application timings led to significantly lower mean arcsine-square-root-transformed IND and FDK (arcIND and arcFDK) and log-transformed (logDON) than in the untreated check; however, arcIND, arcFDK, and logDON for the postanthesis applications were generally not significantly different from those for the anthesis applications. Relative to the check, A+2 resulted in the highest percent control for both IND and DON, 69 and 54%, respectively, followed by A+4 (62 and 52%), A+6 (62 and 48%), and A (56 and 50%). A+2 and A+6 significantly reduced IND by 30 and 14%, respectively, relative to the anthesis application. Postanthesis applications did not, however, reduce DON relative to the anthesis application. These results suggest that applications made up to 6 days following anthesis may be just as effective as, and sometimes more effective than, anthesis applications at reducing FHB and DON. Fusarium head blight (FHB), commonly known as scab, is a fungal disease caused by Fusarium graminearum and other related species (26) that affect small grain crops such as wheat, barley, and rye in many regions around the world. FHB causes significant losses in grain yield and quality due to floret sterility, production of small, shriveled light-weight kernels, and contamination of grain with mycotoxins, especially deoxynivalenol (DON). FHB development is often positively correlated with DON contamination (31). Cultivation of FHB-affected seeds may lead to poor stand establishment as a result of reduced seed vigor and germination, and seedling blight (15). In addition, FHB is a concern for the milling and baking industries as it affects the quality of the flour produced from infected grain (11). It may also have negative effects on animal health, especially nonruminant animals, if mycotoxin-contaminated grain is consumed (12). Efforts to manage FHB and DON are most effective when cultural practices such as rotation with nonhost crops and tillage are employed along with genetic resistance and a well-timed fungicide application (37,39). Lori et al. (22) suggested that although cultural practices alone may be effective at reducing in-field inoculum and FHB severity, under favorable weather conditions, an integrated management approach that includes an accurate prediction model and timely use of a fungicide is necessary to effectively manage FHB. The use of such a model is now an integral part of FHB management programs in the United States, providing estimates of disease risk in 30 states to help guide fungicide application (9,33). Usually only a single anthesis application is justified, as the cost of additional treatments is rarely offset by increased yield in U.S. wheat production systems (24). Results from multiple years of FHB management experiments showed that, depending on the level of disease and susceptibility of the cultivar being treated, a welltimed application of prothioconazole (Proline 480 SC; Bayer CropScience, Research Triangle Park, NC), tebuconazole + prothioconazole (Prosaro 421 SC; Bayer CropScience), or metconazole (Caramba 90 SL; BASF Corporation Agricultural Products, Research Triangle Park, NC) provided between 40 and 70% reduction of FHB and DON (29,30,39). High relative humidity, rainfall, and surface wetness during anthesis and early grain fill, the period of greatest host susceptibility to infection, are environmental risk factors for FHB development and DON contamination. These are the conditions required for spore production (13), dissemination (27,35), and infection of the wheat spike (2). Consequently, fungicide application for FHB management is especially emphasized when anthesis coincides with wet weather (3,17). However, under wet field conditions, when fungicides are most warranted, current recommendations may be difficult to implement due to physical limitations of spraying a fungicide in the rain and driving equipment through wet fields. These limitations have led to questions being asked about the benefit of preand postanthesis fungicide application for FHB and DON management. Edwards and Godley (14) evaluated the effects of preanthesis application of prothioconazole (Proline 480 SC; Bayer CropScience) on FHB and DON in winter wheat in the United Kingdom, and reported that applications made at Zadoks GS31 (Feekes GS 6, stem elongation), GS39 (Feekes GS 9, full flag leaf emergence), and GS65 (Feekes GS 10.5.2, midanthesis) reduced FHB incidence and DON by 50, 58, and 83%, and 27, 49, and 57%, respectively, relative to the untreated check. Applications made at all three growth stages provided 97% control of FHB incidence and 83% control DON. Based on results from a similar study conducted in Canada in which tebuconazole (Folicur 3.6 F; Bayer CropScience) was applied to hard red spring wheat at GS39 and GS60 (Feekes 10.5.1, early anthesis), Wiersma and Motteberg (38) also reported that, across several cultivars, the best application timing for FHB control (as well as foliar diseases) was at early anthesis, but concluded that FHB levels were too low to adequately Corresponding author: P. A. Paul, E-mail: [email protected] Accepted for publication 16 April 2014. http://dx.doi.org/10.1094 / PDIS-01-14-0091-RE © 2014 The American Phytopathological Society