Efficacy and Economics of Integrating In-Field and Harvesting Strategies to Manage Fusarium Head Blight of Wheat

Salgado, J. D., Madden, L. V., and Paul, P. A. 2014. Efficacy and economics of integrating in-field and harvesting strategies to manage Fusarium head blight of wheat. Plant Dis. 98:1407-1421. Fusarium head blight (FHB), a fungal disease of wheat caused by Fusarium graminearum, and its associated toxins, particularly deoxynivalenol (DON), are best managed by integrating multiple strategies. Experiments were established in 2011 and 2013 to evaluate the effects of integrating cultivar resistance, fungicide application, and grain harvesting strategy on FHB index (IND; field severity), DON, grain yield (YLD), and grain test weight (TW; weight per unit volume). Plots of two moderately resistant and two susceptible cultivars were either treated with 19% tebuconazole + 19% prothioconazole or left untreated, and then inoculated with F. graminearum. IND was rated as the mean percentage of diseased spikelets per spike. Separate subsets of the plots of each cultivar–treatment combination were harvested with one of two combine harvester configuration: C1 (the default, set at a fan speed of 1,375 rpm and a shutter opening of 70 mm) and C4 (modified, with the same fan speeds but a wider shutter opening of 90 mm). YLD and TW data were collected, and grain samples were rated for percent Fusarium-damaged kernels (FDK) and tested for DON. Results from linear mixed-model analyses showed that the cultivar– treatment interaction was significant for all FHB-related responses, with the magnitude of the difference in mean arcsine-square-root-transformed IND and FDK (arcIND and arcFDK) and log-transformed DON (logDON) between treated and untreated being higher for susceptible than moderately resistant cultivars. Plots harvested with the C4 combine configuration had significantly higher mean TW than those harvested with C1. Treated plots had significantly higher YLD and TW than untreated plots, regardless of cultivar and configuration. Relative to the reference management program (untreated, susceptible cultivar, harvested with C1), the greatest percent reduction in FDK and DON and increase in YLD was observed for programs that included moderate resistance and fungicide treatment. The greatest percent increase in TW relative to the reference was observed when C4 adjusted combine setting was integrated with resistance and fungicide. Overall, the most effective management programs all included fungicide treatment, two included moderate resistance, and two included C4 combine setting. Relative to the reference management program, these programs resulted in 30 to 51% reduction in total estimated price discount, $127 to 312 ha–1 increase in gross cash income, and economic benefit of $31 to 272 ha–1, depending on the level of FHB IND (5 to 15%), grain price ($118 to 276 metric ton–1), and fungicide application cost ($40 to 96 ha–1). The integration of host resistance, chemical control, crop rotation, and other cultural practices is the most effective approach for managing Fusarium head blight (FHB), a disease of small grain crops caused by Fusarium graminearum Schwabe, and its associated toxins, particularly deoxynivalenol (DON) (6,7,12,22,23, 47,50). This is largely because no individual approach provides adequate FHB and DON reduction under highly favorable weather conditions (wet and humid weather before and during anthesis and early grain fill). For instance, whereas resistance may be the most economical, practical, and environmentally friendly approach for managing FHB, no soft red winter cultivar is immune to FHB and DON and, as such, even the most resistant cultivars may become infected (26,45) and accumulate DON above critical levels. Similarly, because fungicides are less than 100% effective against this disease, treated fields may still become infected and contaminated with DON (8,9,13,15,32,33). A quantitative synthesis of data from more than 100 uniform fungicide trials showed that, when applied at anthesis, the demethylation inhibitor fungicides 8.6% metconazole (Caramba 90 SL; BASF Corporation Agricultural Products), 41% prothioconazole (Proline 480 SC; Bayer CropScience), and 19% tebuconazole + 19% prothioconazole (Prosaro 421 SC; Bayer CropScience) were the most effective products against FHB and DON, providing 50, 48, and 52% control of FHB index (IND) and 45, 43, and 42% control of DON, respectively (33). These fungicides were also most effective at increasing grain yield (YLD) and test weight (TW) relative to untreated controls (35). Willyerd et al. (51) subsequently reported that, when Prosaro was combined with a moderately resistant (MR) cultivar, percent reduction of both FHB IND and DON, relative to the untreated, susceptible (S) check, exceeded 70%. The combination of fungicide and resistance had an additive effect in terms of percent control for both responses. Analyses based on a nonparametric rank-based variance homogeneity test (17,21,36) showed that there was a significant interaction between management combination and environment for IND, indicating that the rank order of fungicide–resistance combinations in terms of the level of FHB control depended on the environment (51). In some years, particularly when conditions are wet and humid during anthesis and early grain-fill, even when the best preharvest integrated management practices are implemented, Fusariumdamaged kernels (FDK) and DON contamination of grain cannot be avoided and grain YLD and quality losses may still occur (3,26,53). For instance, if the baseline level of DON is 8 ppm (in a nontreated, S cultivar), a 70% control with fungicide + resistance will reduce the toxin level to 2.4 ppm. This may still lead to price discounts and economic losses, because grain with DON in excess of 2 ppm and FDK greater than 1% may be priced down at grain elevators. In addition, FHB also has a negative effect on TW (weight per unit grain volume), a quality trait used by grain buyers to grade and price wheat. Grain with Corresponding author: P. A. Paul, E-mail: [email protected] This investigation is based upon work supported by the United States Department of Agriculture (USDA) through the U.S. Wheat & Barley Scab Initiative (agreement number 59-0206-9-071). Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the USDA. Accepted for publication 14 April 2014. http://dx.doi.org/10.1094/PDIS-01-14-0093-RE © 2014 The American Phytopathological Society