Profitability of integrated management of fusarium head blight in North Carolina winter wheat

Authors: Cowger, Christina; WEISZ, RANDY - North Carolina State University; ARELLANO, CONSUELO - North Carolina State University; MURPHY, J - North Carolina State University

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2016
Publication Date: 6/20/2016
Citation: Cowger, C., Weisz, R., Arellano, C., Murphy, J.P. 2016. Profitability of integrated management of fusarium head blight in North Carolina winter wheat. Phytopathology. 106:814-823.

Interpretive Summary: Fusarium head blight (scab) is one of the most difficult small-grain diseases to manage, due to the partial effectiveness of management techniques and the narrow window of time within which to apply fungicides profitably. The most effective management approach is to integrate variety resistance with scab-specific fungicide applications. Yet when forecasted risk is intermediate, it is often unclear whether such an application will be profitable. We conducted a two-year field experiment to investigate the profitability of scab management under varying conditions. We planted high-yielding soft red winter wheat varieties: four were moderately resistant (MR) and three were susceptible (S) to scab. Some plots were sprayed at flowering with Prosaro or Caramba, while others were left untreated. The experiment was planted in seven North Carolina environments; three were irrigated to promote scab development and four were not irrigated. We measured yield, test weight, disease incidence, disease severity, vomitoxin (DON), Fusarium-damaged kernels, and percent infected kernels. Partial profits were compared by categorizing environments as low-, medium- or high-DON, and also by categorizing varieties in particular locations as “do spray” or “don’t spray” based on the forecasted scab risk. After surveying DON and test weight dockage among 21 North Carolina wheat purchasers, we also estimated profitability separately for the feed-wheat, flexible (feed or flour), and the flour markets. We found that MR varieties were always at least as profitable as S varieties. Fungicides were profitable in the feed-grain and flexible markets when DON was high; with MR varieties in the flexible or flour markets when DON was intermediate; and on S varieties aimed at the flexible market.

Technical Abstract: Fusarium head blight (FHB) is one of the most difficult small-grain diseases to manage, due to the partial effectiveness of management techniques and the narrow window of time within which to apply fungicides profitably. The most effective management approach is to integrate cultivar resistance with scab-specific fungicide applications, yet when forecasted risk is intermediate, it is often unclear whether such an application will be profitable. To model the profitability of scab management under varying conditions, we conducted a two-year split-plot field experiment having as main plots high-yielding soft red winter wheat cultivars, four moderately resistant (MR) and three susceptible (S) to scab . Sub-plots were sprayed at flowering with Prosaro or Caramba, or left untreated. The experiment was planted in seven North Carolina environments; three were irrigated to promote FHB development and four were not irrigated. Response variables were yield, test weight, disease incidence, disease severity, deoxynivalenol (DON), Fusarium-damaged kernels, and percent infected kernels. Partial profits were compared in two ways: first, across low-, medium- or high-DON environments; and second, across location-by-cultivar combinations divided by risk forecast into “do spray” and “don’t spray” categories. After surveying DON and test weight dockage among 21 North Carolina wheat purchasers, three typical market scenarios were used for modeling profitability: feed-wheat, flexible (feed or flour), and the flour market. A major finding was that the MR cultivars were always at least as profitable as S cultivars, regardless of analysis type, epidemic severity, or market. Fungicides were profitable in the feed-grain and flexible markets when DON was high; with MR cultivars in the flexible or flour markets when DON was intermediate; and on S cultivars aimed at the flexible market. The flour market was only profitable when scab was present if DON levels were intermediate and cultivar resistance was combined with a fungicide. Overall, the results indicated that: cultivar resistance to FHB was important for profitability; an FHB-targeted fungicide expanded market options when risk was moderate or high; and the efficacy of fungicide decision-making was reduced by factors that limit the accuracy of risk forecasts.