Performance Story: Revisiting the Value of Early Fungicide Applications in Wheat
Protection from fungal plant pathogens is key for optimizing the yield and quality of wheat. However, current grower practices and historical research do not always align with respect to optimum fungicide timing to maximize disease control, yield, quality and profitability of Canadian Western Red Spring (CWRS) wheat.
Six fungicide treatments were evaluated at eight site-years across Alberta in 2018 and 2019 to determine the optimum time for a single fungicide application. The treatments included early fungicide applications at BBCH 22-23 (herbicide timing), early to mid-season application at BBCH 30-32 [plant growth regulator (PGR) timing], ‘traditional’ timing at BBCH 39-45 (flag leaf), head timing at BBCH 61-63 (fusarium head blight timing) and were compared with a non- treated control. Experiments were conducted with the CWRS wheat cultivars ‘AAC Brandon’ and ‘AAC Viewfield’, which were registered recently and have intermediate resistance to leaf spot diseases. Yield responses to fungicide treatments occurred at 50% of the site-years when disease pressure was 32% higher than in non-responsive site-years. Responsive site-years were characterized by higher relative humidity (65.4-74.0%) and an average 273 mm of precipitation. At responsive site-years, McFadden leaf spot disease severity ratings were 50% greater in early August when fungicides were applied at BBCH 22-23 and 30-32 versus at BBCH 39-45. At responsive sites, yield was 9.3% higher for fungicide applications at BBCH 39-45 and BBCH 61- 63 compared with fungicide applications at BBCH 22-23 and BBCH 30-32. The most economically beneficial practices were fungicide applications at BBCH 39-45 or BBCH 61-63 when environmental conditions were conducive for disease development.
The responsible application of fungicides was determined by testing, 12 fungicide treatments across eight site-years in Alberta, to determine the yield, quality and economic benefits associated with: multiple fungicide modes of action (MOA), higher (above product label) application rates, and multiple applications per season. No differences were observed between one and three MOA fungicide applications at BBCH 22-23. In cases where fungicide insensitivity is developing in a field, multiple MOA treatments may show increased efficacy since they would dilute the risk of fungicide insensitivity and delay fungicide resistance. There was no difference between label-recommended rates (30 gai ha-1) and high rates (75 gai ha-1) of fungicide applied at BBCH 30-32. Given the lack of agronomic and economic response associated with higher fungicide rates, it would be best to maintain label rates of fungicide. In comparing the benefits of single, dual and triple fungicide applications, at one of eight site- years, dual fungicide had an additional 0.28 t ha-1 yield and 15% less leaf spot disease while triple fungicide had an additional 0.52 t ha-1 yield and 20% less leaf spot disease compared with a single BBCH 39-45 fungicide application. Fungicide applications were unnecessary 63% of the time. However, dual and triple fungicide applications were not economically beneficial under the conditions of our study.