The Value of Early Fungicide Applications in Wheat

  • Author / Creator
    Asif, Mahnoor
  • Leaf spot diseases and, to a lesser extent, fusarium head blight (FHB), are a serious threat to wheat production in Alberta. To manage leaf spots, some growers apply fungicides tank-mixed with herbicides or plant growth regulators (PGR) at early growth stages. These practices, however, conflict with previous research suggesting later fungicide applications to be more effective. In fact, over time these practices may increase the risk of fungicide resistance, making current fungicide tools ineffective. Twelve fungicide treatments were tested in 2018 and 2019 across eight site-years in Alberta, to determine the yield and quality benefits of fungicide rates, multiple fungicide applications (single, dual and triple), and the performance of single and multiple fungicide modes of action (MOA) at four different growth stages: BBCH 22-23 (herbicide timing), BBCH 30-32 (PGR timing), BBCH 39-45 (flag leaf), BBCH 61-63 (head timing). Treatments were applied to two Canadian Western Red Spring cultivars, AAC Brandon and AAC Viewfield, and compared with a non-treated control. Both cultivars have ‘intermediate’ resistance to leaf spots and different genetic resistance to FHB according to the Alberta seed guide 2020. These commonly grown cultivars are recently registered and have improved genetic disease resistance. Four of eight site-years showed significant yield responses to fungicide treatments. Overall, earlier fungicide applications (BBCH 22-23 and BBCH 30-32) had lower yield and quality versus the later fungicide applications (BBCH 39-45 and BBCH 6163). Foliar and flag leaf disease levels, at the end of the growing season, were also higher when fungicides were applied at early growth stages versus when fungicide treatments were applied at later growth stages. This is due to the fungicide applications at later growth stages (BBCH 39-45 and BBCH 61-63) protecting the top yielding leaves in the upper canopy. Generally, single fungicide applications had 3% (0.2 t ha-1) lower yields and 45% higher foliar disease compared with dual or triple fungicide applications. At most sites, there were no significant differences between AAC Viewfield and AAC Brandon with respect to leaf spot severity, fusarium damaged kernels, or mycotoxin levels. There was no difference among fungicides rates (recommended versus 1.5x label rate) and single versus multiple fungicide MOA, likely due to the limited disease pressure observed at earlier growth stages. Based on this study, single fungicide applications at BBCH 39-45 (flag leaf) and BBCH 61-63 (head timing), or dual fungicide applications at these same growth stages, are recommended to maintain productivity and profitability. However, results were highly dependent on whether or not the environmental conditions were conducive for disease development. Four site years in this study had conducive conditions for disease development and fungicide applications were economically justified. In contrast, at the other four sites, conditions were not favorable and fungicide applications were unnecessary.

  • Subjects / Keywords
  • Graduation date
    Fall 2020
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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