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ViewAttendees 5

TECHNICAL SESSION: Chemical Control

The evolving landscape of fungicide insensitivity: lessons from cucurbit powdery mildew

Monday, August 4, 2025
3:15 PM - 3:30 PM HST
Location: Room 313 A
Abstract Text: Fungicide selection pressure has historically driven shifts in pathogen sensitivity, reducing the long-term efficacy of single-site fungicides. Cucurbit powdery mildew (CPM), caused by Podosphaera xanthii, is highly responsive to fungicide-driven shifts in sensitivity due to the short asexual lifecycle and prolific conidia production, which increase the likelihood of resistant isolates persisting under selection pressure. As a result, CPM serves as a useful system for monitoring fungicide sensitivity trends and evaluating the impact of management strategies within cucurbit production. This study evaluated CPM fungicide sensitivity through laboratory bioassays and a field trial to inform management strategies in Florida. In the lab assay, isolates were collected throughout Florida and screened against penthiopyrad (FRAC 7), azoxystrobin (FRAC 11), and metrafenone (FRAC 50), revealing emerging penthiopyrad insensitivity and confirming widespread azoxystrobin insensitivity. The ongoing field trial assesses fungicides from FRAC groups 3, 7, 9, 12, 13, 50, and U6, applied in rotation with chlorothalonil (FRAC M5) to evaluate practical management strategies. These findings underscore the importance of ongoing monitoring of P. xanthii populations for shifts in fungicide sensitivity. As chemical control remains central to CPM management in conventional farming, integrating lab and field sensitivity assessments is crucial for providing growers with the necessary information to make cost-effective, efficacious management decisions that enhance fungicide longevity.