Quinoxyfen--resistance management and sensitivity monitoring in wheat: 1995-2000

Wheat powdery mildew, Blumeria (= Erysiphe) graminis DC f sp tritici Marschal is one of the most important foliar diseases of cereals in Europe, and has shown a high potential for adaptability in sensitivity towards modern fungicides during the last 20 years. Quinoxyfen is a surface-mobile fungicide from a new chemical class that has been commercially used for the control of B graminis in Europe since 1997. When the compound was launched, a Resistance Management Strategy was implemented which included: no seed treatments, no autumn use, a specified window of application and recommendations for appropriate tank-mixing. To assess the success of this Management Strategy, a European-wide resistance monitoring programme was carried out between 1995 and 2000 using spore trap sampling, and a whole plant assay. The mean EC50 values found by year were 0.060 mg litre-1 in 1995, 0.052 mg litre-1 in 1996, 0.071 ml litre-1 in 1997, 0.039 mg litre-1 in 1998, 0.039 mg litre-1 in 1999 and 0.063 mg litre-1 in 2000. No new sensitivity classes were found. The slight shift to lower sensitivity in 1998 and 1999 was correlated with similar shifts in three wildtype isolates, and was ascribed to experimental variation. The monitoring programme will continue to assess the long-term impact of the management recommendations on the resistance status of quinoxyfen.