Fungicide resistance in Sclerotinia sclerotiorum

Resistance to benzimidazole fungicides (e.g. carbendazim, thiophanate methyl) is now common in north-east and central France. The development of resistance occurred rapidly and was associated with short rotations of oilseed rape (every 2 or 3 years) and at least 5 sprays of benzimidazole fungicide during the last 10 years.

In England, previous monitoring of sclerotinia from oilseed rape during 1993-1998 did not find any resistance to benzimidazoles. Continued vigilance is required as resistance to benzimidazoles and other fungicides could appear. Unexplained cases of poor sclerotinia control should be investigated to see if they are due to fungicide resistance.

Strategies to reduce the risk of fungicide resistance

• Only use fungicides for sclerotinia control where it is essential
  
• Extend the rotation of oilseed rape cropping if sclerotinia is causing significant loss of yield
  
• Use fungicide mixtures
  
• Avoid repeated use of the same active ingredient in the same field
  
• Monitor disease control and have sclerotinia tested for fungicide resistance if unsatisfactory control is not explained by poor spray timing