Phoma leaf spotting has made an earlier than usual appearance in early-sown oilseed rape crops in eastern counties, according to ADAS.
The disease has been found on volunteers and crops with 3-6 leaves and its early appearance is thought to be a consequence of the wet August, which allowed air-borne phoma spores to mature on stubbles.
Growers are being advised to monitor plants closely for signs of spotting, particularly those close to stubble residues. Further rain this week could lead to new symptoms in emerged crops within the next 7-10 days.
ADAS advice to growers:
• Monitor crops at least weekly from emergence
• Bury stem residues by ploughing or cultivation ASAP
• Fungicide treatment recommended when 10-20% plants have phoma spotting
• Some plant losses may occur if phoma develops on cotyledons
• Product choice will depend on need for plant growth regulatory activity
• Consider follow-up treatments when re-infection occurs (usually 3-4 weeks after application)
A regional forecast of the risk to winter oilseed rape crops from phoma canker can be found by clicking here.