Pressure from phoma disease infection in oilseed rape remains high, and some fields will need a second fungicide treatment this season, warned ADAS disease control expert Peter Gladders.

Inspect crops treated 4-6 weeks ago for new infections, he advised.

“They will be increasingly susceptible to a second wave of phoma attack.”

High numbers of spores continue to be caught on most ADAS monitoring sites, and the Syngenta Phoma Advance Warning System (SPAWS) issued a high risk warning for all growers this week (w/c Nov 22).

“In many crops phoma is still incubating within the leaves and new spots will occur over the next few weeks. Crops with 10-20% plants infected urgently require a fungicide treatment.”

Thresholds for small or backward crops, or those with a canker resistance of 6 or less, should be reduced to 10% plants infected, or even 5% if rain is likely to prevent spraying, added Syngenta‘s technical manager Iain Hamilton.