INCREASED LEVELS of phoma leaf spot in oilseed rape this season mean accurate timing of fungicide applications is essential, growers have been told.
Moist conditions in August and September have allowed oilseed rape crops to develop rapidly, increasing the risk of phoma leaf spot this autumn and stem cankers next spring, according to experts.
“Applications need to be made within a short time frame subsequent to Ascospores being released from the stubbles,” advised NIAB‘s Dr David Kenyon.
“These spores landing on leaves give rise to the initial Phoma Leaf Spot infection within 7 – 14 days.”
He warned growers to maintain flexibility, as spores can be released throughout the autumn and winter, therefore a split application may be required.
This was reinforced by Masstock‘s Clare Bend, who suggested growers should monitor crops a month after spraying to check for reinfection.
“A 0.2t/ha yield response from an additional application has proved cost effective in our experience,” she noted.
Growers should also consider the use of adjuvants to improve plant uptake of fungicides, she said.
She urged growers to be sure it is phoma they are dealing with before treatment, as the disease can be very similar in appearance to downy mildew.