Wet weather raises osr disease risk

Recent unsettled, humid weather could increase the risk of wet weather diseases such as Botrytis and Alternaria in oilseed rape crops, BASF has warned growers.

Botrytis is already spreading, particularly on leaves that have been damaged by machines or fertiliser scorch, said the firm’s oilseed rape product manager, Diane Heath.

“It can be seen as a grey superficial fungal mould on any part of the plant that is damaged. Alternaria is seen as small brown or black spots on leaves and pods, about 1 to 3 mm in size.

“Larger spots have distinctive concentric rings. It is spread by rain-splash in warm, wet weather.”

The problem could be increased in thick crops, some of which have started to lodge due to heavy rain, she said.

She suggests using Compass (iprodione + thiophanate-methyl) at dose rates between 1.5 litres/ha as a top up spray where a late stem extension fungicide has already been used-and 2.0 litres/ha where Alternaria is the key target.

Treatments should be targeted from 20% pod set onwards, she noted.

For weekly reports direct from a team of agronomists around the country, see FWi’s Crop Watch, updated every Tuesday.