Scotland’s spring cropping at risk from leatherjackets

UK - March 09, 2004

The risk from leatherjackets is low in England this spring, but Scotland could be facing an epidemic warns Dow AgroSciences.

Dow AgroSciences’ Pestwatch monitoring service, in conjunction with SAC Auchincruive, has flagged up very high levels of leatherjackets in grassland across west and central Scotland. David Roberts, Dow Agrosciences’ Technical Services Leader, advises farmers that there is a substantial risk of damage to spring cereals following grass and a real threat to grass yields in a high proportion of fields.

“More than 50% of the fields sampled in Scotland were infested with in excess of 0.6 million leatherjackets per hectare, and over one third contained population densities above the million per hectare threshold in permanent pasture,” says Mr Roberts. “This is a significant increase from the previous year when the average was only 0.39 million per hectare. We’re now looking at an average of 1.19 million.”

The population levels in Scotland are the second highest detected since 1990 and the highest since 1999.

Populations remain low in all regions of England, although Pestwatch monitoring, in conjunction with ADAS, detected fields in Cheshire, Staffordshire and North Yorkshire where the advisory threshold had been reached.

Spring cereals have a threshold of 0.5 million leatherjackets per hectare. Sugar beet and other row crops need treating at 0.25 million per hectare.

“Any easy check is to look for large numbers of rooks and crows feeding on the larvae in fields with a known history,” says Mr Roberts. “A risk assessment should always be conducted and a test for the presence of larvae can be done. If all indications are that the threshold has been reached spray Dursban* WG at 1.0 kg/ha in at least 200 litres of water.”

Farmers should be aware that control could be reduced if temperatures are below 5°C as the larvae will move deeper into the soil profile.