The Dow AgroSciences Technical Hotline is being inundated with queries about leatherjackets. Many advisors are seeing very high levels of the adult crane flies in the field and are asking what this means to grass and cereal growers, reports Sarah Hurry of Dow AgroSciences.
“No specific assessment has been made recently, but there appear to be many more adult crane flies about than normal and even some reports of their larvae, leatherjackets, in crops already, reflecting high pest pressure. Earlier this year SURC reported leatherjackets at the highest level for many years and some spring crops in England were damaged,” says Sarah.
The key messages I would give to growers is, firstly, to do a risk assessment of your cereals and grass and secondly look for indicators of leatherjackets in these crop. Crops most at risk are cereals going out of established grass or a grassy stubble, permanent grassland, newly sown leys and crops which have had a history of leatherjackets. The indicators are large number of adult crane flies, which is just what we are seeing now, large numbers of rooks, crows and starlings feeding and bare patches appearing in the crop, says Sarah.
Sarah emphasizes that it is important to use thresholds for spraying.
“In cereals the threshold is 0.3 to 0.5 million leatherjackets per hectare which is 30-50 leatherjackets per metre squared. In pasture the threshold is higher at 100/m². If these thresholds are exceeded, then use Dursban WG at 1.0 kg/ha or Equity at 1.5 l/ha applied in 200 to 1000 litres of water. Dursban is the standard treatment for leatherjackets. Many cereals following grass are already at risk from frit fly and so these crops may be treated for both frit fly and leatherjackets at the same time.”
“Dursban is an effective soil insecticide. It can save the crop from months of feeding damage from leatherjackets and hence protect yield. Control will be reduced if temperatures are below 5oC as the larvae move deeper into the soil profile,” she continues.
When applying Dursban WG or Equity for leatherjackets, growers should use LERAP rated 3 star nozzles and adopt a 20 metre no-spray buffer zone near to watercourses or a 1 metre near to dry ditches. This advice is part of the Stewardship ‘Say NO to drift’ initiative which aims to support the future availability and use of insecticides containing chlorpyrifos. Growers and advisors can go to www.saynotodrift.co.uk/arable/ for further details.
Leatherjackets are the larvae of the crane fly. Adults lay up to 300 eggs between July and September on grassland or grassy stubbles. They hatch within 2 to 3 weeks and grow into grey legless headless larvae. Leatherjackets cause damage by feeding on seedlings below and above ground. The larvae reach maturity during late May to June, when they pupate.
