Scottish growers are being urged to make sure that they spray responsibly against leatherjackets in grass and cereals, especially if pest populations are higher than usual.
“In the autumn last year SRUC reported leatherjackets at the highest level for many years and now, in their latest newsletter, they are warning that grass sown after grass will be at high risk as the size of grubs is larger than usual at this time of year. Initial results from the SRUC survey, which is currently on-going, are indicating very high populations in grass. Certainly that is my experience in Ayrshire and the south west of Scotland,” says Iain Sampson of Dow AgroSciences.
“Growers should do a risk assessment of their cereals and grass. Crops most at risk are cereals going out of established grass, permanent grassland, newly sown leys and crops which have had a history of leatherjackets. Last year was an unusual one with leatherjackets being found throughout the autumn and winter into the New year. The mild winter will have encouraged leatherjackets.”
Derek Robertson of Agrovista agrees, adding that if growers were worried about leatherjackets, they should monitor their crops and call in a BASIS registered agronomist to walk their fields properly. “The advisor can then decide on whether treatment is required on a field by field and farm by farm basis. Although the mild autumn and winter has encouraged leatherjackets, the saturated soils in some parts of Scotland have meant that the larvae have been forced to move down into the soil. The wet conditions are currently not conducive to travelling,” he says.
Derek reports that insecticide treatment started very early last autumn in September, the earliest for 38 years, and some reseeds and winter cereals were lost. “Dursban WG is an effective soil insecticide. It can save the crop from months of feeding damage from leatherjackets and hence protect yield.”
With the first foliar insecticide sprays of the year imminent, growers may need reminding of the need to abide by Stewardship measures for chlorpyrifos applications. When applying Dursban WG 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. Just recently the UK CRD has recognized low drift nozzles as risk mitigation for applications of plant protection products on arable and grassland crops. Growers, advisors and contractors 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 from October onwards. Leatherjackets cause damage by feeding on seedlings below and above ground. The larvae reach maturity during late May to June, when they pupate. In cereals the threshold for spraying 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 applied in 200 to 1000 litres of water. Dursban is the standard treatment for leatherjackets.
Dursban WG (75% w/w chlorpyrifos formulated as a Water Dispersible Granule) is recommended for the control of Leatherjackets as well as Wheat Bulb fly, Frit fly and Wheat Blossom Midge. For Leatherjackets in cereals and grassland, the application rate is 1 kg/ha. It is packed in a 1 kg pack.