Scotland set for plague of leatherjackets

UK - April 24, 2006

Winter cereals and spring crops in Scotland are at risk of damage from the highest levels of leatherjackets seen in over 30 years of monitoring.  

Dow AgroSciences’ PestWatch Service is advising careful monitoring for leatherjackets, the larvae of crane flies or daddy-long-legs, in late-planted winter cereals and all spring planted crops.  

Risk of damage is extremely high in most areas, especially in the West of Scotland – particularly Ayrshire, Bute, Dumfries and Kirkcudbright, Lanarkshire, Renfrew and Wigtownshire.  

“Our sampling has shown leatherjacket larval populations in Scotland are at the highest recorded levels in 30 years, with an average population is 250 grubs/m²,” says Dow’s technical services specialist Jim Butchart. 

“We sampled 165 fields in west and central Scotland over the winter.  Over 80% of fields were infested with more than 0.6 million leatherjackets/ha, and 75% contained populations above 1.0 million/ha.  Nearly 40% contained population densities higher than 2.0 million/ha.”  

Treatment thresholds are only 50 leatherjackets/m², equivalent to 500,000/ha for spring cereals; 100/m² for established grassland; and 25/m² for high value vegetable crops.  

Leatherjackets that hatched last autumn have grazed through the winter, increasing in size.  Crows and rooks feeding is a common sign of infested fields.  However, growers who wait to find visible crop symptoms may be too late for effective treatment.  In affected areas, digging just below the surface will readily reveal active larvae.  

“As a general rule of thumb if you can find 15 or more leatherjackets per 30 cm of row in a spring cereal or a ley reseed, control is most likely to be necessary.  The most effective product for leatherjacket control is Dursban WG (chlorpyrifos).  All applications should be at 1 kg/ha in 200-1,000 l/ha of water,” says Mr Butchart.