Leatherjackets set for bumper year

UK - April 24, 2006

Winter cereals and spring crops in North and West of England are at risk of damage from the highest levels of leatherjackets seen in over 15 years of monitoring.

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

"Our sampling has shown the potential for damage by leatherjacket larvae to crops in North and West of England is higher than any years ince 1991.  Crops at highest risk are those planted after grassland, or following grassy unsprayed winter stubbles." says Dow's technical services specialist Jim Butchart.

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.

"The average population in the North of England has more than tripled since last year at close to 200 leatherjackets/m², equivalent to 2 million grubs/ha.  95% of fields are showing populations greater that 50m², compared to only 40% of fields in 2004 falling within this catergory and only 5% in 2002."

“The average population in the Midlands and West England is 190 leatherjackets/m², equivalent to nearly 2 million grubs/ha.  With over 80% of fields showing populations greater than 50m/², compared to only 33% of fields in 2004 falling within this category and none in 2003, farmers need to be vigilant.” 

Mr Butchart highlights Herefordshire.  The county has the highest levels of leatherjackets in the region with field sampling registering over 800 grubs/m².

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 30cm 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.