Leatherjackets nearly write-off sugar beet crop

UK - May 31, 2006

Sugar beet growers should continue checking for leatherjackets even if there is no grass in the rotation. 

Leatherjackets were so numerous on one Shropshire sugar beet field that without a timely application of Dursban WG the crop would have been a total write-off.   With a rotation of sugar beet, winter wheat, winter rape, winter wheat the field had not been grass for 20 years.    

Sugar beet grower Charles Dakin of Shifnal, Shropshire noticed some leatherjacket activity when drilling on 6th April.  Wrekin Farmers agronomist Kate Cooke checked the crop a week later and measured up to 40 larvae/m² or 400,000/ha.  The treatment threshold is 250,000/ha. 

“The whole field was infected with the highest leatherjacket population I have ever seen.  An earlier application of methiocarb slug pellets had had no effect on the leatherjackets, so I recommended an immediate application of Dursban WG (chlorpyrifos) in 200 l/ha of water,” said Ms Cooke. 

There was 100% kill within 24 hours, helped along by rainfall shortly after application.  Mr Dakin was fortunate to only lose 5% of his crop.  

Despite the lack of a previous grass crop Mrs Cooke believes the problem arose due to the high numbers of adult cranes flies seen in the autumn, mainly coming from surrounding grass fields. The stubble was sprayed with glyphosate in mid September for control of grassweeds, and ploughed in January.   

“The leatherjackets problem is particularly bad on grassland this season, with even permanent pasture being redrilled.  Many short-term leys planted last autumn have been successfully treated for leatherjackets with Dursban WG.  Be aware of this serious problem and be quick to treat any crop showing damage. Don’t let your guard down,” says Kate Cooke.