Daddy-long-legs larval poulations are at the highest level for several years, Dow AgroScience’s PestWatch service is warning.
Sampling in the Midlands and the north of England shows the highest level of leatherjackets for 15 years, Dow’s Jim Butchart says.
“Of the 47 sites sampled in England, 83% contained leatherjacket populations above the advisory threshold, compared to only 34% last year.”
In Scotland populations top the scale with grubs per square metre on average the highest for 30 years. The treatment threshold for an economic response is just 50 leatherjackets per square metre equivalent to 500,000/ha for spring cereals. For sugar beet and high-value vegetable crops the threshold is just 25 per square metre, Mr Butchart warns.
“Crops at highest risk are those planted after grassland, or following grassy unsprayed autumn stubbles. By far the most effective product for control is Dursban WG. For best results applications should be at 1kg/ha in 200-1000 litres of water per hectare.”
Extra cultivations pre-drilling and rolling a crop can help reduce damage, he notes. And early nitrogen can help crops recover through increased tillering.
Leatherjackets feed at night on the soil surface causing shredding and holes in leaves. The damage is easy to confuse with slug grazing, Mr Butchart points out.
Other symptoms include bare patches with discoloured leaves, and seedlings or tillers that can be easily pulled from the ground having been severed below the surface.