The leatherjacket larvae feed on the roots. They are the larvae of crane fly (Tipula spp.). Attacks are more likely to occur after a grass rotation and if there are damp conditions in late summer and early autumn. Dry weather reduces the pest risk because eggs and young leatherjackets are vulnerable to dessication. The pest can interfere with crop establishment and reduce yield by up to 80% in places. Cereal crops are susceptible to damage as seedlings but can withstand attack better once they have tillered.
Ploughing in July and early August (before the main pest egg laying period) can help to control it.
Large numbers of adult crane flies in July and August and rooks, crows and starlings feeding on grubs indicate possible leatherjacket problems. Monitoring can be done by driving plastic pipes into the ground and filling them to near the brim with brine so that leatherjackets float to the surface. Thresholds for econmomic damage are 50 per m2, or 5 in 12 pipes or 5 per m of row.
Dursban WG (chlorpyrifos) insecticide gives reliable, consistently high levels of control of leatherjackets. Temperatures above 5°C give best results as that is when leatherjackets are near the soil surface. 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. Update, 12 Feb 2016: chlorpyrifos withdrawal - growers cannot spray Dursban or Equity after the 31st March 2016 - read more here
The parasitic nematode Steinernema feltiae (available as 'Nemasys') can be used as an alternative and can be watered onto soil. These parasites infect the grubs with bacteria to kill them. Treat between August and October.