Risk factors and management of leatherjackets in field crops

Soil-inhabiting larvae of crane flies, leatherjackets feed on the roots and underground parts of the stem on a wide range of crops, including carrots, oilseeds, peas, cereals, potatoes, field beans, sugar beet, lettuce, and vegetable brassicas. Attacks are most common in crops following a grass rotation, and symptoms can become apparent several weeks after emergence.

• Crops following a grass rotation are at high risk. Larvae continue feeding in ploughed-down turf, moving on to feed on the new crop when the turf rots away. This leads to damage suddenly appearing weeks after crops emerge
• Cereal crops are less likely to suffer economic damage once they have tillered
• Winter cereals, particularly late-sown ones, may be attacked when soil temperatures are above 0.5°C
• Spring-sown crops are most vulnerable in April and May when the leatherjackets are large and voracious
• Prolonged damp conditions in late summer and early autumn increases leatherjacket numbers
• Dry September weather can considerably reduce numbers because eggs and young leatherjackets are vulnerable to desiccation

Scientific name: Tipula paludosa and Tipula oleracea

Larvae (leatherjackets) are greyish-black and grow to 40 mm in length. They have a tough skin and are plump and soft.

Adults (crane flies) have a long body (approximately 25 mm in length), long gangly legs and narrow wings.

Aug–Sep: Adults emerge and lay eggs.

Sep: Eggs hatch.

Late Sep–Feb: Larvae feed when soil is above 0.5°C.

Mar–May: Main larval feeding period.

May: Larvae pupate near soil surface.

Jun–Jul: Pupae.

Leatherjackets usually feed just below the soil on roots and stems. However, on warm, damp nights they may feed on the surface, making ragged holes in leaves, and cutting off stems like cutworms.

Non-chemical control

Cultivations decrease populations of this pest. Ploughing in July and early August (before the main egg-laying period) and covering the old sward well with soil can limit attacks. However, this could increase the risk of wheat bulb fly.

If ploughing occurs later, thorough consolidation and a good tilth can enable a crop to grow away and minimise the vulnerable period.

The larvae of the main pest species, Tipula paludosa, stop feeding by mid-June, so establishing crops, particularly vegetable brassicas, later than this can avoid damage to seedlings.

Monitoring

Assess leatherjacket numbers before ploughing. Use a 10-cm diameter soil corer. Take 20 cores for areas of up to 4 ha. Soil is washed and sieved in a laboratory to extract the leatherjackets. Alternatively, a Blasdale apparatus can be used, which drives leatherjackets into trays of water by heating the soil cores from above.

An alternative method is to drive plastic pipes (30 x 10 cm) into the ground (by 5 cm) and fill them near to the brim with brine. Any leatherjackets will float to the surface. This method is less effective in recently cultivated soil because pipes are less effective at retaining brine. Proprietary brine-based testing kits are available.

Thresholds

Spring cereals: 50 leatherjackets/m², or five in 12 pipes, or 5/m of row.

Oilseeds: >50 leatherjackets/m², or more than five in 12 pipes, or greater than 5/m of row.

Insecticide resistance

None known.