Leatherjackets

Key Points

• Leatherjacket infestations can devastate crops that are attacked
• Crops following grass represent the highest risk of economic damage
• Use Risk Assessment Charts to establish fields at most risk
• Soil sampling indicates pest levels in individual fields
• Dursban WG is established as the product of choice for control of Leatherjackets

Introduction

Leatherjackets are the larvae of the Crane fly — Tipula paludosa — or ‘Daddy Long-legs’ and cause widespread damage to winter and spring cereals, grassland, root crops and vegetables. Young cereals are attacked both below and above ground. Underground damage is noticed in winter and spring when seedlings turn yellow and die, leaving bare patches. Affected plants are easily pulled from the ground as their root systems have been severed. During suitable weather conditions in spring, severed leaves indicate surface feeding during the night.

For winter cereals, damage may go unnoticed until the spring, when warmer conditions enable the crop to grow away. However, damage is still being caused, and potential yield compromised, despite the absence of visible symptoms.

Biology

Adult females of the Common Crane fly are seen on the wing from late July to September. They lay around 300 eggs in the soil surface which hatch within 2 to 3 weeks. The larvae immediately begin feeding voraciously on roots and underground stems, particularly during periods of mild weather throughout winter, but also as the temperature rises in the early spring months.

The larvae reach maturity during late May and in to June. They then pupate in the soil and adults emerge again in late July to early September. Leatherjacket larvae are normally grey-brown in colour, soft, fleshy and legless. They can reach 50mm in length when fully grown.

The threshold for damage to winter and spring cereals is 0.3 to 0.5 million larvae per hectare. This is equivalent to 30 – 50/m². By the time threshold populations are detectable in the spring as much as 0.25t/ha of crop could have been lost already. Early treatment will protect this yield.

Crops following grass leys, permanent pasture or arable crops with a grass weed infestation are particularly at risk. Ploughing grassland in July and subsequent cultivations can destroy up to 50% of Leatherjackets.

Product Choice

The first action must always be to carry out a Risk Assessment. This can be done using the Dursban* WG Leatherjacket Pocket Card (64KB PDF). If the Risk Assessment indicates treatment is justified, Dursban WG should be applied at 1.0kg/ha in a water volume of 200 – 1000 litres per hectare when damage is seen or predicted. Controlling Leatherjackets early gives the best economic response to treatment but application during periods of prolonged frosts should be avoided as Leatherjackets are less active near the soil surface under these conditions. Applications when  temperatures are  above 5°C give best results.

Examples of the actions required as a result of carrying out a Risk Assessment are shown below.

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