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 sugar beet plants can be attacked both below and above ground. Underground damage is noticed when seedlings turn yellow and die, leaving bare patches.

The worst attacks usually occur in spring with young plants being most affected. 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. Widely spaced crops with few plants per square metre, such as sugar beet, can be severely damaged by relatively low populations of Leatherjackets.

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 sugar beet crops is 0.25 million larvae per hectare. This is equivalent to 25/m². By the time threshold populations are detectable a significant threat to final yield exists. 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 (134KB 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.

Where sugar beet is to follow grass the recommended method of control is to detect and treat with Dursban WG in the grassland prior to cultivation and drilling of the sugar beet crop. As a follow up treatment to this, or when prior treatment has not been possible, Dursban WG should be applied to the sugar beet crop if high pest levels are found or at the first sign of damage by Leatherjackets. Applications can be made at any time after drilling, but an interval of four days must always be observed between application of Dursban WG and any herbicide. When prior treatment of the grass crop has not been possible damage may be reduced rather than prevented.

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

Always check the Sugar Beet Pestwatch pages for the most recent bulletins.

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