Is your grass under attack?

Several farms in County Fermanagh experienced significant sward damage last spring.  The damage was caused by leatherjackets and farmers should be aware of the harm they can do.  The sooner you check whether you have a potential problem, the more can be done to reduce sward damage.

How can leatherjackets affect Fermanagh swards ?

Leatherjackets populations tend to be higher and more damaging in warmer and wetter areas.  Modest leatherjacket populations can significantly reduce silage and grazing yields and higher populations, if unchecked, can decimate the sward.  Newly sown reseeds are particularly prone to attack and these fields should be given priority when inspecting  for leatherjacket infestations.

What are leatherjackets ?

Leatherjackets are the larvae of crane flies which are better known as daddy-long-legs.  They hatch in August/September and they feed all winter until the following May on grass roots.  Leatherjackets prefer to feed on the high yielding grasses (eg ryegrasses).   Craneflies regularly stay and lay their eggs near where they emerged from pupae in the summer.  This can cause the population to build up within a field if not controlled.

How can you recognise leatherjackets ?

Large numbers of craneflies in fields in autumn should prompt a look for leatherjackets in later weeks.  Frost, slurry and other grubs can also cause sward damage so it is essential to carry out a close inspection to determine the nature of the problem.  A simple inspection of fields will pinpoint the problem.  Dig a shallow sod as the leatherjackets are present just below the soil surface.  The grubs at this time of year are 1-2 cm long, legless and have a tough grey or brown coloured skin.  The presence of large number of crows or starlings in a field can indicate the presence of leatherjackets because they feed on the grubs.

Signs of leatherjacket damage include:

Some damage occurs in late autumn and during mild winter periods  when leatherjackets are more active but most damage occurs in April/May when the leatherjackets are large and feeding voraciously.

Where leatherjackets are found in large numbers (more than one hundred per metre) chemical control will be appropriate.  Spraying with pesticides containing chlorpyrifos (eg Dursban WG, Cyren) can provide effective control.  For the best control chlorpyrifos should be applied using high water volumes ideally followed by light rain.  

In cases of mild attack increasing fertiliser nitrogen application (within the regulations) can counteract the damage by encouraging rapid grass growth.

Rolling can also help as this will restrict the movement of the grubs in the sward.

When should leatherjackets be controlled ?

This can be done anytime from mid November. Sooner is better than later as there is a steady decline in grass yield response after spraying from November to May.

Late spring control may control the grubs but by this stage most of the damage will have occurred.  If control is delayed until March grass yields can be approximately half of that which could be obtained if spraying was carried out in November.  Avoid spraying in prolonged periods of frost when grubs are less active.