Adult Crane Fly will emerge and mate in July and lay eggs in August/September. The larvae usually hatch in September when the grubs will begin to grow in the rootzone feeding on roots and move deeper into the soil profile over the winter months raising through the profile in the spring and the life cycle begins again.
When are they a problem?
Damage to turf becomes most apparent when they feed on the roots during the Autumn and Winter indicated by a yellowing of the turf due to the damaged root structure.
This feeding is an issue for your turf as it stunts the growth of the grass plant, but there are other dangers that leatherjackets pose in an indirect way. Leatherjackets are a source of food for badgers, rooks and other wildlife species. The damage caused by these animals, when searching for leatherjackets in your turf’s soil, can be significant and costly to fix.
The most important thing to do when the first signs of a leatherjacket infestation have been spotted is to confirm the size and scale of the potential infestation. Doing so will help you to understand the level of response that will be required. The best way to see how large an infestation will be is to cover your turf overnight with a black tarpaulin. Then, in the morning, you should uncover the turf and if there is any infestation, the grubs will have come to the surface. Populations of over 25 grubs per m2 can signify a serious problem.
What can we do to prevent/reduce their impact?
As is the case with many aspects of turf maintenance,
prevention is often better than cure, so carrying out regular grounds
maintenance practices on your turf, such as regular aeration, a decompaction
programme, and scarifying the turf surface to minimise levels of thatch, will
all be effective ways of significantly minimising any chance of an infestation
in the first place.
This is because mossy, thatchy surfaces are ideal for female
crane flies to lay their eggs in, by carrying out the above tasks regularly,
you prevent the crane flies from being able to make a home in your turf and
beginning the early stages of a leatherjacket infestation.
For operations to be most effective, they must be done based
on the life cycle of the pest.
Do regular rotary mowing (with collection) on the affected
areas in late August and September when the Crane Fly is on the wing (usually a
2 week period) to disrupt the adult mating and egg laying process and help
control the adult population.
How can we deal with Leatherjackets in the soil?
Chemical pesticide options for leatherjacket control are
limited, especially with increasing regulations on pesticides for environmental
and safety reasons. Some professionals may have access to restricted-use
insecticides that target soil-dwelling larvae; however, these are not available
for general public use.
Biological control such as the use of nematodes is available
but has mixed success as soil conditions must be suitable for a 2-week period
for nematodes to be effective. The nematode penetrates the grub and kills it.
The nematodes need to be applied mixed with a nematode friendly wetting agent
to moist areas during March to Mid-May and August to Mid-October when the soil
temperatures are above 12 degrees when the grubs are active and near the
surface. Sufficient water needs to be applied after the nematodes have been
introduced to bring them into contact with the grubs. Specialist advice should
be sought if taking this approach.
Extending the sheet testing using large black tarpaulin sheets put down overnight can be used. This tricks the grubs into thinking it is still night and they stay on the surface until the sheeting is removed. They can then be collected using mowing, brushing or hand sweep and shovelling operations but this can be difficult on longer mown turf.
