Adult crane flies emerge at this time of year from their pupae. Typically they live only a few days and females will mate and lay eggs within 24 hours. These take about three weeks to hatch and appear from the end of August and through September.
The larvae of adult crane flies have tubular bodies up to 30mm long and are greyish brown. Once hatched, leatherjackets are phenomenal feeders, eating the roots of the turf, which prevents it drawing water from the soil. Grass soon turns yellow and in its weakened state is more susceptible to all types of disease. This means leatherjackets can easily be confused with drought stress. Well-fed leatherjackets attract predators such as badgers, foxes and birds, particularly starlings, which can damage turfed areas by pecking to get at grubs.
Now that insecticides have been banned for amenity use, it is more important than ever to catch an infestation early. Dr Kate Entwistle of the Turf Disease Centre, which offers independent advice to turf managers, said: "It's one of many problems now we don't have the insecticides such as Imidabloprid available. Where people had invertebrate pest problems in the past they used insecticides. They are going to struggle to manage those populations going forward.
"It's going to be a very difficult time for the turf manager. There are a whole group of entonopathegenic nematodes used for leatherjackets, chafer grubs and vine weevils. They go in and multiply inside them. They use the larvae as a food source, they feed on them and also introduce toxins."
Steve Braddock, head groundsman at Arsenal FC's 58ha training centre in London Colney, Hertfordshire, said nematodes are expensive and not as effective as chemical treatments. "It's a big problem if you have them but it's very sporadic. Weather conditions, I believe, do not play a part. It can be very problematical to turf because the roots of plants can be destroyed, which then causes problems with stability on turf."
Braddock advised soaking a hessian sack - about 1sq m in size - with water and leaving it on the turf overnight. "If next morning the surface is full of leatherjacket grubs then treatment is necessary. There are no chemical treatments available due to legislation so other treatments are limited and very expensive."
BASF Agricultural Specialities is one firm that sells nematodes, under the Nemasys Leatherjacket Killer brand name. It calls leatherjackets "one of the most voracious insects pests of turf in the UK". Business manager Gavin Wood advised applying Nemasys from late August to October when the soil temperature is above 10 degsC. "Don't forget to cut the grass prior to application and apply in the evening or in dull conditions," he added. "Ideally apply during rainfall. One application can last up to six weeks when soil is kept moist."