Over recent years the winters have become gradually warmer and wetter, with only one small cold snap, usually at the beginning of spring rather than throughout the winter months like in times gone by. This change, along with the reduction of licensed chemical control, has seen an increase in garden pests such as leatherjackets.
These pests are the larvae/grubs of crane-flies, part of the tipula species, also commonly known as the daddy long-legs. There are several types of crane-fly identifiable by their long thin legs, narrow body and slim wings but all of which can produce damaging leatherjacket grubs.
The reason leatherjackets cause such a problem for gardeners is because they eat the underground structures of plants as well as seeds. Leatherjackets that are present in lawns can result in unsightly dead bare patches; damage caused by them coming up to the surface to feed. In areas of planting, such as vegetable gardens and borders, the damage can seem to appear suddenly when plants wilt and die. You can confirm if leatherjackets are the culprit of the damage by lifting a section of turf or scraping away the soil around affected plants where they’ll be revealed.
A leatherjacket can be identified reasonably easily - once you’ve managed to spot them as their greyish/brown (sometimes black) colour makes them well camouflaged! What you’re looking for is a grub roughly 2.5cm - 4cm in length, no distinct head or legs with a soft body enclosed in a leathery skin.
The occurrence of leatherjackets can be difficult to explain, but it can be linked to the exposure of the area to south westly prevailing winds where the wind eddies create sheltered pockets. Areas which retain heat such as rendered or whitewashed walls are another key area where leatherjackets have been found. Some eggs can also be transported in turf, although the grub forms will usually live below the harvesting layer of the turf. Crane-flies are often in abundance late summer and can lay up to 300 eggs in the soil at a time which hatch within two weeks.
However, if the weather/soil is dry many of the eggs will perish with any that survive feeding on plant roots. As a rough guide, grass areas can tolerate approximately 20 leatherjackets per square metre. However, this can vary as mature, well maintained lawns will be able to tolerate more attacks due to having an established depth of root than younger grass or new turf due to their shallower roots.
During the colder winter months, leatherjacket growth and feeding rates will be slow and any damage may not be noticeable. As the weather warms from spring into summer, they will have grown larger and have an increased appetite causing noticeable damage to lawns and plants before retreating deeper into the soil late summer to pupate and emerge to start the cycle again as crane flies.
One question we are often asked is ‘how can I kill leatherjackets?’ and unfortunately there are no chemicals approved for amateurs or professionals for use on eradicating leatherjackets. There are, however, methods of reducing numbers.
One such method, which is effective on smaller lawned areas, is to saturate the soil with water in the evening and cover with dark tarpaulin/plastic sheeting. This flushes the leatherjackets out of the soil to the surface so when the tarpaulin/ plastic sheeting is removed the grubs can simply be picked up and collected or left for the birds. The other control method is the use of nematodes, commonly known as roundworms. The use of nematodes can be a good choice for both organic and non-organic gardeners for the control of pests as they are completely safe for pets, children, birds, bees and other wildlife and can be used in spring and autumn.
It is often said that prevention is better than cure and for leatherjackets preventative measures can definitely help to reduce numbers. Some preventative measures are:
- Leave the lawn long
- Crane flies will emerge in late summer crane flies. As soon as you see them, allow your lawn to grow longer (10cm) as this extra growth will make it more difficult to get to the soil and lay eggs.
- Don’t irrigate
- This is again time specific and only for the period where the crane flies emerge and want to lay eggs. Many eggs will perish if the ground is hard as they are unable to get into the soil.
- Autumn fertiliser
- Feeding lawns with an iron rich fertiliser after the adult crane flies have emerged may have a detrimental effect on any eggs laid. A good option is Sherborne Turf’s Green and Black Fertiliser.
- Good ongoing maintenance
- A healthy well maintained lawn that has been correctly fed, aerated etc. will be better equipped to defend against an attack than a lawn that hasn’t been maintained throughout the year.
