Leatherjackets Tipula Spp. are the soil-dwelling larvae of the crane fly (also known as the daddy long-legs). These small grubs can cause widespread damage to lawns, as they feed aggressively on the roots of the plant. This causes the grass to turn yellow or brown, often resulting in the death if the infestation is severe.
Further damage is caused by birds, such as crows and starlings plucking out the turf as they search for the grubs. Foxes and badgers may also cause extensive damage, as they too will tear up the turf to feed on the leatherjackets.
The life cycle starts with the emergence of the crane flies (daddy long-legs) during August – September. Once they emerge from the turf during the autumn period, they mate and soon lay their eggs in the turf. Once the eggs have been laid, they die soon after, often within 24 hours. Each crane fly can lay up to 300 eggs.
The eggs hatch within two weeks and immediately start feeding on the roots of the turf. They keep feeding throughout the winter and into the spring. By spring time they will have increased in size with the feeding becoming even more aggressive.
It is during the spring – early summer months when the most severe damage is caused by the leatherjackets. The grubs continue feeding until fully grown, then in June they pupate, before emerging again in early autumn and the life cycle begins once more.
The initial indication that leatherjackets may cause problems is a high number of crane flies during the autumn. If they are abnormally high in number, then it is possible, given the correct conditions there is a high likelihood of damage the following season.
During the early spring time it pays to be vigilant and be on the look out for any abnormal bird activity on the lawn. If birds are pecking at the lawn, it is wise to investigate to find out what they are after. The grubs are usually found about 25-50mm below the surface of the lawn.
Also keep an eye out for any patches of irregular yellow / brown discoloration during this period. If anything is observed, try and pluck the grass from the lawn. If it is easily plucked from the lawn, this may be a sign of leatherjacket damage and further investigation will be required.
When searching for the grubs always look on the edge of the damaged area, as they tend to move from the center and work outwards.
A small knife, trowel or soil sampler can be used to dig into the soil and inspect for grubs.
The larvae are grub shaped, with a brown body, they are leg-less and can measure up to 30mm in length. Don’t confuse them with chafer grubs, which tend to be white in colour.
Another way of testing for grubs is to soak an area of turf, then lay a black plastic sheet over the soaked area. Leave the sheet there overnight and remove it the following morning. If there are grubs in the lawn this method will encourage them to the surface.
Conditions that favour leatherjackets
Leatherjacket populations may fluctuate from year to year. This is largely down to the climatic differences that each year throws at us. If there is a large amount of rainfall during the autumn-winter period this will be beneficial to the development of the grubs.
Extremely dry conditions when the grubs are developing, can have an adverse effect them. Mild conditions will also increase leatherjacket activity, while extremely cold temperatures will decrease activity.
Control of leatherjacket grubs
There are a couple of products available for the control of leatherjackets in turf. These being Provado Lawn Grub Killer (a systemic insecticide) that contains imidacloprid and Nemasys Natural Leatherjacket Killer (a natural product that contains nematodes).
Provado Lawn Grub Killer
This product is used as a preventative treatment that acts on the nervous system of the grubs. It can also be used to control chafer grubs too. The product is mixed with water and applied to the turf with a watering can. It should be watered in sufficiently (approx 10 liters of water per square meter).
It should be applied during the egg laying stage of the leatherjacket life cycle. An application during August or September should yield the most effective results. Early evening is the best time to apply this product.
Once the grubs are developed Provado lawn grub killer will not be as effective. The systemic action of this product travels into the whole of the root system. When a grub ingests a piece, it stops feeding and subsequently dies.
Nemasys Natural Letherjacket Killer
This is a natural product (chemical free) that contains nematodes (Steinernema feltiae). These nematodes attack the leatherjackets by entering their bodies, releasing a bacteria, which eventually kills the grubs. The product should applied about 14 days after you first notice crane flies in the garden.
The soil should be moist and the soil temperature should be 12 degrees Celsius or greater when applying Nemasys. Apply in the evening and never apply in sunlight as ultra violet light is harmful to the nematodes. Water in thoroughly following the application to wash the nematodes down to the roots where the grubs are feeding.
Keep the lawn moist for the next two weeks for the most effective results. Once the leatherjackets are dead, the nematodes continue feeding on the dead grubs, increasing in population, dispersing and attacking other leatherjackets.