Leatherjackets and Chafer Grubs
Leatherjackets and chafer grubs are serious pests of lawns and there are not chemical controls available to amateur gardeners. Recent research has show that if applied correctly at the right time of year nematodes will control both chafer grubs and leatherjackets.
About Leatherjackets
What damage do they do to the lawn?
Leatherjackets are the grubs (larvae) of crane flies (commonly called daddy long legs). They feed just below the surface destroying the root system and the underground stems of grass plants. Most damage is done in spring when they are most actively feeding. Grass turns yellowish brown in mid summer and in the autumn birds will peck at the lawn feeding on the leatherjackets.
What do they look like?
Leatherjackets are about 4cms long, brown or greyish black, soft and fat but with a tough skin. They have no legs and no discernible head. They can be encouraged to the surface by placing a sheet of black plastic on the grass overnight and grubs will come to the surface to feed. A positive identification can then be made.
What is the life cycle?
The adult daddy long legs emerge in early September and often come into the house. They mate and lay up to 300 eggs on the lawn surface. These eggs, like minute seeds, hatch to produce small legless grubs which reach the grass roots on which they start to feed. Feeding continues slowly throughout the autumn and winter. In spring, they gorge themselves growing quickly. Through the summer they pupate and then push to the surface with the adult emerging in late summer.
About Chafer Grubs
There are a number of species of chafer grubs – the most damaging is the garden chafer.
What damage do they do to the lawn?
Garden chafer feed on grass roots severing the root from the shoot. The grubs are most active in the late summer and autumn when they cause the grass to turn yellow. Because they are often present in large numbers whole areas of grass can be affected and the grass can be peeled back to reveal the grubs below. The grubs are an attractive food source for birds, hedgehogs, badgers and even foxes which do further damage as they search for the grubs.
What do they look like?
The chafer grub is white, plump with a dark head and 3 pairs of legs. About 2cms long, they curl up into a characteristic C shape when disturbed. They are often present in large numbers just below the soil surface.
What is the life cycle?
The adult chafer beetles emerge in late May/early June. They are 1cm long and with a metallic green head and body with brown wing cases. They mate immediately and the female burrows back down into the soil to lay her eggs. (Once infested, the same piece of turf continues to be affected over a number of years.) The eggs hatch in mid summer and the grubs start to feed on grass roots. Although they have legs, the grubs move very little. Feeding will continue until late autumn when the grubs burrow down into the soil to pupate. Adults emerge in late May/early June.
About Natural Control
There is no chemical control available for either leatherjackets or chafer grubs. Biological control using nematodes is a safe, effective method of control that will not affect wildlife and the lawn is safe to walk and play on immediately after application.
How does biological control work?
Leatherjackets: controlled by a parasitic nematode Steinernema feltiae applied in mid Sept.
Chafer grubs: controlled by a parasitic nematode Heterohabditis megidis applied from mid July.
These are just two of many species of naturally occurring nematodes in the soil. Most live on dead or decaying organic matter, but a number are parasitic. These particular microscopic nematodes are parasites of soft-bodied grubs. They are in garden soil naturally in a very small number, but by boosting their numbers effective control of lawn pests can be achieved. Supplied as a powder, they are mixed with water and watered onto the lawn and then washed in so that they are as close to the pest as possible. The nematodes swim in the soil water and will enter the pest. Once there they release a bacterium which multiplies and on which the nematodes feed. The pest will stop feeding and die within 2 weeks, disintegrating harmlessly back into the soil.
How is it applied?
It is applied as a dilute solution to the lawn through a watering can and then washed in.
When should it be applied?
Chafer grubs
- soil moist
- soil temperature over 12C
- apply when the grubs are active from mid July to late August
Leatherjackets
soil temperature over 10C
Apply mid September to mid October when the leatherjackets have just hatched and before they develop a hard skin which protects them from the nematodes.
Note: Even if the temperature drops below the optimum, the nematodes will remain alive in the soil searching for the pest. However the bacterium, which actually kills the pest, will not be active. As temperatures rise the bacterium which actually kills the pest will not be active. As temperatures rise the bacterium is activated and starts working again. The nematodes will survive for up to 4 weeks actively searching out the pest.
In what form is it applied?
The nematodes are supplied as a harmless powder which is mixed with water to make a concentrated solution. This solution is diluted and applied through a watering can with a coarse rose the lawn. Following application it should be watered in thoroughly and the soil/lawn kept as moist as possible for the next 2 to 3 weeks. Each pack containing 10 million nematodes will treat 20 sqm/25 sq.yds.
Are these nematodes dangerous?
Only if you are a chafer grub or a leatherjacket! They only attack these pests and are harmless to you, your children, pets and other wildlife. This is particularly important in treating a lawn- you can let children and pets play on it immediately after application.
Will chemicals affect the treatment?
The use of fertilisers, weedkillers and moss killers will not affect the action of the nematodes.
How do I order?
Phone the helpline of Green Gardener based in Norfolk, given below for further information.
Telephone: 01603 715096
www.greengardener.co.uk
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