Dealing With Leatherjackets

I have seen a few daddy long legs (crane flies) attached to window panes, this week - a sure sign of leatherjacket trouble next year.

For anyone who has just seen a leatherjacket (thick rubbery brown-grey grub about 4 cm (inch and a half) long) for the first time, it is hard to believe that it represents the larval stage of the daddy long legs, let alone the sort of devastation these grubs can do to a lawn.

When you see the adult flies hopping over the lawn, they are laying hundreds of eggs in the damp turf. These quickly hatch into grubs which immediately commence feeding on young tender grass roots (exactly those we have nurtured for next year).

The damage goes undetected until the weather gets drier, the following year - the lack of roots causes premature browning and dying of the grass, which can then be easily pulled out in handfulls leaving almost bare earth. Further trouble is caused by starlings (and even animals such as badgers) and the like which scratch up the turf looking for the grubs.

Although both cultural and biological controls are possible, the worst of the damage will have already been done over the winter and spring months. So, even though the grubs can be killed, the lawn will not recover.

Although expensive, I have found 'Provado Lawn Grub Killer' to be an excellent product for dealing with leatherjackets (it can also be used for chafer grubs). My lawn always used to have dead patches each summer before I started using it.

However, it is not the easiest of products to use, since it needs to be washed through the turf (to get to the grubs) without being diluted too much, or even washed right through the soil. Furthermore, because it is a powerful insecticide, it can only be applied once per year without affecting the balance of soil micro-organisms.

The best way to apply it is to wait until the soil has drained, then apply and wash it in with half an inch (1.5 cm) water from a sprinkler. You need to be confident that the weather will remain dry for two or three days to give the plant roots time to take it up, from whence it acts as an effective systemic insecticide.

If only the weather would settle down.