This can be a difficult time of year for lawns, and for the gardeners who have to look after them. The weather is often warm enough for grass to continue growing well into November, but when it's also wet there are few opportunities to get out with the mower.

For many of us it has been almost impossible to walk on our lawns this autumn, never mind to run a machine over them.

Insect larvae such as leatherjackets and chafer grubs, which feed on grass roots, have now reached a size and state of succulence that tempts birds to dig for them, spoiling lawns in the process.

A colleague of mine has had a nine-hole golf course badly damaged this autumn by the activities of crows and rooks digging for insect larvae. Almost all of his grass has been pecked up by birds in search of a tasty meal. He's tried various methods of scaring them off, but while the root cause of the problem remains - ie the presence of grubs under the soil surface - then the birds will keep coming back.

In the past the answer to this dilemma would have been quite straightforward an application of a chemical drench to kill the grubs would have solved the problem overnight.

Nowadays it's not so easy. Almost all such chemicals have been withdrawn from the market because they are as dangerous to the gardener as they are to the pests involved.

My friend's best bet now is to resort to biological warfarein the form of nematodes.

The withdrawal of toxic chemicals from the market has been matched by research into the use of natural predators of the pests that plague both horticulture and agriculture. At first such biological controls were not widely available, but it is now possible for the amateur gardener to purchase predators for a wide range of pests, including glasshouse white fly, vine weevil, caterpillars, slugs, red spider mite and, of course, chafer grubs and leatherjackets.

While biological controls have the advantage of being safe for humans, pets and beneficial wildlife, they are quite expensive and must be applied with care in order for them to be effective. Among other things, the time of year, soil temperature and moisture content have to be taken into account, as does the life cycle of the pest involved. It may be necessary to make more than one application, over the course of one or two years, before success is noticed.

Biological control products can be obtained from HDRA at: www.hdra.org.uk, from Green Gardener at : www.greengardener.co.uk, and from larger nurseries and garden centres.

..........

Jobs for the gardener this week...

l Plant new crowns of rhubarb now. Grow them in the vegetable plot or as an architectural plant in a border.

l Dry and sunny autumn days may be the last chance this year to give garden seats and benches a protective coat of woodstain before really bad weather arrives.

l Sow seeds of sweet peas in small pots, to overwinter in a coldframe or cold greenhouse. They can be planted out in early spring.