MORE effort is needed to curb the risk to the country of pests and plant disease, a watchdog has warned.

The call for action by the Department for Environment, Food and Rural Affairs comes from the National Audit Office in a report highlighting the threat to England and Wales.

Although there is a good record of containing and eradicating major outbreaks of plant pests and diseases, the NAO says there are several ways in which Defra could improve its work.

The financial impacts of plant pests and disease on the country could be extremely large, it warns.

In 2001, it was estimated that &#xA3;270m of potato crops in southern England might be at risk from Colorado beetle and &#xA3;133m of crops such as tomatoes, cucumbers and ornamental plants were at risk from tobacco whitefly.

There is also a risk to the environment, where pests and diseases can impact on wild flora.

The number of recorded outbreaks of pests and diseases has been rising, from an average of 150 a year over the period 1993 to 2000 to more than 200 in 2001 and some 370 in 2002.

Increased and changing patterns of trade and travel, changes in farming practices and climate change provide potential opportunities for plant pests and diseases to enter and become established in England and Wales.

The risks are underlined by the threat posed by a condition known as sudden oak death which is causing the death of some species of oak trees in California and Oregon in the United States and has prompted European Union wide emergency legislation to contain and eradicate the disease.

The fungus has been found at over 280 sites on rhododendron and viburnum in England and Wales, although none has been found on oaks or other established trees.

Head of the National Audit Office, Sir John Bourn said, "The Department should now take steps to improve its plant health inspection regime and research and how it works with others to keep new and emerging threats at bay."

Defra said scientists were turning to sex as a weapon against pests which damage millions of pounds worth of fruit and vegetable crops.

The Government has approved a &#xA3;1m package of new research projects aimed at finding more natural alternatives to chemical pesticides for farmers and growers.

Researchers in one project will target the apple leaf midge, a widespread pest which attacks orchards and nurseries, by designing traps containing female midge pheromones - substances given off to attract the opposite sex.

This will lure male midges to a sticky end so that growers get an early warning of an impending invasion and can take measures to protect their apples.

Other projects include a study to combat clubroot, a disease which ruins plants such as turnips, brussels sprouts and oilseed rape and costs industry around &#xA3;30m a year in lost crops.

Defra spends almost &#xA3;13m a year on research into alternative pesticide and plant protection.