23 October 1998

Rare flea beetle causes wheat growers concern

By Andrew Blake

cereal growers in the south of England are being advised to check for a rare flea beetle species causing slug-like crop damage.

Psylliodes luteola is already widespread on three Velcourt-managed farms in Hants and ADAS reports numerous sightings elsewhere in Hants, Wilts and Dorset. Adults hollow out seeds and feed on developing leaves and sheaths to create bare field areas.

"The damage is easily confused with that from slugs," says Velcourts southern farms director Richard Williamson who oversees 2400ha (6000 acres) of chalkland arable in the Newbury/ Micheldever/Romsey triangle. "Its easy to find everywhere, but worse on heavier soil."

Already 7ha (17 acres) of wheat have been re-drilled and 20ha (50 acres) of worst affected fields spray- ed with reduced-rate Gamma-Col (gamma-HCH). Some new herbage seed leys also merit patching up because of the pest, says Whitchurch-based farm manager Norman Bragg.

First identified in German potato flowers in 1776 the species was almost unknown in the UK until this season, says ADAS entomologist Jon Oakley. "It differs from the normal cereal flea beetle whose larvae cause damage to crops after grass." It is also lighter brown and smaller than cabbage stem flea beetle which attacks newly sown oilseed rape.

Its damage has two distinguishing features, says Mr Williamson. "We find seed hollowed out on the surface, full of small beetles. And while slugs generally cause ragged leaf shredding, the beetle holes are smaller and rounder."

No variety seems more susceptible than others, and it is too soon to tell whether drilling date has had any effect, he adds. "When we get to the end of the season we may be able to tell."

The pest is also plentiful on barley volunteers in oilseed rape and has recently been found in a malting crop.

"We think we can control it because we were onto it very quickly. But we were caught out. Next year we may have to consider dual purpose seed dressing."

All three farms have a history of grass for seed, and there have been reports of similar damage in the area in the past two years, notes technical director Keith Norman who first passed samples to the Central Science Laboratory for identification.

"Its a new pest and concerning that it produces similar plant losses to slugs. Hants wheat growers should certainly be looking closely at their crops.

"I think it has been building up over several years because it is so widespread." Treatment has been very much on a threshold basis, he stresses. "In places you can put a hand down and find ten beetles underneath so you have got to spray," says Mr Williamson.

Gamma-Col is not specifically approved for the pest, but its recommended application for leatherjackets provides incidental control, says Mr Oakley. "I would advocate Gamma-Col, but I expect growers would be better off with a seed treatment – although there may be compatability problems with some of the more expensive fungicides." &#42

NOVELFLEABEETLE

&#8226 Widespread in Hants cereals.

&#8226 Slug-style damage by adults.

&#8226 Gamma-HCH spray weapon.

&#8226 Seed treatment in future?