12 December 1997

Dutch say tight controls will curb brown rot risk

Fresh brown rot outbreaks

have hit the Dutch potato

industry. But experts believe

the disease poses little

threat. Robert Harris

discovers why

DESPITE a rise in the number of brown rot outbreaks this season, Dutch experts are confident that potato seed exports will rise.

They maintain continued, more targeted, seed inspection, an irrigation ban on infected water-courses and stricter controls on seed movement from infected farms keeps disease under control.

Brown rot has been discovered in 15 seed potato crops this year, in two ware crops and one destined for starch. That compares with a total of 14 in 1996, and the number could still rise, explains Ineke Mastenbroek, technical director of NAK, the Dutch seeds inspection service based at Emmerloord.

Some lots are under suspicion, and produce from farms linked to outbreak areas is also being tested, she adds. "We had hoped to end up with fewer than five cases this year. We are not happy with the situation."

But the number of outbreaks should be kept in context, she adds. "We visited 3000 farms and carried out 65,000-70,000 tests."

Rigorous testing will continue, though cost-cutting measures may be introduced, says Dr Mastenbroek. This year, all seed was tested, which cost growers £2.6m.

She believes concentrating on certified seed, which is at least four generations old and carries the highest risk, will identify most cases. No brown rot has been discovered in basic seed, so tests on that sector may be dropped. Seed for home use may be exempted, too. She predicts the number of tests will fall by 10,000-15,000.

Other ways to reduce disease spread include a ban on irrigation from water infected with brown rot. "We are continually checking waterways for bacteria," says Henk Baarveld, agronomist for NIVAA, a grower-funded export promotion organisation based in The Hague. "That enables us to identify infected ones quickly."

Tighter quarantine laws now require all seed grown on an infected farm to be destroyed, rather than just the infected lot, he adds.

He is confident that seed exports will rise as a result of Dutch efforts. "Over the past two seasons we have exported 1.2m tonnes of seed. There was not one complaint of rot in a growing crop."

He predicts the UK will import 50,000t of Dutch seed by the end of the decade, up 20,000t on last season. "I think growers are more concerned about seed size, virus, and scab levels than brown rot." Further tightening of standards, especially powdery scab, will address those needs, he believes.

Widespread testing for brown rot identifies infected waterways. Irrigation bans then follow to cut disease spread, says Henk Baarveld (inset).

BROWN ROT UPDATE

&#8226 15 new outbreaks in seed potatoes – more predicted

&#8226 Targeted seed inspection.

&#8226 Widespread water testing.

&#8226 Irrigation ban from infected water.

&#8226 Whole farm seed destruction.

&#8226 Seed tests cost – £2.6m.