24 August 2001

Blight weapons are at risk

By Charles Abel

BLIGHT control could become a whole lot harder if the important potato fungicides oxadixyl (as in Trustan) and tin are lost from the growers armoury.

In an effort to counter the potential problem, agrochemicals distributor Agrovista is evaluating 48 programmes on 200 plots this summer at a major trials site at Saxham, near Bury St Edmunds, Suffolk.

"Im not saying Trustan and tin are going to go this autumn, theyre not," says trials manager John Keer. "But they are under pressure from the EU review programme and commercial pressures, and we want to be sure we have something in place in case they do go."

Two new products launched this year and a further one due for 2002 mark a significant step forward in blight control, he says. "In recent years it was difficult to find a difference in the blight activity of new products. But Ranman and Electis are a quantum leap forward and EXP 10810A (fenomen) from Aventis looks set to further boost blight control next year."

In Agrovista trials last year, Ranman (cyazofamid) topped the list for foliar blight control and has the added bonus of mid-season tuber blight control. The formulation is more user-friendly than powders.

However, its fast arrival on the market has left some quirky label restrictions and Dr Keer is concerned that its single mode of strob-like action could create resistance problems.

By contrast, he says the robustness of Electis is almost beyond question, containing full rate mancozeb plus zoxium, to give excellent foliar control and good tuber blight control.

But a direct replacement for the systemic and phenylamide-resistant blight busting activity of Trustan is unlikely. "Trustan has been an important systemic blight spray. "In theory a mix of Merlin, containing propamocarb and chlorothalonil, with new straight cymoxanil product C50 should match it. But in practice it does not and that is already being borne out by this years trials."

Although the combination should match Trustan, formulators seem to be unable to overcome an antagonism between cymoxanil and chlorothalonil when used together. "They are fine when used separately, but not together."

Tattoo plus C50 may be a better bet, replacing chlorothalonil with mancozeb – the backbone of many Agrovista blight programmes. "It does look to be a more effective combination."

Older, foliar blight-based products are becoming outmoded, says Dr Keer, as newcomers Ranman and Electis bring worthwhile mid-season tuber blight control.

That could prove useful if tin is lost. "Some growers lost a fortune where tuber blight hit two years ago, so we need to be looking at using these new products to help keep it at bay in case we lose tin.

"The UK is virtually the only country using it and it is up for EU review soon."

Dr Keer also questions the attitudes of supermarket protocols to blight sprays. "Last year Tescos Natures Choice banned Merlin, now its back on again. This year Bravo is out of favour. It seems to be based on perceptions, not science, so we need to look at all the options in case we get further 180 degree changes."

Agrovista is also researching a novel adjuvant, Exp 4396. "It has clearly improved the activity of blight fungicides, but we dont want to say too much more until we have it registered," says Dr Keer.

BETTERBLIGHTCONTROL

&#8226 Oxadixyl set to go?

&#8226 Tin under pressure.

&#8226 New product benefits.

&#8226 How to replace Trustan?

&#8226 Focus on tuber blight.

New potato blight fungicides Electis and Ranman, plus yet-to-be-launched fenomen, offer a quantum leap in foliar and tuber blight control, Agrovista technical manager John Keer (right) explains to visitors at the companys Saxham trials site.