7 March 1997

…while mixes give cost-effective returns

HOW much will farmers have to change disease control programmes to get the best from the new strobilurins? Very little, says Mr Clark.

Though mainly protectant, which suggests they are best applied early, he reckons most growers will use them in mixtures with triazoles. That will boost eradicant activity, making timing more flexible.

"If they were used on their own, you would have spray much earlier, about GS30-31. That means you would almost certainly have to go again before the flag leaf was fully emerged. You are then left with the problem of what to put on the ear, because it wont be protected by the earlier spray."

Mixtures will allow farmers to stick close to current timings, he says. "Strobilurins might give you some leeway to go earlier, to take advantage of their persistence. But I do not think timings will change dramatically."

Neil Waddingham, Novartis product manager, agrees the future lies with mixing.

He examined the effects of adding the firms Alto (cyproconazole) to either kresoxim-methyl or azoxystrobin in trials last year.

The effects on both septoria and mildew were studied in France and Germany, using fairly high product rates. "Strobilurins are essentially protective materials, so are dependent on timing when used alone. Get it right, and they work well."

Including a triazole, with its curative action, adds flexibility, he says. "A mixture may not necessarily save money. But it increases the chance of getting a cost-effective return."

Any triazole will help, but Mr Waddingham claims Altos properties make it an ideal partner. "It is very systemic."

"Azoxystrobin is fairly systemic, and has good preventative action against septoria, and will control rusts. But its curative action could be questionable, and it is weak on mildew. Kresoxim-methyl is not particularly systemic and has limited control of rust and septoria."

Adding Alto will not only boost disease control but serves as a good anti-resistance strategy, Mr Waddingham maintains. Both strobilurins have a different mode of action to cyproconazole.

Although kresoxim-methyl will be sold by BASF in a co-formulation with fenpropimorph (as in Corbel), Mr Waddingham maintains growers will still gain by adding cyproconazole. This is because the mixture will have three modes of action against mildew and broaden the disease spectrum of the strobilurin.

"Used with imagination, existing chemistry can match strobilurins," says Mr Waddingham. "The question is which is the most economical way forward? In reality, the most consistent and cost-effective strategy is likely to be one using the strengths of both existing and new fungicide chemistry."n


&#8226 Kresoxim-methyl from BASF.

&#8226 Azoxystrobin + another from Zeneca.

&#8226 One each from Bayer and Novartis.

&#8226 Patents held by 20+ other companies.