New mildewicides not the same

6 March 1998




New mildewicides not the same

CEREAL growers plagued by mildew have two novel defences in quinoxyfen and spiroxamine this season. But direct comparisons between them are misleading, suggests Doug Stevens, Morley Research Centre agronomist.

"They are quite different compounds." Quinoxyfen, sold as Fortress, offers much longer disease control than current morpholines, but is specific to mildew and solely protectant, he explains.

"Spiroxamine, as Torch, is much more like a morpholine being eradicant and protectant. It also has some action on other diseases like the rusts, and rhynchosporium and net blotch in barley.

"Quinoxyfen is in a league of its own when it comes to mildew control," says Mr Stevens. "It is a very kind product, but exceptionally persistent." It kills spores before they have a chance to penetrate the leaves and cause damage, he explains.

"In the field you never see complete mildew eradication as you do with a morpholine, but it holds it for a very long time." In Morley trials wheat after an early April quinoxyfen spray was still relatively mildew-free 12 weeks later, while a morpholine-treated comparison was reinfected within four weeks, he notes.

A price cut from last year, when it was test marketed on about 50,000ha (120,000 acres), according to Dow Agrosciences, makes quinoxyfen as competitive as the morpholines, says Mr Stevens.

"It is very dose flexible." A typical 0.1 litre/ha application should cost about the same as 0.5 litres/ha of a morpholine.

Treatment may have to be slightly earlier than normal, but that should not deter growers, he believes. "But it only deals with mildew. One option where other diseases such as rusts are present is to tank mix 0.25 litres/ha of a morpholine as a clean-up." An alternative is preformulated Okra (fenpropimorph + quinoxyfen), he says.

Spiroxamine is a broader spectrum fungicide, which maker Bayer sees as an ideal tank-mix partner for triazoles and strobilurins, giving robust mildew control at least as good as the morpholines.

A key feature is said to be its ability to boost uptake of triazoles. Indeed, the firm already offers a co-formulation with tebuconazole called Beam.

Mr Stevens says that when first announced, spiroxamine was claimed to be a good match for fenpropimorph against mildew and just as good as fenpropidin against the rusts. He believes this is a fair positioning of the product. "But fenpropidin is better than fenpropimorph for mildew on wheat," he notes.

"It is very similar to the morpholines and will compete mainly on price," says Mr Stevens.

NOVEL MILDEWICIDES

Quinoxyfen

&#8226 Is mildew specific, protectant only and offers persistent control.

Spiroxamine

&#8226 Is broader spectrum, an ideal tank-mixer and boosts triazole uptake.

The two latest mildewicides available to growers this spring – quinoxyfen and spiroxamine – are very different products.


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