1 March 2002

Triazoles have key role…

…Throughout the spray programme

BE careful not to lose sight of the value of triazole fungicides in the publicity surrounding strobilurins, advises David Jones, a plant pathologist at ADAS Rosemaund.

"Its also important not to farm this years crops as if they were last years.

"Disease levels in the 2000/01 season were the lowest since 1995. But all the indications are that 2002 is likely to be a high disease year.

"Even if we get some hard frosts between now and the first main spray timing, there will be strong need for early disease eradication. Thats where triazoles really fit in.

"Triazoles are ideal partners to protect the strobilurins from resistance." There are no signs that resistance to strobilurins has gone beyond wheat or barley mildew, he says.

But without a sensible anti-resistance strategy, the strobs ability to control septoria, rusts, net blotch and rhynchosporium could be jeopardised.

"They are a vulnerable group, and the strongest method of protection we have is to use good rates mixed with sufficient dose of a partner. In the case of wheat that is likely to be a triazole."

TRIAZOLES will be vital components in T1 sprays this season, says plant pathologist David Jones. "And they will be just as important later in programmes to protect the strobs."

Picoxystrobin and pyraclostrobin, the two latest strobs, offer rather more eradication than the earlier ones, he says. "But I think there will still be a need for applying triazoles with them."

In theory, growers using triazoles are spoiled for choice. But in practice some of the older actives, notably tridimenol, flutriafol, flusilazole and propiconazole will find it hard to justify a place in spray tanks, he suggests.

The best way to choose the wheat fungicide likely to be most cost-effective at a known price is to compare the dose-response curves in the HGCAs Wheat Disease Management Guide. For barley the options are far fewer (see box).

In general, it will be the more robust actives, such as epoxiconazole, which growers should consider (see HGCA star chart). "Much depends on which diseases are your main targets."

Among the list are three relative newcomers fluquinconazole, metconazole, and tetraconazole, though the latter appears the "poor relation" in terms of disease activity.

Varietal resistance can influence triazole choice and dose. "You need to take disease susceptibility into account and tweak application rates accordingly."

For Consort, epoxiconazole (as in Opus) at a "robust" rate could be justified. For the rather more disease-resistant varieties, such as Malacca and Claire, a reduced rate or an alternative triazole might be more appropriate, he says.

Whatever the tactics, spray timing is as important as product choice, he adds. "And unless they are extremely cheap I wouldnt use some of the older products because they are generally weaker."

With more brown rust about than last autumn, growers should be wary of reducing doses too far this spring, he advises.

Most triazoles have a useful effect on mildew and can keep it under control on relatively resistant varieties. "But its not sufficient to deal with severe infection. If you have mildew at the start of the spraying season on a high-risk variety you are looking at quinoxyfen instead, or perhaps a morpholine later on." &#42

&#8226 Fungicides Special continues on page 68

Try not to be blinded by the strobs potential, advises David Jones. Modern triazoles are still key components in spray programmes.

Limited in barley

Triazoles have a relatively small role to play in controlling barley diseases, says Dr Jones. Few offer much control of net blotch or rhynchosporium. "Its effectively down to a basic choice between epoxiconazole and flusilazole.

"But in parts of Scotland it is difficult to get much rhyncho control from triazoles, although resistance is not proven. In those cases a strob/Unix (cyprodinil) mix as a protectant at first node is probably the best option, though it doesnt offer much eradicant activity."

&#8226 Ideal strobilurin partners.

&#8226 Valuable infection eradicants.

&#8226 Wide range of disease targets.

&#8226 Limited scope for older products.

Eyespot Mildew Septoria Septoria Yellow Brown

nodorum tritici rust rust

Bromuconazole ** * ** ** ** **

Cyproconazole * ** ** *** **** ***

Difenoconazole NL *NL *** *** * ***

Epoxiconazole ** ** **** **** **** ****

Flusilazole ** ** *** ** ** **

Fluquinconazole NL ** *** **** *** ***

Flutriafol NL * ** ** ** **

Metconazole NL ** *** *** *** ***

Propiconazole * * ** ** ** **

Tebuconazole NL ** *** *** **** ****

Tetraconazole NL ** ** ** ** **

Triadimenol NL * NL * ** **

Key: **** = excellent; *** = very good; ** = moderate; * = low; NL = no label recommendation. Source: HGCA.