5 March 1999

Bargain prices look set to protect triazole use

Strobilurins have stolen the

show on cereal fungicides.

But for some timings, in

certain crops, non-strob

sprays will be the best bet.

Louise Impey finds out

when and where, from

advisers in Shropshire and

the Home Counties

CROP yield potential and value, as well as disease, means some cereals at some timings will not justify the expense of a strobilurin, say advisers.

Herts-based independent agro-nomist Caroline Hayes reckons the non-strob route is limited to post-Christmas drilled wheats.

But Dalgetys Shrewsbury-based senior agronomist, Arthur Moreton, says bargain opportunities in the triazole market will mean a non-strob programme has a wider use.

"On milling wheats, the extra cost of a strobilurin programme is justified at yields of 7t/ha or more. But with feed varieties, it is only worth it if yields are going to exceed 8t/ha," he calculates (see table ).

Many growers will be anxious to secure supplies of strobilurins, but there may not be enough product to satisfy demand, he warns. "And there will be some very good buys in the triazole market this year."

He says T1 and T3 are the best timings for triazoles on wheat. "If growers are going to use a strobilurin, then it should be applied at flag leaf."

A pre-T1 triazole may be justified, too, this season. "If yellow rust needs attention, which is likely on early drilled varieties such as Madrigal, Equinox, Savannah and Brigadier, then a third or half rate of tebuconazole will do the job."

Which triazole to use at T1 will depend on the diseases present. "If eyespot is severe, use cyprodinil (Unix) mixed with a triazole. Moderate infections can be treated with a triazole alone, such as bromuconazole (Granit) or flusilazole. That will stop the disease penetrating leaf sheaths and help manage any other disease problems."

Where eyespot is not present, a straight triazole will tackle both the rust and septoria effectively. "Triazoles are good on rusts, especially tebuconazole. And the older triazoles will be fine where there is a low disease risk and the variety has good disease resistance -Claire is a good example."

At ear emergence, early treatments give the best response. If disease is already present, then that should be with a triazole. "If any brown rust is about a strobilurin will not be curative enough. Tebuconazole should be first choice," he advises.

Spring barleys lower yield potential means triazoles may also be the best bet here. "There has been little work done, but yields are unlikely to justify the extra cost of strobilurins in most situations. The only exception is crops drilled in November, which have the potential to yield more."

But on winter barley the case for strobilurins is more solid. "It would be a job to make the crop pay without them," he notes.

The triazoles curative action cannot be replaced with strobilurins, so even where strobs are used, triazoles are an essential partner, he says. "It is sensible to adopt a mixing strategy to preserve the new chemistry. Do not use a strobilurin on its own."

Such a view is echoed by Ms Hayes, but she believes there are only a few crops that will not merit a strobilurin.

"Even crops being grown on poor soils show a better response," she argues. "Providing they get enough water, yields can really be pushed with the new chemistry."

Epoxiconazole is the one triazole which will feature in her disease control programs this season, but mostly mixed with a strobilurin. Her one exception to this approach will be wheats drilled after Christmas, which have low potential and went into poor seed-beds.

"But crops drilled just before Christmas are looking good. We have had an easy winter, so they have made excellent progress. They will justify the extra expense of a strobilurin."

She expects to be recommending epoxiconazole at GS 30-31 and again at GS 37, to capitalise on its curative action. "There is no justification for using a cheaper triazole, although price per unit dose will be worth considering nearer the time. Some of the older triazoles do have specific strengths."

Triazoles feature in her earwash plans, but probably with a strobilurin rather than straight. "Tebuconazole has a useful role here. It is better on fusarium culmorum than any of the alternatives. But again I will be mixing it with azoxystrobin," she adds.

Client objections to strobilurins are due to green straw rather than performance or cost, she notes. "I have had comments that they slow down combine output. But last year was a difficult harvest.

"I think there will be a number of non-strobilurin programmes being used, but I for one wont be recommending them."

That may be easier said than done, says Mr Moreton. Supplies of strobilurins will only be enough to treat about 40% of the UK cereal area, he maintains. "So triazoles are going to be needed. They still have a useful role to play, especially where yields are not going to break any records. Save the strobilurins for your quality crops." &#42

NON-STROBTIPS

&#8226 Match fungicide spend to yield potential.

&#8226 Use variety resistance to cut cost.

&#8226 Save strobs for best crops?

&#8226 Triazole prices down 10%-15%.

Dalgety strobilurin break-even calculation

Net gain £/ha

Expected 6% strob response

Yield (t/ha) over triazole program Feed wheat @ £80/t Milling wheat @ £95/t

10 0.60 18 27

9 0.54 13.2 21.3

8 0.48 8.4 15.6

7 0.42 3.6 9.9

6 0.36 -1.2 4.2

5 0.30 -6.0 -1.5

Based on strobilurins adding £30/ha cost to fungicide program.

Source: Dalgety Arable Ltd.

Only wheat drilled after Christmas will get a non-strob programme, says Herts-based independent agronomist Caroline Hayes.

Be sure the crop has the yield potential before using strobs, says Dalgety Shrewsburys Arthur Moreton. Triazoles could be a better buy for some.