23 July 1999


HOPES that one or more of the three cereal seed treatments in the approvals pipeline would be available for this drilling season have been dashed.

The launches of AgrEvos fluquinconazole, Monsantos silthiophan (MON 65500) and Rhone-Poulenc Agricultures triticonazole have been delayed until 2000.

But the wait should be worthwhile because two of the fungicides break new ground by having at least fair activity against take-all. One also offers good control of foliar diseases up to or beyond GS31-32, while the third combats most seed-borne diseases and gives longer-term control of foliar problems than other products of the same type.

"We anticipated approval for fluquinconazole for this season, but the timetable proved too tight so we missed the boat," admits Adrian Cottey, AgrEvos crop manager for cereals. "The product will be recommended only for wheat here, although in Germany it is being developed for barley too."

Arguably its most remarkable feature is extended activity, giving it the potential to eliminate the need for a T1 spray on the more disease resistant varieties, particularly where infection pressure is not too severe.

"It caters very well for growers adopting earlier drilling at lower seed rates," says Mr Cottey. "In such cases the normal T1 and T2 spray programme will be needed, but for later drilling it will be a case of judging whether the T1 spray is necessary variety by variety."

Fluquinconazoles good stability and crop safety are conferred by its double ring molecular structure and single isomer content, both unusual for a conazole. Normally a conazoles inactive isomer is responsible for its adverse crop effects like leaf tipping, he explains.

"This attribute allows us to load more active ingredient on to the seed than otherwise, so that it reduces the effect of take-all and controls some seed-borne diseases and the main foliar ones too," he says. "Other conazoles may have a similar disease spectrum but you cannot get enough chemical on for them be any good for that purpose."

Banishes bunt

Mr Cottey maintains fluquinconazole is very active against bunt and also offers some fusarium control. It is also particularly active against Septoria tritici and quite effective against the rusts. Although mildew control will not appear on the label, early attacks of the disease are checked by the dressing, he maintains.

The products take-all suppression is said to surpass that of any fungicide yet available, particularly during the pathogens most active stage in the autumn. This means that where early drilled second or third wheat would have been badly hit by the disease, the dressing will significantly reduce the symptoms.

"On the worst take-all sites fluquinconazole has given yield responses of up to 40%. But its difficult to say how much of that was due to the suppression of take-all," says Mr Cottey. "The average yield increase has been around 10% or 0.75-1.0t/ha – more or less what youd expect from the first foliar spray."

Thanks to the products take-all activity he foresees it making longer runs of wheat more viable or allowing second and third wheats to be drilled earlier with reduced yield loss.

Cost of the dressing, which will be based on its economic value to growers, has not yet been decided. But it will be significantly above that of basic dressings.

The same applies to MON 65500 from the completely new hindered silylamide (HSA) group. It has unusually specific activity, more or less confined to take-all, and will be registered for both wheat and barley.

Monsanto trials show its activity against take-all is consistently better than fluquinconazoles, maintains technical manager David Leaper. Its control of the disease, estimated to cost wheat and barley growers some £60m/yr, drops from about 70% early in the season to 45% by the grain-fill period as the active ingredient degrades.

The £60m estimate is based on the typical yield reduction of about 1.2t/ha (0.5t/acre) between first and second wheats and the continued decline up to the fourth wheat. Although the yield stabilises in longer runs, possibly due to the build up of antagonistic organisms, the disease continues to take a toll, says Mr Leaper.

"Growers go for as high a proportion of first wheat as possible, largely to minimise take-alls impact. Last year second wheat was quite badly hit as was wheat after set-aside and grass. But it wasnt as bad as it could have been because generally the crop had adequate moisture."

Continuous wheat

He believes MON65500s use will encourage production of an extra one or two wheats before a break. It will also improve the profitability of continuous wheat, although he does not advocate its use for that purpose.

The dressing will also help overcome logistical difficulties faced by farmers growing more wheat under Agenda 2000. And it should allow growers to reduce nitrogen inputs for second and third wheats without yield loss, he says.

Monsanto has six long-term trials assessing take-all decline in wheat and how this is affected by the dressing.

Among the main claims made by RPA for triticonazole are its considerable crop safety, and, unlike most other conazoles, no growth regulator effect. Its spectrum includes all seed-borne diseases of wheat and barley apart from fusarium, as well as yellow and brown rust, Septoria tritici and mildew on wheat, and brown rust, rhynchosporium, and net blotch on barley.

"We expect it to be very competitive with Baytan because it has proved more persistent in our trials, controlling rusts until May or June," says product manager Tim Holt. "Its activity against septoria and mildew lasts until the T1 timing which might enable growers to delay that spray." &#42

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