14 March 1996

Early spray call for wheat men

AN earlier-than-usual first wheat fungicide spray may be needed in many areas this season.

The late emergence of many crops last autumn, coupled with the cold January, makes plants appear less advanced than they actually are, Bill Clark, ADAS national cereal pathologist, told an ISK Biosciences seminar on Monday .

Such crops try to make up lost time by telescoping their development. But while leaves may emerge faster, nodal development, governed by temperature, lags.

So leaf three emergence, which usually occurs at GS32 (second node detectable), can often happen at GS31 (first node detectable).

That happened last year. "Many people sprayed crops at GS31/32 when leaf three and all the other leaves below it were already infected, and had been infected for so long that no spray could have any effect," he says.

Fortunately, ensuing dry weather stopped a disease epidemic. "In a more normal year, it could have been a disaster."

Growers should check leaf number before GS31, by using an adviser with dissection skills.

Alternatively, an insurance mix of at least half-rate triazole and chlorothalonil (eg Bravo) can be applied at GS31. The former eradicates established disease, and the latter will protect new growth.

, he explains.