31 May 1996

Winter rape sprays can pay in north

EARLY petal fall fungicide sprays on winter rape are nearly always rewarding in the north and could be even more so this season.

So says Dr Keith Dawson, technical manager of Perth-based CSC Cropcare after five years of trials at five sites in Scotland and Northern England.

On average it needed only an extra 0.22t/ha (1.75cwt/acre) to cover the chemical and application costs. But the mean response was 0.3-0.5t/ha (2.4-4cwt/acre). And in bad sclerotinia years responses have been over 2.5t/ha (1t/acre), he notes.

The higher yields of the sprayed plots came from a combination of good disease control and reduced seed losses at harvest, he explains. "This happens because the treatments tend to make the pods more rubbery and less prone to shattering."

Northern rape crops tend to branch a lot leading to a microclimate which particularly favours sclerotinia and light leaf spot, he adds.

May is often showery, which encourages sclerotia germination and the spread of spores that land on petals lodging in leaf axils to infect the plants. "This year the risk is even higher. We have been sopping wet up here."

80% of northern crops normally get sprayed at this timing, he estimates. "But people tend to forget and they are always looking to reduce costs." Missed opportunities this season could be regretted, he suggests. "The higher rapeseed price this year means you probably need only 0.2t/ha to recoup the cost."

Two-day kickback

Launched last year, BASFs Konker (carbendazim + vinclozolin) has proved an "excellent product", its contact and systemic activity giving a two-day kickback where sclerotinia has already occurred, he explains. It also protects against late season light leaf spot and suppresses botrytis and alternaria, he adds.

"Early petal fall is the best fungicide spray timing for most diseases, particularly sclerotinia," he says.

The chemical coats the petals so that when they stick to the plants it forms a barrier between the cuticle and the spores.