Strobs on rapeseed hold promise in sclerotinia and alternaria control

USING THE strobilurin fungicide Amistar (azoxystrobin) to control sclerotinia and alternaria in oilseed rape will help growers achieve yields closer to the crop”s ultimate yield potential of over 5t/ha, according to Syngenta”s technical manager Beth Hall.

“Average oilseed rape yields nationally are just over 3t/ha, but the biological potential is much higher, maybe as much as 7t/ha. Everyone agrees we”re not making the most of the crop”s potential.”

But she believes the imminent approval of Amistar, expected from the Pesticides Safety Directorate in February, will be a useful tool for growers to begin building that yield.

Yield increases from using Amistar to control sclerotinia have been consistently around 0.4t/ha in trials across Europe, matching the current standard Filan (boscalid), she reports. “That”s worth over 50/ha.”

Alternaria will also be on the Amistar label with similar yield responses of 0.4t/ha. Amistar will also control botrytis and appears to have some physiological effects. “Even in low disease situations Amistar has delivered extra yield. The physiological benefits of green leaf retention, seen in other brassica crops, are being investigated in oilseed rape.”

Optimum timing for Amistar to control sclerotinia and alternaria are different, Mrs Hall notes. “Growers will have to make decisions about disease and when to spray. Usually sclerotinia will drive the decision.”

Targeting sclerotinia means spraying early to mid-flowering, says The Arable Group agronomist Andrew Wells. “The key is coating petals with fungicide, and it”s much more effective going early rather than late flowering, as [with the latter] petals will already have fallen, which could cause stem infection.”

Early flowering sprays do have some effect on alternaria, says Mrs Hall. “But for high-risk alternaria infections, more will come from a late flowering spray,” he says.

To minimise the risk of resistance developing Syngenta suggests Amistar be tank-mixed with a partner product, such as MBC or a triazole. But, unlike cereals, it can be used as a straight in oilseed rape. “If it”s used alone it should be at the full recommended 1 litre/ha dose.”