Petal fall OSR disease warning

WATCH OUT for alternaria and sclerotinia infections in oilseed rape this season, The Arable Group‘s Andrew Wells has warned.

The growing trend for one oilseed rape crop in two or three years is increasing sclerotinia pressure, he said. “There are not many low risk crops now in England.”

The last really bad year for the disease was in 1991 and since then agronomists have become very risk averse, he said.

Growers should also be alert to alternaria risk, he added. “It hasn‘t been a major problem since the 80s mainly because growers have been using autumn and early spring fungicides, which damp down alternaria infection.”

The trend towards low biomass varieties, which reduce lodging, lessening infection on pods, has also helped, he said.

But there was quite a bit of late season alternaria in 2004, particularly on spring oilseed rape, and growers need to watch out for it in 2005, Mr Wells warned.

Unfortunately fungicide timing for each disease is slightly different, he said, adding that the decision is normally guided by sclerotinia control.

“Control is much more effective going early flowering rather than late, but rates need to be kept up to get enough persistence through the flowering period.”

But optimum alternaria timing is late flowering, he said.

This year, strobilurin fungicide Amistar (azoxystrobin), once approval is granted, will be an option to consider for controlling both diseases, he suggested.

“It will fit with a lot of growers, since they already are likely to have it in the shed for other crops.”