After up to 90 millimetres of rain on Sunday, northern Victorian wine growers were spraying crops yesterday against downy and powdery mildew, which took a heavy toll last year, The Australian Financial Review reports.

But some who grow chardonnay grapes for sparkling wines are in the 30-day window before harvest when they are prohibited from spraying, leaving their crops vulnerable during this unusually wet summer.

Murray Valley Wine Grape Growers chairman Dennis Mills said mildew had been devastating last year after years of drought and a glut, but prices were promising this year. The rain and humidity could change that.

"If the weather continues like this, the danger gets bigger as the crop approaches maturity. And there's more rain forecast," Mr Mills said.