GRAIN growers in western Victoria and the Riverina face further heartbreak with recent soaking rain dampening hopes of a bumper harvest.

More than 63mm of rain was recorded at Mildura in the past fortnight, three times the November average, while Horsham recorded 61mm, twice its average.

The unseasonably heavy rain followed a topsy-turvy season marked by poor world grain prices.

The rain has delayed the harvest by up to a week in some places and farmers fear their wheat could be downgraded from milling quality to feed, leading to a discount of about $50 a tonne.

GrainCorp manager of corporate affairs David Ginns said there were already reports of wheat starting to shoot in the Riverina.

"It's heartbreaking for people who were going to get a good harvest before the rain," Mr Ginns said.

Albury agronomist John Sykes said falls in some areas had reached 70mm, which would "totally destroy quality".

"Almost all of the canola and barley was off but just 20-30 per cent of the wheat crops had been harvested," he said.

"It's not so much the amount of rain but the duration that has caused the damage.

"And the frustrating thing is that we only needed another week to get most of the wheat off."

Mr Sykes said the rain would cause wheat protein levels and test weights to drop and there was also the risk of the grain becoming shot and sprung.

"We had a dry October and a wet November, but we wanted it the other way round," he said.

Further west at Deniliquin, farmers have not been able to get back on their paddocks, after about 50mm of rain fell over the past 10 days.

Investment and Industries NSW district agronomist John Fowler said the rain-affected harvest added to a cereal-growing season that was "not much fun".

"We were having an ordinary season anyway, and the rain has just made it more ordinary," Mr Fowler said.

Fellow Deniliquin agronomist Ross Newton said farmers were frustrated that they could not harvest their crops and it would be mid-week before they could get back into their paddocks.

"A few of our clients have had 80mm in the past week or so and just 150mm from May to October and a wet harvest has just topped off the year nicely," he said.

Further north, the rain came too late to do too much damage.

Griffith agronomist Rachael Whitworth said 25-50mm in the past 10 days had delayed some of the last crops to be stripped, but most dryland and irrigated cereals had been harvested.

In the Goulburn Valley and the North East, heavy rain destroyed some canola crops, with more than 60mm falling at Benalla and Shepparton.

Murchison East silo committee president Brian Burke said any canola not delivered into the silo before the rain was destroyed.

"We had 50 points (12mm) in three minutes and it created havoc with the canola," he said.

"Wheat will be downgraded to feed because it's shot and sprung. It's a bit of a sad story."

Department of Primary Industries'  Wimmera grains project manager Chris Sounness said most pulse crops had been shedding pods due to their brittleness and unharvested barley could start to show signs of stain.

He said the rain could affect hay that had not been baled or stacked.

Murtoa grain grower Wayne Adler said while the rain would not affect yield, malting-grade barley might be downgraded to feed.

He said 46mm of rain in four days had halted the harvest.

Lake Bolac farmer and Southern Farming Systems Streatham branch chairman, Neil Vallance, said he expected a one to two tonnes/ha wheat loss from the heat, but said the rain would help the grain fill.

"It would have been a perfect season if the rain and the hot temperatures had have been reversed," Mr Vallance said.

SFS agronomist Rohan Wardle said if all the cereals were feed-grain quality, people "won't know where to put it all".

"They might be putting it on the ground at home and putting a tarp over it," he said.

David Cook, who farms at Pine Lodge South near Shepparton, said the worst of the storms missed his farm.

He said crops further south had been flattened and silos tipped over.

Mallee Sustainable Farming agronomist Michael Moodie said there had been reports of isolated damage south of Swan Hill.

"Wheat is the biggest concern, but we won't know until people get back on the paddocks," he said.

Murrayville farmer Matt Parker said while some grain had already shot, other crops would be fine.