The weekend's wild weather may have surprised Perth's northern suburbs hard but WA farmers have been hit harder - with an estimated five per cent yield loss around the state.

WA Farmers Federation senior vice president Tony York said grain losses on some farms could be as high as 20 per cent.

He said the loss would be particularly hard to swallow at a stage when, just before harvest, the money from the damaged grain would have effectively been "in the bank".

Mr York said Condingup, Dumbleyung and Lake Grace had been hit the hardest and although some farms had escaped unscathed, the loss across the board for WA farmers could be as high as five per cent.

"It was patchy rain over the weekend but in the places it hit, it hit relatively hard and there are going to be issues with waterlogging and degradation of quality," he said.

"Some of the crop in the south was still green so the damage isn't too bad, but where the crop has ripened off, it's definitely affected the grain quality. Malting barley is now going to be feed barley, some of the premium wheats will be downgraded."

"There are isolated patches where there has been hail damage.

"Across the state it will be less, about five per cent in loss of value across the whole grain crop. It's not what you want at this time of year, because you're almost at the stage where that money is in the bank.

"That's the risk that comes with farming though, it's just a really unfortunate situation. Some farmers will have devastating losses, some will see this as a minor inconvenience...it's a really mixed bag."

Source - http://www.watoday.com.au/