AS TEMPERATURES soar around the state, growers are frantically irrigating to keep up.

Many vegetable farms have reported having to double their irrigation in the past few weeks as the heatwave continues.

AusVeg spokesman Hugh Gurney said "winter" vegetables such as cauliflower and pumpkin could experience a glut.

"The heat will cause them to ripen early, meaning more on the market, and consumers are less likely to buy them because they prefer salad to cooked vegetables when it's hot," he said.

"This will lead to lower margins for growers during this time."

He said while warm weather - 30C-35C - was optimal for lettuce, it started to burn when the mercury hit 40C.

"Tomatoes from up around Shepparton will also suffer as they ripen quickly and go soft," Mr Gurney said.

Murray Valley Citrus development officer Mary Cannard said there was about a 5 per cent loss in citrus production due to the heat.

"There's a fair bit of sunburn out there on the trees," she said. "It's been a bit more than what we would have expected, but it won't cause supply issues.

"As long as growers are keeping water up to their crops to compensate for what's been lost in the heatwave, they should come through all right with minimal damage. There's no water issues this year so it shouldn't be a problem."

Murray Valley Winegrowers chief executive Mark McKenzie said there had been reports of sunburned grapes, but losses were unlikely to be more than 5 per cent.

Australian Table Grape Association chief executive Jeff Scott said the heatwave hadn't affected production and growers were expecting a good season amid increasing export demand.

"Growers are expecting a huge increase in mainland China exports this year, about 200-300 containers, up from 11 last year," he said.

"We're also hoping to send containers across to Vietnam, Indonesia, Malaysia, Korea and The Philippines. Many growers have made additional plantings and even the smaller growers hope to export up to 150 containers each to Asia."