Flood damage on banana farms in north Queensland — Australia's largest growing area — is expected to lead to reduced supply and a rise in prices.

The full extent of crop losses will not be known until later this week, but farmers who have been able to inspect their plantations estimate tens of thousands of trees will have to be cut down.

More than a metre of rain has fallen in some areas of north Queensland over the past week, leading to major rivers between Cardwell and Cairns bursting their banks and the worst flooding of surrounding farmland in 20 years.

Tully Valley banana grower Leon Collins estimated he had lost a quarter of his crop, because it had been submerged for too long.

"It is severe, we've had whole bunches submerged in the flood, whole trees underwater, only the tips of the leaves poking out," he said.

"After 48 hours of water being in a paddock you start to get major loss and some of them have definitely had more than that.

"It won't be a pretty sight over the next week around the farms in Tully, in the valley where you can see these bunches of trees chopped down."

North Queensland supplies 95 per cent of Australia's bananas, with most of that coming from the flood-affected Cassowary Coast.

Mr Collins said the damage was guaranteed to push up prices.

"I'd say next month there'll be fewer bananas on the market," he said.

"Prices are going to have to move upwards."

Growers have also been worried about the water spreading Panama Tropical Race Four disease.

In the Tully Valley, there have already been three cases of the soil-borne fungus and flooding is a known vector.

Ongoing monitoring will aim to determine any new outbreaks.

"It's always a concern. Flooding is water movement which can't be contained, but that's just something we've got to live with and keep the monitoring process up and keep doing what we've been doing," Mr Collins said.

Cane crops flattened

The floodwaters have dumped debris on cane fields in the Ingham region. ( Supplied: Lawrence Di Bella )

Further south, in the Ingham region, where 90 per cent of homes have been flooded or damaged, sugar cane farms have also been swamped.

Lawrence Di Bella, who has a farm on the Herbert River, said the flooding on his property was higher than the 2009 flood.

"The water actually breached in places I haven't seen it breach over our river banks," Mr Di Bella said.

"We can see debris like logs and oil drums that have floated into paddocks."

There are reports of extensive damage to cane rail networks from Ingham to Babinda. ( Supplied: Lawrence Di Bella )

The floodwater has flattened cane crops, washed away top soil, and damaged cane rail infrastructure.

"There are bridges and train lines that are sitting up without the ballast and drainage pipes underneath them," Mr Di Bella said.

"I've seen a block where the pipes actually washed out and are actually sitting in a cane paddock next to the train track and all the ballast is now sitting in the cane paddock."

Sugar cane has been inundated for more than three days, which will affect yields come harvest time. ( ABC Rural: Renee Cluff )

He said the crop itself is hardy and most of it should recover, but quality will be affected.

"Looking at previous history there have been yield decreases because of water logging," Mr Di Bella said.

"Having a cane crop sitting in water for long periods of time isn't good."

For now, the farmers are getting on with the tough and messy job of cleaning up in a display of resilience north Queenslanders are famous for.