It's pot growing season in rural Ontario.

One grain farmer, who also owns a pesticide spraying company servicing farms, estimates five per cent of the province's corn fields have pot illegally growing in them.

"There’s definitely more. It used to be a novelty if you found it. Now, you almost expect to find it in a good chunk of the fields," said Bruce Court, who farms near Tillsonburg, Ont.

'You expect to find [pot] in a good chunk of the fields.'— Farmer Bruce Court

Court tweeted a photo of a marijuana plant he found in one of his fields this week.

"I'm finding a lot of this in fields this year," he tweeted.

He went on to say farmers find "thousands" of pot plants in Ontario every year.

Belle River corn and soybean grower Leo Guilbeault, who lives outside Windsor, Ont., said he usually discovers an empty section in his field at harvest and knows marijuana had been transplanted there.

"Right now, the corn is about knee high, we're done doing what we need to do in the field. We don't come back to fertilize anymore, we don't come back to spray anymore. So really, if they go in 100 feet into the field —[and] we have seven corn fields so we don't walk every square feet of our field every day — the chances of us finding it until we get in at harvest time is pretty minimal," Guilbeault said.

Guilbeault said most of the marijuana is found in fall. But he found some already this spring.

"You find marijuana in corn fields pretty much every year. It's pretty common around the county. Everybody runs across it," Guilbeault said. "They spot a corn field and the entrepreneurs come in and do their thing."

Guilbeault said farmers have been dealing with this issue for years. He calls police when he discovers the plants.

Good cover and 'pre-fertilized fields'

Guilbeault said pot growers usually use corn for canopy and cover.

"Corn grows six or seven feet tall so it hides the marijuana plant pretty good," Guilbeault said. "Typically what they'll do is they'll go into the field about a hundred feet or so and take out a row of corn, transplant their plants in there and it just gets hidden in between two corn rows and they're good to go until harvest."

Guilbeault said the soil even comes "pre-fertilized."

"But the main idea is to hide it from authorities," he said. "They scout around and look for isolated fields."

Guilbeault said he's never caught anyone planting pot.

"They're pretty smart," he said.

But they are also brazen, Court said.

"They’re getting to be more and more brave about where they put it. It used to be fairly well hidden. They used to hide where they put it," Court said. "But there’s not a lot of effort put into keeping it disguised."

Nor is there effort put into preventing the problem, Court said.

Pot costs farmers money

"You see police now and again, but there’s so much of it. It’s probably not the best use of their resources," Court said.

He said pot costs him money — only about $100 when the pot is first planted and smaller corn stalks are ripped out.

The real problem, he said, is those who didn't plant the pot but are looking for it anyway.

"That’s where most of the damage comes. They zig-zag around a field when the corn is 10 feet tall. It’s really hard on our corn. It’s ruined where they drive," Court said.

Those scavenging for the pot could cost a farmer $5,000 worth of crops "fairly fast," Court said.

Court estimates the biggest pot plantation he has come across would have been worth $20,000 on the street.

He no longer calls police when he finds the weed. He simply sprays it with Round Up.

"It will die within a matter of days," Court said.