Home gardeners on Prince Edward Island are being warned to watch their plots for signs of late blight as a warm, humid summer stretches on.
Late blight is a disease that disfigures and destroys solanaceous (or nightshade) crops like tomatoes, potatoes, peppers and eggplants. A fungus-like micro-organism called Phytophthora infestans causes brown spots on the leaves or the fruit itself, eventually leading them to rot.
This type of blight was the primary cause of the Irish Potato Famine, leading to mass death and emigration out of Ireland from 1845–1852 as the country's main subsistence crop rotted in the fields.
"We've had a lot more moisture this year and a lot more humidity," said Agriculture and Agri-Food Canada research scientist Rick Peters. "The conditions are much more conducive to the development of late blight in both potatoes and tomatoes in a year like we're having."
The commercial potato industry monitors and sprays against late blight, but Peters said home gardens are not watched nearly as closely.
"We are having some outbreaks in Ontario and Quebec in Central Canada. There's a concern that some of those spores could travel to us," Peters said, adding that spores have been known to travel through the air over long distances as weather systems move east.
Rick Peters, a research scientist with Agriculture and Agri-Food Canada, says Islanders who believe they have blight in their home gardens should send a sample to the provincial plant diagnostic lab and dispose of the rest of the plant in their waste bin, not their compost bin. (Nicola MacLeod/CBC)
"The movement of tomato transplants that are affected has been an issue in recent years," he added
Industry concerned, needs things to dry out
The P.E.I. Potato Board is also worried about blight this year.
General manager Greg Donald said there hasn't been a case on P.E.I. for about 10 years, and they would like it to stay that way.
"It would make it very hard to grow healthy tubers, and ultimately affect yield and quality of potato crop," he said.
"It can spread really easily with spores wind blown — and if it takes hold, it can do a lot of damage and have a severe impact."
Early warning programs
Many farmers participate in spore collection programs, which serves as an early warning sign that the spores are in the atmosphere before they've had a chance to infect plants.
Donald said blight is just another things potato farmers have had to worry about this year. In past years, the industry has had to content with droughts brought on by low rainfall and high heat.
Potato Board general manager Greg Donald says there has not been a case of late blight on P.E.I. for about 10 years, and he'd like to keep it that way. (Nicola MacLeod/CBC)
This year, the excess rain has been good for getting the crop started, but Donald said they need dry weather and sun to finish out the season.
"We're in that critical phase where the tubers are developing and sizing up. So, size, quality — external, internal quality — is really important," he said.
"To this point we've been growing healthy tops but we need some dry weather for tubers."
'Very difficult to control'
Peters said home gardeners can help keep the disease from spreading by looking out for the signs of blight in their backyard gardens, and sending any suspected samples to the provincial plant diagnostic lab to have it identified.
This potato infected with late blight would not be harmful if eaten, but the disease can disfigure crops and reduce the yield — something the commercial industry would like to prevent. (Submitted by Agriculture and Agri-Food Canada)
Infected plants should be cut off at the soil line, bagged, and disposed of in waste, avoiding compost piles where it could continue to spore and spread.
"The fruit can also get this kind of reddy rusty lesion on it, and they quickly melt the plants down, so you'd notice it moving very rapidly," Peters said.
Because the spores spread through the air and travel long distances, late blight is not a disease where a quarantine would be effective, he said.
Many farmers participate in spore collection programs using devices like this one. They can serve as an early warning sign that the spores are in the atmosphere before they’ve infected plants. (Nicola MacLeod/CBC)
"Once it gets started, it's very difficult to control," Peters said.
Both Peters and Donald suggested gardeners also look into blight-resistant varieties of tomatoes for future growing seasons.
Blight-resistant potatoes are still in the development process.