Gardeners who enjoy planting impatiens may have to find an alternative for a few years, according to the Ministry of Agriculture and Food.
A fungus called downy mildew is attacking impatiens this summer. People who have the plants in their gardens may have noticed the leaves are falling off.
Greenhouse floriculture specialist Wayne Brown said the fungus attacks most common types of impatiens.
Brown said the sale of impatiens plants make up approximately 30 per cent of the flower industry – gardeners love them because of the variety in colours when they flower.
"Downy mildew is a fungus that attacks the foliage of some impatiens plants," said Brown, who points out that leaf loss – which looks like an animal may have eaten them away – causes the plant to die.
Brown is quick to point out that some varieties of impatiens, such as the New Guinea or Sun Impatiens are not susceptible, but the most commonly used plants are.
"It’s one of those things for most gardeners and even commercial growers, that when it first showed up a few years ago in this region that goes unnoticed because little is seen initially," he said. "It may look discoloured at first but suddenly you’ll notice a mass breakdown of the plant structure."
"Last year it was seen in low levels, but because we had a hot dry summer when people saw their plants didn’t look well in August, they thought it was because they didn’t water enough and the hot humid weather was too much for the impatiens," said Brown.
The fungus has shown up sporadically since early 2000 in isolated areas of the U.S. but has been widespread in Europe since 2003 – It’s all over Ontario this year, according to Brown.
"Nobody really knows for sure where it comes from," Brown said. "It started in Europe … it’s pretty much worldwide now."
Brown says our wet weather this summer helped the fungus thrive – it likes a cool damp environment.
Downy mildew can devastate the flower industry in Ontario because gardeners won't be able to plant them for up to five years, according to Brown.
"The fungus has developed survival techniques. It develops resting spores in the plant tissue which remains in the soil waiting for another impatiens plant. So if you plant it, the fungi will come back," he said.
He went on to say that moving the plants to fresh soil in a different location can’t guarantee they will survive because the spores are airborne.
Brown says breeders are working frantically to try and develop a new line of impatiens that's resistant to the fungus.