Fruit & Vegetable Magazine

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Fire blight risk increases in Ontario with rising temperatures

May 22, 2024  By ONFruit

According to OMAFRA’s apple specialists, it’s time to be on the lookout for fire blight in your apples, especially if there were infections in your orchard or the surrounding area last year. While the cooler average daily temperatures of early May meant the risk of fire blight was lower, the ONFruit fire blight prediction maps show that the risk level has risen over the past two weeks. Most areas where fire blight was found in the neighbourhood are showing a risk level of “caution” (second lowest level out of four), whereas farms where fire blight was found in 2023 are showing risk levels of mainly “high,” with some “caution” and some “extreme.”

Fire blight bacteria multiply rapidly in a very short period of time when temperatures are above 18 C and relative humidity above 90 per cent. Bacteria can be transferred to new blooms by rain, wind or insect. Bees and other pollinators can easily spread the bacteria around.

Susceptibility to fire blight decreases as the blossom ages and the calyx begins to close, so blossom blight risk ends following petal fall. The staggered bloom that some growers are seeing this year within blocks will extend the risk until the last blossom falls.


However, in areas of the province that are seeing petal fall, growers should be aware of delayed bloom, particularly in young trees, or rat-tail bloom. Protecting these open blossoms from infection will be critical during times of high risk. |READ MORE


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