The Ontario fire blight prediction maps have been updated for June 6 – 11, 2020. With the warm weather expected to continue into the weekend and early next week, the conditions are optimal for fire blight infection. Forecasted rain in many regions this weekend can wash the bacteria into the blossom which begins the infection process.
Regions that are at petal fall or fruit set should be diligent and monitor their orchards closely for new plantings that may still be blooming or for secondary, or “rat tail” blossoms. There have been a number of reports of fairly substantial rat tail bloom in some varieties such as Ambrosia, Gala, Empire, Cortland and Crimson Crisp. Take necessary action to remove or protect open blossoms from infection. Keep in mind, the antibiotics (Streptomycin, Kasumin) provide control for only 2-3 days prior to a rain event. So for extended infection periods, a subsequent spray may be needed. Be mindful of preharvest intervals when using these products.
However if time and labour are available, it may be best to go through the orchard and remove the rat tail blooms altogether since the fruit produced by the late blossoms are more of a risk than they are an asset.
According to Dr. George Sundin from Michigan State University, temperatures conducive for growth can result in fire blight populations multiplying to one million cells per flower within 1-2 days. Imagine how quickly pollinators could spread infection around an orchard with bacterial populations like that, even if there are just a few blooms!
Soon you will see if the fruits (pun intended) of your labour paid off or if fire blight symptoms develop. Scout your orchard for wilting flower clusters and strikes, or the characteristic “shepherd’s crook” every week until terminal bud set.