CNGA LooseLeaf June/July 2019

19 colorad o nga.org LooseLeaf June/July 2019 plants, cankered tissue should be removed in winter months, when the pathogen is not active, and then destroyed. When removing a cankered branch, find the lowest part of the canker, trace the branch to its point of attachment, and cut at the next branch juncture. In the case of large cankers on trunks, scrape down the bark around the canker to the cambium. Pay attention to wood color as it can be an indicator of infection. Wood directly underneath a canker is usually dead and turns a red color further out, eventually becoming red flecks. Beyond that, the tissue is healthy. Fire blight is difficult to manage but not hopeless in most years. Management should focus on environment and host modifications as a means of reducing disease pressure. Cultural practices combined with mechanical strategies can help, but in some years (like 2018), almost nothing seems to help. Fire blight prefers succulent growth; therefore, avoid actions that encourage new, vigorous growth, such as excessive nitrogen fertilization, high soil moisture, and aggressive pruning. Typical fire blight canker on pear. Note the darkened, sunken, water-soaked appearance. Pear fruitlet infected the previous year often turn black and remain attached to branches. About the contributor: Jill Calabro manages all things science-y for AmericanHort and the Horticultural Research Institute (HRI), including HRI’s annual grants program. She also promotes HRI-supported research results and dabbles in regulatory advocacy to help ensure success of the green industry.