Canker Identification and Canker Management Apply to Landscape Trees

Summary: Canker identification and canker management apply to landscape trees with damaged bark and phloem, ghostly foliage and weakened branches.

symptoms of perennial target canker (Neonectra sp.) on birch: Robert L. Anderson, USDA Forest Service, Bugwood.org, CC BY 3.0 United States, via Forestry Images

Canker identification and canker management apply to landscape trees whose bark, branches, foliage and phloem a bacterial or fungal pathogen attacks, according to the April 2020 issue of Arboriculture & Urban Forestry.

Marion Murray bases baring causes, blocking further spreads and building the best management programs by beginning with broaching whether abiotic or pathogenic factors bring about bark damage. The Utah State University Professional Practice Extension Associate characterizes cankers' dead brown-white to black inner bark, discolored outer bark and phloem and elongated or oval expansion. She describes cracking, flaking, ridged, splitting, sunken, thick bark around bulls-eye-appearing callus regrowth, dead twigs and pruning cuts; dark, raised, small fruiting bodies; oozing, pitching centers and margins.

Drought stress, flat-headed borer larval feeding, frost cracks, lightning strikes, mammal damage, slime flux, sunscald, vehicular damage and weed trimmers entertain canker-lookalike, albeit abiotically-factored, bark damage.

Sugar maple, walnut, yellow poplar Fusarium cankers, unlike perennial diffuse and target cankers, annually flourish until felled by natural tree defenses or as one-season pathogenic life-cycle fatalities.

Slow-growing fungal pathogens generate perennial target cankers by growing when landscape trees go dormant from fall through late winter and thereby get cankered, failure-prone, weakened branches. Eutypella parasitica, Neonectria ditissima and Strumella coryneoidea target cankers respectively harry Norway, red, sugar maple; birch, oak, sugar maple, walnut; black oak, red oak, shagbark hickory. Aggressive pathogens initiate diffuse, fungal-caused ash, maple, poplar, spruce, stone fruit, willow (Cytospora) cankers; aspen, oak, poplar (Hypoxylon) cankers; and cherry, dogwood, redbud, rhododendron (Botryosphaeria) cankers.

Canker identification and canker management of landscape trees join classic fungal-caused chestnut blight (Cryphonectria parasitica) with bacterial-caused fire blight (Erwinia amylovora) into perennial diffuse canker classifications.

Bark openings naturally as lenticels or injuriously as wounds and optimum weather for non-actively invasive, opportunistic inoculum, as fungal spores or oozing bacteria, kindle canker infections.

Preventive tree care practices lead away from canker-friendly drought stress, nutrient deficiencies and weather conditions through proper siting, mulching, irrigating, feeding, pruning, soils and winter protection. They mandate no cold-season, late-season fertilizer applications; commercial tree-wound dressings and paints; crossing or rubbing branches; dormant, flush, low-temperature, stub or wet-weather cuts; or nutrient deficiencies. Cold-climate, newly-planted, thin-barked landscape trees need early-winter, early-spring trunks white-painted with latex diluted to 50 percent in water, or white-wrapped, against freezing, thawing sunscald southwest injuries.

Canker identification and canker management of landscape trees observe 4-inch (10.16-centimeter) to 8-inch (20.32-centimeter) and 12-plus-inch (30.48-plus-centimeter) pruning beyond fungal and bacterial-cankered edges into healthy tissues.

Tools sanitized, between spring and summer growing-season cuts, by bleach wipes or dips of 10 percent bleach or 70 percent alcohol prune limb, not trunk, cankers.

Bark tracing by knives sterilized between cuts quits main trunks of cankered bark and phloem on small, young cankers not large, old, xylem vascular tissue-compromised cankers. Rare canker repressants range from chemicals for Kahatina-infected and Phomopsis-infected succulent shoots to post-pruning, wound-protective direct and foliar fungal sprays for agricultural-crop rather than landscape trees. Phosphite fungicides strengthen cell-wall thickness and lignin and secondary-metabolite production against Phytophthora and Pseudomonas syringae bleeding cankers on beech and maple and on birch and horsechestnut.

Canker identification and canker management through copper treatments tether spreads of, without terminating, bacteria-triggered cankers such as fire blight's Erwinia amylovora and stone fruit's Pseudomonas syringae.

Hypoxylon canker (Hypoxylon mammatum) on trunk of an aspen (Populus tremuloides) displays the disease's characteristically mottled, black-and-white checkerboarding of the tree's bark: William Jacobi, Colorado State University, Bugwood.org, CC BY 3.0 United States, via Forestry Images

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

symptoms of perennial target canker (Neonectra sp.) on birch: Robert L. Anderson, USDA Forest Service, Bugwood.org, CC BY 3.0 United States, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=3037024

Hypoxylon canker (Hypoxylon mammatum) on trunk of an aspen (Populus tremuloides) displays the disease's characteristically mottled, black-and-white checkerboarding of the tree's bark: William Jacobi, Colorado State University, Bugwood.org, CC BY 3.0 United States, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=5366677

For further information:

Gilman, Ed. 2011. An Illustrated Guide to Pruning. Third Edition. Boston MA: Cengage.

Hayes, Ed. 2001. Evaluating Tree Defects. Revised, Special Edition. Rochester MN: Safe Trees.

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