Weeping cherries are prized for their cascading branches, and most of their problems come from a short list of diseases, insects, soil conditions and the way the tree is built. Many of those problems get in through an injury, such as a pruning cut, a frost crack or a nick from a string trimmer, so how you treat the tree matters as much as any spray.1Garden Dilemmas, Delights & Discoveries, Ask Mary Stone. When a Weeping Cherry “Bleeds”: What Lies Beneath A weeping cherry is usually two trees joined together, a weeping top grafted onto an upright trunk, and that explains one of its strangest habits.
Why Your Weeping Cherry Is Oozing Sap
Amber, sticky sap oozing from the bark is called gummosis, and trees don’t do it without a reason.2Garden Dilemmas, Delights & Discoveries, Ask Mary Stone. When a Weeping Cherry “Bleeds”: What Lies Beneath It can come from wood-boring insects, bacterial or fungal infections, or general stress and injury.3Ask Extension. Grafted Weeping Cherry oozing sap The causes are hard to tell apart because there is often little other outward sign until the problem is advanced.4Ask Extension. Grafted Weeping Cherry oozing sap
Start with a slow walk around the trunk, looking at eye level and then down at the ground, and note where each blob of sap sits. Press gently on the bark near the ooze. Soft, sunken or cracked bark points toward a canker, while sawdust piles at the soil line point toward borers.
To look for borers, watch for small holes with sawdust-like material being pushed out. That material is a mix of insect droppings and chewed wood. Check the trunk base, especially the first 6 to 8 inches above the ground, but also higher on the trunk and where large branches join it.5Extension Ask Extension. Ornamental Cherry Tree with Advanced Gummosis Infections tend to stain the wood a darker color under the bark rather than leaving tunnels.6Ask Extension. Grafted Weeping Cherry oozing sap If you find neither tunnels nor stained wood, poor soil conditions that killed some roots may be the cause.7Ask Extension. Grafted Weeping Cherry oozing sap
Call an arborist if the ooze wraps around most of the trunk, since the trunk may be girdled. A large patch of exposed, decaying wood makes the trunk more likely to snap at that spot in a storm.8Extension Ask Extension. Ornamental Cherry Tree with Advanced Gummosis9Extension Ask Extension. Ornamental Cherry Tree with Advanced Gummosis Decaying wood over a walkway, car or house is also worth a professional look. An arborist can cut into suspect bark to check for tunnels or staining you can’t see from outside.
Bacterial Canker and How to Stop It Spreading
A canker is a dead, sunken patch of bark, and in cherries one common cause is bacteria that live on the tree’s surface.10Pacific Northwest Pest Management Handbooks. Cherry (Prunus spp.)-Bacterial Canker They only cause disease once they get inside the tissue through an opening.11Pacific Northwest Pest Management Handbooks. Cherry (Prunus spp.)-Bacterial Canker They also make a protein that helps ice form on the tree, which worsens the frost wounds they then invade.12Pacific Northwest Pest Management Handbooks. Cherry (Prunus spp.)-Bacterial Canker Frost-damaged bark is one of the easiest ways in, and natural leaf scars in fall are another important entry point.13Pacific Northwest Pest Management Handbooks. Cherry (Prunus spp.)-Bacterial Canker
On your tree, look for a sunken, darker patch of bark, often with amber gum at its edge. Cankers often show up near pruning cuts, branch crotches or old frost cracks. Branches beyond a canker may leaf out poorly or wilt in spring.
Wounds, frost damage, pruning early in the dormant season, stub cuts, wrong soil pH and poor nutrition all make cankers more likely.14Pacific Northwest Pest Management Handbooks. Cherry (Prunus spp.)-Bacterial Canker Planting where frost is least likely to settle lowers the risk.15WSU Extension. Ornamental Cherry Bacterial canker
To treat it, prune out and destroy infected branches before wet fall weather begins.16WSU Extension. Ornamental Cherry Bacterial canker Cut well below the infected area and disinfect your tools between cuts so you don’t spread the bacteria.17WSU Extension. Ornamental Cherry Bacterial canker In practice, that means wiping or dipping the blades in rubbing alcohol or a household disinfectant after every cut into diseased wood, letting them dry a moment, and cleaning them again before they touch healthy trees. Burning out cankers with a propane torch has had some success.18WSU Extension. Ornamental Cherry Bacterial canker A severely infected tree is best removed.19WSU Extension. Ornamental Cherry Bacterial canker
Black Knot and Other Fungal Diseases
Black knot begins in autumn as light-brown swellings on young twigs that split as they grow.20The Morton Arboretum. Black knot | Symptoms, Life Cycle, Management | The Morton Arboretum The next spring the knots grow quickly and are covered in a velvety olive-green layer.21The Morton Arboretum. Black knot | Symptoms, Life Cycle, Management | The Morton Arboretum By fall they are hard, rough and black.22The Morton Arboretum. Black knot | Symptoms, Life Cycle, Management | The Morton Arboretum The knots slowly encircle the twig or branch and kill it, though this can take several years.23The Morton Arboretum. Black knot | Symptoms, Life Cycle, Management | The Morton Arboretum The fungus spreads from mature knots by wind and rain from early spring to early summer, mostly in wet weather between 55 and 77°F.24The Morton Arboretum. Black knot | Symptoms, Life Cycle, Management | The Morton Arboretum
A knot is elongated and lumpy along the twig, unlike a round bud, and it feels hard and crusty once mature. Neighboring wild cherries or plums with knots can keep reinfecting your tree.
Pruning is the main control, and it can cut infection by about 80%.25The Morton Arboretum. Black knot | Symptoms, Life Cycle, Management | The Morton Arboretum Remove all knots in late winter or early spring before new growth starts.26The Morton Arboretum. Black knot | Symptoms, Life Cycle, Management | The Morton Arboretum Cut at least 4 to 8 inches below each knot, because the fungus grows past its visible edge.27The Morton Arboretum. Black knot | Symptoms, Life Cycle, Management | The Morton Arboretum Bury, burn or compost the removed pieces so spores don’t spread.28The Morton Arboretum. Black knot | Symptoms, Life Cycle, Management | The Morton Arboretum
Brown rot can kill cherry blossoms when they stay wet during bloom.29Phytopathology. Influence of environment and inoculum density on the incidence of brown rot blossom blight of sour cherry Most blossoms become infected after about 10 hours of wet weather at mild temperatures.30Phytopathology. Influence of environment and inoculum density on the incidence of brown rot blossom blight of sour cherry
Powdery mildew shows as light, powdery patches on young leaves, which may twist, distort or turn pale.31Lawnstarter. 7 Common Cherry Tree Diseases and How to Treat Them It favors humid weather. Pruning to open up the canopy improves air flow and reduces leaf diseases.32University of Maryland Extension. Ornamental Cherry Trees: Identify and Manage Problems
Borers and Scale Insects
Borers are most likely in trees that are already stressed. Keep mulch no more than 2 to 3 inches deep and at least 6 inches away from the trunk, because mulch piled against the trunk invites borers, voles and trunk diseases.33Extension Ask Extension. Ornamental Cherry Tree with Advanced Gummosis
Scale insects are tiny, shell-covered insects that suck sap and weaken the tree.34Walter Reeves: The Georgia Gardener. Cherry tree heavily infested with scale insects To spot them, look for small bumps on twigs that scrape off with a fingernail. Sticky, shiny leaves or a black sooty coating below can signal sap-sucking insects. In winter, when the leaves are gone, check the undersides of branches and twig joints.
Horticultural oil, a refined oil spray that smothers insects, kills overwintering scales when sprayed in winter.35PubMed Central. Scale Insects on Shade Trees and Shrubs It doesn’t kill kinds that spend winter as eggs under the shell.36PubMed Central. Scale Insects on Shade Trees and Shrubs A schedule of sprays in early winter, late January and early April covers both.37Walter Reeves: The Georgia Gardener. Cherry tree heavily infested with scale insects The April spray catches young scales as they crawl out from under their mother’s cover.38Walter Reeves: The Georgia Gardener. Cherry tree heavily infested with scale insects Prune off and destroy heavily infested branches.39Hortsense. Ornamental Cherry: Scales
Follow the label rate for dormant versus growing season, and spray on a calm day above freezing so the oil coats evenly. Cover the bark thoroughly, since oil works only where it touches insects.
Small numbers of spider mites can be ignored, since predatory mites usually keep them in check.40Utah State University Extension. The Backyard Orchard – Cherry Pests Outbreaks often follow pesticide sprays that kill those predators.41Utah State University Extension. The Backyard Orchard – Cherry Pests
Upright Shoots and Grafting Problems
Upright growth is the trunk’s own tree growing up through the grafted weeping top.42Sprigs & Twigs. Common Weeping Cherry Tree Problems and How to Handle Them Left alone, these shoots can eventually choke out the grafted weeping part.43Tree Awareness. Weeping Cherry Rootstock Issue
To find the graft union, look for a swollen ring or change in bark near the top of the trunk where the weeping branches start. Anything sprouting below that line is rootstock, and its leaves may look slightly different from those on the weeping branches.
Cut shoots growing from the base and any growing straight up as soon as you see them.44Sprigs & Twigs. Common Weeping Cherry Tree Problems and How to Handle Them Cut them back to where they start, not partway.45Sprigs & Twigs. Common Weeping Cherry Tree Problems and How to Handle Them
Waiting costs you. Rootstock shoots grow faster and more vigorously than weeping branches, so over a few seasons they shade and starve the weeping top. Removing large shoots later also leaves bigger wounds that invite canker.
Yellow Leaves, Wet Soil and Root Rot
Iron chlorosis is a common shortage of usable iron in soils above pH 6.5.46Purdue Plant Doctor. Common Weeping Cherry Tree Problems and How to Handle Them Leaves turn pale green to yellow while the veins stay darker green.47Purdue Plant Doctor. Common Weeping Cherry Tree Problems and How to Handle Them On hot sunny days leaf edges may scorch and leaves drop early.48Purdue Plant Doctor. Common Weeping Cherry Tree Problems and How to Handle Them A manganese shortage can cause similar symptoms, so a soil test is needed to know for sure.49Purdue Plant Doctor. Common Weeping Cherry Tree Problems and How to Handle Them Very acidic soil also hurts, throwing off nutrient balance and killing young cherry rootstocks.50HortScience. Soil pH Affects Nutrient Balance in Cherry Rootstock Leaves
For a test, contact your local extension office for an inexpensive kit. Collect soil from several spots under the canopy, a few inches deep. The report gives pH and nutrient levels with recommendations, and it’s better to fix pH gradually, as recommended, than to guess with fertilizer.
Cherries in soil that stays saturated can develop root and collar rot, with weak growth and yellowing leaves.51PubMed. First Report of Root and Collar Rot by Phytophthora cryptogea on Sweet Cherry in Italy The inner bark at the base turns reddish brown.52PubMed. First Report of Root and Collar Rot by Phytophthora cryptogea on Sweet Cherry in Italy Flooding plus root rot organisms hurt ornamental cherries far more than either alone.53HortScience. Ornamental Cherry Tolerance of Flooding and Phytophthora Root Rot Good drainage is the best protection.
To check it, dig a hole nearby, fill it with water, and see if it drains within a day. Keep sprinklers from soaking the trunk area. Low spots where water pools are poor places for a weeping cherry.
Frost, Sunscald and Herbicide Damage
Young trees with thin bark can crack from winter sun on the south and southwest sides. Avoid planting susceptible trees with strong south-southwest exposure.54Home Garden Education Office. Frost Cracks and Sunscald on Trees Apply white tree wrap in fall before freezing weather, which reflects sun and keeps bark cooler.55Home Garden Education Office. Frost Cracks and Sunscald on Trees Remove it in spring once frosty nights end, because wrap left on keeps bark damp and can harbor pests and disease.56Home Garden Education Office. Frost Cracks and Sunscald on Trees Use wrap for 2 to 3 winters until the bark thickens.57Home Garden Education Office. Frost Cracks and Sunscald on Trees White latex exterior paint has protected young fruit trees from summer sunscald.58HortScience. Tree Trunk Applicators for Sunscald Protection
Lawn and field weed killers like 2,4-D and dicamba can drift onto trees.59CropWatch. Take Steps to Avoid Unintended Targets Affected leaves may be stunted, twisted, leathery, curled or drop.60CropWatch. Take Steps to Avoid Unintended Targets If you can smell the spray in the air, nearby trees may be getting exposed to drift.61CropWatch. Take Steps to Avoid Unintended Targets
Herbicide damage tends to appear suddenly on new growth after nearby lawn spraying, and it often affects other broadleaf plants nearby too. Disease usually spreads gradually and shows spots or lesions.
When you use weed killers yourself, skip windy or hot days. Keep weed-and-feed products off the area over the roots, and hand-pull weeds under the canopy instead.
Pruning and Care That Prevents Problems
Do routine pruning in January or February.62WSU Extension. Ornamental Cherry Bacterial canker Pruning date strongly affects how many cuts become infected with bacterial canker.63New Zealand Plant Protection. Pruning date affects bacterial canker of sweet cherry Trim shoots that touch the ground and thin out crowded inner branches.64Atlanta Arbor. Common Weeping Cherry Tree Problems and How to Handle Them Keep the arches open rather than shortening them, since the cascading look depends on it.65Atlanta Arbor. Common Weeping Cherry Tree Problems and How to Handle Them Remove dead or broken branches, which invite disease and insects.66University of Maryland Extension. Ornamental Cherry Trees: Identify and Manage Problems Avoid cuts that shorten branches to a stub, which make canker more likely.67Pacific Northwest Pest Management Handbooks. Cherry (Prunus spp.)-Bacterial Canker68University of Maryland Extension. Ornamental Cherry Trees: Identify and Manage Problems
For a clean cut, make it just outside the slight bulge where a branch joins a larger one. Sharp, clean tools avoid tearing bark. Remove no more than a modest share of live growth in one year.
Water deeply during dry spells, but don’t keep the soil soggy. A mulched ring around the trunk keeps string trimmers and mowers from nicking the bark.