The Yoshino Cherry (Prunus yedoensis) is a popular ornamental tree, known for its spectacular, cloud-like display of pink to white spring blossoms. While offering seasonal beauty, these trees belong to the Prunus genus, making them susceptible to pests, pathogens, and environmental stressors. Understanding these common vulnerabilities allows homeowners to quickly diagnose problems and apply targeted solutions, ensuring the long-term health of this iconic flowering tree.
Common Insect Pests and Their Control
One of the most destructive insect threats is the Peach Tree Borer (Synanthedon exitiosa). Infestation is identified by thick, gummy sap mixed with reddish-brown sawdust (frass) oozing from the trunk near the soil line or root crown. The larvae feed on the cambium layer, which can ultimately girdle and kill younger trees by disrupting the flow of water and nutrients.
Controlling borers requires a proactive approach. Preventive trunk sprays, often containing permethrin, should be applied to the lower trunk and ground in late spring and mid-summer when adult moths are laying eggs. For small trees, mechanical removal involves using a knife or wire to probe the larval tunnels and extract the borer. Maintaining tree health is a strong defense, as borers preferentially attack stressed or wounded trees.
Sap-sucking insects like aphids and scale insects also pose a threat, particularly to new growth. Black Cherry Aphids (Myzus cerasi) cluster on new shoots and the undersides of leaves, injecting toxins that cause the foliage to curl severely, which then shields the insects from predators and treatments. These pests excrete a sticky, sugary substance known as honeydew, which fosters the growth of unsightly black Sooty Mold on leaves and branches.
Scale insects appear as small, stationary bumps adhering to the bark of twigs and branches. Mature scales are protected by waxy coverings, but the mobile young, known as crawlers, are vulnerable to horticultural oil applications. For both aphids and scale, a dormant oil spray applied before bud break in late winter can effectively smother overwintering eggs. During the growing season, minor aphid infestations can be dislodged with a strong jet of water, while significant outbreaks respond well to insecticidal soap or neem oil.
Identifying and Treating Pathogenic Diseases
Yoshino Cherry trees are highly susceptible to a group of fungal and bacterial pathogens that can cause significant damage, especially during cool, wet weather. Brown Rot Blossom Blight, caused by the fungus Monilinia fructicola, is a common disease that attacks the flowers in early spring. Infected blossoms quickly turn brown, wilt, and often remain attached to the branch, sometimes developing into a canker on the adjacent twig.
The fungus overwinters in blighted blossoms and mummified fruit from the previous year. Management focuses on sanitation and chemical protection. Fungicides should be applied preventatively during the bloom period, usually at the popcorn stage and again at full bloom, especially if wet conditions persist. Remove and destroy infected twigs and mummified fruit to reduce the amount of pathogen present for the next season.
Canker diseases, often caused by fungi like Cytospora species or the bacterium Pseudomonas syringae, manifest as sunken, discolored areas on the bark of branches or the trunk. The tree responds to this invasion by exuding a thick, amber-colored gum from the edges of the infected area. These cankers slowly expand, eventually girdling the branch and leading to “flagging,” where the foliage on the infected limb suddenly wilts and dies while still attached.
Treatment for canker is primarily cultural and mechanical, as chemical controls are ineffective. Infected branches must be pruned out entirely, cutting back into healthy wood well below the visible canker margin. Pruning should be done during dry periods to prevent spore spread, and tools must be sterilized between cuts (using a 10% bleach solution or 70% alcohol). Since these diseases often invade through wounds, protecting the bark from injury is the best defense.
Solving Problems Related to Site and Care
A common sign of general stress in Prunus trees is gummosis, the oozing of sap from the trunk or branches. While it can signal borers or canker diseases, gummosis is often a non-specific response to environmental or cultural stressors. Causes unrelated to pests include poor drainage, drought stress, winter injury, or mechanical damage from lawn equipment. The solution lies in identifying and alleviating the underlying stressor.
A frequent concern is the lack of flowering, especially on younger trees. Yoshino Cherries may take several years to establish, with full displays often appearing between five and seven years after planting. Other causes include late spring frost damage to the flower buds or improper pruning timing. Since the trees set buds for the following year shortly after the current bloom, pruning should occur immediately after flowering to avoid removing the next year’s buds.
Cultural practices like planting depth and soil health are fundamental to preventing problems. Planting the tree too deeply or in heavy, poorly drained soil can lead to root suffocation and crown rot. The root flare, where the trunk meets the roots, should be slightly visible above the soil line. Excessive application of high-nitrogen fertilizers encourages leafy growth at the expense of flower production; therefore, using a balanced or potassium-rich fertilizer in spring is recommended for optimal blooming.