Physiological Shothole
Physiological Abiotic disorder
Last updated
This profile contains basic abiotic disorder data. Regional field notes and expert review are in progress.
What Causes It
A non-pathogenic abscission response in which leaf tissue damaged by stress is walled off and shed, leaving round or irregular holes and tattered edges in otherwise healthy leaves. The plant forms an abscission layer around the damaged spot and drops the dead tissue, a process analogous to how deciduous leaves separate from the stem in fall. The underlying stress that triggers the original injury has been investigated without clear resolution; environmental and cultural stressors are implicated but no single cause is confirmed. (Source: PNW Plant Disease Management Handbook, Prunus - Physiological Shothole.)
Quick Reference
Symptoms
First visible as necrotic leaf spots with circular to irregular margins. Abscission layers form around the necrotic tissue and the dead center drops out, leaving round holes or tattered areas in the leaf. After the tissue drops, the original cause of the initial injury is usually impossible to determine. Symptoms commonly show up on laurels (particularly cherry laurel, Prunus laurocerasus), flowering plums, and Portuguese laurel in the Pacific Northwest. (Source: PNW Plant Disease Management Handbook.)
Round or irregular holes in otherwise healthy foliage, often on multiple leaves across a plant, with no visible fungal fruiting structures or bacterial ooze. The ragged edges of the holes typically appear dry and clean, not wet or decomposing. Distinguishing from true shothole (Wilsonomyces carpophilus) requires checking for fungal fruiting bodies on the dropped tissue edges.
Timeline: Appears as a scattered pattern across the plant during the growing season, most noticeably in late spring and summer. Does not progress through the canopy over time the way a pathogen would.
Triggers & Conditions
Cultural or environmental stress of unspecified origin. Research has failed to identify a single specific cause. Contributing factors may include temperature swings, inconsistent soil moisture, heavy shearing injury, spray drift, and general plant stress. (Source: PNW Plant Disease Management Handbook.)
Growing season, most visible late spring and summer.
Cherry laurel hedges (Prunus laurocerasus) across Puget Sound commonly show physiological shothole. It is among the most frequent cosmetic complaints on established laurel hedges. Plants under stress from heavy shearing, drought, or root constraints show more shothole than unstressed plants, supporting the general cultural-stress theory even though no specific cause has been pinned down.
Management
Prevention
- Maintain general plant vigor and reduce cultural stress
Place laurel hedges on sites with consistent soil moisture and away from cold-air pockets. Consider alternative evergreen hedge species on sites where shothole is chronic and cosmetically unacceptable.
Plant Tolerance
Prunus laurocerasus (cherry laurel) and other evergreen Prunus species used as hedges. Less commonly reported on flowering stone fruits.
More Sensitive
- Prunus laurocerasus
- Prunus lusitanica (Portuguese laurel)
General plant vigor and stress level. Stressed plants show more shothole; well-tended plants in appropriate sites show less.