Bacterial Leaf Spot and Dieback

Pseudomonas syringae

45 host plants

Last updated

Data Maturity Structured

This profile synthesizes data from multiple published sources. Expert field review is in progress.

Leaf spots merge and expand, eventually killing shoots as cankers develop. This aggressive disease requires aggressive pruning.

Plant resistant cultivars or avoid highly susceptible cultivars. Carefully handle young plants. Rake up and destroy fallen leaves to reduce the spore load for the next season. Improve air circulation and avoid overhead irrigation. For valuable plants with recurring problems, preventive fungicide applications during leaf emergence can reduce severity.

Quick Reference

Causal Agent
Pseudomonas syringae
Host Plants
45
Spread
wind, rain-splash, contact" # Windblown rain, insects, and pruning tools
Favorable Conditions
Cool wet weather, particularly in fall through spring. Frost damage is a majo...

Management

Vulnerability Window

Dormant season through early spring for canker and twig dieback development. Buds are vulnerable from late winter through spring break. Young expanding leaves are most susceptible in spring during cool rainy periods. Trees weakened by Verticillium wilt or other stressors are at increased risk." # Source: PNW Plant Disease Management Handbook (Maple - Bacterial Leaf Spot and Dieback)

What Triggers Infection

Cool wet weather, particularly in fall through spring. Frost damage is a major predisposing factor — P. syringae produces ice nucleation proteins that promote frost injury at 28-25°F, creating wounds for bacterial colonization. High nitrogen fertilization (especially late summer) produces succulent growth susceptible to winter injury and subsequent infection. Heavy rains and overhead irrigation facilitate spread." # Source: PNW Plant Disease Management Handbook (Maple - Bacterial Leaf Spot and Dieback)

Cultural Controls

  • Plant resistant cultivars or avoid highly susceptible cultivars.
  • Carefully handle young plants.
  • If possible, do all pruning and budding, or any practice that wounds plants, in dry weather.
  • Protect from rain and frost, if feasible, in early spring or late fall.
  • Plastic shelters have been as good as or better than chemical methods against the same disease on other crops.
  • Remove and destroy dead and/or blackened twigs and fallen leaves.

Host Plants (45)

Acer buergerianum Trident Maple, Three-toothed Maple Acer campestre Hedge Maple, Field Maple, Common Maple Acer capillipes Red Stripebark Maple, Red Snakebark Maple, Hakkoda Maple Acer carpinifolium Hornbeam Maple Acer circinatum Vine, Maple Acer coriaceifolium Leatherleaf Maple Acer crataegifolium Hawthorn, Maple Acer davidii David Maple, Père David's Maple Acer freemanii Freeman Maple, Hybrid Red Maple Acer ginnala Acer ginnala Acer glabrum Rocky Mountain Maple, Rock Maple, Douglas Maple, Dwarf Maple Acer glabrum var. douglasii Douglas Maple, Dwarf Maple, Rocky Mountain Maple Acer grandidentatum Bigtooth Maple, Western Mountain Sugar Maple, Rocky Mountain Sugar Maple Acer griseum Paperbark Maple Acer henryi Henry's Maple Acer japonicum Fullmoon Maple Acer macrophyllum Bigleaf Maple Acer maximowiczianum Nikko Maple Acer miyabei Miyabe Maple Acer monspessulanum Montpellier Maple Acer negundo Boxelder Manitoba Maple, Ash-leaved Maple Acer nipponicum Nippon Maple Acer oblongum Evergreen Maple, Smooth Leaf Maple Acer oliverianum Oliver Maple Acer opalus subsp. obtusatum Bosnian Maple Acer palmatum Japanese Maple Acer palmatum var. dissectum Dissected Japanese Maple Acer pensylvanicum Striped Maple, Moosewood Maple Acer pentaphyllum Acer pentaphyllum (no common name) Acer pictum Painted Maple Acer platanoides Norway Maple Acer pseudoplatanus Planetree Maple, Sycamore, Maple Acer rubrum Red Maple Acer rufinerve Redvein Maple, Honshu Maple Acer saccharinum Silver Maple Acer saccharum Sugar Maple Acer sempervirens Cretan Maple Acer shirasawanum Shirasawa Maple Acer spicatum Mountain Maple, Moose Maple Acer tataricum Tatarian Maple, Tartarian Maple Acer tataricum subsp. ginnala Amur Maple Acer tegmentosum Manchurian Stripebark Maple, Manchustriped Maple Acer triflorum Three Flowered Maple Acer truncatum Purpleblow Maple, Shantung Maple Acer velutinum Velvet Maple