Bacterial Blight

Pseudomonas syringae pv. syringae

122 host plants

Last updated

Data Maturity Structured

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

Bacterial blight shows up as water-soaked lesions on leaves and shoots, typically during wet spring weather when plants are just leafing out. You'll notice affected foliage may curl, wilt, or drop prematurely, particularly on forsythia, Magnolia, or mock orange. The damage is most visible in years with prolonged wet springs, when high moisture and cool temperatures create ideal infection windows. Shoots and branches may have dark, sunken lesions with a greasy appearance.

This disease thrives in overhead watering, poor air circulation, and crowded plantings. Since the bacterium (Pseudomonas syringae) survives on infected plant tissue, your best management is spacing plants properly to allow air flow, avoiding overhead irrigation, and promptly removing infected branches and shoots. Maintaining healthy, vigorous plants through good nutrition helps them resist infection better. Avoid unnecessary pruning or handling of plants when wet to reduce wound entry.

Quick Reference

Causal Agent
Pseudomonas syringae pv. syringae
Host Plants
122
Favorable Conditions
Cool wet weather (40-65°F with rain) from fall through spring. Frost events a...

Management

Vulnerability Window

Fall through spring. Fall leaf drop creates entry points through leaf scars (October-November). Late winter through spring (February-May) is the peak infection window when cool wet conditions and frost events coincide with new growth. Young shoots and flower clusters are most susceptible during spring flush." # Source: PNW Plant Disease Management Handbook (multiple host entries)

What Triggers Infection

Cool wet weather (40-65°F with rain) from fall through spring. Frost events are critical triggers — P. syringae produces ice nucleation proteins that promote frost damage at 28-31°F, creating wounds for bacterial entry. Mild, moist weather favors rapid bacterial multiplication. Rain splash spreads bacteria to new tissues. Late frosts in maritime PNW are common and drive spring outbreaks." # Source: PNW Plant Disease Management Handbook (multiple host entries); lifecycle stages documented in this profile

Cultural Controls

  • Maintain proper plant nutrition.
  • Healthy plants resist disease better.
  • Avoid overhead irrigation.
  • Space plants properly and prune to provide good air circulation.
  • This will slow down spread of the disease.
  • Avoid injuring plants to reduce possibility of infection.

Host Plants (122)

Buddleia davidii Butterfly Bush, Summer Lilac Castanea dentata American Chestnut Castanea mollissima Chinese Chestnut Castanea sativa European Chestnut, Sweet Chestnut, Spanish Chestnut Ceratonia siliqua Carob St. John's Bread Locust, Bean Corylus americana American Hazel, American Filbert Corylus avellana Common Filbert Corylus chinensis Chinese Hazel Corylus colurna Turkish Hazel Corylus cornuta var. californica Western Hazel, California Hazel, Western Beaked Hazel Corylus heterophylla Siberian Hazelnut Asian Hazel Cotoneaster apiculatus Cranberry Cotoneaster Cotoneaster bullatus Hollyberry Cotoneaster Cotoneaster congestus Pyrenees Cotoneaster Cotoneaster dammeri Bearberry Cotoneaster Cotoneaster divaricatus Spreading Cotoneaster Cotoneaster franchetii Franchet Cotoneaster Cotoneaster horizontalis Rockspray Cotoneaster Cotoneaster intergerrimus European Cotoneaster Cotoneaster lucidus Hedge Cotoneaster Cotoneaster microphyllus Littleleaf Cotoneaster Cotoneaster multiflorus Many-flowered Cotoneaster Cotoneaster salicifolius Willowleaf Cotoneaster Cotoneaster simonsii Simons Cotoneaster Cotoneaster suecicus Cotoneaster suecicus Daphne genkwa Lilac Daphne Dermatophyllum secundiflorum Mescal Bean Texas Mountain Laurel, Frijolito Euonymus alatus Euonymus alatus Euonymus americanus American Euonymus, Hearts-a-Burstin', Strawberry Bush Euonymus atropurpureus Eastern Wahoo Euonymus europaeus Common Spindle Tree, European Euonymus Euonymus fortunei Wintercreeper Euonymus, Wintercreeper Euonymus japonicus Japanese Spindle Euonymus kiautschovicus Euonymus kiautschovicus Forsythia viridissima Greenstem Forsythia Geranium Cranesbill Magnolia acuminata Cucumber Magnolia, Cucumbertree Magnolia, Mountain Magnolia Magnolia black Magnolia, black Magnolia butterflies Butterflies Magnolia Magnolia caerhays Magnolia, caerhays Magnolia campbellii Campbell's Magnolia, Campbell Magnolia Pink Tuliptree Magnolia denudata Yulan Magnolia Magnolia elizabeth Elizabeth Magnolia Magnolia ernestii Yellow Lily, Tree Magnolia galaxy Galaxy Magnolia Magnolia grandiflora Southern Magnolia Magnolia insignis Red Lotus Tree Magnolia kobus Kobus Magnolia Magnolia liliiflora Lily Magnolia Magnolia loebneri Loebner Magnolia Magnolia lotungensis Eastern Joy Lotus Tree Magnolia macrophylla Bigleaf Magnolia Magnolia randy Randy Magnolia Magnolia salicifolia Willowleaf Magnolia, Anise Magnolia Magnolia sargentiana Sargent's Magnolia Magnolia sieboldii Siebold Magnolia, Oyama Magnolia Magnolia soulangiana Saucer Magnolia Magnolia star Magnolia, star Magnolia stellata Star Magnolia Magnolia sunsation Sunsation Magnolia Magnolia tripetala Umbrella Magnolia Umbrella Tree, Elkwood Magnolia virginiana Sweetbay Magnolia Morus alba White Mulberry, Common Mulberry, Silkworm Mulberry, Russian Mulberry Philadelphus buckleys Philadelphus buckleys Philadelphus lewisii Lewis' Mock Orange Philadelphus snowdwarf Snowdwarf Mockorange Philadelphus virginalis Virginal Mockorange Populus alba White Poplar European White Poplar, Silver Poplar Populus angustifolia Narrowleaf Cottonwood, Mountain Cottonwood Populus balsamifera Balsam Poplar Populus canescens Gray Poplar Populus deltoides Eastern Cottonwood Populus fremontii Fremont Cottonwood, Western Cottonwood Populus grandidentata Bigtooth Aspen Populus nigra Black Poplar Populus tremula European Aspen European Trembling Aspen European Quaking Aspen Populus tremuloides Quaking Aspen Populus trichocarpa Black Cottonwood Sophora secundiflora Mescal Bean Texas Mountain Laurel, Frijolito Syringa chinensis Chinese Lilac Rouen Lilac Syringa hyacinthiflora Early Flowering Lilac, Early Hybrid Lilac Syringa josikaea Hungarian Lilac Syringa laciniata Cutleaf Lilac Syringa meyeri Syringa meyeri Syringa microphylla Syringa microphylla Syringa patula Syringa patula Syringa pekinensis Peking Lilac Chinese Tree, Lilac Syringa prestoniae Preston Lilac, Canadian Lilac Syringa reticulata Japanese Tree Lilac, Giant Tree Lilac Syringa vulgaris Common Lilac Viburnum × bodnantense Bodnant Viburnum, Dawn Viburnum Viburnum awabuki Sweet Viburnum Viburnum bracteatum Bracted Viburnum, Limerock Arrowwood Viburnum Viburnum burkwoodii Burkwood Viburnum Viburnum carlesii Koreanspice Viburnum Viburnum cassinoides Witherod Viburnum, Northern Wild Raisin Viburnum cinnamomifolium Cinnamon Viburnum Viburnum davidii David's Viburnum Viburnum dentatum Arrowwood Viburnum Viburnum dilatatum Linden, Viburnum, Linden, Arrowwood Viburnum edule Mooseberry Highbush Cranberry, Moosewood Viburnum, Squashberry Viburnum ellipticum Oregon Viburnum, Western Wayfaring Tree Viburnum farreri Fragrant Viburnum Viburnum juddii Judd Viburnum Viburnum lantana Wayfaringtree Viburnum Viburnum lantanoides Hobblebush Viburnum lentago Nannyberry Sheepberry Viburnum nudum Possumhaw Smooth Witherod Northern Wild Raisin Viburnum opulus var. americanum American Cranberrybush Viburnum Viburnum opulus var. opulus European Cranberrybush Viburnum, Guelder-rose Viburnum opulus var. sargentii Sargent Viburnum Viburnum plicatum var. plicatum Japanese Snowball Viburnum Viburnum plicatum var. tomentosum Doublefile Viburnum Viburnum pragense Prague Viburnum Viburnum prunifolium Blackhaw Viburnum Viburnum rafinesquianum Downy Arrowwood Viburnum, Rafinesque Viburnum Viburnum rhytidophyllum Leatherleaf Viburnum Viburnum rufidulum Rusty Blackhaw Viburnum, Southern Blackhaw Viburnum setigerum Tea Viburnum Viburnum suspensum Sandankwa Viburnum, Sandanqua Viburnum Viburnum tinus Laurustinus Viburnum trilobum American Cranberrybush Viburnum