{"id":22017,"date":"2023-05-03T09:00:08","date_gmt":"2023-05-03T13:00:08","guid":{"rendered":"https:\/\/www.purdue.edu\/fnr\/extension\/?p=22017"},"modified":"2026-04-17T14:42:04","modified_gmt":"2026-04-17T18:42:04","slug":"pseudomonas-syringae-pv-syringae-on-lilac-and-other-woody-ornamentals-landscape-report","status":"publish","type":"post","link":"https:\/\/www.purdue.edu\/fnr\/extension\/pseudomonas-syringae-pv-syringae-on-lilac-and-other-woody-ornamentals-landscape-report\/","title":{"rendered":"Pseudomonas syringae pv. syringae on lilac and other woody ornamentals – Landscape Report"},"content":{"rendered":"
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Bacterial leaf spots are often angular with chlorotic halos, as seen on this high bush-cranberry. Photo by Janna Beckerman.<\/p><\/div>\n

Purdue Landscape Report<\/a>: Pseudomonas syringae pv. syringae is an opportunistic bacterial pathogen that attacks a diversity of woody ornamental plants. The bacteria cause flower blights, cankers, shoot blights, and diebacks.<\/p>\n

Symptoms
\n<\/strong>Symptoms often begin as expanding leaf spots. On lilac and viburnum, small spots expand to irregularly shaped brown lesions with yellow halos (Fig. 1). For most other hosts (cherry, pear, basswood, dogwood, hydrangea, high bush-cranberry, mountain-ash), infected leaves turn reddish brown or black and usually remain on the branch after they die (Fig. 2). As the bacteria spread into woody tissue, dark, sunken sections of the stem (cankers) expand, working their way back toward the trunk from infected leaves and flowers. Leaves attached to a cankered branch will wilt while the tip of the affected branch curls and droops like a shepherd\u2019s crook (Fig. 3). Cloudy droplets of sticky fluid (ooze) may accumulate on leaf tips, leaf surfaces, stems, and even infected fruit.<\/p>\n

Image of infected flowers result in blossom blast.
\nFigure 2. Infected flowers result in blossom blast. The continued growth of the bacteria can result in cankering and blight. Photo by George Sundin.<\/p>\n

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Figure 2. Infected flowers result in blossom blast. The continued growth of the bacteria can result in cankering and blight. Photo by George Sundin.<\/p><\/div>\n<\/div>\n

Life Cycle
\nThe bacteria overwinter and persist in cankers, along with asymptomatic bud and twig tissue. In presence of water and warming temperatures, bacteria multiply and may ooze from infected tissue. Wind-driven rain, insect, or mechanical pruning spread Pseudomonas. Bacteria enter the plant through flowers or injury.<\/p>\n

Management
\n<\/strong>All bacterial pathogens, including Pseudomonas, invade flowers or wounded tissue. To prevent or minimize the risk of infection:<\/p>\n