LILAC BACTERIAL BLIGHT Pseudomonas syringe pv. syringe   F A C T S H E E T

Introduction

Bacterial blight of lilac is caused by the bacterium Pseudomonas syringae pv. syringae. The disease is also commonly referred to as Shoot Blight and Blossom Blight. The pathogen is capable of causing damage to all types of lilacs including Japanese, Chinese, Persian and common varieties. Some researchers suggest that white flowering varieties may be more susceptible to infection than other varieties. The disease is usually associated with plants that have been stressed by drought conditions, improper fertilization, and/or have been wounded. The pathogen has also been reported on Forsythia, Blueberry, and other ornamental plants.

Symptoms

Infections result in the appearance of brown spots on the leaves and stems on the plants. The spots may enlarge and cause malformations of the leaf tissue. Leaves may die and drop from the stems. The symptoms may move from the leaves to the stems as the disease progresses, turning the tissue black and causing it to wilt. The stems infection causes girdling of the tissue resulting in the death of shoots and blossoms.

Figure 1: Twigs turn black and wilt from the tips back to the stem. (provided by Karen L. Snover-Clift, Cornell University)

Figure 2: Leaves often show damage around the margins and/or along the central vein. (provided by Karen L. Snover-Clift, Cornell University)

Disease Cycle

New infections are initiated in the spring during wet weather. The bacterium may have overwintered in disease cankers on the plants, on healthy plant material, in plant debris, in perennial weeds, and/or in the soil around the area. The bacterium is spread to new growth of the susceptible plant in the spring by insect vectors, on pruning tools, blowing wind and splashing rain. Once the bacterium reaches the host plant, it needs a natural opening or wound to gain access to the internal tissues. When infection takes place it produced the symptoms listed above.

Control Strategies

Cultural Management
Take the proper actions required to keep the plant as healthy as possible. Practice proper fertilization and water management. Stresses caused by the lack of nutrients and/or water can predispose the plants to an infection. Avoid wetting the foliage and overhead irrigation to minimize splashing of the bacterium on to the host plants. Prune plants to allow for increased air circulation through the canopy. Also proper spacing of plants is recommended.

Resistant Varieties
Some varieties of lilac show a resistance to infections by the Bacterial Blight pathogen. Some varieties that have shown good resistance characteristics include Syringae oblata var. dilatata 'Cheyenne', S. vulgaris 'Edith Cavelle', 'Fr. John L. Fiala', 'General Sheridan','Katherine Havenmayer', 'Krasavitsa Moskvy', 'Montaigne', 'Nadezhda', and 'President Grevy', S. chinensis 'Red Rothamagensis' and 'Saugeana' and S. meyeri. Some varieties that show poor resistance characteristics include S. hyacinthiflora 'Annabel', S. vulgaris 'Agincourt Beauty', 'Bridal Memories', 'Burgundy Queen', 'California Rose', 'Charles Joly', 'Charm', 'Edward Boissier', 'Edward Gardner', 'Etna', 'Firmament', 'Lavendar Lady', 'Little Boy Blue', 'Miss Ellen Willmott', 'Monge', 'Olimpiada Kolesnilova', 'Paul Thirion', 'Royal Purple', Ruhm van Horstenstein', 'Wonderblue', and Yankee Doodle'.

Pruning
Infected branches should be pruned 20 to 25 cm (10-12 inches) below the visible infection. Pruning should be done during dry weather to minimize the chance of spreading the pathogen. Pruned branches should be destroyed or discarded. Always sterilize pruning tools between cuts to prevent spreading the bacterium to other areas on the tree.

Chemical Management
Pesticides should only be used if the disease is severe. In New York State, homeowners may be able to use some fungicides containing copper (as elemental copper, copper ammonium carbonate, or basic cupric sulfate) for management of Bacterial Blight. Some products containing Bacillus subtilis may also be used. An application needs to be made early in the spring before the pathogen infects the host plant. See individual pesticide labels for instructions.

References:
Perry, Leonard, 2000., http://pss.uvm.edu/ppp/wplilacs.html Lilac trials and photos. University of Vermont.

Created, KLS, 05/02; Updated, SLJ, 02/05