I have a ‘Palibin’ lilac that appears to have a bit of bacterial
blight. I have pruned out the diseased branches. Is it too late to
spray to control the disease? I didn’t do a dormant spray this year,
and haven’t done any preventive spraying to this point, either. If it
isn’t too late, what spray product would you recommend? What else can I do to keep the blight under control?
There are cultural methods of dealing with bacterial blight you should try before using any spray. The information below should help.
Washington State University Extension’s HortSense website recommends:
- Avoid injuring plants to reduce possibility of infection.
- Avoid overhead irrigation.
- Maintain proper plant nutrition. Healthy plants resist disease better.
- Plant disease-resistant species such as Syringa perkinensis, S. microphylla, or S. vulgaris vars. ‘Alphonse Lavallec’, ‘Crepuscule’, ‘Floreal’, ‘Guinevere’, ‘Jeanne d’Art’, ‘Lutece’, ‘Maud Notcutt’, ‘Mrs. W.W. Marshall’, ‘Rutilant’, or ‘William Robinson’.
- Prune and destroy infected tissues as soon as they are noticed.
- Space plants properly and prune to provide good air circulation. This will slow down spread of the disease.
Here is more information from University of California, Davis’s
Integrated Pest Management site. Excerpt:
“Bacterial blight is promoted by prolonged rainy springs. Symptoms may be
more extensive in wetter areas. Prune branches showing dieback and severe
blight. Space plants to provide good air circulation. Prune during the
dry season when infection is less likely to occur. Do not wet foliage
with overhead irrigation; do not overfertilize. Small plants can be
protected to some degree by keeping them covered by plastic (or moved
under plastic). Plant resistant species if available. If the disease is
systemic or cankers appear on the trunk, the tree will probably die and
should be removed. If the disease is confined to leaves, damage is not
usually serious and trees normally recover. Sprays do not give reliable
control.”