CORVALLIS, Ore. – Legions of lilac lovers look forward to spring when the pink, lavender or white flowers open and send their sweet scent into the air. An unsightly case of lilac blight can turn that excitement to disappointment in no time.
Lilac blight is difficult to control so it’s recommended that you buy blight-resistant varieties whenever you plant new lilacs.
Cool, wet springs favor development of lilac blight, especially if rains follow a late frost or winter injury, according to Jay Pscheidt, Oregon State University Extension plant pathologist.
Actually known to scientists by the complete name of “lilac bacterial blight,” this disease is caused by the bacteria Pseudomonas syringae pv. syringae. The same organism is the source of bacterial blight on pear, blueberry, cherry, maple and many other woody plants. The symptoms of lilac blight are similar in appearance to fire blight in fruit trees.
At first, leaves look perfectly healthy and then a short time later they look as though someone has placed an open flame near them. Dark black streaks form on one side of young shoots. The flowers wilt and turn brown and unopened flower buds become blackened.
To help avoid lilac blight, don’t fertilize late in the growing season and don’t over fertilize young plants because high nitrogen favors disease development, Pscheidt said. It also helps to space and prune lilac plants so they’re not rubbing against each other and air can circulate freely between plants.
Lilac blight is difficult to control so it’s recommended that you buy blight-resistant varieties whenever you plant new lilacs.
Some species have shown resistance, including S. josikaea, S. komarowii, S. microphylla, S. pekinensis and S. reflexa. Most cultivars of S. vulgaris, which are most commonly grown, are susceptible, but some have been observed with less disease in gardens, including Edith Cavell, Glory, Ludwig Spaeth and Pink Elizabeth.
If your lilac bush does have infection, prune and burn all infected parts as soon as you notice them. A spray of a copper-based pesticide, which is organic, during the early spring each year should help prevent the problem before the buds begin to break.
Lilac blight bacteria over-winter on diseased twigs or healthy wood. Factors that weaken or injure plants – wounds, frost damage, soil pH, poor or improper nutrition and infection by other pathogens – predispose them to the disease.
Lilac bushes are prized for their sweet-smelling, colorful blooms that signal the arrival of spring. But when your lilac bush starts to decline, with scorched leaves, sparse blooms, and bare branches, it can be worrying The good news is a dying lilac bush can often be revived with proper care and maintenance By identifying and addressing the underlying causes of the decline, you can coax new growth from old, overgrown lilac plants.
Common Reasons for Lilac Bush Decline
There are several factors that can lead to lilac bushes deteriorating:
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Old age – Lilacs live around 20-30 years typically. As they reach maturity, they start to naturally deteriorate. Old wood becomes less productive, branches die back, and flowering decreases.
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Poor drainage – Wet, compacted soil leads to damaged roots and disease Good drainage is essential.
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Lack of sunlight – Lilacs need at least 6 hours of direct sun daily to bloom well. Too much shade hinders growth.
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Insufficient watering – Drought stress after planting new lilacs can cause failure to establish. Mature plants also need watering during dry periods.
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Pest damage – Borers, mites, scales, and other pests can damage foliage and woody growth over time.
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Diseases – Bacterial blight, powdery mildew, and other fungal diseases infect lilacs, causing defoliation, dieback, and decline.
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Poor nutrition – Lack of nitrogen, phosphorus, and potassium leads to reduced flowering and growth. Fertilization is needed.
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Harsh weather – Late spring frosts, winter damage, pollution, and other environmental factors stress lilacs.
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Root injury – Trenching, construction work, or aggressive weeding can destroy roots and cut off water uptake.
Signs Your Lilac is Dying
Lilacs exhibiting these symptoms need corrective care:
- Small, curled, scorched, yellowing, or dropping leaves
- Fewer, smaller flowers or no blooms
- Dead wood with peeling bark on older branches
- Dieback starting on individual branches
- Sparse growth with large areas of bare wood
- Suckers emerging from the base
Without treatment, affected branches continue dying until the whole bush perishes. Addressing problems promptly gives the best chance of reviving declining lilacs.
How to Revive an Overgrown, Mature Lilac
Old, overgrown lilac bushes can often be rejuvenated with proper care:
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Prune aggressively – In late winter, remove all dead wood. Cut remaining healthy stems to 6-12 inches above ground to force new growth.
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Water deeply – Water thoroughly after pruning to help recovery. Continue watering during dry periods.
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Loosen roots – Carefully dig and loosen compacted roots to stimulate new feeder root growth.
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Fertilize – Apply a balanced fertilizer like 10-10-10 in early spring and after new growth appears.
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Add organic mulch – Spread 2-4 inches of mulch over the root zone to retain moisture and nourish the soil.
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Pest management – Use horticultural oils or organic methods to control lilac pests as needed.
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Remove suckers – Prune out new shoots at the base to direct growth to the main bush.
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Be patient – It takes 2-3 years for the lilac bush to fully recover after rejuvenation pruning.
Proper Care to Prevent Lilac Decline
With attentive care, lilac bushes can thrive for years:
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Plant in well-draining soil in full sun. Avoid wet, compacted clay.
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Space at least 8 feet apart and remove nearby competing trees/shrubs.
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Prune annually after flowering to shape the bush and remove old wood.
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Water deeply 1-2 times per week if rainfall is inadequate.
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Apply balanced fertilizer or compost in early spring when growth resumes.
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Add 2-4 inches of organic mulch to conserve moisture and reduce weeds.
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Scout for borers and other pests. Take corrective action before infestations occur.
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Promptly remove diseased or dead branches.
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Stake heavy branches that bend to the ground to prevent breakage.
With attentive care, lilacs can grow vigorously for decades before naturally declining.
Signs It’s Time to Remove and Replace a Lilac
Sometimes lilac bushes decline to the point where they cannot be revived. It may be time to remove and replace them if:
- Less than 25% of the original bush remains alive
- Main branches and suckers die back after pruning
- No leaf buds form even after heavy pruning
- The base shows signs of rot
- The bush becomes unsightly or stops flowering
If the lilac is beyond saving, replacing it with a new, healthy plant suited to the site may be needed.
Choosing a New Lilac Bush
When selecting a replacement lilac, consider:
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Mature size – Standard lilacs reach 8-15 feet tall. Dwarf varieties grow just 3-6 feet. Choose an appropriate size.
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Flower color – Blooms come in purple, pink, white, lavender and more. Visit nurseries to see colors.
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Fragrance – Some varieties have stronger scents. Choose fragrant types to enjoy the aroma.
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Bloom time – Look for reblooming lilacs that flower again in summer for extended color.
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Pest/disease resistance – Select newer disease-resistant introductions if fungal problems are common in your area.
Aim for younger plants under 10 years old for maximum lifespan. Shop at reputable nurseries, not big box stores.
Preventing Premature Lilac Decline
You can grow long-lived, vigorous lilac bushes by:
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Purchasing high-quality nursery plants and inspecting roots before planting
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Planting in spring, not fall, to establish plants before winter dormancy
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Watering frequently the first 2 years until deeply rooted
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Using preventative organic pest and disease control measures
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Providing optimal growing conditions suited to lilacs
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Pruning yearly to maintain ideal bush shape and vigor
With attentive care from the start, your lilac bush will be less prone to premature decline. You can then enjoy an abundance of blooms for many years to come.
The Takeaway
If your mature lilac bush starts to fail, don’t give up on it yet. Heavy renewal pruning and improved care often revives old shrubs. However, lilacs beyond saving should be removed and replaced with new, healthy plants. With preventative maintenance, you can avoid premature decline and extend the life of your lilac bushes.
Sources of the disease
Sources of this disease can include old cankers, healthy buds, leaf surfaces and nearby weeds and grasses. Wind, rain, insects, tools and infected nursery stock spread the bacteria.
The disease starts as brown spots on stems and leaves of young shoots as they develop in early spring. A yellow halo may also be around the spot. Spots become black and grow rapidly, especially during rainy periods.
On young stems, infection spreads around the stem and girdles it so the shoot bends over at the lesion and the parts above it wither and die. Infections on mature wood occur only on cherry trees, not on lilacs.
Young, infected leaves blacken rapidly starting near the margin and continuing in a wedge-shaped pattern down to the petiole. Eventually the entire leaf dies. On older leaves, spots enlarge slowly. Sometimes, several spots will run together, and the leaf may crinkle at the edge or along the mid-vein. Flower clusters also may be infected and rapidly blighted and blackened. Buds may fail to open or may turn black and die shortly after opening. Symptoms are similar to those of winter injury or drought damage.
To see photos of this disease, visit OSU Extensions “PNW Plant Disease Management Handbook.“
Want to learn more about this topic? Explore more resources from OSU Extension:
Lilac plant damaged by bacteria – flower blight. Photo: Lynn Ketchum
When shoots begin to die they tip over in what is called a Shepards crook symptom. Photo by Jay W. Pscheidt
Why Does My Lilac Look Scorched? Diagnosing and Treating Lilac Blight
FAQ
How do you revive a dying lilac bush?
Cut branches (especially the damaged branches) so there’s more airflow and during the growing season, use a fungicide to help prevent disease. Since it’s dormant, you can actually cut it back pretty far as well to give it a fresh start. Lilacs are slow growing so it will take a while to get back to the size it is now.
What is killing my lilac bush?
Fungal leaf diseases of lilac. Fungal leaf diseases like Septoria and powdery mildew can cause concern as people watch the leaves of otherwise healthy lilacs (and sometimes other shrubs) turn yellow, then brown, and then drop to the ground.
Why are the leaves on my lilac bush curling brown?
Melinda: Lilac blight caused by bacteria may lead to curling leaves. Brown blemishes or lesions may appear on the leaves and new shoots. Pruning out infected branches below the diseased portion is the only control. Be sure to disinfect your tools with alcohol or a disinfectant spray between cuts.