CORVALLIS, Ore. – A lot of lilac lovers can’t wait for spring, when the pink, lavender, or white flowers bloom and fill the air with their sweet scent. An unsightly case of lilac blight can turn that excitement to disappointment in no time.
Lilac blight is hard to get rid of, so when you buy new lilacs, you should choose varieties that are resistant to blight.
Jay Pscheidt, a plant pathologist at Oregon State University Extension, says that lilac blight grows best in cool, wet springs, especially if it rains after a late frost or winter damage.
This sickness is caused by the bacteria Pseudomonas syringae pv and is officially known as “lilac bacterial blight” by scientists. syringae. Blight on pear, blueberry, cherry, maple, and many other woody plants is caused by the same organism. The symptoms of lilac blight are similar in appearance to fire blight in fruit trees.
After a short time, leaves start to look like someone put an open flame next to them. At first, the leaves look perfectly healthy. Dark black streaks form on one side of young shoots. The flowers wilt and turn brown and unopened flower buds become blackened.
Pscheidt said that to help keep lilac blight at bay, don’t fertilize too late in the growing season or too much on young plants, since high nitrogen levels make diseases more likely to spread. Lilac plants should also be spaced out and trimmed back so they don’t rub against each other and air can flow freely between them.
Lilac blight is hard to get rid of, so when you buy new lilacs, you should choose varieties that are resistant to blight.
Some species have shown resistance, including S. josikaea, S. komarowii, S. microphylla, S. pekinensis and S. reflexa. Most cultivars of S. vulgaris, which are the most common type, are susceptible, but some others, like Edith Cavell, Glory, Ludwig Spaeth, and Pink Elizabeth, have been seen to be less likely to get sick in gardens.
Infected parts of your lilac bush should be cut off and burned as soon as you see them. Every year in early spring, before the buds start to break, you should spray an organic copper-based pesticide on the plants to stop the problem.
Lilac blight bacteria over-winter on diseased twigs or healthy wood. Plants are more likely to get the disease if they are weak or hurt in some way, like by wounds, frost damage, low soil pH, bad nutrition, or infections from other pathogens.
Lilac bushes are beloved for their fragrant spring blooms in shades of purple pink and white. But when a prized lilac starts looking sickly with sparse flowers, curled leaves, and bare branches, it can be worrying. A dying lilac bush may still be rescued if you identify and address the underlying causes. With proper care and maintenance, new growth can be coaxed from old plants.
Common Reasons for Lilac Bushes Declining or Dying
There are several potential factors that can lead to lilac bush decline:
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Old age – Lilacs live approximately 20-30 years on average. After reaching maturity, they start to naturally deteriorate. Old wood becomes less productive, branches die back, and flowering decreases.
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Poor nutrition – Lilacs need adequate levels of nitrogen, phosphorus, and potassium for good flowering and growth. Nutrient deficiency causes yellowing leaves, sparse blooms, and dieback.
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Compacted roots – Dense clay soil or restricted roots from rocks/foundations prevent roots from spreading to take up water and nutrients, This stresses the plant
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Pests – Borers, scales, mites, and other insects can damage lilac foliage and woody growth. Pest infestations sap plant vigor over time.
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Diseases – Bacterial blight, powdery mildew, verticillium wilt, and other diseases infect lilacs, leading to defoliation, dieback, and decline.
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Environmental issues – Insufficient water, overwatering, pollution, salt damage, and extreme weather like drought or late frosts stress lilacs.
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Root damage – Trenching, construction work, or aggressive weeding around the roots destroys the root system and cuts off water uptake.
Signs Your Lilac Bush is Dying
Lilacs exhibiting these symptoms are in decline and need corrective care:
- Leaves are small, curled, wilted, scorched, or dropping early
- Fewer, smaller flower clusters or no blooms
- Dead wood with peeled bark on older branches
- Dieback starting on individual branches
- Thin growth with large areas of bare wood
- Suckers emerging from the base more than usual
Without treatment, affected branches continue to die back until the entire lilac bush perishes. Addressing problems promptly gives the best chance of reviving declining plants.
How to Revive an Old, Overgrown Lilac Bush
Mature lilac bushes can often be rejuvenated through proper pruning and care:
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Prune aggressively – In late winter, remove all dead wood. Then cut back healthy stems to 6-12 inches above the ground to force new growth.
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Loosen roots – Carefully dig around the root zone and cut any girdling roots to stimulate new feeder root growth.
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Fertilize – Apply a balanced fertilizer like 10-10-10 in early spring and again after pruning new growth. Compost also provides nutrition.
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Water – Water deeply after pruning to help the plant recover. Provide supplemental water during dry spells.
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Mulch – Spread 2-4 inches of bark chips or other organic mulch over the root zone to retain moisture and improve soil.
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Pest management – Inspect regularly and use organic methods like horticultural oil sprays to control lilac pests.
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Remove suckers – Prune out new shoots emerging from the base to focus growth on the main bush.
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Be patient – It may take 2-3 years for the lilac bush to fully recover and flower well again after rejuvenation pruning.
Caring for Lilacs Properly to Avoid Decline
With proper site conditions and care, lilac bushes can live a long, healthy life:
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Plant in well-draining soil in full sun. Avoid wet, dense clay soil.
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Space lilacs at least 8 feet apart and keep competing trees/shrubs away.
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Prune annually right after flowering to shape bush and remove old wood.
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Water deeply 1-2 times per week if rainfall is lacking. Avoid overwatering.
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Apply balanced fertilizer or compost in early spring when growth resumes.
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Spread mulch around the base to conserve soil moisture and reduce weeds.
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Scout regularly for pests like borers. Take corrective action before damaging infestations occur.
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Remove and destroy diseased, pest-infested or dead branches promptly.
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Stake or support overly heavy branches that bend to the ground to prevent breakage.
With attentive care, lilacs can thrive for decades before naturally starting to deteriorate.
Signs it’s Time to Remove and Replace a Lilac Bush
Unfortunately, some lilac bushes decline to the point where they cannot be revived. It may be time to pull out and replace severely weakened lilacs if:
- Less than 25% of the original bush remains alive
- Main branches and suckers die back immediately after pruning
- No new leaf buds form even after aggressive rejuvenation pruning
- The roots or base of the bush show signs of rot
- The lilac bush becomes unsightly or stops flowering
Check first for signs of soil compaction, root damage from construction, or aggressive plant diseases before removing lilacs. But those in irreversible decline will likely continue to deteriorate. Replanting with a new, healthy lilac suited to the site may be needed.
Choosing a New Lilac Bush to Replace Dead or Dying Plants
When selecting a new lilac bush, consider:
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Mature size – Standard lilacs grow 8-15 feet tall. Dwarf types reach just 3-6 feet. Choose a size appropriate for the space.
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Flower color – Popular lilac blooms come in purple, lavender, pink, white and more. Visit nurseries to see colors firsthand.
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Fragrance – Some lilac varieties have stronger fragrances. Select highly fragrant types to fully enjoy the flowers.
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Bloom time – Look for reblooming lilac varieties that flower in spring and again in summer for extended color.
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Pest/disease resistance – Choose newer lilac introductions bred with improved disease resistance if fungi are an issue in your area.
With hundreds of lilac varieties to select from, you can likely find a replacement bush well-suited to your needs. Aim for younger plants under 10 years old for the longest lifespan in your landscape.
Preventing Lilac Bush Decline from the Start
You can boost the odds of growing vigorous, long-lived lilac bushes by:
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Purchasing nursery plants from reputable sources, not big box stores.
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Inspecting roots and rejecting potbound or damaged plants.
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Planting in spring, not fall, to allow the lilac to establish before winter dormancy.
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Watering new lilacs regularly the first two years until deeply rooted.
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Applying preventative, organic pest/disease control measures.
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Providing excellent growing conditions suited to lilac’s needs.
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Pruning every year to maintain an ideal bush shape and vigor.
With attentive care from the start, your lilac bush is less likely to decline prematurely. You can then enjoy plentiful blooms and fragrance for many years to come.
The Takeaway on Reviving Dying Lilac Bushes
If your mature lilac bush starts to decline with small leaves, sparse blooms, and dieback, don’t give up on it yet. Heavy rejuvenation pruning combined with improved plant care often coaxes new growth from old shrubs. However, lilacs beyond rescuing should be removed and replaced with new, healthy plants. With preventative care, you can ward off premature lilac bush decline and extend their life in your garden.
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.
As young shoots grow in early spring, brown spots appear on their stems and leaves. This is the first sign of the disease. A yellow halo may also be around the spot. Spots become black and grow rapidly, especially during rainy periods.
When an infection starts on a young stem, it wraps around it and makes it bend over at the wound. The parts above the wound die and wither. Infections on mature wood occur only on cherry trees, not on lilacs.
Young, infected leaves turn black quickly, first near the edge and then in a wedge-shaped pattern all the way 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.
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