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.
Lilacs are one of the most beloved spring-flowering shrubs lighting up gardens with their fragrant blooms in shades of purple, pink and white. But sometimes those gorgeous blooms are followed by frustration, as the leaves turn brown and drop prematurely.
If your lilac bush is losing its leaves too soon don’t despair. In most cases brown and dropping lilac leaves are a sign of a problem that can be corrected with a few adjustments to care. Read on to learn the most common causes of premature leaf drop, along with solutions to revive your lilac.
Common Causes of Lilac Leaf Browning
Here are some of the most likely reasons for lilac leaves turning brown and falling off before fall
Improper Pruning
Lilacs only bloom on old wood, meaning branches that grew the previous season. Pruning at the wrong time removes potential flowering stems. The most common mistake is pruning in summer or fall after blooming ends. Late pruning triggers new growth that doesn’t have time to mature and flower the following spring.
Insufficient Water
Lilacs need about an inch of water per week from spring growth through summer. Extended dry periods cause leaves to brown, curl, and drop. This often happens repeatedly over the season, with leaves reviving after rain then declining again during drought.
Bacterial Blight
This disease causes brown spots and lesions on leaves, often with curling. It spreads in wet conditions and is more common in humid climates. Repeated defoliation can weaken plants over time.
Pest Damage
Lilac leaves chewed by pests like Japanese beetles, scale insects, or caterpillars often turn brown. Look closely to see if there are insects present or visible feeding damage.
Root Damage
Girdling roots, compacted soil, or bark damage from lawn mowers and string trimmers stresses lilac roots. Without healthy roots, plants can’t take up water and nutrients, leading to leaf browning.
Nutrient Deficiency
Lilacs need balanced levels of nitrogen, phosphorus, and potassium for healthy growth. Low nutrients causes distinctive patterns of yellowing, browning, or stunting. Have soil tested to identify deficiencies.
What to Do About Lilac Leaf Drop
Once you determine the cause of your lilac’s premature leaf drop, you can take steps to get your plant back to full health:
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Improve watering – Maintain moist (but not soaked) soil with deep weekly soakings. Water at the base, not overhead.
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Add mulch – A 2-4 inch layer of wood chips or shredded bark helps retain soil moisture and insulates roots.
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Prune properly – Remove spent blooms immediately after flowering by cutting back clusters to just above a leaf. Save major shaping for winter when the plant is dormant.
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Treat diseases – Disinfect tools between cuts when pruning out blight. Remove and destroy affected branches.
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Eliminate pests – Apply horticultural oil or insecticidal soap to deter insects. Attract birds to feed on caterpillars.
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Fix root issues – Loosen compacted soil and cut circling roots. Protect the root zone from damage.
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Correct nutrient deficiencies – Apply a balanced fertilizer in early spring based on soil test results.
With proper care tailored to the cause of leaf drop, your lilac can recover its summer foliage and bloom again next spring. Be patient – it may take a season or two to regain full vigor.
How to Keep Lilac Leaves Healthy
To prevent recurrent leaf drop issues, adopt these best practices for care:
- Select disease-resistant cultivars.
- Plant in well-drained soil in full sun.
- Water 1 inch per week from spring through fall.
- Apply mulch to conserve moisture and protect roots.
- Prune right after blooming and disinfect tools between cuts.
- Scout regularly for pests and treat promptly if found.
- Fertilize in early spring based on soil test recommendations.
- Protect roots from damage year-round.
With proper siting, watering, and pruning, your lilac will be less stressed and better able to resist issues that cause leaf browning and drop.
When to Worry About Lilac Leaf Drop
It’s normal for some interior leaves on lilac bushes to turn brown late in summer as the plant prepares for dormancy. This is nothing to worry about.
However, significant leaf browning and defoliation earlier in summer is almost always a sign of underlying problems. If the whole plant is rapidly losing leaves, you’ll want to intervene with corrective care.
Seeking early treatment for leaf drop gives the best chance of recovery in time to set flower buds for the following spring. So inspect lilacs closely and be prepared to act at the first sign of unusual leaf browning.
Lilac Leaf Questions Answered
Here are some answers to frequently asked questions about lilac leaf problems:
Q: Why do lilac leaves turn brown right after blooming?
A: This is often caused by improper pruning that removed potential flowering wood. Time pruning carefully to avoid removing next year’s blooms.
Q: Do lilac leaves turn brown in fall?
A: Some interior leaf browning in late summer is normal as the plant shuts down. But extensive browning early in summer indicates a care issue.
Q: How can I revive a lilac bush with brown leaves?
A: Improve care practices like watering, pruning, and pest management. Remove any dead or diseased branches. Fertilize lightly in early spring. Wait patiently for recovery.
Q: Should I cut off lilac leaves that are turning brown?
A: Remove only individual leaves that are fully brown and crispy. Don’t cut off branches with partially brown foliage – they can potentially recover with improved care.
Q: Can lilac blight cause leaf drop?
A: Yes, bacterial blight can lead to defoliation, especially in cool, wet weather. Prune out infected branches and avoid overhead watering.
Don’t give up on your lilacs just because their leaves are struggling. A bit of detective work to identify causes and attentive care can restore the health and productivity of your plants. With the right fixes, you can look forward to an explosion of colorful blooms next spring.
Enjoy the Lilac Show Each Year
Lilacs are treasured for their sweet fragrance and brief but spectacular spring flower display. But when lilac leaves brown and drop prematurely, it detracts from their beauty and satisfaction in the garden.
Fortunately, early intervention to resolve improper care, pest damage, diseases, and other stresses can get your lilacs back on track. Patience and diligence will be rewarded with more lush, verdant foliage and abundant blooms in seasons to come.
Have you battled browning lilac leaves? I’d love to hear what cured your plants in the comments below! Let’s work together to keep these lovely shrubs gracing our gardens with their vibrant colors and perfume.
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.
Why are the Leaves on my Lilac Turning Brown?
How do I know if my lilac plant has bacterial blight?
If Pseudomonas syringae has infected your lilac plant, you will notice brown or black spots on your plant’s leaves. The leaves will also wilt away and start to drop off. You will have to remove these affected leaves and branches — it’s the only way to control bacterial blight.
What causes brown spots on Lilac leaves?
Bacterial blight and powdery mildew are among the most common diseases affecting lilacs, often causing brown spots, lesions, and curling on leaves. These fungi-related diseases thrive in moist conditions and can spread rapidly if not controlled. Pruning affected areas and using suitable fungicides can help control these diseases.
Why do lilacs die?
But in lilacs, it mostly just makes them ugly. Witches’ broom causes new branches to die, or it can create abnormal growth like a bunch of tangled, weak shoots, and distorted or yellow leaves. Leaf edges might also turn brown, and new leaves might be small and pale. Eventually, this growth will spread, and the plant will die.
Why do lilac leaves discolor?
It can also cause the leaves to discolor. It usually starts in late spring as the temperatures increase, especially in high humidity. Don’t panic if your lilacs contract this disease. While it’s not ideal, it won’t kill your plant. It’s just kind of ugly and, in extreme cases, can reduce the vigor of your plant.
