Privet is one of the easiest hedges to grow and has few serious health problems.1Nature Hills Nursery. Privet Hedge Pruning Guide | Nature Hills When it does get sick, the cause is usually a fungus taking advantage of a plant that is stressed, wounded or kept wet. That means most of the treatment is simple work, such as cutting out damaged growth, clearing fallen leaves and easing the stress on the plant, rather than reaching for a spray. The real danger hides underground, where root rots can quietly kill whole stretches of hedge.
How to Tell Which Disease Your Privet Has
The place where the damage shows up sorts most problems into groups:
- Spots on the leaves, stems still healthy: usually a fungal leaf spot or anthracnose.2Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Leaf Spot
- Dead twigs or branches with leaves still clinging: suggests a stem canker.3Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Anthracnose
- White or grey powdery coating on the leaves: powdery mildew, which favours warm, dry weather.4Hopes Grove Nurseries. How To Treat Powdery Mildew
- Yellow mottling or ring patterns: can point to a virus.5PubMed. A Novel Ilarvirus Is Associated with Privet Necrotic Ringspot Disease in the Southern United States
- Thinning, wilting or dying of whole plants: points to a root problem.6Royal Horticultural Society. Phytophthora Root Rot: Prevention Guide
A quick inspection narrows things further. Check the top and underside of several affected leaves. Follow any dead shoot down to see where the healthy wood begins, and scrape the base of the stem to look for discoloured bark or white growth. Note which part of the hedge is affected too, because one spot versus the whole run is a useful clue.
Timing and recent weather help as well. Leaf spot often follows a run of wet weather, while dieback often follows drought, frost or a hard clip. A decline that builds over months suggests the roots rather than the leaves.
Treat all of this as a first guess, since problems overlap and one hedge can have leaf spots and dieback at once. If the clues point two ways, deal with the more serious possibility first, which usually means checking the roots.
Leaf Spot and Anthracnose
Cercospora leaf spot begins as yellow patches that turn brown in the centre, with reddish-brown to purple borders.7Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Leaf Spot Some spots have a yellow halo around them.8Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Leaf Spot As the spots grow, they can join together and cause the leaves to fall.9Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Leaf Spot A related leaf spot fungus produces spots about 5 to 15 mm across, roughly pea-sized, with tan centres.10Plant Disease. First Report of Leaf Spot Caused by Pseudocercospora ligustri on Ligustrum japonicum ‘Howardii’ in China
Anthracnose causes round to oval spots with tan centres and scattered dark dots.11Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Anthracnose In moist weather a pinkish-white spore mass may show inside the spots.12Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Anthracnose Spots that start at the leaf edge are often linked to earlier damage to the leaf.13Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Anthracnose On the underside of the leaf, look for tiny tan to brown dots about the size of a pinhead.14Extension. Privet Hedge fungus
It helps to know what leaf spot is not. Leaf spots have a definite edge and a differently coloured centre, so you can point to one spot. Sun or wind scorch browns the leaf edges evenly and has no dark dots, and yellowing across the whole leaf with no spots is more likely a feeding or watering problem. Old leaves also yellow and drop in small numbers, especially on semi-evergreen privet in cold weather. If you can’t find spots on either side of the leaf, weather, watering or feeding is the better explanation.
The fungus spends the winter in dead twigs and fallen leaves.15Extension. Privet Hedge fungus Rain then splashes its spores onto weak or damaged leaves.16Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Anthracnose Hot, dry weather stops the disease, though it can return when conditions suit it again.17Extension. Privet Hedge fungus The problem can come back year after year, but it is rarely fatal.18Extension. Privet Hedge fungus
Twig Dieback and Stem Cankers
The anthracnose fungus can invade the stubs of cut twigs and form a canker, a sunken dead patch on the stem.19Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Anthracnose Cankers may be dotted with tiny pink pustules.20Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Anthracnose A canker on the side of a stem keeps spreading and can ring the stem completely.21Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Anthracnose Every leaf above that point then dries out and may stay clinging to the stem.22Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Anthracnose
Botryosphaeria fungi cause cankers and dieback on most trees and shrubs, but they only cause disease on plants that are already stressed.23Virginia Cooperative Extension. Botryosphaeria Canker and Dieback of Trees and Shrubs in the Landscape They get in through wounds, cracks, leaf scars and the small pores on stems.24Virginia Cooperative Extension. Botryosphaeria Canker and Dieback of Trees and Shrubs in the Landscape On privet, the leaf spots these fungi cause can spread into nearby shoots and kill them.25Plant Disease. First Report of Leaf Spot and Shoot Dieback of Ligustrum japonicum Caused by Botryosphaeria dothidea in China Heat, drought, frost damage and compacted soil all make plants more open to infection.26Virginia Cooperative Extension. Botryosphaeria Canker and Dieback of Trees and Shrubs in the Landscape
That is why ragged pruning invites trouble. Torn cuts and long stubs give fungi an easy way in, and dead stubs can be colonised first, after which the fungus moves down into healthy wood. Clean cuts close to a bud or branch heal faster.
Dead tips alone don’t prove a canker, since frost, drought and hard clipping can all brown shoots without any fungus. A canker usually leaves a clear line, with a sunken or cracked patch where living wood meets dead. Scattered dieback after a hard winter or dry summer points to stress as the trigger, with a fungus perhaps following behind. Dieback concentrated around old pruning cuts suggests fungi entering through those wounds.
Root Rots That Can Kill a Hedge
Honey fungus is a root rot that is especially common on privet in gardens.27PubMed. Associations Between Armillaria Species and Host Plants in U.K. Gardens In UK gardens, every recorded infection of privet, the plant it attacked most often, was caused by one species, Armillaria mellea.28PubMed. Associations Between Armillaria Species and Host Plants in U.K. Gardens
To check for it, peel back the bark at the base of a dying plant. A creamy-white fungal sheet under the bark that smells of mushrooms is the clearest sign. Honey-coloured toadstools at the base in autumn are another sign, and dead plants in a line that spreads along the hedge fit honey fungus too.
Phytophthora root rot is mainly a disease of heavy, waterlogged soils.29Royal Horticultural Society. Phytophthora Root Rot: Prevention Guide Its symptoms are very hard to tell apart from waterlogging alone, so digging to look at the roots is the way to check.30Royal Horticultural Society. Phytophthora Root Rot: Prevention Guide An affected plant has a poor root system, with many of its fine roots rotted away.31Royal Horticultural Society. Phytophthora Root Rot: Prevention Guide The larger roots are brown or black inside, softer than normal, and break easily.32Royal Horticultural Society. Phytophthora Root Rot: Prevention Guide
Root rot is easy to miss until it is advanced, since the first sign is usually leaves thinning, yellowing or wilting above ground. Wilting despite plenty of moisture in the soil suggests the roots can no longer take up water.
Neither rot can be cured once established, and no garden fungicide reliably helps. Dig out the dead plants along with as much of the root as possible. After Phytophthora, improve drainage before replanting. If honey fungus is confirmed, consider a less susceptible plant in that gap.
Virus Problems and Galls
Necrotic ringspot is a virus disease of Japanese privet in the southern United States.33PubMed. A Novel Ilarvirus Is Associated with Privet Necrotic Ringspot Disease in the Southern United States It spreads through grafting and has been known for more than 50 years.34PubMed. A Novel Ilarvirus Is Associated with Privet Necrotic Ringspot Disease in the Southern United States In Europe, a different virus causes leaf blotch with ring-shaped spots on privet.35PubMed Central. Identification and Molecular Characterization of a Novel Hordeivirus Associated With Yellow Mosaic Disease of Privet (Ligustrum vulgare) in Europe
Ring-shaped or mottled patterns that follow the leaf shape, rather than forming separate bordered spots, are more typical of a virus. Nutrient shortages can also produce yellow patterns, so a virus is more likely when the pattern persists and shows on new growth as well as old. Viruses are rare in ordinary hedges, so a fungal leaf spot is the likelier explanation unless the pattern is clearly odd.
Swellings, or galls, on privet stems are thought to be caused by a Phomopsis fungus.36Extension Pest Management. Crown Galls They are managed with cultural methods rather than sprays.37Extension Pest Management. Crown Galls
Sprays have no effect on viruses. Cut off galled stems below the swelling and bin them, and remove plants with severe virus symptoms rather than taking cuttings from them. An extension service or plant clinic can confirm the problem.
How to Treat Leaf and Stem Diseases
Cut cankered or dead stems back into healthy wood below the damage, because the fungus can keep spreading down the stem from a canker.38Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Anthracnose To find the spot, follow the dead stem down until the bark scratches green and alive. Cut a little below that point, just above a bud, side shoot or the main stem, so the wound can seal and the plant has somewhere to regrow from. Check the cut face: if the inside is still brown or stained, cut further back until it is clean and pale.
Rake up and bin fallen leaves and dead twigs rather than composting them, because the fungus spends the winter in that debris.39Extension. Privet Hedge fungus A home compost heap often doesn’t get hot enough to kill fungi, so bin or burn where local rules permit. Clear under and around the hedge once it has stopped dropping leaves, so you don’t repeat the job. Water at the base and not over the leaves, since rain splash spreads the spores.40Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Anthracnose
Wipe pruning blades with alcohol between cuts on infected wood. Prune in dry weather so rain doesn’t splash spores into fresh cuts, and make clean cuts without leaving stubs.
For leaf spot, fungicide is applied every 2 weeks during wet weather.41Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Leaf Spot Home-garden products listed for privet leaf spot include chlorothalonil (Bonide Fung-onil) and myclobutanil (Spectracide Immunox).42Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Leaf Spot Start spraying as new leaves open in a wet spring rather than after the damage has appeared. But since leaf disease is rarely fatal, a hedge that recovers by summer may need no spray at all.43Extension. Privet Hedge fungus
If you do spray, follow the label’s rate exactly and cover both sides of the leaves. If you spray all season, alternate between products that work in different ways, such as the two above.
Keeping Privet Healthy So Disease Doesn’t Return
Avoiding plant stress is the best way to prevent Botryosphaeria.44Virginia Cooperative Extension. Botryosphaeria Canker and Dieback of Trees and Shrubs in the Landscape Stressed and weakened plants also favour anthracnose.45Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Anthracnose Watering during drought and relieving compacted soil help.46Virginia Cooperative Extension. Botryosphaeria Canker and Dieback of Trees and Shrubs in the Landscape A workable schedule is a light trim in late spring and another in late summer. Avoid hard cutting during heat or drought, save renovation cuts for late winter, and don’t trim when the foliage is wet.
Give the hedge airflow and good soil as well. Space new plants so air can move between them, and mulch to hold moisture but keep it away from the stems. Fix poor drainage before planting into heavy soil.
European privet is highly prone to anthracnose, but Amur, California, Ibota and Regal privets are fairly resistant.47Pacific Northwest Pest Management Handbooks. Privet (Ligustrum spp.)-Anthracnose Pick one of these when replacing or extending a hedge.