Shab Disease
Phomopsis lavandulae
The most serious disease of lavender, a fungus that makes shoots wilt and die back and can kill an established plant. It often lurks unseen for a long time, then suddenly collapses shoots across the plant, and there is no chemical cure.
🔎 How to spot it
Symptoms begin on new growth, which wilts and develops dark spots or browns and dies, then spread to the older, lower stems until whole shoots are brown and dead. Tiny black fruiting bodies appear on the affected woody stems, releasing spores that spread to other plants. The disease can take months or years to show, then bring on a sudden, widespread wilt.
🥀 Damage it causes
Affected shoots die back and, as the infection spreads through the plant, it can kill the whole lavender. Because symptoms come on suddenly after a long hidden phase, a planting can decline rapidly once shab takes hold.
🔬 What causes it
The fungus Phomopsis lavandulae, whose spores are spread by wind and splashing water and enter through leaf axils on young summer shoots or through fresh wounds. Damp conditions and crowded, poorly aired plantings favor it. English lavender is susceptible, while some types such as French lavender (Lavandula dentata) show resistance.
🛡️ Prevent it
Start with certified disease-free plants and never take cuttings from a plant showing any dieback. Give lavender the open, sunny, sharply drained, airy conditions it wants, avoid overhead watering and unnecessary wounding, and space plants well. Grow resistant lavender types where shab is a known problem.
🧯 If it is already here
There are no effective fungicides for shab, so it is managed by removal: cut out and destroy affected shoots well into healthy wood, or dig up and dispose of badly infected plants to stop spores spreading. Replace losses with clean stock, ideally on a fresh site, and propagate only from healthy plants.
💡 Good to know
Shab is easily confused with winter cold or waterlogging dieback; the giveaway is the tiny black fruiting bodies on dead stems and the spread from plant to plant. Keeping plants lean, open, and dry is the best defense.
For educational and informational purposes only. Disease management advice is general guidance drawn from university cooperative extension sources; always identify a problem positively and read and follow the label on any product before use, especially around food crops, children, and pets.