Garden doctor new plant diseases
Nick Bailey looks at recently arrived plant diseases – and what to do about them
Thanks to a combination of climate change, globalisation and the free movement of goods, new plant diseases are arriving on our shores at an unprecedented rate. Some kill plants outright, while others simply disfigure them. Still, with good garden management and careful plant selection, it’s certainly possible to lessen the impact of these diseases. Perhaps the best-known recent arrival is box blight. This fungal disease causes box leaves to turn brown and fall, and can lead to black streaks on young stems. Dead patches should be cut out and burned, along with all the fallen leaves at the base. If the entire plant is affected, it’s often best to remove and burn the whole lot. Symptoms to look for There are a host of other diseases that attack woody plants. One newcomer that made headlines recently is ash dieback, or chalara. This fungal disease can be lethal to our native ash trees. Look out for crown dieback, brown stains or lesions on stems, leaf buds failing to open in spring, and clusters of blackened leaves in early autumn. Good garden hygiene and removal of affected branches is the only control. Sweet chestnut blight was found in the UK in 2011 and is now spreading. The first sign is usually splitting bark on the trunk and branches, as the cankers take hold. It can kill sweet chestnuts, and may also attack oaks. Plane trees are now at risk from massaria disease. This first shows itself as lesions or wound-like scars on higher branches. These can go on to cause the branch to die and fall. There is no effective treatment, but good tool hygiene can limit its spread. The disease currently running amok more than any other I know is Phytophthora ramorum. It can affect a huge range of woody plants, proving fatal to some species, while others act as hosts. Symptoms include dieback of shoot tips, dark patches on leaves, and dark sap bleeding from the trunk and stems. The pathogen is near impossible to eradicate, even with chemicals, so early detection and removal of affected plants is crucial. It’s not just woody plants that are under attack from diseases. Perennials can be affected too. One disease that is new to the UK and currently causing concern is aquilegia downy mildew. All of these diseases are already established in the UK, but there’s a new threat on the horizon – Xylella fastidiosa. Spread by sap-sucking insects, this bacterium affects a wide range of productive and ornamental plants, such as olives, oaks, grapes and citrus. Symptoms include wilted or scorched leaves and areas of significant or total dieback. Now UK nurseries are not permitted to import plants from outside the EU without certification that they are disease free, which requires an inspection. Similarly, anyone importing host plants from the EU must ensure they are accompanied by a plant passport confirming they have been sourced from a xylella-free area. As gardeners we can help by being vigilant but do bear in mind that there are many diseases that look like each other and plants often look unhealthy in winter. So don’t panic, check the websites in the panel on the right if you’re worried and only buy your plants from sources you trust.