This important bacterial disease first manifests as blight in the leaves and flower clusters. Bacterial Diseases Bacterial Wilt ( Ralstonia solanacearum) If you know that rust is likely to be a problem, you can grow the cultivar ‘Frosty,’ which is resistant to this disease. Thin inside the hydrangea making sure to disinfect your pruning shears. This disease is difficult to control, but you can manage it by cleaning up infected leaves and debris that has fallen to the ground around both hosts.
The first symptoms are orange pustules on the bottoms of the hydrangea leaves and yellow spots on top. arborescens, and hemlock as its alternate host. This rust only infects the smooth hydrangea, H.
Like other rusts, hydrangea rust needs two hosts to survive and does not kill either of them. One way to control this disease is to apply a fungicide as soon as you discover it. You can prevent the disease by reducing humidity and increasing air circulation. Powdery mildew is most likely to be a problem on hydrangeas when the days are warm and the nights cool. Left unchecked, the fungus can infect the newly developing buds and stunt their growth. As the lesions get larger, the leaves can turn yellow and fall off the plant.Ī severe case of powdery mildew. Leaf Spots ( Cercospora species and Phyllosticta hydrangea)Ĭercospora manifests as circular purple or brown spots on the bottom of the plant. Options include iprodione, or thiophanate-methyl. If you have a persistent problem, you may need to use fungicides. Clean up debris around the plant, so that Botrytis can’t live on the dead tissue. Treat your pruning shears with bleach as you prune, so you don’t accidentally spread any disease.Īlso remove dead or damaged flowers and leaves to prevent the fungus from gaining egress into the plant. Space them properly, and prune branches that are closely spaced. If you can, keep good airflow around your plants. Don’t water late in the day, and only water at the roots, so you don’t get the flowers and leaves wet. You can take steps to try and prevent this infection. fabae).The reddish lesions on the leaves are a sure sign of Botrytis Blight.īotrytis is more likely to be a problem under cool and damp conditions, such as several days of cloudy, humid, and rainy weather. These can stay dormant for some time, but will eventually germinate to produce more spores.īotrytis cinerea has a very wide host range, but there a number of closely-related species which are much more specific to their host, including those infecting snowdrop ( B. The fungus forms black, seed-like resting structures (sclerotia) in dead plant tissue, which can carry the fungus through periods when host plants are scarce. It can also cause latent infections in primulas, where research has shown the fungus is seed-borne and develops with the plant, only breaking out after considerable growth has occurred.
This is very noticeable with strawberries. In some fruit crops the fungus enters flowers and colonises the developing fruit, but does not break out and cause a rot until the fruit begins to ripen and the sugar content rises. It is also able to cause latent infections, where the plant is infected but symptoms of the disease may not be produced for a considerable time. On green plant parts a wound or other stress is usually needed for infection, but on flowers and fruits it can infect without wounds, particularly under humid conditions. It thrives as a saprophyte (a micro-organism living on dead organic material), but can also infect living plants under certain conditions. Malvern Autumn Show - 22–24 September 2023īotrytis cinerea is an ubiquitous fungus, whose airborne spores are always present.RHS Garden Wisley Flower Show - 5–10 September 2023.RHS Garden Rosemoor Flower Show - 18–20 August 2023.RHS Garden Hyde Hall Flower Show - 2–6 August 2023.RHS Flower Show Tatton Park - 19–23 July 2023.RHS Hampton Court Palace Garden Festival - 4–9 July 2023.
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