It is one of the commonest diseases of Oak leaves, and right now, Oak mildew is particularly visible thanks to the cold spring and early summer heatwave.
The disease, caused by the fungus Erysiphe alphitoides, attacks young leaves and sometimes the young shoots, and is characterised by a white or greyish-white powdery coating on leaves and shoots.
It appears from May onwards in its primary phase of infection, but also affects the second flush of new Oak leaves in late summer.
Oak mildew can be particularly severe after a cool wet spring followed by warmer, humid weather in early summer – a pattern experienced across Britain in 2013.
Secondary late summer infections such as these can cause the trees to lose their leaves too early from affected shoots and prevent proper hardening off of young shoots. This can lead to further damage in winter if temperatures dip to -10C or below, as these unhardened buds and shoots may be killed.
This is why scientists need you to take part in the OPAL tree health survey before the end of September. Help us map the spread of Oak mildew by keeping your eyes peeled for signs of the disease and sending us your results.
- Find out how to spot Oak mildew and other pests and diseases
- Take part in the OPAL tree health survey
- Send us your results