In late summer and autumn, many plants get an attack of powdery mildew. Herbaceous perennials such as phlox and asters are particularly prone, with dry soil but plenty of moisture on the foliage as a result of dew. The plants are particularly stressed by the lack of moisture at the roots so are particularly susceptible. Plants aren’t killed by mildew, but their good looks and health are hit hard.
What is powdery mildew
Powdery mildews are a group of fungi that make a beeline for a wide range of ornamental and edible plants. With millions of their microscopic spores released into the air, infection is pretty inevitable. There are many different types of mildew that impact different plant species, but the result is similar. You will spot the white powdery fungal threads on stems, leaves and flowers often in late summer and autumn. In very bad cases leaves will become distorted.
Is there a cure for mildew
Chemical fungicides can be used to control the fungus but before you opt for this option try and solve the issue by simply gardening in a different way. Fungal diseases thrive where there is little air circulation so planting in an open, sunny spot away from walls is a way of reducing the risks. Mildew spores will readily germinate on damp foliage, so are likely to be an issue where plants are growing closely together and their leaves don’t dry out. Give susceptible plants space and, on shrubs, prune out overcrowded branches.
Maintaining good moisture levels at the roots of plants is key to reducing plant stress which can make them more vulnerable to mildew. Keeping the soil in good condition with regular mulches of organic matter to act as a sponge will help. When it comes to any watering that might be required during dry weather, apply it at the roots, first thing in the morning taking care to keep it off the foliage of plants.
Help reduce the immediate risks of mildew spread by picking off infected foliage as soon as it is seen, and collect infected leaves in the autumn to lessen the chances of the spores remaining in the soil until the following spring.
Are there any mildew resistant plants
Not all plants suffer from powdery mildew. But when selecting plants from vulnerable species, it is worth looking out for varieties that have been selected or bred specifically for resistance to the disease. For example, Aster x frikartii ‘Monch’ and Phlox paniculata ‘Franz Schubert’. You’ll notice that many of the seed companies highlight resistant courgettes, cucumbers and strawberries too, so give them a try.