Cornus anthracnose is a fungal disease caused by Discula destructiva, which arrived in the UK from North America in the late 1990s.

It infects and kills the leaves and young shoots of some North American Cornus species (dogwoods). Cornus florida is particularly susceptible, Cornus nuttallii and Cornus kousa may also be attacked. Native UK Cornus species appear unaffected.

Damage occurs from late spring until leaf fall in the autumn.

You may see the following symptoms:

• On leaves: Spots and blotches of dead tissue appear. Under wet conditions, the blotches expand and the leaf shrivels and falls. A severe attack can completely defoliate a tree
• On stems: Young stems die back and under wet conditions tiny raised pimples (fruiting bodies of the fungus) can be seen on the bark
• Bark cankers have been reported on susceptible Cornus species in the USA

The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.

Non-chemical control

• There is anecdotal evidence that the disease varies in severity from year to year, so raking up and destroying infected leaves may be helpful in reducing the amount of infection in the following year
• Choose resistant species. The most susceptible species are Cornus florida and C. nuttallii and, to a possibly lesser extent, C. kousa. In studies in the USA, C. controversa and C. sericea were also susceptible. Native European Cornus species in the UK appear unaffected. There is currently insufficient information available for other species

Fungicides

The RHS recommends that you don't use fungicides. Fungicides (including organic types) may reduce biodiversity, impact soil health and have wider adverse environmental effects. If you do intend to use a fungicide, please read the information given in the link and download below to ensure that use, storage and disposal of the product is done in a responsible and legally compliant manner.
  
The products listed in the ‘Fungicides for gardeners’ document below are legally available for use by home gardeners in the UK. This information is provided to avoid misuse of legal products and the use of unauthorised and untested products, which potentially has more serious consequences for the environment and wildlife than when products are used legally. Homemade products are not recommended as they are unregulated and usually untested.

There is no specific information available on the efficacy of any home garden fungicide against cornus anthracnose.

Download

Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)

Link

Chemicals: storing and disposing safely

The fungus Discula destructiva causes extensive damage in North America to the native Cornus species, which are an important landscape feature. The disease is known there as anthracnose and was first noted in the 1970s. The fungus is not thought to be native to North America, but its origins are unknown. It was first detected in the UK in the late 1990s and was probably introduced accidentally on infected plant material.

The fungus produces very small, pimple-like fruiting bodies on dead leaves and stems and in wet weather minute spores are released from these and  dispersed by rain-splash, wind-blown rain and, probably, by animals and birds. Wet conditions are required for infection.

No other spore types are known and it is assumed that the fungus can remain dormant in affected twigs and bark during the winter, to produce fresh spores the following spring.