What is Apple Anthracnose/Bull’s Eye Rot?
Apple anthracnose is a fungal disease that is predominantly caused by several species of fungus that cause anthracnose (Cryptosporiopsis curvispora, Neofabraea malicorticis, etc) and bull’s eye rot (Neofabraea alba, Neofabraea perennans, etc). This disease is most prominent in regions with cool-humid summers and heavy rain in the spring such as Eastern North America and coastal British Columbia. However, there have not been many reports of this disease in New York State. The two most prominent symptoms of Apple anthracnose are: anthracnose cankers on the tree and bull’s eye rot on harvested fruit. Anthracnose infection compromises the long-term health and structure of the trees, and the post-harvest symptoms can destroy large portions of the harvested apples if not managed properly.
What does Apple Anthracnose/Bull’s Eye Rot look like?
First infection occurs in the fall, but becomes visible in the spring on the bark of younger branches as reddish brown circles, working down into tissue layers just below. Actively growing cankers will then start showing on small, young branches and increase in frequency if left unattended. Over multiple seasons, as the number and size of cankers increases, noticeable girdling will affect those branches, damaging health in specific areas of the tree. As the infection develops, the anthracnose can travel to larger branches where the cankers can cause long-term structural damage to the whole tree. Noticeable signs of reddish-brown broken and cracked bark can be seen where cankers are growing.
The fruit infection, bull’s eye rot, increases in frequency as the season approaches harvest time. The first appearance will be on the fruit skin as pale yellow to brown specks >1 inch in diameter. After harvest, the affected sites will be sunken on the fruit, developing a U-shaped area of browning, mealy tissue. The lesion on the skin will show light brown to dark brown rings that will resemble a “bull’s eye”.
Where does Apple Anthracnose/Bull’s Eye Rot come from?
Anthracnose fungus overwinters in the cankers through a dormancy period, continuing development the following spring. Some alternate hosts of anthracnose fungus are crabapples, hawthorn, mountain ash, and most pome fruits. The main transmission of this disease is through wind and rain splashes. The fungus infects damaged wood at higher rates, but is also capable of entering undamaged bark. A key contributor to the success of anthracnose is the presence of wooly apple aphids in the orchard. Bark cracking and damage caused by cankers provide easy entry spots for wooly apple aphids. Their injections along the edges of the cankers result in direct pathways into the tissue of the tree so the fungus can re-enter those areas.
How do I prevent and control Apple Anthracnose/Bull’s Eye Rot?
– Avoid planting cultivars that are highly susceptible to anthracnose (e.g., ‘Empire’, ‘Gala’, ‘Spartan’)1
– Scout consistently and prune cankerous branches
– Cut out cankers with a pruning knife with several extra inches of buffer
– Remove and burn trees with extreme infections
– Screen new incoming plant material for cankers
– Keep fruit dry after harvest
– Control woolly apple aphids
For more information on Apple Anthracnose and Bull’s Eye Rot:
Timing of Apple Fruit Infection in Stored Apple Fruit (Aguilar et al. 2017)