Edible garden – Spikes on serviceberry fruits


Is this serviceberry? Why are there white spikes on the berries?


Yes, this is serviceberry. The white spikes on the berries is likely a Cedar Rust disease, a fungal disease that can affect serviceberries.  There are several types of cedar rust disease that affect different pairs of trees.  Despite the name, the primary host is any of several different varieties of juniper.  Cedar rust has a complex lifecycle that takes two different hosts and two years to complete. Depending on the type of cedar rust disease, secondary hosts include specific members of the Rose family such as apples, crabapples, hawthorn, pears, quince and serviceberry.

On junipers, a gelatinous gall forms about after about 18 months from the initial infection.  The gall sprouts “horns” that turn bright orange and release spores triggered by spring rains.  These spores cannot infect other junipers, but rather need to find a new secondary host, such as serviceberry.   The disease takes different forms on different hosts, but depending on the specific cedar rust disease, you may also notice brown rusty spots on twigs or leaves.

Fungal diseases have been fairly common this year because of our wet spring, which contributes to both the spread and growth of fungal diseases. While unsightly, the disease is unlikely to cause any permanent damage to your tree.  Control can be difficult because you need to address the disease in two different hosts.  The spores can spread between hosts up to 7 kilometers apart, but typically the hosts are within a few hundred meters of each other.  Chemical control with a preventative fungicide in the spring is possible, but the Ontario pesticide ban restricts the use of most fungicides, with some limited exceptions.  You can find out more about what types of pesticides are allowable under the ban here.  If you or a neighbor have a juniper, look for the emerging of galls, and physically remove the branch with the galls, which may help reduce the likelihood of infection in future years.