Win Cowgill, Professor and Area Fruit Agent
Bacterial Canker continues to be a serious bacterial disease of both sweet and tart cherry in New Jersey as well as all other regions where the climate is humid.
Bacterial canker or bacterial gummosis of sweet cherry is caused by several Pseudomonas bacterium.
This disease infects flower buds and spurs.
It can completely kill new spurs and leaves and then move into the trunk on cherry. This is especially problematic with our new Geslia Dwarf cherries as losing a scaffold or getting infection into the trunk will limit production as the tree rapidly declines.
Control now with Copper if your flower buds are not yet open. I like to have two applications of copper applied in the spring, the first application made right at bud swell, as a Bordeaux spray using copper sulfate.
If you still do not have flowers showing you can apply additional copper, as a fixed copper.
Thorough coverage is then important; I apply this spray as full dilute spray as calculated by tree row volume.
Note: In our humid climate in New Jersey the cankers can continue to develop in lateral branches and the central leader. In some cases the cankers have grown to girdle and kill two-year wood. I have observed central leader dieback as a result.
This bacterial disease is most troublesome in young plantings where it can cause loses of up to ten percent of the trees. On mature trees it can reduce yields from 10–50%.
Many growers who did not think they had bacterial canker are beginning to see it on three and four year old trees.
The source of inoculum may come from wild cherry trees in our hedgerows, Black Cherry; Prunus serotina may be one source of inoculum for the Pseudomonas during wind and rainstorms in the spring and summer months. Removal may be beneficial.
Pruning Cherries and Bacterial Canker
We should avoid large, dormant pruning cuts; and use summer pruning (immediately after harvest) to minimize the impact of the disease. Note that on trees utilizing Geslia Rootstocks, some cuts have to be made in the dormant stage. I suggest waiting to close to bloom.
Look for three days of clear sunny low humidity to begin pruning. Spray copper before starting and immediately after pruning before the next rain event.
Bacterial Canker Management of Cherry In Oregon is a fact sheet with an 11-step program to minimize bacterial canker in cherry. To my knowledge we have no resistance to Copper with bacterial canker in NJ.