Cytospora Canker (Leucostoma Canker)

Causal agent: Leucostoma cincta

Symptoms include the presence of dead twigs or branches after the tree has leafed out in the spring. Closer examination of dead limbs often reveals slightly sunken areas in the bark. Small, black, pimple-like fruiting bodies of the fungus often develop under the bark in these sunken areas. Later in the spring, hair-like masses of spores are extruded from these pimple-like structures. Conidia (spores) are most abundant in the fall and spring. During rain or irrigation, spores are splashed and blown around the orchard. Infection occurs through injuries to the bark such as pruning wounds, leaf scars, winter injury, and sunburn. After the fruiting bodies have been washed by numerous rains, small white dots remain on top of the pimple-like structures and serve as useful indicators of the fungus.

Young cytospora cankers can be difficult to distinguish from bacterial canker.

Cytospora canker Photo courtesy Agriculture & Agri-Food Canada

Cytospora canker. Note hair-like masses of spores. Photo courtesy Agriculture & Agri-Food Canada

Normally cytospora canker is not serious in apple trees, although in the past it has become troublesome in some orchards in the Creston area following early cold winter temperatures. The Cytospora species which infects apples is a different species from the one which infects stonefruit and does not spread from apple trees to healthy stonefruit trees or vice-versa.

Cultural Control

1. Trees should be maintained in a vigorous state.
2. Prune as late in the spring as possible to take advantage of the more rapid rate of wound healing which occurs at higher temperatures.
3. To encourage rapid healing-over, cut branches just beyond the ridge of the thickened bark which connects them to larger limbs. Do not leave pruning stubs. Avoid large pruning cuts.
4. Trees should be trained properly so that wide crotch angles are developed.
5. Sporulating infections on scaffold limbs or trees should be removed immediately and burned because they are a source of spores.
6. Use preventative measures to minimize winter injury, sunburn, rodent damage and insect damage.

Chemical Control

1. There are no fungicides registered in Canada for the control of cytospora canker on stone fruit.