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

Recent research in Washington found that spores were produced throughout the year and were present in highest numbers during spring and summer on both cherry and peach. Spore production and dispersal resulted from the use of over-head and under-tree impact sprinklers. It was concluded that disease management could be improved by alteration of horticultural and irrigation practices.

Cultural Control

1. Trees should be maintained in a vigorous state.
2. Prune during mid- to late-winter when inoculum levels are lower.
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. Summer pruning results in many wounds that can be infected by cytospora canker. Summer prune in dry weather and allow time for pruning wounds to heal before using overhead sprinklers.
6. Sporulating infections on scaffold limbs or trees should be removed immediately and burned because they are a source of spores.
7. Use preventative measures to minimize winter injury, sunburn, rodent damage and insect damage.
8. Do not plant new blocks of stone fruit next to old cankered blocks. Nursery stock should be canker free and protected from wood boring insects such as peach tree borer.
9. Consider the effects of irrigation systems on disease development when planning new orchards. E.g. Drip or microsprinkler irrigation would result in less disease pressure than overheads.

Chemical Control

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