Cytospora canker on hardwoods, particularly caused by Valsa sordida, and Leucostoma sp. is a significant and destructive disease affecting various hardwood trees. Cytospora canker on hardwoods is notorious for its detrimental impact on fruit trees( Prunus species, apples, pears, cherries, peaches, and plums.), ornamental trees(maples, ash, birch, oaks, elms. Mountain ash, etc. ), and forest species ( aspen, poplars, and willows).
The fungus thrives in poor sites, cool, wet conditions, which facilitate the dispersal of spores and infection of host plants. Stressed trees, particularly those experiencing drought, nutrient deficiency, or other diseases( such as fire blight), are more susceptible to infection. The fungus often enters through wounds caused by severe pruning, injuries by pruning, drought, frost, mechanical damage, insect activity, or environmental stress.
Symptoms
Cytospora canker caused by Valsa sordida presents a variety of symptoms depending on the host species and environmental conditions. Cytospora canker are known to cause branch dieback and cankers on trees of all ages. The cankers on trunks and limbs typically appear as elongated, slightly sunken, discolored areas on the bark. The bark often splits along the canker margin due to the formation of wound wood by the host. The fungus can swiftly girdle and kill twigs without forming visible cankers. Symptoms vary depending on the host species and the stage of disease development. Common symptoms include:
- Cankers: Infected bark above cambium appear sunken, discolored areas on the bark that often exude gummy or resinous sap.
- Dieback: Progressive death of branches from the tips downward creating a Shepard’s crook.
- Discoloration: Affected areas may turn dark brown or black, and underlying tissues may show reddish or brown discoloration.
- Gum exudation(Gummosis): Resinous gum often oozes from cankers, especially in stone fruits like cherries and peaches.
- Leaf yellowing and premature leaf drop: Infected branches may show yellowing leaves that drop prematurely.
Picture 1. Sunken bark on aspen tree ( L ) yellow spore tendrils on aspen ( C ) early infections and gummosis on cherry tree( R )
Management and Control
For fruit growers and nurseries, Cytospora canker can lead to substantial economic losses due to reduced yield, increased tree mortality, and the cost of management practices. There are few management options for the control of the Cytospora canker:
- Accurate identification of Cytospora canker through laboratory testing is essential for proper management
- Treat the first symptoms as soon as possible. Regularly inspect trees for early signs of infection, such as resin exudation, canker formation, and needle discoloration. Early detection allows for timely intervention and reduces the spread of the disease.
- For fruit tree remove the gum from the bark before applying any treatments
- Prune fruit trees during dry weather to minimize the risk of infection and ensure proper wound healing. Burn or dispose of pruned branches away from healthy trees.
- Sterilize pruning tools between cuts to prevent cross-contamination. Do proper pruning and do not leave pruning stubs.
- Evaluate for nutrient availability in soil and leaf tissue for exhibited deficiencies of many different micronutrients, especially iron (Fe), manganese (Mn) and zinc (Zn),
- Minimize environmental stresses by providing adequate water during dry periods, applying mulch to conserve soil moisture.
- Chemical/fungicide treatments are generally not very effective in controlling Cytospora canker
