| Gummosis is the oozing of sap from wounds or
cankers on fruit trees. Gummosis can result from
environmental stress, mechanical injury, or disease
and insect infestation. Cytospora canker or Valsa
canker, the fungal cause of gummosis, affects stone
fruit trees like apricot, cherry, peach, and plum.
Cytospora infection is distinguishable from insect
damage and mechanical injuries because sawdust or
pieces of bark are not mixed in the sap, as it would
be with insect or mechanical damage. Cytospora
canker is also known as perennial canker.
Symptoms and Diagnosis
On trees infected with Cytospora canker, new shoots
or leaves may turn yellow or wilt. Sunken lesions
develop on the bark. These lesions enlarge, and
gummy, amber-colored sap oozes from the bark.
Curly orange threads (fungal chains) may grow out
of the bark as the disease progresses. Leaves may
brown and drop. The disease kills the wood
underneath the cankers, often causing whole
branches to die. Infected wood and the defoliation
that may occur weakens the tree, but if the disease
infects the trunk, the whole tree may die.
Life Cycle
Cytospora canker is caused by one of two different
fungi. The fungus overwinters on dead wood or in
sunken lesions. Curly orange fungal chains will
release spores in the spring which are distributed by
winds and rain splash. Once the spores land on a
host tree, they enter through wounds made from
insect boring, mechanical injuries, or winter injury.
Symptoms are more prevalent during warm (70–85
degrees F), wet spring weather as the moisture
facilitates entry into wounds. Trees just coming out
of dormancy are most susceptible to the pathogen.
Integrated Pest Management Strategies
1. Be careful not to damage trunks with lawn
mowers or other yard and garden equipment.
Fungal spores enter the tree through injured tissue
where they germinate and penetrate the tissue.
This is the primary mode of infection.
2. Take steps to prevent winter injuries. Plant in
well-drained soils or amend soils to improve
drainage as needed. Avoid planting in open or
windy areas to reduce desiccation. Select winterhardy
cultivars matched to your hardiness zone.
Paint the lower branches and trunks of 1–3 year
old trees with white latex paint to reduce cold
damage.
3. Proper care and maintenance. Prevent insect
boring damage by maintaining the health of the
tree. Prune and dispose of diseased branches in
late winter. Burn infected wood, if possible.
4. Plant more resistant varieties. None of these are
immune, but fungal development is slower if the
disease becomes established.
Peach: ‘Bisco’, ‘Carmen’, ‘Champion’,
‘Harvelle’, ‘Jayhaven’, ‘Redqueen’,
Reliance’, or ‘Veteran’. |
