Cytospora Canker of Peach and other Stone Fruit Trees

This past week I visited a peach orchard in Palisade at the request of the owner. His question was how to prevent and manage Cytospora canker (gummosis).


Cytospora enters through wounds such as those caused by
sunscald.

 The majority of the infection in his trees, and it was considerable, had gained entry through damage from sunscald and improper pruning cuts. The sunscald problem (South West Disease) was on the trunks but mostly on the upper side of horizontal branches.




sunscald damage on the trunk is a grat plant for
 Cytosopora to enter



Sunscald is the result of exposure to the winter sun between the months of November and March. Pruning during those months exposes previously shaded branches, especially the upper surface, often resulting in sunscald of that tissue. The bark cracks open due to its alternate freezing and thawing resulting in infection sites. This can be prevented by spraying the newly exposed branches with a mix of one part latex paint and nine parts water. This spray could also be applied prior to pruning. This is the same reflective spray used to protect the trunks of newly planted trees from winter sunscald damage.

This same spray should be applied on the trunk of established trees, especially if pruning or tree removal will expose a previously shaded trunk to the effects of the winter sun. You can learn more about sunscald at my sunscald web page at http://www.coopext.colostate.edu/TRA/PLANTS/sunscald.shtml.


Bad pruning cuts are great spots where Cytospora can
start an infection.



This photo shows sunscald on the upper side of a branch as well as infection of Cytospora through branch stubs. Note the cut made into the bark by a chainsaw. That is another possible infection site.



The infections at pruning cuts were due to leaving long stubs, not leaving enough of a stub, or damaging neighboring branches during the pruning process. Both of these prevent the rapid callusing over of the wound creating a great spot where the Cytospora fungus can invade the tree. Disinfecting the pruning equipment on occasion during the pruning process also would limit the extent of infection. Spraying the cuts with amber (orange) shellac, while time consuming, will help reduce infection at those sites. Pruning during wet weather should be avoided.



Crotch attachmentsa are some of the last areas on the tree
to proper acclimate for winter and thus susceptible to
winter damage and injury if the tree is not properly
prepared for winter.

 This Palisade orchard had a lot of dead wood due to Cytospora infection that needed to be removed making proper cuts in the process. Without clearing out and disposing of the dead wood by burial or fire, the infection potential will increase.

In addition to limiting infection sites for the fungus, keeping the trees healthy is equally important. Cytospora canker is a stress disease. It likes trees that are not in the peak of health. Cultivating the established orchard removes many of the feeder roots of the trees reducing tree health. Applying nitrogen fertilizer after mid-season and not drying the trees out in late summer just before your last irrigation of the year affect winter acclimation and increases the possibility of winter damage. This damage equates to more entry points for fungal attack. You can find more information on winter acclimation at http://www.coopext.colostate.edu/TRA/PLANTS/winteracclimation.shtml.

Proper management of Cytospora canker is critical to the longevity of the orchard. While the steps necessary to avoid infection and clean up diseased trees will take more of your valuable time and resources, you need to decide if these efforts are worth extending the life of the orchard and its fruit-producing years.

If you have a commercial orchard in Mesa, Delta, Montrose or Ouray Counties and would like me to visit your orchard give me a call at 970.244-1840. If you are a backyard orchardist and need a site visit call 970.244.1836.

You can learn more about Cytospora canker in the 2011 Utah-Colorado Commercial Tree Fruit Production Guide available from the Western Colorado Research Orchard Mesa Center (970 434-4364 ext 201) and read more about Cytospora at http://www.coopext.colostate.edu/TRA/PLANTS/gummosis.shtml.

Curtis Swift, Ph.D., Colorado State University Extension, Area Agent - Horticulture