|Cytospora enters through wounds such as those caused by|
|sunscald damage on the trunk is a grat plant for|
Cytosopora to enter
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.
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