Monday, February 18, 2008

Landscape - Bleeding Cankers on Deciduous Trees

The following is an article by John Hartman, University of Kentucky plant pathologist on bleeding cankers caused by the Phytophthora fungus in deciduous trees.

In recent years there has been much discussion about Phytophthora ramorum, cause of bleeding cankers and sudden oak death disease. Other Phytophthora-caused bleeding cankers on landscape trees have recently been described by Dr. George Hudler of Cornell University in an article in the 2007 volume of Arboriculture and Urban Forestry. In addition to journal articles, I have had the opportunity to hear Dr. Hudler speak on this topic.

Bleeding canker diseases are characterized by trunk lesions that leak fluid through the bark or leave fluid stains on the bark. Bleeding cankers can be caused not only by fungus-like organisms such as Phytophthora, but also by fungi, bacteria, pruning, other tree wounds, or insects. Field diagnosis of a Phytophthora canker requires a specialized kit (e.g., Alert LF Strip; containing a five-minute test that detects only Phytophthora. For laboratory samples of bleeding cankers, the Plant Disease Diagnostic Laboratory uses a Phytophthora-specific ELISA ( test.

Bleeding cankers of landscape trees may be caused by a number of Phytophthora species including P. cactorum, P. cambivora, P. cinnamomi, P. citricola, P. nemorosa, P. palmivora, and P. ramorum. Some, like P. ramorum, are not known to be present in Kentucky. To determine the which species of Phytophthora is in a sample, laboratory cultures or PCR tests would also be needed.

The following landscape trees which grow in Kentucky (and Delaware) are known hosts of bleeding cankers caused by species of Phytophthora. Although some bleeding cankers lead to tree decline or death, many of the Phytophthora bleeding cankers are not lethal and trees may be able to compartmentalize the lesions before they spread and girdle the tree.

-Beech can often be seen with Phytophthora-caused bleeding cankers.
-Birch bleeding cankers associated with P. cactorum can cause tree decline.
-Chestnuts are susceptible to ink disease, caused by P. cambivora or P. cinnamomi, and results in bleeding cankers on the roots and lower trunk. This disease was a serious disease of American chestnut before the arrival of Chestnut blight.
-Dogwood crown rot sometimes breaks out into bleeding cankers caused by P. cactorum.
-Elm infected with P. cactorum shows bleeding canker symptoms.
-Horsechestnut bleeding cankers have been attributed to P. cactorum and P. citricola.
-Linden is listed as a host of P. cactorum and producer of bleeding cankers.
-Maple bleeding cankers are often observed in Kentucky. At least five species of Phytophthora have been implicated as causes. Fusarium solani, a completely unrelated fungus, has also been implicated in maple bleeding cankers.
-Oak, in addition to being susceptible to P. ramorum, cause of sudden oak death (not present in Kentucky or Delaware) is also susceptible to P. cactorum, P. cinnamomi, and P. citricola, which cause bleeding cankers.
-Willow bleeding cankers have been attributed to P. cactorum.
-Other trees with bleeding cankers, but not caused by Phytophthora include: Crabapple (Botryosphaeria dothidea), Poplar (Cryptosphaeria populina and Ceratocystis fimbriata), Prunus species (a bacterium, Pseudomonas syringae), Sweetgum (Botryosphaeria ribis), Walnut (two species of the bacterium Brenneria).

Management of Phytophthora bleeding cankers of landscape trees is difficult. Recent development and approval of formulations of phosphorous acid such as Agri-Fos®, Alude®, Arborfos®, and Whippet® provide tools that may be helpful in combating Phytophthora cankers. Such treatments can either be injected or applied with the aid of an adjuvant/penetrant such as Pentra-Bark® that assists in the movement of chemicals directly through the bark into trees. Although much research needs to be done, preliminary results suggest that these treatments will gradually slow the growth of cankers and after a year or two, reduce their size.

Reprinted from PHYTOPHTHORA CAUSES BLEEDING CANKERS ON DECIDUOUS TREES By John Hartman in the February 11, 2008 edition of the Kentucky Pest News from the University of Kentucky College of Agriculture.

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