Black Knot is affecting more and more trees in the Ponoka area and should be regarded as a serious flora problem.
The disease is caused by the fungus Apiosporina morbosa and commonly affects Amur Cherry, Apricot, Black Cherry, Chokecherry, Dropmore Cherry, Flowering Almond, Japanese Plum, Korean Cherry, Mayday Tree, Mongolian Cherry, Nanking Cherry, Pin Cherry, Cultivated Plum, Wild Plum, Prunus Hybrids, Sand Cherry and Sour Cherry trees.
Shayne Steffen, Ponoka county manager of agricultural services says infected trees should have their diseased limbs pruned and heavily infected trees need to be completely removed. The materials should be burned or buried in a landfill and any tools used for pruning or removal should be disinfected before using on another tree
“I have seen the number of Black Knot infected trees growing in the Ponoka area. Some of the infections in the trees are high up so I would recommend using a professional certified arborist for removing these high up branches,” said Steffen.
According to the Alberta Government’s Agriculture and Rural Development website Black Knot reduces the aesthetic value of infected plants, spreads rapidly and may result in the death of the plant.
As the airborne fungi spores land on the tree, a small olive green growth will appear on the tree and if not dealt with, will mature over a two to three year period into a large black, tar-like growth. The growths may rupture and release large amounts of spores into the environment. It may also continue to grow internally and eventually cause death.
When pruning, if the branch is not removed beyond the internal infection the fungi can re-grow.
There are other options to combat the disease, such as chemical control or buffer zones between plants, but they aren’t recommended.
For more information on Black Knot visit http://www1.agric.gov.ab.ca/%24department/deptdocs.nsf/all/faq7622