Poop on a Stick: Odd and Alien Like Tree Problems.
By: Margaret Miller, Director of UFP
If you are anything like me you probably hike through the woods or stroll down the streets examining all of the trees and shrubs along the way. I am sure, like me, you have encountered some odd and possibly even alien like tree problems.
“Poop on a stick” is by far one of the strangest and more noticeable tree problems, and unfortunately is it not actually called poop on a stick… it just looks like it.
(above) choke cherry near Grand River in Donald Lamoreaux Park here in Kent County, Michigan.
You’re probably wondering what is this strange disease? The answer my friends is black knot disease. Black knot disease, also known as Apiosporina morbosa, is an unusual disease that affects the genus, Prunus. In Michigan, this is a major problem for plum trees, but can also be found on wild cherries and some ornamental cherries. Black, corky, bulging galls (which resemble poop on a stick) are found on the woody parts of the tree usual twigs and branches, but sometimes even the trunk. These galls often deforms the branch and causes them to bend and eventually the branch dies because the flow of nutrients is cut off at the gall. During the first year of infection, growths on the twigs are tan, smooth and velvety and difficult to spot. During the second year of the infection, the galls turn black and corky and much more noticeable.
A fungus (Apiosporina morbosa) which overwinters in the galls causes black knot disease. The fungus produces a fruit body that is embedded into the gall, in the spring, two winters after the initial infections, the fungus produces sexual spores that are released into the air via a heavy wind, rain or other disturbance. These spores land on other healthy branches or twigs and begins to infect a different healthy part of the tree or maybe a new tree all together.
Black knot disease has been reported on 24 species of Prunus and is found throughout North America but is most commonly found in the northeast. It was first reported as a destructive disease in Massachusetts in 1811. It was first described in 1821 by L. D. Schweinitz from specimens collected in Pennsylvania.
To control black knot disease the galls should be pruned from the tree during the winter, but remember that these infections are at least a year old and you will see another round of infection next year from infections that occurred the previous year. Once you have a gall on your tree it cannot be cured, you must remove the gall. It is important that you burn all infected clippings/removed branches because fungus spores can still develop and spread from galls left on the ground or in brush piles. So burn that poop on a stick!
Fungicides are rarely effective to prevent black knot disease. Most people do not notice this tree problem until the galls become obvious, which is usually two to three years after the initial infection. I know describing this disease as “poop on a stick” is a strange and “potty mouth” way to identify a tree problem, but trust me from now on you will always remember black knot disease! As always, feel free to contact a local arborist for more extensive management strategies and stay tune for my nest blog post addition of “Odd and Alien Like Tree Problems” when I talk about fascinating “alien tree gummies.”