Crabapples, Hawthorns, Pines
and the Fungi that attack them
by Jim Cameron - April 2006
Jim Cameron has a master’s degree in hardwood management and is an International Society of Arboriculture certified arborist. We are fast approaching the time of year when trees in our landscape are prone to attack by common fungi. During the spring when rains return and temperatures rise, several fungi become active.
The most common plants that are prone to attack this time of year are: crabapples, hawthorns, Austrian pines and Scotch pines. These fungi do their damage April through Early June; however, we do not see the damage on our trees until July and August.
On crabapples and hawthorns, the damage appears on the leaves. You will usually see yellowing leaves with black or red spots. Eventually, the trees will lose a majority of their leaves and fruit. In pines, damage occurs on the newly expanding tips. These expanding tips will turn brown. After several weeks, the brown tips will die and turn grey. See photos below for examples of these diseases.
The names of the fungi are Apple Scab (crabapples and hawthorn), Cedar-Apple Rust (hawthorn and crabapple), and Tip-blight (Austrian and Scotch pines).
The problem with these fungi is that you must treat them before you see damage to your tree. This means the time to begin treating your trees is fast approaching.
The first part of April is the best time to start treating crabapples and hawthorns. Usually, mid to late April is the best time to begin treatment on the Austrian and Scotch pines.
As mentioned above, the fungi do their damage over a span of three months; thus, you must protect your trees for this amount of time. Trees need to be treated at 2-4 week intervals, depending on the fungicide used and the particular tree (i.e. crabapple, hawthorn, pines) being treated.
There are a limited number of products that are designed to stop fungi if the tree is already infected; however, you will still see damage to your tree.
Treatment of your trees is best left to a professional plant health care company. However, you can treat your trees yourself. You will find products at local lawn and garden stores for fungal treatment. Keep in mind, it is difficult to get proper coverage from a hose-end sprayer. Professional companies will have access to the best products and proper equipment. If you decide to hire a professional company, review its program and make sure that you are getting the proper timing and number of applications.
