How to identify and treat diseased trees
This year seems to be particularly bad for fire blight and other diseases on trees so I thought I’d pass on some information on a couple of diseases that seem to be showing up and how to identify and treat them.
Warm and humid weather conditions in the summer are ideal for tree growth but unfortunately, they are also ideal for the development of a bacterial disease of fruit trees known as fire blight. Fire blight affects primarily the rose family of trees and shrubs. Common members of this family include apple and crabapple, pear, mountain ash, cotoneaster, raspberry, flowering almond and Saskatoon. The bacteria can kill flowers, twigs and branches and sometimes whole trees and shrubs.
The diseased leaves appear red and fire-scorched, hence the name. Blighted leaves eventually brown and die but remain attached to the tree. New growth exhibits a dramatic downward wilting at the tips, resulting in a distinct shepherd’s crook on the ends of the infected twigs. A clear amber liquid may be found oozing from the diseased twigs. This liquid is highly charged with the bacterium, which causes the disease. Transferring even a minute amount to healthy trees can generate new infections. Some trees may develop secondary infections indicated by bark cankers, which appear as indented, discoloured areas on the branches and trunks. Bark cankers are usually more serious infections and kill the tree.
The fire blight bacteria can spread a number of ways, including insect transmission, use of contaminated pruning tools and strong winds and rain. Hailstorms help spread the disease by wounding the bark and making the tree vulnerable to infection.
If your tree is infected with fire blight, the first step to controlling the disease is to prune, remove and destroy all diseased wood.
However, since pruning can also be a means of transmission it is critical that the correct procedure is followed to ensure that no diseased wood is left and no healthy wood is accidentally infected. In the summer, all pruning cuts should be made a minimum of 10 inches into healthy wood. The bacteria are less infective during the winter, and therefore pruning cuts only need to be five inches from points of infection.
Using a clean, sharp knife to excise a strip of bark around the infected area can arrest the growth of bark cankers. The knife blade must be sanitized after each cut. Cotoneaster hedges should be inspected prior to shearing and suspect twigs or stems cut and removed well below the infection.
Tree blight is a group of bacterial and fungi diseases that affect a variety of trees. Diplodia blight is a common type of disease that affects conifers or pine trees. Trees infected show signs of stunted growth. Maple wilt, also common, affects maple varieties and is caused by a fungus. Other blights affect hardwood trees, chestnut trees, Dutch elms and orchard trees.
The best battle plan is to take preventative measures. First, it is best to have a professional examine your trees regularly. Also, if you are in a position to do so, plant trees that are resistant to tree blight. Lastly, spray your trees with fungicides to kill fungus-related diseases and insecticides to kill the insects on the infected tree and make it impossible for them to carry that infection to other trees.
Unfortunately, there are no cures for many forms of tree blight, either the bacterial or the fungal kinds. Sometimes a blight that proves lethal for one type of tree does not kill another type. The only treatments are fumigants, which kill pests and sever root systems to protect healthy trees.
Although tree blight seriously cripples and kills trees, being proactive is a major step in the battle. Take notice of your trees and shrubs. Spray them with the necessary fungicides (Safer’s Defender Fungicide or Bordo Copper Spray) and fumigants. Defender Fungicide and Bordo Copper Spray also control black spots, rust and mildew. Most importantly, when a tree is infected remove it immediately to stop the spread of the disease.
Joyce Swaren is the owner and head horticulturalist at Blondie's Gift and Garden.