Diseases leave a prominent sign on the plants and trees they affect. Examples are leaf spot, powdery mildew, and verticillium wilt.
Leaf Spot
What distinguish plants with leaf spot disease from plants with other diseases are the brownish or, some times, tan or black spots on the leaves.
Trees or shrubs that exhibit brownish, tan or black spots may suffer from leaf spots.
(Courtesy: Minnesota Dept. of Natural Resources Archive)
It can be a threat to the entire garden when conditions are wet. Defoliation could occur if conditions are favorable for the fungus. Although there could be severe defoliation, the disease will not kill an otherwise healthy tree.
The best way to handle this ailment is to prevent it from happening because once the spots are obvious; it is often too late to treat.
It is essential that you heavily water your trees during dry periods to minimize stress. Don’t water over the top of the leaves. Instead, soak the roots with a hose. Rake up and burn diseased leaves that have fallen off the affected tree and fertilize the tree to restore its health.
You can use fungicides that are available from most local hardware stores to control the leaf spot. However, use the substance cautiously because it can injure some plants. Read the label before applying and follow directions during use. The severity of the damage will determine if you have to apply more fungicide.
Powdery Mildew
White or gray film on leaves in the late summer may show signs of powdery mildew. The leaves will ultimately turn brown and drop off early. The disease can spread from one part of a tree to another when wind carries spores from leaf to leaf.
White or gray film on leaves of trees or shrubs may indicate powdery mildew.
(Courtesy: Wikipedia https://en.wikipedia.org/wiki/Powdery_mildew)
As time passes, the mildew will cause stress and harsh or recurring inflection could weaken the plant. While the powdery mildew will not kill the tree or plant, it will become more vulnerable to other issues and cause plant defoliation, fall dormancy, or adversely affect appearance.
Some things you can do to prevent the disease is to locate the plant or tree in full sunlight in a well-drained area of the lawn. Do not crowd plants and assure that there is good airflow and ventilation to prevent mildew growth. Water the roots of the plant in the morning so it has the rest of the day to dry off.
If symptoms appear, prune affected parts off the plant. Disinfect the pruning tool before using with a solution of one part bleach to four parts water. If the infestations are severe, remove and destroy the plant.
The best fungicides to deal with Powdery mildew are sulfur-based sprays. However, use the substance with caution because it could injure other plants. You may have to apply the fungicide more than once depending on the severity of the infection.
Verticillium Wilt
If the leaves of a tree appear singed, then there is a good chance the tree is affected with verticillium wilt. If one is infected, then it may
Trees or shrubs with Leaves that appear to be singed show signs verticillium wilt.
(Courtesy: Joseph O’Brien, USDA Forest Service)
experience a rapid decline. The disease starts on the leaves, and then moves to twig shoots. It can spread until it takes out the entire tree. It is so devastating it can take out a healthy Norway maple tree in just one season.
A soil born illness that is almost always fatal, verticillium wilt compares to the hardening of the arteries on a human. It restricts nutrient movement through the veins of the tree. It may take a few years for signs of the disease to show itself, but once visibly noticed the tree will die and needs to be removed. Infected soil can spread the disease to other trees.
To proper treat you need to enhance the growing conditions of the tree or shrub affected. That means fertilizing the tree or plant to encourage growth and watering it to prevent drought stress. Since saturated soils are bad for plant roots, do not over water. The fungus exists throughout the plant, so pruning will not free the tree. However, pruning off weakened limbs does help to guard against other types of fungi and insects.
