We all know what healthy leaves look like, but what happens when they’re not healthy? Leaves can become discolored, have bumps or brown or red lesions. Smudgy spots on foliage or leaves that appear dried out or burned are also a sign of poor health. Problems impacting the leaves of trees have many causes. These foliar issues may be serious or simply cosmetic. Insects or mites are sometimes the cause. Further, drought or improper watering as well as root disease can make leaves turn yellow and die. However, foliar fungal diseases are most often the culprit.
Common Foliar Diseases
Some common foliar diseases are dogwood anthracnose, cherry brown rot, and apple scab to name a few. Depending on the disease, a specific tree or shrub species may be impacted or many types may be at risk. The symptoms vary from species to species. These diseases typically thrive in moist, cool weather so they are most prominent in spring. A rainy spring will further increase the likelihood of fungal infection and lengthen the time pathogens are active.
Different issues often yield similar symptoms. With this in mind, identifying the disease is key. For example, dogwood anthracnose can kill flowering dogwoods whereas dogwood spot anthracnose causes leaf and bract spots or whole-leaf blight, but does not typically not kill trees. People often confuse these diseases.
As with most things in life, it’s near impossible to fix an issue without correctly establishing the underlying cause. This is especially true in tree care since treatment recommendations can be vastly different depending on the problem. That’s why the first step in addressing any issues with the leaves should always be accurate identification of the cause. If a fungal disease is present, you can then take appropriate action to protect your trees.
Preventing Disease to Keep Leaves Healthy
One of the best things you can do in treating and preventing foliar diseases is to remove all diseased tissue. Bag impacted leaves and securely close before disposal. Do not compost them or leave them on the ground. Proper disposal of leaves eliminates the source of fungal spores that initiate infection. You may need to check again in autumn as any leaves left on the ground will re-infect the plant next spring.
As you can imagine, disposing of all infected plant tissue can be a challenge, particularly with certain species. Cherry brown rot is an example. The number of ornamental flowering cherry trees in landscapes and on neighboring properties make it easy for the disease to multiply. The ability of spores to spread easily with wind and rain exasperates the problem. Removal of infected tissue from a site usually does not eliminate the re-introduction of spores the following season. In these cases, the only disease management measures are to treat preventively or to plant varieties with proven resistance.
Treatment can be highly effective when it is timed right. A good understanding of managing foliar disease goes a long way. One example is the treatment of apple scab in ornamental apple and crabapple trees. Treat apple scab preventively during spring to stop premature leaf loss. When fruit production is important, additional treatments later in the season will help maintain fruit quality and appearance even when the disease is well past the point of damaging foliage.
Foliar diseases are very common. You should always keep an eye on the appearance of your trees’ leaves. If you notice anything amiss, a Certified Arborist can help you figure out if disease is present or there is another issue.