The 5 Most Common Tree, Shrub and Bush Diseases

Imagine it's a warm Midwest summer day in Southeastern Wisconsin. Your backyard is alive with the rustle of lush green leaves and pretty flowers from your favorite plants. But wait—something is not quite right. You notice that your fruit tree is loaded with apples, but its leaves are yellow and are dropping to the ground. You also notice that your favorite hydrangea is covered in a white powder and your rose bushes’ leaves and blossoms look like they have been scorched. What the heck is going on?

Sadly, this has become a familiar sight, much to the frustration of homeowners, like you, who have carefully placed ornamental trees, shrubs, and bushes in your yards for the beauty and the bounty of fruit, shade, blossoms, and comfort. Trees, shrubs, and bushes are often the focal point and beacon of beauty in your landscape; however, summer brings prime conditions for diseases to flourish bringing that beacon of beauty to an abrupt halt. Here's the good news… with proper knowledge and timely intervention, you can protect and keep your plants strong.

The 5 Most Common Tree, Shrub, and Bush Diseases

Apple Scab

What Is It? This is one of the most prevalent fungal diseases afflicting apple, crabapple, and other flowering ornamental trees. It flourishes under cool, wet spring conditions and leaves olive green to brown spots on foliage as well as brown to black lesions, and in severe cases, deep cracks on the fruit.

Impact: As the season progresses, affected leaves turn yellow and drop off the tree. By mid-summer, your once-lush tree may be nearly bare, with only a few stubborn pieces of fruit hanging on. This sneaky disease will wait out the cold, winter months and begin spreading again next spring. The leaves will return in spring and the tree will look fine at first, however without treatment, the disease will most likely come back.

Solution: Raking fallen leaves to prevent the spores from infecting next year’s leaves, pruning your tree to allow more airflow, and a well-timed spring fungicide treatment are key to controlling Apple Scab. Fungicides must be applied at certain critical intervals starting in early spring to prevent the disease from taking hold and ensure your tree stays healthy and full of leaves all season long. If you plan on eating your fruit, understanding which fungicide to use for treatment will be critical.

Anthracnose

What Is It? A fungal disease that loves cool, wet conditions, especially in the spring. It's notorious for attacking a variety of trees, including sycamores, oaks, maples, and dogwoods.

Impact: This disease makes dark, sunken spots on the host tree's leaves and can cause significant leaf drop. It could defoliate the entire tree by early summer and make it look like it's the middle of winter. In some tree species, such as sycamore, twigs can also become infected leading to twigs dying back.

Solution: For many trees, anthracnose is a cosmetic disease. However, if the tree has been defoliated by this fungal disease for several years, or the tree is susceptible to twig infection, you may want to use fungicide treatments to get it under control along with fertilizing and watering.

Cedar-Apple Rust

What Is It? This unique fungal disease requires two types of host trees. The fungus starts out on the branches of the first host trees such as juniper or cedar. A brown, golf ball-shaped growth known as a gall, will form on the branches of these trees and will remain on the branches over winter. During the moist periods of early spring, the galls produce an orange, gelatinous slime that can sometimes look like fingers. These orange masses produce spores that are carried on the wind. While these spores cannot infect another juniper or cedar tree, they do find their way to the second type of host trees like apple, crabapple, hawthorn, or quince. Here the spores attach themselves to the leaves and the fruit of these trees creating bright orange, circles that look like rust. These orange circles are full of spores that will be taken by the wind and deposited back on a juniper or cedar tree and the cycle will start all over again.

Impact: While the disease doesn't usually kill trees outright, it weakens them over time, making them more susceptible to other issues. Bright orange spots on the fruit and leaves of infected trees will appear in early summer. By late summer, affected trees may be sparse, with just a few leaves and misshapen fruit remaining.

Solution: Junipers and cedar trees can be treated by pruning branches about four to six inches above the galls. Be sure to clean your pruning shears with a 10% bleach solution in between cutting each branch to prevent the fungus from spreading. Burn or bury the pruned branches. You can also control this fungus by applying protective fungicides to both types of host trees. Each type of host tree will need different fungicides so be sure you know which fungicide to apply.

Fire Blight

What Is It? A destructive bacterial disease that affects trees in the rose family such as apple, crabapple, pear, mountain ash, and hawthorn as well as bushes like spirea and roses. It's known for its "scorched" appearance, with leaves and blossoms turning black as if burned and a robust array of dead twigs hanging about. Cankers form on branches and stems that secrete a sticky bacterial ooze where it can remain over the winter and then multiply when the temperatures start to rise in the spring.

Impact: The disease can spread quickly once spring arrives since rainwater will spread the sticky bacterial ooze to other plants where it enters through the plant’s vascular system. It can also be spread by insects that feed on the bacterial ooze and then transport the disease to other flowers and plants as they collect pollen. Leaves, buds, and flowers can all turn ashen, leading to damage, diminished health, and lack of fruit. Infected branches can die back. This disease can kill a tree or bush if left untreated.

Solution: Pruning and cutting back 12 inches below affected areas as soon as possible after you notice the symptoms. Branches should be pruned when dry and can remain dry for several days. Be sure to clean your pruning shears with a 10% bleach solution in between cutting each branch to prevent the fungus from spreading. Burn or bury the pruned branches. A specialized treatment can be sprayed on the tree or shrub before the buds begin to break. The treatment must be specific to this disease. A tree or bush with fire blight will not be healthy or productive without the proper medicine, but the disease can be managed, and the tree or bush can flourish once again.

Powdery Mildew

What is it? This common fungal disease often occurs in late summer and early fall when warm, dry conditions are most prevalent. This disease affects a wide variety of trees, shrubs, bushes as well as crops and can even infect indoor house plants.

Impact: It produces a powdery white coating on leaves, buds, stems, and fruit. The "mildew" looks harmless, like powdered sugar, but it isn't. Infected plants can have their growth severely stunted, especially young leaves and green shoots. Leaves will curl, then turn yellow, and some will drop. If not treated early in the infection, the plant can become weakened, making it more susceptible to other diseases.

Solution: For many trees, shrubs, and bushes, powdery mildew is cosmetic and non-lethal. However, if you have a highly valued plant that has had powdery mildew for several years in a row or have a young plant that presents with symptoms, this disease can be effectively controlled with fungicidal treatment in the early stages of infection. You can also help to prevent the disease by spacing your plants further apart to allow better airflow which reduces the humidity. Do not overwater your plants and remove and destroy any infected plant debris when you see it since this disease can survive over the winter and reinfect the plant again in spring.

Be Proactive

The key to keeping your trees, shrubs, and bushes healthy is proactively watching and treating these illnesses at the earliest stage. Once plants start showing signs consistent with the stresses caused by the disease, it's often too late to reverse the damage for that season. However, you can effectively manage the disease and prevent its recurrence with early intervention.

Preschedule a preventative treatment plan with your favorite reputable professional in the fall so as not to disrupt proper spring service timing. Timed spring prevention will help avoid intense leaf loss in July, avoiding damage, or even death of your plants.

Spotting early signs of disease can be easier than you think. If you see specks on your plant’s leaves, leaves turning yellow or changing color, or any other unusual signs, don't wait! Contact a reputable specialist before complete defoliation. These symptoms are the plant's way of signaling that something is amiss and needs help. Preventive or curative intervention, when the plant exhibits these early signs, can keep a small problem from getting bigger and severely affecting or killing your tree, shrub, or bush.

Lastly, it's crucial to understand the difference between dormancy due to disease and a plant that is too far gone. When trees shed their leaves in the middle of the season because of sickness, they can become dormant. This can be unnerving, and many homeowners mistakenly think they have lost the tree for good. However, with the proper care and treatment, many afflicted trees can make it through the winter and leaf out again come spring. This hopeful prospect should encourage homeowners to seek professional advice before taking drastic measures, such as removing the tree.

Common illnesses that afflict plants shouldn't be allowed to bring down your attractive landscape. By understanding the threats and taking the necessary measures, you can keep your trees, shrubs, and bushes healthy, full of life, and—even more critical—growing for a long time.

At Be Green Pro, we work with you to nurse your trees, shrubs, and bushes back to health, keeping them healthy and looking sharp. Contact us about your tree care if your trees, shrubs, or bushes may be experiencing a bacterial or fungal disease. We can help!

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