It’s heartbreaking to see a beloved tree in a bad state—stepping outside to sit under your favorite source of shade, only to discover that its leaves are covered in brown spots. Over time, those spots grow larger, eventually turning into unsightly blotches. If the problem isn’t dealt with, the leaves of the tree will eventually turn completely brown and simply drop off of the tree.
This is a condition known as leaf spot, and it’s common among many different types of plants, not just trees. Being common, it’s likely you’ll deal with leaf spot on your tree at some point. It’s important to learn how to identify it and prevent it from spreading before it leads to complete defoliation of your tree.
What Is Leaf Spot?
Leaf spot is a disease where brown or black spots form upon the leaves of trees or other plants. It can have many causes, including air pollution, but it’s most commonly caused by a fungus growing within the leaves. Fungal leaf spot is contagious. As the fungus spreads on your tree, it will produce spores that can then spread to other parts of the tree and even to other plants in your yard. While it’s usually not actually harmful to the health of a tree, it can absolutely ruin its aesthetic appeal. Left unchecked, it can ultimately lead to a barren, leafless tree.
Identifying leaf spot isn’t always as simple as it sounds. This is because there are several other things that can cause the leaves of your tree to become unhealthy and turn brown. In each case, the solution to the problem will be different. For example, your tree might start showing brown leaves if it hasn’t been getting enough water. In that case, spraying it with the garden hose might solve the problem. However, if the problem is leaf spot, as opposed to dehydration, that same garden hose may only make the problem worse. That’s why it’s important to learn to identify the subtle differences in the various health issues that may affect your tree.
How It Happens
There are many common types of fungi that spread when conditions become favorable for them to produce spores. All fungi prefer damp conditions and usually cooler weather. As a result, they are most likely to attack your tree during the wet months of spring. Springtime also happens to be when your tree is beginning to sprout new leaves after the winter. These newly grown leaves have yet to become strong and resilient and are therefore more vulnerable to a fungal infection.
When the conditions become favorable for their growth, fungal spores take hold in wet leaves and begin to grow and spread. As they do so, they interfere with the leaves’ ability to photosynthesize, leading to the tell-tale brown and black spots. If the fungus spreads enough, and the leaf turns completely brown, it will die, and the tree will shed it.
While leaf spot itself generally isn’t harmful to your tree, over time, it can weaken the tree and leave it vulnerable to other, more serious diseases, such as root rot. That’s why it’s important to address the issue early, before it puts your tree at risk of an attack from something that will end up being harmful or fatal to it.
Leaf Spot Prevention
Because leaf spot is caused by unchecked fungal growth, your first step in prevention is to ensure that your yard doesn’t have conditions favorable to fungus. Often, the fungus that causes leaf spot starts taking hold in leaves that have already fallen. That’s why it’s a good idea to always rake up fallen leaves; it will help to protect the leaves that are still attached to your tree.
Watering your tree incorrectly can also encourage the growth of leaf spot fungus. In most cases, you don’t really even need to be watering your tree; trees happen to already be very good at getting the water they need from their environment. There are situations, however, where giving your tree some water may be necessary. Saplings, for example, may need to be watered for a certain amount of time. Similarly, you might need to spray your tree with the hose every once in a while during a drought.
If you do need to water your tree, however, you should take great care not to overwater it. It is damp conditions that promote fungal growth, and you can easily create those conditions yourself if you’re not careful with the garden hose. When you do use the hose, don’t spray a great deal of water on the leaves: you may inadvertently be creating the conditions that a debilitating fungus needs to thrive.
Treating the Problem After It Starts
If you notice that leaf spot has already begun to take hold in your tree, you can still often prevent it from spreading further. As we’ve mentioned, the first step in preventing leaf spot is to learn to identify the problem and to distinguish it from other common tree diseases. Because you can actually make leaf spot worse if you don’t address it correctly, you must be sure you know what you’re dealing with before you take any steps to fix the problem.
Leaf spot leads to black and brown spots that may be ringed with red. If you notice brown leaves with holes in them, you may instead be dealing with insect damage. If you notice the leaves are turning brown without developing spots first, your tree may simply be malnourished. Learn to identify the different symptoms of tree diseases so that you can address them correctly.
If you think your tree has been infected by a fungus, you may be able to purchase a chemical fungicide to help. However, in most cases, these won’t actually end up doing much because, by the time you notice the tell-tale spots, the problem will have already spread a great deal. Only use a fungicide if you haven’t been able to get the problem under control for several years.
It may be better to simply have your tree pruned by a professional arborist, such as one from Mr. Tree. Regular pruning can be the most effective step you can take in preventing leaf spot from spreading through the leaves of your tree, as well as keeping it from spreading to other plants in your yard. Your arborist can also make recommendations to keep the problem from reoccurring in subsequent seasons.