Why are There Brown Spots on the Leaves of My Maple Trees?

Have the leaves on your gorgeous maple tree become blotted with ugly, dark brown spots? If so, you’re probably thinking that your once beautiful maple tree has become an eyesore. Never fear. The Mr. Tree arborists are here. We’ll tell you exactly what’s causing those troublesome spots and just how to fix them!

Let’s first get to the root of the matter and talk about the cause of those blemishes. Brown spots appearing on maple tree leaves or on the leaves of box elder trees are typically caused by something known as tar spot. This fungal disease gets its name from the fact that the dark brown spots resemble tar. The good news is that while this disease causes blotchy brown spots to pop up on the tree’s leaves, it doesn’t impact the tree’s overall health. The bad news is that in addition to the fact that the spots aren’t exactly aesthetically pleasing, tar spot often causes the tree’s leaves to prematurely fall.

So what should a homeowner look out for when it comes to tar spot? You’ll want to begin checking your maple trees in early spring. If a maple tree has become diseased, you’ll begin to notice light green or yellowish green spots. The spots will gradually become larger and darker until they begin to resemble tar, usually around late September.

Now that we’ve diagnosed the problem, how exactly do we fix it? Since tar spot causes the tree to lose its foliage, you’ll want to be diligent in raking and destroying the fallen leaves by burning, burying, or composting them. This removal process will reduce the chance that the diseased leaves will infect new spring foliage. Without properly disposing of the leaves, however, you run the risk that the fungal spores will be carried on the wind and spread back to the tree’s new foliage.

While destroying all the infected leaves should do the trick, there are certain situations that may call for additional measures. Perhaps, for instance, tar spot has been a persistent problem on your maple tree and you’re looking for a more permanent solution. If this is the case, you may want to contact your local arborist at Mr. Tree to apply fungicide to your maple tree. While it may be possible to tackle this as a do-it-yourself project on smaller trees, larger trees often require a professional fungicide application.

To rid the tree of tar spot, the fungicide must cover every leaf on your maple tree. For mature trees, this can be quite the task. The last thing you want is to take the time and effort to apply fungicide, only to have tar spot return again next year. In order to ensure that the fungicide is applied properly and that every leaf is sprayed, you should contact your local arborist to professionally treat your maple tree.

If you do decide to treat the tree with fungicide yourself, remember that you’ll have to perform multiple sprays in order for the fungicide to be effective. You should perform the first application at bud break and then twice more after a period of seven to fourteen days.

Since tar spot is often a recurring problem, it’s best to try to prevent it altogether. There are several steps you can take in order to decrease the likelihood your maple tree will become infested with tar spot. First, remember that diseases often flourish in wet conditions, so be careful not to overwater your tree. A good rule of thumb is to water the tree so that only six to eight inches of the soil is moist. The soil should be completely dry by the time of the next watering.

You should also prune your tree on a regular basis to increase the amount of sunlight it receives and improve air circulation through the tree’s canopy. Ornamental trees, such as maple trees, should be pruned every year. Finally, add a layer of mulch to your tree on an annual basis as well. The layer should be three to four inches deep and located at least two inches away from the tree.

It’s also a good idea to perform a soil test on your tree from time to time to make sure it’s adequately nourished. A soil test will determine if and what nutrients are lacking. Applying fertilizer can provide nutrients for your soil if there is a deficiency and it is also a good preventative measure for maintaining the overall health of your tree. Soil nutrients should be added to trees every one to three years. While even properly maintained and cared for trees can become diseased, taking these preventative measures will greatly reduce the risk that a tree will become infected.

In addition to properly caring for your trees, it’s also important to have them regularly serviced by a certified professional. Our expert arborists are able to assess your tree’s health and provide honest feedback and recommendations for its upkeep. Not only will regular service appointments increase your tree’s longevity, it will also save you more money over time. Improperly maintained trees will require more attention and may even need to be removed altogether.

While it may be upsetting to see unsightly, brown or black spots on your maple tree’s leaves, you can be assured that this is a problem that can be fixed with just a little time and effort. Your tree’s overall health likely won’t be compromised and with a little TLC, your tree’s leaves will return to normal by the next growing season.

If for some reason the problem persists, just give us a call. We’re more than happy to help you get rid of those pesky spots for good!