It’s one of the last warm summer days and you decide to host an end-of-the-season barbeque. You invite your friends and family, plan the perfect potluck dinner, and set the mood in your inviting backyard.
However, on the day of the event, as you’re admiring your beautifully decorated backyard, you notice your tree isn’t looking as green as usual. You lament the changing seasons, but walk over to check it out just in case when you notice brown spots on the leaves. What could it be? You brush it off for now, but make a mental note to investigate further.
So, what could be the cause of the brown spots you see on your tree’s leaves?
If you see brown spots on leaves it is likely caused by a fungal infection. However, it is sometimes caused by bacteria and other times caused by insects mimicking a leaf spot disease.
This is a very common issue afflicting ornamental and shade trees and most of the time no action needs to be taken and your tree will remain in overall good health.
However, if you notice lots of leaves falling off, you may have a problem as only more established trees could tolerate this dramatic shift.
What symptoms will you see?
The spots you see may vary in appearance. The leaves may have dark speckles on the top or underside. If on the top, the speckles may look like they are not part of the leaf tissue or the underside speckles are raised. These symptoms could lead to a number of diagnoses including aphids, mites, leaf mealybugs, scale, and whiteflies.
If, however, the spots are on the top of the leaf, seem to be a part of the tissue, and appears dry or soft and oozy, then the diagnosis is different from above. In this instance, the issue may stem from bacterial leaf blight, manganese imbalance in the fertilizer, pH imbalance, too much sunlight, or stagnant water on the leaves.
If the brown spots on leaves are only on the undersize and appear dry or shiny, the cause is likely leaf nematodes or thrips.
What can be done?
If you notice leaf spots affecting your trees early in the spring, the afflicted leaves may fall off and new leaves could return sans spots. If however, your tree undergoes this defoliation process more than three years in a row, the tree could be negatively impacted.
Remove Infected Leaves – Once you notice your tree has spots, it’s important to halt the spread of infection. For this reason, you will need to diligently rake up and dispose of leaves as they fall and prune away the affected area. While this is not a cure, these steps could help care for healthy leaves.
Since this is quite an undertaking and your tree may be tall, it’s recommended you consult a local tree expert to perform the pruning. This person should also be able to properly diagnose your tree and perform any additional steps that should be taken to return your tree to a healthy state.
Keep Leaves Dry – There’s not much you can do as we enter the rainy season toward the end of summer, but once you notice brown spots you should do everything in your power to limit overhead watering. The easiest way to do this is with focused watering.
While manually watering trees with a hose, in addition to providing the base of a tree with a rigorous soaking, we’ll often spray off the leaves as well. Skip this last step to prevent brown spots as the splashing can cause the disease to spread. Similarly, if you rely on a sprinkler system to water your tree, adjust the setting to avoid watering the leaves.
Focus on Health – When trees undergo defoliation they are in a weakened state. For this reason, it’s essential to pay extra attention to your tree during this time. This weakness leaves your tree more vulnerable to pest infestation and other diseases, so if you want your tree to re-leaf, make sure it gets the attention it needs while recovering from leaf spot.
Use Fungicides – While this should not be your first option and you should absolutely discuss the exact cause of your tree’s leaf spot with a trained expert, if the cause is indeed fungal, a fungicide may be a viable solution. A spray will not cure the infection, so this may have limited value and should only be used in extreme cases, but if your tree has experienced leaf spot in the past, it could be a good option moving forward.
If applicable, spraying would often start as the buds break in spring and be repeated in 10-14 increments. This will likely do little if your tree is already infected, but it may be a positive preventative option moving forward.
If your tree is infected by leaf spot, know that is not your fault. Even the most diligent amateur arborists encounter this problem with their trees. The important thing is that you recognized the problem and took steps to try to keep your tree healthy.
Unfortunately, if your tree has undergone defoliation a number of years in a row or if leaf spot is afflicting a younger tree, then it may not survive the disease.
While it’s worth consulting a local tree specialist to understand what is occurring and confirm any possible treatments modalities, the reality may be that your tree will not recover and will ultimately be overcome by the fungal or bacterial infection, leaving it susceptible to additional diseases and pest infestation. If this occurs, tree removal may be your best option in order to keep the rest of the plants in your yard healthy and mitigate any dangers caused by weakened trees.
To keep your trees healthy year after year, don’t rely on your care alone. Work with your local tree experts to ensure your trees remain green for decades to come.