Black Spots on Tree Leaves: Should You Be Worried?

Discovering black spots on your tree leaves may be concerning, depending on the cause. Black spots can indicate infected leaves, but they are also sometimes merely cosmetic. The problem is that it can be challenging to determine what may have caused your leaf spots. 

If you find black spots on tree leaves, our certified arborists here at Collins Tree can help! We are proud to be the number one professional tree care company in Concord, NH. We offer affordable, reliable, and trustworthy tree care services for Concord and the surrounding areas. 

What Causes Leaf Spots?

Generally, four factors can cause leaf spots.

Leaf Spot Diseases

Leaf spot diseases are the result of pathogens such as fungi or bacteria. Diseases like Cercospora leaf spot and maple tar spot have fungal pathogens, while Pseudomonas and Xanthomonas are common bacterial pathogens. 

You can distinguish fungal leaf spot diseases through the presence of spores within the leaf spots. On the other hand, bacterial leaf spot diseases display a yellow “halo” that borders the black spots. 

Insect Pest Damage

Insect activities like feeding or laying eggs on leaf surfaces can cause leaf spots. However, these spots are generally whitish or yellowish and are not necessarily a problem for healthy trees. 

If you notice insect pest damage, you should still monitor your tree health. These leaf spots can serve as entry points for leaf spot pathogens. 

Cultural Practices

Poor cultural practices such as adding too much fertilizer or water can cause leaf spots. However, these leaf spots simply indicate that you need to change your care method rather than an existing disease.

When cultural practices cause leaf spots, you will notice that the spots do not spread to other leaves. Instead, the affected leaves typically wither and fall off. 

Environmental Damage

Strong winds, hail, and other environmental factors can puncture leaf surfaces and cause leaf spots. However, these spots are usually cosmetic and won’t affect your tree’s health. You can remove damaged leaves through pruning to prevent insect or pathogen infestation. 

Which Trees Are Susceptible to Leaf Spots?

While all tree species can get leaf spots, some are more susceptible. Broadleaf deciduous trees are among the most vulnerable species. These include:

  • Sycamore
  • Horse chestnut
  • Oaks
  • Maples

Deciduous trees infected with leaf spots generally have leaves that display reduced fall colors. The leaves often wilt and drop prematurely. 

How Do Leaf Spots Spread?

Black spots on tree leaves spread depending on the causal agent. Fungal diseases, for example, spread through spores located in the fruiting bodies on the spots. These spores look and feel powdery. 

Bacterial diseases spread through oozing cankers or insect vectors. For example, a wood borer that feeds on the sap from an infected tree can spread the bacteria when they feed on an uninfected tree.

Finally, leaf spots can spread through human actions. If you use tools on an infected tree and don’t clean them afterward, you can spread the disease during succeeding tree care activities. 

How to Treat Leaf Spots

The most effective control for black spots on tree leaves is keeping your trees healthy! Regular pruning, proper fertilizer and water application, and cleaning your tools after every use are all great ways to prevent leaf spots. 

Give Your Trees the Care They Deserve with Collins Tree

Here at Collins Tree, we take tree health seriously. Don’t hesitate to call us if you notice black spots on tree leaves!

Our experienced team can identify the cause and determine the best course of action. Call us at 603-485-4761 for a free estimate. You can also learn more summer tree trimming tips with this guide


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