Diagnosing Black Spots on Tree Leaves: Causes and Solutions

Finding black spots on tree leaves is a cause of concern for hundreds of business owners and residents across Phoenix. They call our arborists for checkups nearly every week, wanting to know whether their trees are starting to harbor a potentially contagious fungal disease, bug infestations, or even rot. Our licensed arborists at the Tree Workers of Phoenix are proud to be their leading source of advice and information, and through this explainer, we will let you know whether you should start buying fungicide sprays or wait until the seasons change.

Whenever you need a health checkup from Phoenix’s trusted arborist, call our 24/7 hotline, and we will be on your property for an on-site checkup within an hour.

What Causes Black Spots on Tree Leaves and What Should You Do About It?

Research from the National Association of State Foresters reveals that over 60% of woodlands in the United States are under private ownership, which means millions of people see developing black spots on their bushes, trees, and house plants every year. It is not a pretty sight, and first-time plant owners love attributing it to nutrient deficiencies, aging, and bacterial infections before a thorough examination. We get calls from many people who believe their tree is dying, and they are always relieved after we do an on-site checkup.

Black spots on tree leaves can look jagged, round, or sometimes feature irregular edges, making them look even more alarming.

Our arborists have decades of combined experience dealing with black marks on all kinds of plants and trees. Black spots and other forms of discoloration usually come from three sources.

Are You Overwatering Your Plants and Trees?

Most black spots on tree leaves and plants in indoor areas come from overwatering. Damage from overwatering will first affect the roots before slowly affecting the barks and stems and finally discoloring the leaves.

Dig around the roots of your trees and smell the surrounding soil. If you spot brown or blackened root sections and detect the smell of decomposition, your tree has root rot. Overwatering encourages the growth of oomycetes, fungi, and bacteria while lowering the resistance of your tree to disease.

Letting the surrounding soil dry out and providing ample drainage should eliminate this illness.

Looking for Signs of a Fungal Infection

Fungus is an essential component in a forest ecosystem as it curbs the growth of invasive plant species and provides food for arthropods, microbes, and mammals. However, in a commercial or residential environment, they are pests that can take out entire farms and plantations in just one season. Fungal spores travel through the air and thrive in moist environments, like the soil around your tree.

Fungal diseases like cedar apple rust, oak wilt, and tree cankers feature black spots on tree leaves as symptoms. To shield your trees from fungus, eliminate fallen foliage from your yard, keep your tree well-nourished with fertilizers, and clean your garden tools between uses.

Eliminating Tree Pests

Tree pests like mealybugs, spider mites, and aphids cause leaves to appear sickly, yellowish, and riddled with black spots. Aphids emit a soot-like mold, while spider mites leave webs underneath branch joints. Mealybugs create cotton-like masses beneath spots on leaves, and scale bugs cause mold growth on leaves and branches.

Neem oil, insecticidal soap, and diatomaceous earth will eliminate these pests.

Contact Us Today

Climbing up branches to check infected leaves can be dangerous. When you find discoloration, holes, and signs of malnutrition on the leaf surface of your bushes and trees, contact a Google Guaranteed tree service for an assessment. Whenever you find black spots on tree leaves, call 602-320-2797 to reach the professionals at Tree Workers of Phoenix and get a free consultation.


Tree Workers of Phoenix has been in business since 1994 and is a member of the Better Business Bureau (BBB) and International Society of
Arboriculture (ISA).


18402 N. 19th Ave. #115

Phoenix, AZ 85023

Phone: 602-320-2797

Email : rickthetreeexpert@gmail.com

Hours of Operation :

Monday - Sunday : 9:00am-5:00pm


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