3 Common Tree Diseases to Watch For in Late Summer in New Jersey

As the long, hot days of a New Jersey summer begin to wind down, you might notice your trees looking a little weary. While some browning and leaf drop can be normal, a change in your tree’s appearance can also be an early sign of disease. Late summer is a prime time for certain fungal and bacterial issues to become highly visible, as the cumulative stress of the season weakens a tree’s natural defenses.

Being able to identify the signs of common NJ tree diseases is a critical skill for any homeowner. Early detection can often mean the difference between simple treatment and irreversible decline. This guide will walk you through three of the most common tree diseases to watch for in late summer, helping you know when to take action.

Why Late Summer is a Prime Time for Tree Diseases

The combination of high humidity, occasional heavy rains, and the stress from summer heat creates a perfect breeding ground for pathogens. A tree that has been struggling with low moisture and high temperatures is like a person with a weakened immune system—it’s far more susceptible to infections that a healthy tree could easily fight off.

1. Powdery Mildew

What it is: One of the most easily recognizable fungal diseases, powdery mildew presents as a superficial fungus that grows on the surface of leaves, stems, and flowers.

Trees Affected: It has a wide range of hosts, but in New Jersey, it’s particularly common on Dogwoods, Lilacs, Crabapples, and Sycamores.

What to Look For: The tell-tale sign is the appearance of white to grayish, talcum-powder-like patches on the leaves. In severe cases, it can cover the entire leaf surface, causing leaves to yellow, distort, and drop prematurely. While it rarely kills a mature tree, it reduces its photosynthetic ability and is highly unsightly.

What to Do: Improving air circulation by selectively pruning dense canopy sections can help. Rake and destroy fallen leaves in the autumn to reduce overwintering spores. For persistent infections, professional fungicide treatments may be necessary.

2. Anthracnose

What it is: Anthracnose is a group of fungal diseases that cause dark, sunken lesions (blotches) on leaves, stems, flowers, and fruits.

Trees Affected: It is a major issue for Sycamores, Dogwoods, and Ash trees, and it also commonly affects Oaks and Maples.

What to Look For: Symptoms vary by tree, but generally include irregular, blotchy dead areas on leaves that often follow the leaf veins. On Dogwoods, you might see tan-to-brown spots with purple borders. On Sycamores, it can cause significant and sudden leaf drop in early summer. The disease is most active in cool, wet spring weather, but the symptoms and dieback become much more pronounced during the stress of late summer.

What to Do: Sanitation is key. Rake up and destroy all fallen leaves and twigs. Prune out any dead or cankered branches to improve air circulation. Preventative fungicide applications in the spring are the most effective professional treatment.

3. Bacterial Leaf Scorch

What it is: A systemic bacterial disease that clogs the tree’s water-conducting tissues (xylem). This prevents water from reaching the leaves, causing them to scorch and die.

Trees Affected: Very common and serious in Oaks (especially the red oak group), but also affects Elms, Sycamores, and Maples.

What to Look For: This is often mistaken for simple drought stress. The key difference is the pattern: Bacterial Leaf Scorch causes an irregular browning along the leaf margin, often with a yellow “halo” separating the dead tissue from the healthy green tissue. Symptoms typically appear in mid-to-late summer and intensify as the heat continues, getting progressively worse year after year.

What to Do: There is no cure for Bacterial Leaf Scorch. However, the tree’s life and appearance can be managed for many years with proper care. This includes therapeutic antibiotic injections administered by a professional, proper watering during dry periods, and improving soil health. A proactive approach is essential.

Prevention is the Best Medicine: The most effective way to fight NJ tree diseases is to keep your trees healthy and resilient before they get sick. Our comprehensive Plant Health Care (PHC) programs are designed to do just that, with proactive monitoring, soil treatments, and preventative applications. For more answers to your questions, visit our FAQ page.