Wells Lawn Care & Landscaping Logo

Get Custom Quote!

How to Identify and Manage Black Spot of Elm

At Wells Lawn Care, we’ve noticed a few cases of black spot of elm this year. Known also as elm anthracnose, this disease is caused by the fungus Stegophora ulmea and can affect most elm species. American elm varieties, in particular, seem to be more susceptible.

Understanding the Disease:

The fungus becomes active in the spring once temperatures hit 45°F or above. It releases spores that target newly unfolding leaves, creating chlorotic spots or blotches on the upper leaf surface.

Black fungal fruiting bodies develop within these spots, making them appear as if tar has dotted the leaves. As these spots merge, they create white dead tissue areas that eventually turn brown.

Spreading Mechanism:

The black fungal stromata produce asexual spores (conidia) during the growing season. These conidia are spread in mucilage, loosening in humid conditions and dispersing via water splash from rain or irrigation.

Apart from leaf infections, Stegophora can also infect leaf petioles and twigs, leading to severe leaf spotting, premature leaf drop, and even significant defoliation if petioles are affected. Infections in stems can cause shoot blighting and small limb dieback.

Disease Severity & Weather Impact:

Black spot is typically more severe in cool, moist weather, with the fungus reinfecting the tree throughout the rainy season. When summer turns hot and dry, the disease slows, allowing trees with twig blighting to show some recovery by producing new growth from dormant buds below affected shoots.

It’s important to note that twig blighting can look similar to flagging branches associated with Dutch elm disease (DED), so we recommend pruning the branch and checking for internal vascular streaking to rule out DED.

Management Recommendations

Fungicides

Avoid using fungicides for mature trees in landscapes due to inpracticality and generally non-severe damage.

Nurseries

In nurseries, consider preventative applications to protect new growth and slow disease spread during severe outbreaks, especially where overhead irrigation is used.

Pruning

Rake leaf litter and prune infected stems to remove inoculum for the next season and prevent the spread of existing infections.

Trust Wells Lawn Care

At Wells Lawn Care, we’re dedicated to providing the best care for your trees and ensuring they remain healthy and vibrant. If you’re dealing with black spot of elm, our team is here to help with expert advice and effective solutions.

Contact Wells Lawn Care for a consultation and customized recommendations. Visit Wells Lawn Care Monthly Packages to learn more and get started today!