If you’re noticing brown spots on tree leaves around your property and some of those trees are dropping leaves throughout the season, you might be concerned that your trees are dying. This is a valid concern since it’s not usually natural for trees to drop their leaves in the spring and summer unless they’re under stress.
One of the common causes of brown spots on tree leaves is anthracnose. Anthracnose is a foliar disease that affects several species of trees. It’s composed of a group of fungi that each attack one or a few closely related species. Luckily, only in the very worst cases is your tree in danger of dying.
In this article you’ll learn how to identify the signs of anthracnose, which trees it affects, and what to do about it.
Symptoms & Signs of Anthracnose
The most commonly affected tree species in the Midwest are:
Each of these species are affected by a specific but related strain of the fungi classified within the genus Gleosporium.
Anthracnose symptoms vary by tree and weather conditions. It most often thrives in cool, wet spring weather. If you suspect your tree might be suffering from anthracnose these are the symptoms you should be looking for:
- Irregular beige, dark brown or black spots on the leaf tissue or twigs
- Dead areas on leaves
- Lesions along leaf veins
- Curling leaves: This often happens in young and newly emerging leaves.
- Dropping leaves: Leaves drop from the bottom of the tree first. Heavily affected trees can drop leaves throughout the season and eventually lose all of their leaves. Often they’ll start re-growing new leaves after this happens.
- Defoliation from the bottom of the tree up: Anthracnose affects the tree from the ground up. Often there is a ring of healthy leaves left at the top of the tree.
If after inspecting your trees you’re still not sure whether anthracnose is the issue, make an appointment to consult with a certified arborist.
How does anthracnose spread?
Anthracnose fungi can survive the winter in buds, twigs, fruit and fallen leaves. In the spring, the spores of the fungi are splashed up into the tree by rain or carried by the wind to other trees nearby.
If the spring is cool and wet (which is very common here in Wisconsin) the spores will spread and multiply throughout the tree, creating brown spots on tree leaves and sometimes killing the leaves and causing the three to drop them.
Dry and warm weather will stop the spread of the disease. This often occurs in the summer months. At this time the tree will regrow any lost leaves. But, if the summer is cool and wet anthracnose will continue to spread.
Treatment of Anthracnose
The good news is that Anthracnose is generally just superficial damage to the leaves that won’t ultimately kill your tree. But, it will cause varying amounts of leaf drop depending on the severity and seasonal conditions. The exception is with sycamore trees, where we commonly see twig dieback associated with the infection.
Your trees should be able to fully recover from an anthracnose infection. If your tree loses most or all of its leaves several years in a row there’s more danger long term. You should consult a certified arborist in this case.
One option for treatment of brown spots on leaves resulting from anthracnose is treating your trees with fungicide. Here are ECO we don’t generally recommend treatment for maple, ash, white oak and walnut trees. Instead, we prefer the application of a nutrient and bio-stimulant soil injection to help ensure that your trees weather the infection with as few long-term effects as possible. (Think of this as a science-based probiotic for trees!)
If we diagnose Anthracnose in a sycamore tree, we will strongly recommend a fungicide trunk injection. Anthracnose in sycamores will cause twig dieback and may severely stunt the tree.
Your trees may experience an annual infection of varying degrees of severity. This is very common. If this happens, we highly recommend either a tree growth hormone injection or a Bio-stimulant injection to reduce the overall stress on the tree.
How to Prevent anthracnose
As the homeowner, you can help support your trees to weather anthracnose infections by adopting the following practices.
Water trees: Just like any other plant in your landscape trees need an adequate amount of water to be healthy and thrive. When trees aren’t getting enough water they become stressed, which makes them more vulnerable to pests and diseases.
Since anthracnose spreads in wet conditions make sure you’re watering just the roots of the tree, not wetting the trunk and leaves.
Rake up infected leaves: Before the first snowfall rake up and get rid of infected leaves since they host the overwintering fungi. Infected leaves can also be burned or composted. If composting, make sure your pile reaches a high temperatures (140F and up) to ensure destruction of the spores.
Prune trees: In winter, hire a certified arborist to evaluate your trees and prune out dead and diseased branches to open up more space for light and air circulation. If you live in the Madison, WI area, make an appointment with ECO for a free consultation.
Plant disease resistant varieties: The University of Minnesota has a list of anthracnose resistant varieties of several tree species here.
At the beginning of this article it’s possible you were worried that your trees were dying a slow death. Hopefully you’ve been reassured that they’re likely just suffering from anthracnose, which (luckily!) is not life-threatening to most trees. If you monitor your trees each season and incorporate some of the best practices shared in this article your trees should live and grow for many years to come.