Crab Apple Trees – Fungus

We mentioned that we expect fungal issues to be extensive this year in the Western suburbs. We are certain of that. For those of you whose Crab Apples we treat for Apple Scab, we know you will be happy with your decision to treat your trees. You will realize just how glad as the Summer progresses and you see other area Crabs missing 70% to 90% of their leaves in July, August, September and October.

Keep in mind though that a new fungus hit the area in the past few years called ‘Frogeye’ Fungus. This fungus is different and not nearly as debilitating as Apple Scab. It may create bright yellow spots on the leaves initially and the tree may then drop some bright yellow leaves onto your lawn. This situation too will last a few weeks and then stop. This occurrence happens early enough in the Summer that the trees will still have a chance to re-foliate. It is not anywhere near as harmful as Apple Scab which creates dark brown and black lesions on the leaves. Our Apple Scab products are not labeled for Frogeye. There is a limit to how many products we can mix together and there is no single product that controls every potential fungus that is out there. We focus primarily on Apple Scab which does the most harm by far.


Please see the photos below. These leaf depictions are a result of Anthracnose Fungus which manifests itself in a few different ways.

These are Maple leaves. This situation may or may not be evident just yet but a lot of trees will display similar damage over the coming month. Maple, Oak and a few other tree varieties can get Anthracnose. The wetter the Spring, the more issues there will be with all varieties of fungus and we all know just how wet this Spring has been in the Chicago suburbs.

Anthracnose is an airborne spore which blows onto susceptible trees and even some shrubs. We do ‘not’ recommend treating for this particular fungus because it is ‘not’ a yearly occurrence like it is with Apple Scab Fungus on Crabs or more recently, Rhizosphaera Needle Cast Fungus on Spruce trees. The extent to which Anthracnose Fungus will affect trees is an unknown in any given year. We must be ‘proactive’ in treating for any fungus and once a fungal condition begins to show visible signs, it is already too late to treat for that season. Why spend money on a treatment that is only an issue on occasion?

This next photo shows seemingly healthy green Ash leaves strewn about on a brick patio.This situation is also a result of Anthracnose Fungus. In the case of Ash trees, Anthracnose attacks leaf stems causing them to weaken and disconnect from the branch. As a result, individual leaves or clusters of leaves fall to the ground. Other than being unsightly, this condition should stop occurring after a few weeks. In a bad year, an Ash can lose up to 75% of its leaves but the tree will re-foliate as the Summer progresses. Your tree will not die due to this condition.


Several of you have us spray your Hawthorns for Scab and Quince Rust.  This year you may be noticing that the little round balls of fruit on Hawthorns have orange spikes and may be dropping some orange dust on the leaves and on your sidewalks, patios and driveways.

quince rust

Our main goal is to keep the leaves from turning black and dropping too early and our sprays are accomplishing that. However, the Quince Rust on the little fruiting balls are not responding as well to the spray applications. Why is this?

Those little fruiting balls have a waxy, slippery outer coating making it more difficult for our sprays to adhere to the fruit. The leaves, stems and branches, however, are more porous allowing them to better absorb the product, yielding much better results.

There are all types of funguses out there and the wetter the Spring, the worse fungal issues are, some years worse than others. We can’t control every single fungus that might occur as we can’t predict which strains of fungus might be an issue from year to year. As a comparison, different strains of human flu also vary from year to year. Doctors do their best to determine which strains to vaccinate against when we get our yearly flu shot. As we all know and may have experienced, that doesn’t mean that we won’t get the flu that year. All we can do is control the worst funguses that do the most leaf damage to your Crabs and Hawthorns.

It is important to note that the Quince Rust dust on or from the fruit will not weaken or kill the tree.

You can simply hose off your patios, sidewalks, etc. if you are noticing orange dust.