Just the other day I was asked if I thought fall was going to come early because of all the yellow trees around town. I have no idea if fall will come early or not, I just know the trees aren’t turning their yellow and bronze color because of autumn’s arrival.
There are a few reasons the trees appear to be showing their fall colors prematurely. If you have a honey locust tree that was green earlier in the season and is now a rusty color or yellow, it might have spider mites. Examine the underside of the leaves. Do they appear to be almost dusty and gritty? If so, it’s probably spider mites.
You may even see some very fine webbing. Spraying the underside of the leaves with a strong stream of water and increasing the irrigation will help. If there’s a large population of mites, a product labeled for spider mites may be needed. Keep in mind, a sunburst honeylocust is supposed to be yellow throughout the season. You really don’t see an abundance of them in the area because they tend to not do well here.
Some trees are showing premature fall colors because of blight.
Coryneum blight will cause purple spots and off-colored leaves. As the disease progresses, the center tissue may drop out of the purple spot, leaving holes in the leaves. This disease is also known as “shot hole disease” because of this.
Applying a copper fungicide in the fall right after the leaves have dropped, and again in the spring, will help. Because this is a difficult disease to cure, you’ll have to do this for a few consecutive years.
A lack of water can cause leaves to become yellow with black edges. Sometimes it’s a problem with the root system that’s causing the inability of the tree to take up water. Probing the soil around the root ball using a screwdriver is a good way to check soil moisture.
If the leaves of your tree are yellow with dark green veins, you’re probably dealing with iron deficiency. Our soils generally have adequate or even high levels of iron, but they’re also alkaline which causes a lot of the iron to be in a form that’s not usable by plants.
There are trees that require more iron than others, and some that have a root system that is just insufficient when it comes to taking up the iron. Over-watering or under-watering can exacerbate iron problems. Some trees, such as red, silver, or Amur maples, as well as pin oak and red oaks are susceptible to iron deficiency. White oak, swamp white oak or chinkapin oak are far better choices. Even aspen, apple, crabapple and peach can have iron uptake problems.
If you really love maple trees, Norway maples are hard wooded and less susceptible to iron problems as well as storm damage. However, if this tree is planted in a dry or hot site, the leaves will scorch in the summer heat.
Bigtooth maple is also a good tree for our area. Ginnala or Tatarian maples are good smaller maples. You could even use a Tatarian as a large multi-stemmed shrub. A sensation boxelder (maple) is another great tree with nice fall color. Best of all, this boxelder doesn’t attract boxelder bugs.
I don’t know about you but I’m getting kind of tired of the hot weather. I’m hoping for an early fall and I’m getting anxious to see beautiful autumn colored trees. I think for the time being, I’m going to pretend the colored trees are telling me fall is arriving.
Linda Corwine McIntosh is a licensed commercial pesticide applicator, ISA certified arborist, and advanced master gardener.