Hi, I'm Fred Brown the nursery manager at White Oak Garden Center. I want to help all of our customers have an easier time at managing their properties. Today I have an observation that could help you save trees, shrubs and potentially money.
As I drive around I have noticed that some fall colors are just starting to show on many plants. How this procees sets in on our trees and shrubs can be quite telling. As the cooler temperatures set in and the days get shorter, deciduous plants prepare to drop their leaves. They do this by growing a layer of cells at the base of the petiole that allows the leaf to drop off. This layer is called the abscision layer, which means 'to cut'. As this layer grows, the food supply to the leaf is interupted and the leaf begins to starve and eventually will die. The green part of the leaf (chlorophyll) begins to degenerate and the other colors that were always there but hidden begin to show. This is how we get the spectacular fall colors that we love so much.
So what can we learn from that? As I said, this is caused by starving the leaf. There are other mechanisms that can cause the same event. Anything that disrupts the flow of sap up the trunk or out the limbs will cause a slow starvation of the leaves. Damages to the veins in the trunk or limbs of the plant will cause this. Vascular diseases, borers and physical wounds can impede sap (food) flow to the outer or upper parts of the plant. Physical wounds by man are the easiest to correct so let's talk just boring insects and diseases.
Borers and vascular diseases enter the tree without much indication that it happened. They either eat or grow through the living part of the tree. That part is the cambium or veins. As this progresses, the flow of sap to certain parts of the tree decreases and that part of the tree begins to starve. In spring the leaves of a limb may look small (hard to notice), in summer those same leaves may scorch while rest of the tree doesn't (easier to notice) but in fall that particular limb will show fall color earlier than the limb right next to it. So watch the plants in your yard and see if you notice any plant parts oddly turning fall colors before the other limbs. It's normal that one side turns over the other.
Borers need to leave the tree to complete their life cycle so they will bore out of the tree or shrub and leave either D-shaped or circular exit holes. Few have noticeable entry holes. Diseases are tougher to identify. There will be no holes. Maybe some weird fungal fruiting bodies will pop out of the trunk or limbs. Sometimes the plants may ooze a liquid. Sometimes it may show discolorations to the slightly sunken vein layer, if the tree doesn't have a thick corky bark. In both cases (bugs and disease) the bark may become loose and sound or feel hollow.
If we see signs of this happening then we can begin treatments early and potentially ward off losing the tree or enough of it that it gets cut down. We may even prevent it's spread to another host tree in the yard. This can save even more money and work. Make sure you tell the nursery person what kind of plant it is and, hopefully, the shape and size of any holes.
Whether it's insects or disease, we can make sure that our plant is watered well during periods of drought and we can feed it on an annual basis. This will help the tree's own defenses stay off the problem. In the case of borers we can begin treatments for the particular pest and further help your plant. There aren't great treatments for most of the vascular diseases so do what is described above to gain time for a plan to remove and replace the dying tree.
