Alison Arnold: Evaluating Tree Health Risk

Sep 29, 2016

In her gardening segment this week, Alison Arnold talks about evaluating trees for their health and risk as we get into fall.  

Jeremy Loeb: It’s the end of the growing season and some trees already show fall color while others have that end of the summer “wear and tear” look…... is this a good time to evaluate trees for overall health and maybe even risk?

Alison Arnold: That’s an excellent question and one I have to answer with both Yes and No. Yes.. because if leaves are on the tree some assessment can be made.. So for instance do the leaves have good color? Are there signs or symptoms of insect or disease?  And if it’s possible to think back and how the tree looked back in the late spring and early summer when it first leafed out.. did the leaves came out and grow well throughout the canopy .. if they did this is a good sign of health. If they didn't and there were and still are a number of dead branches – this could be of concern.

Why would this NOT be a good time to evaluate tree health?

Well by now it might hard to remember how the tree looked earlier in the season and if it had a full canopy of leaves or not. There might a number of symptoms from insects or diseases that are present on the tree now that may not be life threatening but affect our view of things.  It’s important to keep perspective and remember that heat and lack of rain plays a role in the late summer “Wear and tear” look. Leaf scorch for instance .... where the margins or edges of the leaves are brown and even crispy with the interior part still green - can be seen on many plants throughout the garden.

OK.. so then how is the best way to know what might be normal or not?

First .. it’s helpful to sort things out. For instance -  early fall color – sourwood, dogwood, maples show early fall color – starting with a few leaves and moving to a general overall change. This is typical for the most part but are not necessarily a long term concern. Next you can sort out the trees that have been or typically get hammered by insects and disease.. Locust, tulip trees, ornamental cherries come to mind. These guys have an abundance of yellowing or browning leaves or might even have dropped all their leaves already or a dropping leaves daily. Again these trees can withstand this year to year and so late season leaf drop isn’t necessarily a long term concern.

What trees then are hard to evaluate this time of year?

I think I would put oaks in this category. White oaks tend to fair pretty well. You might find some disease and a little insect damage but nothing compared to red oaks. Red Oaks typically take the brunt of things. Right now it’s very possible to see a number of leaves having fallen to the ground that are brown or dull green. Those remaining the tree can be anywhere from bright to dull green, with brown blotches or edges. You might also see a number of branches that are bare or have no leaves left….These are the trees that can be challenging to evaluate this time of year, especially if it’s hard to trace recent history of the tree.

Seems like there are so many factors that can lead to the symptoms you’ve been talking about.. heat, drought, insects, disease..

Definitely and this doesn't take into account things like construction damage, root compaction, lightening strikes.. even old age. Some of these can take place at some point and cause initial “damage”.

Later as other stressors come into the picture like drought for instance.. secondary factors come into play.. mainly insects and disease. When insects or disease appear on an older well established tree it’s not them causing the damage.. but something that happened long ago or has taken place over a long period of time – like general aging.

It sounds like a complex issue and something that should be investigated well by an arborist or someone who have experience with this.

Absolutely. In fact I’d like to talk about that and more about evaluating tree risk the next time we are together.. how does that sound?