Fall Treatments Help Stressed Trees Recover
Written by: Tony Arnoldi, Board-Certified Master Arborist
It has been a long, stressful year for our trees and many of them are showing the effects of this prolonged strain. Many trees are displaying thinner than normal canopies, early fall colors, early leaf fall caused by fungal leafspot fungi that parasitized the leaves all year, or early leaf fall caused by a weakened root system. Spruce trees have been steadily losing needles due to fungal needlecasts and other combined stresses.
There is a stress timeline to consider. Prior to our “summer” coming (finally in July) we had had approximately 18 months of very wet weather that kept the soil nearly continually saturated. Trees need water, right? But when water is in the soil for prolonged periods the oxygen is displaced out of the soil. Tree roots need oxygen to “breathe,” and if it is missing for too long, roots drown and die. This leaves trees with a diminished root system. Then, in July the weather got dry and hot and the soils quickly dried out. Trees found themselves with the need to get water up to the thirsty leaves but had lost considerable function of the root system to be able to do it with. So, the leaves and shoot tissues were damaged by too little water once the heat was turned on. It was amazing to see how quickly the soil went from wet to too dry in a matter of 1 to 2 weeks.
This is when leaf-wilting and some early fall colors first were noticed. A symptom of the stress of a diminished root system for many trees, including some large silver maples, was a delay in producing the leaves. For some this lasted well into the later summer. Others began to grow extra leaves in mid-summer to make up for lost time. Producing smaller-than-normal leaves was a response seen in trees such as sugar maples.
Another stress to consider in the timeline was the effects of the Polar Vortex last winter. Half-hardy plants such as Japanese maples, magnolias, and burning bushes had suffered damage, but even some normally-hardy trees showed damage if there were pre-existing conditions on limbs or trunks from old or ongoing borer damage or fungal infections.
A main stress for this year is the opportunistic action of root rot fungi. These are everywhere in our soils and play the role of the decomposer of dead and dying roots and other organic matter (a good thing). But if there are many dead roots to feed on (like the drowned roots from this year) they can gain enough strength to be able to attack the remaining (living) roots. This has been the big problem this year.
When trees are weakened, the way back for them must begin with the roots. Root losses must be restored before the foliage can make gains again. There are several ways that roots can be encouraged to grow and restore lost function. Root Biostimulants are especially helpful to re-build critical fine feeder roots and the root rhizosphere that nurtures them. Compost Teas are another component to connecting the beneficial soil life to the root system. Fall Fertilization and soil injected iron can help improve color/help reverse chlorosis (yellow foliage that makes inadequate food for the tree). FAC trunk-injected iron can get more immediate green-up of critically chlorotic trees. Of particular help has been the recent addition of Biological Fungicide that can help stimulate root growth while concurrently helping to deter the attack of the root rot fungi. Keeping up with new products and advancements like this have provided more options to combat tree root issues.
Please call your Wachtel Tree Science Certified Arborist for an assessment of the health and impacts of this stressful time on your trees. We are there to help.