These are the questions on everyone’s mind following the deepest drought on record for southeastern Wisconsin. It is easy to see the problems for annuals, perennials, and turf, but how about the trees? Many look “ok” now – are they?
This drought and heat definitely damaged nearly every tree. Because tree root systems lie just beneath the surface, they are vulnerable to the heat and drying. Because the roots spread so far beyond the drip line, many never receive the watering we give our trees (roots often spread out 2 or more times the height in all directions! This is not what most people expect or remember from their school days, but it is true). Most often people will trickle a hose at the base of the trunk, or at best, water a mulch circle around the base of the tree. This waters only a very small percentage of the total root system. For all those roots that are never receiving water, they will desiccate and die. When this happens, the branches that are supplied by these roots will also die, and an overall dieback or decline of the tree can result. Many trees have root loss that has not yet caused branches to die, so for us the damage remains hidden.
Dryness throughout the tree interferes with photosynthesis (food making), defense, and literally all life functions. Opportunistic insects like the wood-borers are now able to overcome the tree’s defenses and successfully infest. Fungi that attack or enter the root system, like root collar rot or Verticillium wilt, can do so much more readily. Leaves begin to scorch at the edges and later on become dry with dead areas. Many of these damaged leaves are dropped. Other leaves lose chlorophyll and turn early fall colors. They fall off to help the tree reduce the loss of water through them.
The complex of soil life forming the soil food web is also affected. This soil food web functions to enable the roots to perform their job of absorbing water and nutrients. Drought will kill many of the beneficial organisms that make up this web, causing greater moisture stress for the tree. Often, these missing organisms are slow to return.
Trees can and have died suddenly this year as a result of sustained drought stress. More often, however, the compromised trees will begin to succumb to problems like borers, chlorosis, root rots, decay fungi, and to further bouts of dry weather. Historically, tree mortality is much higher for the 5 years following a drought. Unfortunately, we will be busy removing these casualties for years to come.
Efforts to help the trees rebuild their root systems and avoid further losses can make the difference. In the cool of fall, the roots can be helped and increased through Fall Fertilization, Root Biostimulant Therapy, Compost, Compost Tea application and Mycorrhizal Root Inoculation. Mulching will always be a good addition to help with these treatments and conserve soil moisture. Keeping borers from entering the trees will be extremely important, especially for oaks, birch, ash, lindens and even for many spruce and pines. Call on your Wachtel Certified Arborist for help in assisting your trees’ recovery from drought damage.