Old Yeller

By: Anthony C. Arnoldi, Certified Arborist WI-0102A

Summer 2004 Newsletter in Adobe PDF format Yellow leaves during the growing season is generally a bad sign. The several causes and cures for this is disscussed by Wachtel Tree Science & Service Certified Arborists in this article.

This time we are not referring to man’s best friend, but it may describe the current condition of one of your favorite trees.

By mid to late summer every year, many trees begin to show yellow leaf coloration. It can come on slowly or suddenly. It can be subtle or obvious, but always, the condition sneaks up on you. You may say, “Come to think of it, this tree was definitely green last year (or the year before).”

The reason that midsummer is the time this is noticed is that accumulated stresses of the year add up by that time:

  • Periods of drought alternating with periods of waterlogged soil each take their toll on feeder roots, causing them to dry up or rot off.
  • Root rot fungi attacking first the dead roots and then progressing onto living roots.
  • The strain of reduced and compromised root systems trying to meet the demands of trees in summer heat and dryness.
  • Progressive insect feeding of the foliage.
  • Mismatch of tree type to soil type.

The last point is key. Our soil type in southeast Wisconsin is naturally heavy (clay) that is high in pH (alkaline). Very few trees grow their best in this soil type, in fact, most find it a stress to grow in it at all. A consequence of the high pH is that iron (and many other micronutrients) are tightly bound to the soil particles and are difficult for the tree to absorb. Trees with compromised or stressed root systems may not absorb enough iron. When this happens, trees lose their green color because iron is necessary in the manufacturing of chlorophyll, the all-important green substance that is responsible for making food for the tree. So without iron there is no chlorophyll; without chlorophyll there is no green and no food.

Of course Old Yeller can’t stay yeller for long, because it means it is starving. Yellow leaves don’t take long to show symptoms of this: smaller than normal leaves, scorched edges, thinning of the tree, branch death, and eventually tree death. Trees most commonly slipping into this condition are white, red and pin oaks, silver maples, red (rubrum) maples, river and whitespire birches, white pines and magnolias.

Fortunately, there are treatments that can be prescribed, although this can be a very difficult condition to reverse, particularly if the tree gets deeply yellow or if dieback is advanced. One marvelous treatment in particular is called FAC iron. It is a trunk macro-infusion of extremely mobile iron that is capable of greening up oaks and certain other trees for up to 3 years. This strong green-up is necessary for many trees to be caught in time so that starvation is averted. It is a very powerful tool that has saved many otherwise unresponsive trees. It is done in the fall to avoid causing leaf drop, and the following spring leaf-out is often dramatically greener!

So call your Wachtel Certified Arborist so that an assessment can be made of the tree’s condition and the appropriate program be applied, especially if you want people to stop referring to your tree as Old Yeller.

© Copyright 2004 – Wachtel Tree Science & Service, Inc.

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