Plant Growth Regulator for Oak Trees
The information below is appropriate for homeowners that understand the relative superiority that oak tree species enjoy in comparison to other large growing trees in Lincoln with regards to overall durability and longevity. If your large oak(s) seem like “just another tree,” it may be best to let me know so we can come to a common understanding of your goals for your landscape.
A scrutiny of oaks due to scale and leaf feeding insects over the last few years has provided the basis for my “Fall Oaks Progam.” The Kermes scale insect threat of the past several years has served as a reminder of the tenuousness of Lincoln’s mature oak trees. As of late summer 2022 it appears that bug is going away, such that the Fall season preventative insecticide application is no longer necessary for ALL red oaks and pin oaks. Do be awere however that this trend could change next year. Insect management in the landscape is, afterall, a humbling profession; a constant attempt to combine a skillful anticipation of insect threats with an adaptability to sudden, new phenomenon, and to present cost effective treatment directives in a timely manner which the public can understand. Management of stress in oaks has been a three-pronged appraoch: Systemic insecticide to manage scale, iron injection for pinoaks with canopies with less than optimal depth of green to the canopy, and use of “plant growth regulator” to enhance the effects of the iron and a variety of other benefits.
In many instances I have directed you to the information herein because we are as yet NOT applying plant growth regulator to your oak(s). This application is appropriate for homeowners who want to undertake a 10+ year process of improving the fundamental health of their oak tree(s). It takes 5-8 years to observe fundamental improvement in oaks after starting growth regulator treatment for trees with rigorous fundamental stress. The weaknesses present in your oak, are, afterall, the result of decades of stress. Even healthier oaks are logical candidates for growth regulator application in order to thwart development of the stresses which are universal to oaks in Lincoln.
Plant growth regulator, frankly, is among the very few modern technologies deserving of the title as a “magic potion” for oaks. The fundamental action of the active ingredient, “paclobutrazol,” is to “trick” the tree at the hormonal level to direct its energy into developing greater root density instead of “growing bigger.” Greater root density means greater uptake of nutrients from the soil even though the fundamental shortcoming in Lincoln’s soil is that it is the wrong pH (too alkaline due to a limestone bedrock) for oaks. In reality, many mature oaks have root systems that are “shot” from years of dealing with Lincoln’s compaction prone soil. The leaves of treated oak trees grow a little smaller, and have a correspondingly tougher “skin” which resists insect, bacterial, fungal, and drought stresses. Finally, slowing the growth of your tree is rarely a detractor, since it means less less trimming expense over time. In most cases, your oak(s) are already big enough, and this factor alone can easily recover the cost of applications.
In the interest of thoroughness, I should here interject that one other major technology in tree care DOES exist for trees growing in imperfect soil. This involves the use of a specialized air powered wand to delicately excavate thousands of pounds of soil (your lawn) from the dripline of your tree, to be replaced with ammended soils. While I undoubtedly will one day bring this service to Lincoln, your enthusiasm for this service will be moderated by the reality that this undertaking can cost thousands of dollars for large oaks since it involves removing and replacing tons of soil, the cost soil testing and ammendments, and the reestablishing of large areas of turf. It only makes sense to mention this extravagant option now so as to avoid any disappointment for having to later take on a new or different understanding of your options.
In closing, a universal observation that experienced arborists can make regarding Lincoln’s oak trees is that a too-alkaline soil exerts a lifelong stress on these trees, particularly in the root system by the 4rth or 5th decade of growth. This is not an inherent phenomenon for oak species generally, since in their natural habitat these trees can live for 200 years. While 50-100 year old oaks are among Lincoln’s oldest trees, they are actually still quite young. Lincoln is not an old enough city ot have “large” oak trees. There are of course practical factors to consider on a tree by tree and customer by customer basis for oaks growing in the residential/urban environment, and for this reason I urge you to call or text today to discuss whether plant growth regulator application is appropriate for your trees.
Will Frerichs, 402-476-0499
