Frerichs Tree Service
Fall 2020 Lincoln Oak Tree Bulletin
Plant health care has become a focus of the future for Frerichs Tree Service. It is now time to advise you of new and existing threats regarding oak trees in Lincoln. Call anytime to discuss your oak tree(s) or any other tree questions you have. The pupose of this document is to advise you that signficant threats to you oak(s) are present in Lincoln, so that I do not later have to explain why your tree is sick and why I didn’t alert you sooner.
Why do oak trees deserve special attention?
Oaks enjoy the greatest longevity among all trees that grow in Lincoln. Although they are slow growing, their ability to live beyond 200 years of age with good care means that despite the fact they already tend to be the biggest trees in Lincoln, our pin and red oaks are still quite young! The longevity of the oak tree in your lawn can be greatly improved with plant health care and pruning, thus avoiding the disappointment and cost of removing an important tree in your lawn. In short, desireable oak trees growing in a proper location in your lawn warrant heightened attention in Fall 2020. Please call with your questions.
What is Kermes scale?
Kermes scale is an insect that attaches to and feeds on sap from the twigs of your oak tree, causing some leaves to to die and turn brown. The leaves tend to stay attached through the growing season, so an affected tree will have a few or many of its leaves turning brown which contrasts with the otherwise green healthy foliage. A tree in this state is said to be “flagging.” The insect population in your tree grows larger every year. By the time the average homeowner notices that there is a problem that is not going away, the insect will be difficult to control even with professional methods. The best management of Kermes scale involves early detection since systemic insecticides available to the contemporary arborist, while of a high enviromental stewardship, are not particularly powerful. While Kermes scale is endemic to oaks in Lincoln as of 2020, it is NOT yet on the radar of local forestry officials, county extension, media, etc. Since some oaks will be killed by Kermes scale by 2021, an awareness of scale in oaks may occur within a year.
Systemic treatements for Kermes scale:
Success in treating Kermes scale is measured in seasons, not days or weeks. Kermes scale was detected only in north Lincoln in 2019, but in summer of 2020 it is in every neighborhood in Lincoln. It seems possible that most oaks in Lincoln will be affected by 2021, and the slow rate at which Kermes responds to insecticide treatment is the reason that pre-treatment is recommended at this time for all high value oak trees whether they are flagging or not. If systemic treatments are only started after a couple seasons of infestation, the results are slow, even when using the exotic (costlier) variation of neonicotinoid insecticides. Avoiding a heavy infestation is best approach!
What is iron chlorosis?
Chlorois is a yellowing of plant leaves caused from lack of adequate nutrients. In Lincoln’s oaks this is caused by a deficiency of iron. While there is plenty of this nutrient in the soil, Lincoln’s pin oaks are often unable to absorb the iron due to inadequate soil acidity. While mulching and fertilizer can help change soil pH slightly, there really is no option but to inject iron directly into the stem of the tree to correct the severe cases which occur in roughly 10% of all pin oaks in Lincoln. If your lawn needed the same soil pH as your oak tree, we could just make regular sulfur applications to improve the situation. However, your lawn does NOT tolerate the acidity your oak needs. Iron supplements available to homeowners do not supply enough iron to a large oak to make much difference, and for this reason there is a concern that homeowner applied products may do more harm than good. The frequency and number of drilling wounds into the stem of your oak required to give a large dose of iron using implants only adds additional stress to an already sick tree. In summary, when dealing with a high value mature oak tree that is under stress, it is best to identify chlorosis early.
Plant Growth Regulator (PGR) in addition to iron injection:
The application of this root growth stimulant at the time of iron injection doubles the effectiveness of iron injection by tricking your tree into using its energy to grow more roots instead of top growth. PGR is also useful in overcoming root stresses from compaction or construction damage to oaks. PGR is so helpful in overcoming chlorosis in oaks that I no longer offer iron injection without it.
