Summer 2022 Magnolia Scale Bulletin
Magnolia scale is an insect which only affects Magnolia trees and has been a menace in Lincoln for around four years. In my observation Magnolia scale is the most devastating plant health phenomenon affecting Lincoln homeowners at this time. While emerald ash borer (EAB) devastation already causes more damage to our urban forest than Magnolia scale in terms of numbers of affected trees (ash trees outnumber Magnolias by, perhaps, a factor of 50, afterall), EAB is controlled with relative ease compared to Magnolia scale. Owing to the unusual life cycle and metabolic habits of scale species, controlling a severe infestation of Magnolia scale takes several years and is a task suited only to highly experienced professionals. (While light infestations are easier to manage, they go unnoticed by laypersons.) A common belief is that a low count of ladybugs (voracious consumers of scale) explains why Magnolia scale is running rampant in the Country Club area of Lincoln and has spread eastward to 84th St and northward to Holdrege St. I have become suspicious that drought in the month of April for four of the last five years (the same periodicity as the low ladybug count) is related to a failure of ladybugs to reproduce in Spring and/or an enhanced survivability of scale insects from one season to the next. The academic community has not confirmed either theory as to why scale insects are in the worst spike in decades in Lincoln–the real causes could instead be part of much longer, and thus far unknown (and less “interesting”) environmental factors.
Alarming symptoms in Magnolias are observed in the summer as the feeding of the female molting stage scales (the cottony patches on the underside of twigs) produce voluminous honeydew waste which accumulates on the leaves of the tree and any other foliage or targets below the canopy. A swarm of flies, wasps, and other insects is attracted to these nutritious deposits, and a mostly non-injurious black “sooty mold” ultimately forms upon all affected surfaces. Neither phenomenon injures the tree but since Magnolia trees in Lincoln are often a rare and prized accent planting, these effects result in a dismal and inconvenient display! This combination of symptoms and their relatively sudden onset often produces an incorrect conclusion among customers that my tree is “no longer treatable,” “is dead” or “dying,” and “needs to be removed.” While the loss of fluid is the main cause of death or decline in your tree, it can withstand several years of this attack and in the meantime control measures can take hold.
Counterintuitively, Magnolia scale is NOT particularly manageable during the summer period of heightened symptoms and damage described above, since the scales have covered themselves up with a waxy protective coating (a hallmark of scale physiology), such that insecticidal canopy sprays are of no use. Additionally, I believe that the rate of sap loss (the dripping) at this time is so great that the newer technology of systemic insecticides are “running through” the plant at a high rate, and perhaps are lost from plant tissues within as little as a few days—too fast to be fed upon by the insect for a duration sufficient to establish a good “kill.” A potential exception to the lack of possible controls at this stage regards small Magnolia trees and bushes, for which a homeowner may be able to reach a significant percentage of the gestating insect masses to be mechanically scrubbed off with a brush or the careful use of high-pressure blasts of water.
THE INSECT LIFE STAGE WE ARE CONTROLLING is a microscopic, crawling/infant and juvenile stage which is active between September and April. These “crawlers” as they are known, are gestated within the visible white patches which produce the honeydew. Applications to control crawlers are made in late summer and early spring.
Systemic Insecticides: These are insecticides which flow inside the tree, making the tissues of the tree toxic to feeding insects. These include a pair of neonicotinoid insecticides: imidacloprid and dinotefuran. These insecticides are injected in the soil at the base of the tree to be absorbed by the roots. Maintain soil moisture in the root zone of your tree for a week following application.
NOTE: MAGNOLIA TREES ARE A FLOWERING PLANT THAT CAN BE VISITED BY BEES. The use of insecticides on flowering plants is subject to laws and guidelines to protect pollinators. If you wish to have your tree treated and know of beekeeping activities in your neighborhood, please let me know.
Cover Sprays: While spraying of conventional chemical insecticides is effective against scale, their use is impractical in the urban setting due to the notification requirement necessary to keep customers, neighbors and pets safe from exposure to the cloud of chemical created by such applications, and residues which collect on nontarget locations. Also, if insect predators of scale (ladybugs?) are present assisting in curing our scale problem, chemical insecticides will tend to kill them also which is counterproductive. The alternative to chemical pesticides is summer and dormant “horticultural oil.” This is mineral oil (the same ingredient as “baby oil”) which smothers/suffocates scale crawlers but has little effect on nontarget insects and is innocuous to pets and people. A thin film of oil can be deposited on decks and walkways when applied, but it does not seem to not make areas any slippier than water alone as the concentration of oil in water is only one-half to one percent. You can rinse off surfaces under the tree with a hose following the application if you like.
As of summer 2022, we can be certain that ALL Magnolia trees in Lincoln are either affected by Magnolia scale or are at risk of infestation. For this reason, all Magnolia trees and bushes which have value to their owner are candidates for insecticide application. Depending on size and level of infestation and your budget and expectations, affected trees will be treated with varying levels of intensity using a customized configuration of the several insecticides and methods of application.
Infested trees require both applications described above in late summer 2022, and again in early spring of 2023. Newer infestations commonly require an additional year or longer of this application schedule. Now is a good time to consider the long term costs so you can make a determination as to whether this undertaking is appropriate for your situation.
This phenomenon has matured to the point where I can correlate treatments with treatment success. I’m managing scale in roughly 50 Magnolia trees and while many are not “getting better” as fast as we would like, only one tree has died. Mild infections which have been treated for two years have been controlled 100%. Moderate and severe infections are getting better or not getting worse amidst the observation that new infections were slight in 2021, but now up sharply in 2022. Unfortunately scale is not yet starting to “go away” naturally. While it seemed that ladybugs were returning throughout 2021 and requests for treatment of new infestations was waning, incidence of tree symptoms has spiked in summer 2022. It may be most honest for me to refer to my service as achieving a “suppression” of scale rather than an “eradication,” at least with regard to the more heavily affected trees.
Please call or text with any questions you have about your Magnolia or other trees.
