By Mike McKee
ISA Certified Arborist®
June 20, 2024
Hello! We have decided to revisit the topic of magnolia scale and add more information to this previously published article as we are in the middle of a larger magnolia scale infestation compared to last year (2023).
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Please note: This article was originally published on 8/9/2023 and was revised and republished on 6/20/2024.
Is your magnolia tree turning black? Is it attracting ants, flies, bees and wasps? Is there a sticky substance covering the leaves and everything under the plant? If you look closely, you will also see white blotches on the twigs throughout the tree.
This is an invasion of magnolia scale like we have not seen in several years. They happen to thrive in warm summers with abundant moisture. The population is building and is very apparent this year.
The insect overwinters on twigs and is inconspicuous to the untrained eye until it starts feeding and producing honeydew. Honeydew is the very sweet, sticky substance secreted by the insect that in turn coats the leaves and anything under the plant. This is what attracts other insects to the plant. Eventually the insect covers itself with a waxy coating that protects it while feeding. These are the white blotches we are now seeing on the plants starting early summer through August.
Nymphs emerging from a recently plucked adult Magnolia Scale
The juvenile stage of magnolia scale emerges from these waxy coatings (the adults) in mid to late August through September as crawlers. This is when scale are most vulnerable to insecticides and we attempt to control their population. We typically recommend 2 to 3 topical insecticide sprays during this period spaced a couple weeks apart for the best control of the insect due to the extended emergence. During seasons with larger infestations, it is unlikely that insecticide sprays will completely eliminate this insect. The overall goal of plant healthcare is to keep the population at a threshold that minimizes damage and maintains aesthetics of the host tree.
If the tree’s owner is concerned about the population of magnolia scale before the appropriate window for insecticide applications is open, there are a few DIY options that can be done. First, the insects can be scrubbed off from branches and leaves in June and July. This is when the adults are visible before the hatch begins. You could also prune out heavily infested Interior branches to help reduce numbers. Be sure to completely dispose of any pruned branches as the insect will still hatch. Spraying the trees with a medium pressure garden hose can also eliminate some insects as well as reduce the honeydew on the plants.
The insects feed by sucking sap out of the tree. If left untreated the scale population can grow to levels that will cause decline and eventual death in your tree.
Another issue with Magnolia scale is the occurrence of sooty mold which is a byproduct of the honeydew produced by the scale. It is a black fungal growth which is what most people notice first. Although this generally does not harm the tree, it is very unsightly.
In closing, if you have a magnolia in the landscape, give us a call and we will dispatch a certified arborist to your property to come out and complete an evaluation of the tree and make recommendations for the best management strategy. Timing is everything.
Sincerely,
Mike McKee | Regional Manager, Russell Tree Experts
Mike graduated from Hocking College in 1983 with a degree in Natural Resources specializing in urban tree care. He has been a certified arborist since 1991. Mike started his career in the private industry in 1985 before becoming a municipal arborist in 1989. He retired after serving thirty years before joining us at Russell Tree Experts in Sept. of 2018. His love of trees has never waned since trying to climb up the ridges of the massive Cottonwood tree in front of his childhood home.