Hello,

Magnolia scale can be challenging to manage, especially when the infestation is extensive.

Magnolia scale (Neolecanium cornuparvum, is the largest scale found in the United States. Its primary host is magnolia. Star magnolia, saucer magnolia, cucumber tree, and lily magnolia are among the species most commonly infested. Like other scale insects, it is good at disguising itself to escape detection, but its large size – up to 0.5 inches – makes it more conspicuous. Scale insects often resemble small galls, plant parts like buds or lenticels (pores for gas exchange), or seeds. Adult male scales are small and active and superficially resemble tiny flies. Adult female soft scales are comparatively large, sedentary, hemispherical, or lens-shaped and may be covered with wax. More information at this link:

Magnolia scale is having a good year - MSU Extension

Magnolia scale has sucking mouthparts, which it uses to remove large quantities of sap from twigs and young branches. Heavily infested branches can be completely covered by scale and may be weakened or killed. Magnolia scale also produces a sticky, sweet substance called honeydew, which attracts ants, yellow jackets, and other insects that feed on it. Honeydew is largely concentrated plant sap excreted by insects. A fungus called sooty mold can grow on the honeydew, resulting in blackened leaves and branches, greatly reducing the ornamental value of the tree. The appearance of black sooty mold often alerts people to the presence of scale insects on their landscape plants. More information at this link:

Magnolia scale is having a good year - MSU Extension

Both female and male scales undergo significant changes in their appearance as they mature. Tiny, dark nymphs overwinter on one- to two-year-old twigs. As temperatures warm in the spring, the scales resume feeding and differentiate into males and females. The males remain small, about 0.125 inches, turn waxy white, and soon emerge as tiny, pink to yellow gnat-like insects. The females stay on the branches and grow, turning brownish-purple and producing lots of honeydew. In mid-summer, the female magnolia scale is covered with powdery, white wax, which rubs off as the female matures. In early August, the females look white because of a thin coating of white wax over the scale. By mid-to-late August, females begin to turn a yellow-tan color and lose their wax coating. They give birth to tiny, dark nymphs known as crawlers, which overwinter on one- to two-year-old twigs and begin the cycle again.

Here are some steps you can take to control the magnolia scale in Michigan:

Manual Removal: Although you mentioned it’s too prolific to remove manually, this method can be effective for smaller infestations or as a supplementary measure. According to Michigan State University Extension, small infestations can be removed anytime by pruning out infested branches.

Horticultural Oils and Soaps: These can be sprayed to suffocate the scale insects. They are most effective when applied during the crawler stage, typically in late August or early September. More information at this link:

Magnolia scale is having a good year - MSU Extension

Systemic Insecticides: Products containing imidacloprid can be used as a soil drench around the tree's base. This should be applied in late summer, around August, to target the crawlers as they hatch. There are two strategies for treating heavily infested trees. In August, the first option is to use imidacloprid or dinoterfuran as a basal soil drench. Check the product label to ensure it has one of those two active ingredients. Homeowners can purchase imidacloprid as “Tree and Shrub Insect Control” or in several other products. Follow the label directions for mixing the product in a bucket of water and pouring it around the base of your tree. It is unknown how much risk these products would pose to pollinators by a fall soil drench, but it would be less than an application in spring shortly before bloom. The second option, which would pose no real risk to pollinators, is to spray your tree when the magnolia scale is in the crawler stage. Watch for the small, reddish crawlers to emerge between the middle of September and early October. More information at this link:

Magnolia scale is having a good year - MSU Extension

Crawler Spray: In late September, you can apply a contact insecticide to target the crawler stage of the scale. This is when the young scales are mobile and more vulnerable. More information at this link:

Magnolia scale is having a good year - MSU Extension

Horticultural Oil and Soaps: These can be sprayed to suffocate the scale insects. They are most effective when applied during the crawler stage, typically in late August or early September. Dormant horticultural oil can be applied in late fall or early spring to control the scale. Accurately timed application of horticultural oil or insecticidal soap can help reduce scale infestations. Horticultural oils, often called summer oils, applied after the crawlers have emerged in late August, can be very effective in reducing the scale population. Be sure to obtain good coverage. Oils can also be applied in fall before freezing weather and again in early spring before the flower buds swell to kill the overwintering nymphs on the stems. Do not exceed the label rate, which is usually a 2 percent oil concentration in the applied spray. Professional landscapers or arborists can also spray the crawlers with Pyriproxyfen (Distance), an insect growth regulator that is very safe to use. Before using any pesticide, read, understand, and follow the directions on the label. More information at this link:

Magnolia scale is having a good year - MSU Extension

Pruning: Remove and destroy heavily infested branches to reduce the scale population and prevent further spread. More information at this link:

My magnolia is infested with magnolia scale. What are my control options? | Yard and Garden (iastate.edu)

Removal is generally considered a last resort. Removal might be necessary if the tree is significantly weakened and poses a risk. However, treatment is preferable if the tree is still healthy despite the infestation.

As for contagion, the magnolia scale primarily affects magnolia trees. However, if other nearby trees are magnolias, they could be at risk. It’s essential to monitor them for signs of infestation and take appropriate action.

Remember, timing is crucial for controlling the magnolia scale, so apply treatments at the right time for maximum effectiveness. Proper watering, especially during dry periods, is also beneficial for maintaining the tree's overall health and helping it resist and recover from scale infestations. 

I hope this helps