If you have beautiful magnolia trees in your yard, you certainly don’t want them to be destroyed by a small pest. The unfortunate truth is that, they can. Magnolia scale is one of the largest scale insects and are commonly found in the eastern part of the United States. They most commonly attack the Star Magnolia, Saucer Magnolia, Cucumbertree Magnolia and Lily Magnolia. The scales remove fluids from the tree using their mouthparts, which results in substantial dieback and death.
Identifying Magnolia Scale
Magnolia scale have a life cycle that includes nymphs, crawlers and adults. The overwintering nymphs are dark-gray in color and cluster together in groups on branches and trees. In the early summer months, the females develop a waxy covering. The adults are permanently fixated to the branch and can range from a pink-orange to dark brown color.
When the crawlers emerge, the wax covering disappears, which usually occurs in August. Newly hatched crawlers are a medium brown color, and they get darker with their feedings. The males are smaller than females, about ⅛” in size compared to the female size of ½”. These pests are often referred to as “bumps on the twigs.”
Understanding the life cycle of magnolia scale can help in identifying the pests.
Winter: Minute, dark-colored nymphs over-winter on young branches and twigs.
Spring: The scale begin to feed and grow in size.
Summer: Both males and females mature in late summer. The males emerge, mate with the females and die off. In late August and September, the females give birth to the crawlers. The crawlers wander for a short time, then they settle on a twig where they get ready to over-winter. There is one generation.
I Suspect an Infestation. What Now?
Magnolia scales can be found on the undersides of branches that are about 1-2 years in age. If the infestation is bad enough, the scales can encrust the branch. Other signs that your magnolia trees are infected include reduced foliage and flower production, small leaves and twigs and a black mold-like material on the tree. It’s common for magnolia scale to go unnoticed in the beginning since these pests are very small.
What will happen over time is that the scale produce sooty black mold. They digest the plant fluid from the tree, then excrete a sticky fluid (honeydew) that creates a breeding ground for the black mold. When the black mold forms on the foliage, the tree starts exhibiting the symptoms of reduced foliage and dieback. The tree also loses its vigor and has apparent mold spots throughout. Also, the fluid that the scale leave behind serves as food for ants, bees and flies, bringing more pests into the area.
What Treatment Options are Available?
It’s always important to contact a professional arborist when you suspect an infestation. It’s important to know exactly what you’re dealing with so that the proper treatment method can be performed. Insecticides are poisons, and many are not safe for the layperson to use. Also, since magnolia scale can protect themselves under the waxy coatings, it’s easy for them to stay protected when insecticides are used. An effective treatment plan that targets nymphs and crawlers is necessary for the best results.
Generally, there will be a number of management options used to mend the situation and protect the magnolia tree in the future. Contact insecticides are best for killing off magnolia scale that is out in the open and feeding on the tree. Infected parts of the tree will need to be removed to prevent spreading of the pests. There are also insecticidal soaps and horticultural oils that can be used in the spring and fall to target the crawlers. Since the crawlers hide under the waxy coating, contact insecticides are not effective at reducing the population.
If the infestation is bad enough, two fall applications may be necessary. Treatments are done 7-10 days apart, and additional insecticidal treatments may be needed in the spring for added protection.