By Kathleen Cue, Nebraska Extension Horticulture Educator in Dodge County (Week of July 25, 2022)
Now is the time to check magnolia trees in your landscape for magnolia scale, Neolecanium cornuparvum. Unlike hard-shelled scale, this sucking pest is considered a soft scale, damaging branches and twigs by removing sap through a needle-like mouthpart. Branch stunting and death, yellowing leaves, and the development of sooty mold, which forms from the insects’ sugary excretions, called honeydew, occur from scale infestations. With severe infestations, tree death is likely. In addition, honeydew accumulates on vehicles, sidewalks, lawns, and anything located beneath trees, making things sticky and fostering sooty mold development. Often, it is this very thing that alerts tree owners of the presence of scale. At times, ants, wasps, and other insects will feed on honeydew, adding to the level of activity around trees.
Magnolia scale adults are immobile, about ½ inch long, and cream to light pink in color. Body fluids of crushed insects are bright orange in color. When scale numbers are low, Individual scales will be spaced along twigs, but as their numbers increase, the insects will crowd together, in some cases overlapping one another. Immature scales, known as crawlers, are tiny, less than 1/32 of an inch long, have six legs and no protective covering, and are the only stage in the insect’s life cycle to be mobile. Crawlers are the mechanism by which scale spreads from infested branches to those unaffected branches in close physical contact. As crawlers mature to adults, they lose mobility and secrete a waxy substance to protect themselves from weather, which also helps to protect them from insecticide applications.
Scale outbreaks do not tend to go away on their own and, in most cases, worsen over time. Predatory insects like lady beetles will eat scale but often at a rate insufficient to keep up with outbreaks. For small infestations on short tree and shrub magnolias, don a pair of cotton gloves soaked in soapy water to vigorously rub along twigs and branches, killing scale insects and removing the sticky honeydew. Re-dip gloved hands as needed until branches and twigs are clear of scale.
For large trees, hiring a tree service may be necessary to manage scale numbers. By targeting the crawler generation, their lack of covering makes them vulnerable to insecticide applications. As crawlers emerge in August and September, use insecticidal soaps, horticultural oils, or synthetic insecticides to spray infested branches. Two applications spaced according to label directions will provide the best reduction in their numbers.
Less crawlers mean reduced damage and less overwintering insects to reproduce next year. Late summer and early fall applications will be the most effective, with some options for treatment next spring and summer. Monitor magnolia trees and shrubs for any future infestations. For more information about magnolia scale, follow this link: https://hortnews.extension.iastate.edu/magnolia-scale .