The Magnolia Scale, Neolecanium cornuparvum, is a soft scale insect that poses a significant threat to magnolia trees, particularly popular varieties like star and saucer magnolias. This pest extracts sap from the tree’s vascular system, which can cause branch dieback and overall decline in tree health. The mature female scale is large and conspicuous but is protected by a waxy coating, making control difficult. Effective management requires focusing on the most vulnerable and mobile phase: the crawler stage. Identifying this tiny, newly hatched insect is paramount for successful treatment.
Identifying the Magnolia Scale Crawler
The crawler is the first juvenile stage of the Magnolia Scale, characterized by its small size and mobility. These insects measure less than 1/32 of an inch, roughly the size of a pinhead, often making them hard to observe without magnification. Crawlers are oval and flattened in shape, possessing six legs that allow them to actively search for a feeding site. Their color upon emergence is typically pale yellow, reddish-brown, or medium brown. Unlike the sessile, dome-shaped adult females, crawlers are highly active and lack the thick, protective waxy covering that shields older nymphs and adults, leaving them fully exposed to topical treatments.
When Crawlers Emerge and Where They Settle
Crawler emergence is a yearly event tied to environmental temperatures, generally occurring in late summer into early fall. This emergence window often falls between late August and the end of September. Female scales give birth to live young, and the crawlers emerge from beneath the mother’s body. Following emergence, the crawlers briefly wander across the branches to find a permanent feeding location. They typically attach themselves to the newest growth, particularly on one- or two-year-old twigs, where they feed and develop into a second-instar nymph before remaining there through the winter.
Signs of Infestation and Mature Scale Appearance
Before crawlers appear, the most obvious signs of infestation relate to the waste product of the feeding mature scales. As the insects consume sap, they excrete excess fluid as a sticky, sugary substance called honeydew. This honeydew coats leaves, branches, and objects beneath the tree, attracting ants and wasps. A black, crusty layer of sooty mold fungus frequently grows on the honeydew, which is often the first visible sign of a problem. While the sooty mold does not directly harm the tree, a heavy coating can interfere with photosynthesis. The adult female scales are among the largest soft scales, reaching up to a half-inch in diameter, appearing as immobile, dome-shaped bumps on the twigs. These mature scales are initially white, developing a purplish-brown color, and are covered with a white, powdery wax that makes them difficult to eliminate with sprays.
Effective Control Methods Targeting the Crawler
The crawler stage is the only period when the insect is vulnerable to topical treatments. Since they are mobile and lack the thick, waxy covering of the adult, they are easily susceptible to contact insecticides. Timing the application to the late summer emergence window is the most strategic approach for management. Horticultural oils and insecticidal soaps are recommended control methods, as they kill crawlers by suffocation or direct contact while having a minimal impact on beneficial insects. Monitor for the first appearance of crawlers, typically from late August into September, and apply the product thoroughly to ensure complete coverage of the infested twigs and the undersides of leaves.