Carpenter ants associated with tupliptree scale are attracted by the abundance of honeydew.
The following information will assist you in accurately diagnosing the soft scale insect species on a magnolia or tuliptree twig or branch.
The magnolia scale, Neolecanium cornuparvum, is one of the largest scale insects in the United States. It only feeds on magnolia. Magnolia scale prefers attacking star magnolia, Magnolia stellata, cucumbertree magnolia, M. acuminata, lily magnolia, M. liliiflora and saucer magnolia, M. soulangeana. They also attack other cultivars but usually with less frequency. This species is native to the United States and is widely distributed throughout the eastern United States.
Mature females are about 12 mm (1/2 inch) in diameter, smooth, elliptical, convex, pinkish-orange to brown insects that are covered with a white, waxy coating (Fig. 1). The overwintering nymphs are dark gray with a red-brown median ridge.
Magnolia scale overwinters as nymphs on one- or two-year-old twigs. Nymphs mature in late July through early August. Males emerge about the same time as small fly-like insects which mate with females and then die. Females later give birth to living young called crawlers in late August or early September. These nymphs or crawlers wander about for a short period of time prior to settling down on the young twigs where they overwinter. There is only one generation produced each year in Pennsylvania.
Fig. 1 Mature female magnolia scale insects on a host twig. Note how smooth the edges are of this soft scale insect species.
The tuliptree scale, Toumeyella liriodendri, is also a large soft scale insect in the United States. It is often misidentified as the magnolia scale that is larger and has a similar life cycle, but only attacks magnolias. The tuliptree scale is a key pest of yellow poplar or tuliptree, magnolia (star magnolia, Magnolia stellata, saucer magnolia, M. soulangeana, and southern magnolia, M. grandiflora), and occasionally linden, Tilia spp., redbud, Cercis canadensis, walnut, Juglans spp., and hickory, Carya spp. This soft scale insect is so prolific that it quite often covers twigs and branches.
Mature females grow as large as 6-7 mm in diameter. They are oval, convex, and have a distinct flange around the margin of its protective waxy cover (Fig. 2). The waxy cover of a mature female varies from light grayish green to pinkish orange mottled with black. The body fluid of a live female is also pinkish orange. Adult males are small and only have one pair of wings. Adult males may look like tiny wasp parasitoids as they crawl across the surfaces of an infested plant. The crawler stage of this insect is dark red and about 0.5 mm long.
This tuliptree scale overwinters as second instar nymphs. It resumes feeding in early spring. Males mature in June. Males emerge from the waxy scale covering as small, two winged individuals. They mate with females, and then die. In August mature females give birth to first instar nymphs called crawlers. Each female may produce as many as 3,000 crawlers over several weeks. Crawlers are capable of moving around in a tree. They may be spread to new host trees by wind or on the plumage of songbirds. Crawlers feed for a short time before molting into the overwintering second nymphal instar stage. There is one generation produced each year in Pennsylvania.
Fig. 2 A mature female tuliptree scale insect. Note how the edges of the female resemble the edges of the crust of a pie.
Indications of Infestation
Large numbers of these soft scales may give an infested twig a warty appearance. One of the first indications of an infestation of this pest is the abundance of honeydew (sticky, sugar-rich material) secreted by developing soft scales during the growing season. Ant and wasp populations that seek the honeydew are often found in association with this soft scale insect. These ants may need to be managed since they protect this scale insect from predators and parasitoids. The honeydew is a substrate on which black sooty mold grows. The sooty mold may turn the leaves, twigs, and other surfaces beneath an infestation black. Feeding by these pests may weaken young trees by removing plant fluid. In some instances this species may be so prolific that it covers all of the twigs and branches. This could result in a rapid decline of an infested tree.
Managing these soft scale insect pests
There are several natural enemies that attack these soft scale insect pests. To effectively manage either magnolia scale or tuliptree scale, you may apply horticultural spray oil as a dormant treatment. An early spring application of a dormant rate of a registered formulation of horticultural oil applied according to label directions will help reduce infestations of these two soft scale insect species if applied after the danger of freezing nights has passed, but before the host plant buds have opened.
Crawlers may be managed with registered formulations containing acephate, azadirachtin, buprofezin, carbaryl, cyfluthrin, dinotefuran, flonicamid, horticultural oil, hydrophobic extract of neem oil, imidacloprid, insecticidal soap, or thiamethoxam. Be sure to select and apply registered horticultural spray oil formulations according to label directions.
Magnolia scale and tuliptree scale crawlers are active and vulnerable to applications of registered insecticides applied from late August through September. Soil application of systemic insecticides should be applied according to label directions. The size of the tree being treated and having good soil moisture at the time of treatment are variables that need to be considered when treating infested trees. It's currently suggested that all soil-applied insecticides be delivered within 12 inches around the base of a tree to achieve optimal uptake of the product.
Author: Greg Hoover, Penn State Extension Ornamental Entomologist, Retired