Magnolia Scale
By Buggy Joe Boggs
August 21, 2025
Magnolia Scale (Neolecanium cornuparvum) is a native “soft scale” (order Hemiptera, family Coccidae). Coccids are called soft scales because the females are hidden beneath a helmet-like, soft, leathery covering that provides some protection. However, they are easily crushed.
Magnolia scale is the largest soft scales found in Ohio with mature females measuring as much as 1/2" in diameter. This is the time of the season when the females reach maturity and become most evident. Their flesh-tone covering develops a distinct flange around the edge making the scale look like WWI era helmets.
As their common name indicates, magnolia scale only infests members of the Magnolia genus. Native magnolias are more resistant, perhaps because of natural defenses that developed through a shared evolutionary history.
The scale has the greatest impact on non-native magnolias and associated hybrids compared. Magnolias that are most commonly infested include star magnolia (Magnolia stellata), lily magnolia (M. liliiflora), and saucer magnolia (Magnolia × soulangeana).
On small trees, magnolia scale will infest all stems. On large trees, they tend to be confined to the branches but will also be found on woundwood on the main stem.
Magnolia Scale Sucks
As with all soft scales, magnolia scale adults and nymphs insert their piercing-sucking mouthparts into phloem vessels. They tap plant sap to acquire both carbohydrates which provide energy as well as amino acids which are the building blocks for proteins and enzymes.
However, the phloem sap holds only trace amounts of amino acids compared to vast amounts of dissolved carbohydrates. This means the scale must process a large quantity of sap to extract the necessary amino acids. They discharge the excess sugar-rich liquid from their anuses in the form of “honeydew," which is just a nice name for scale diarrhea.
Magnolia scale is notorious for producing copious quantities of sticky, drippy honeydew. The sugary liquid may cause heavily infested trees to literally buzz with insect activity as flies, bees, and wasps seek a sweet treat. A high percentage of the flies are often members of the blow fly family, Calliphoridae. Their maggots may have a taste for decaying flesh, but adults like sweets.
The honeydew drips onto the leaves and stems of the host plant as well as understory plants to eventually become colonized by black sooty molds. Although the molds cause no harm to the overall health of infested trees, the blackened leaves can reduce the aesthetic appeal of heavily infested trees.
A key feature separating soft scales from “armored scales” is the production of sugary, sticky “honeydew.” Armored scales insert their piercing-sucking mouthparts directly into plant cells. They do not exact large quantities of liquid; thus, they do not produce honeydew.
Life Cycle and Changing Appearances
Magnolia scale has one generation per season. Females and males spend the winter as dark-colored nymphs attached to the stems of their host plant. They look nothing like the helmet-shaped mature females currently on display. Indeed, their resemblance to lenticels makes them inconspicuous.
The nymphs mature in the spring, with the males developing into small gnat-like insects that fly to females and mate. The females remain immobile, and as spring progresses, they begin to “inflate.” They also become covered in a heavy coating of white, powdery exudate, making them look like they’re “powder-coated.” The white coating may cause them to be mistaken for mealybugs.
Eventually, the magnolia scale females shed their powdery coating as they rapidly expand to their final size and acquire their current characteristic helmet-like shape. This also indicates that 1st instar nymphs, called “crawlers”, will soon be on the scene. The appearance of the crawlers signals a key management opportunity.
Eggs are produced in late summer to early fall. Like most soft scales, magnolia scale females can produce large numbers of eggs. Numbers ranging from 1,500 to over 3,000 per female is common. This accounts for why populations can build rapidly.
The females are ovoviviparous meaning that eggs are held internally until they hatch creating the illusion that the females are giving birth to the first instar nymphs. Magnolia scale produces eggs over an unusually prolonged period of time meaning that eggs hatch from early August throughout September in Ohio.
The first instar crawlers are highly mobile but become immobile once they insert their piercing-sucking mouthparts into stems. This is the overwintering stage.
Management
Magnolia scale was once common in Ohio but became rare throughout much of the 2000s except for highly localized outbreaks. This has changed in recent years, with this native scale once again becoming common on magnolias throughout the state.
1. Cultural Management
As with most soft scales, magnolia scale is seldom a direct killer of established healthy trees. However, a substantial loss of sap from a heavy scale infestation represents a serious loss of energy resources to the trees. The accumulated stress, coupled with other stress-producing conditions, may cause leaf yellowing and loss, branch dieback and canopy thinning, and even the death of entire trees.
Thus, the best approach to reducing the impacts of this scale is to first focus on reducing tree stress. For example, maintaining adequate soil moisture by watering during droughts can reduce the impact of a scale infestation. Some stress-inducing issues are preordained, such as planting trees in highly compacted soils or in non-irrigated parking lot tree planters.
Although providing proper soil fertility is a vital component of tree health management, fertilizer applications should be used with caution, particularly high nitrogen applications. Numerous studies have shown that high nitrogen benefits phloem-sucking insects by increasing the amino acid concentration in the sap. High nitrogen applications are almost a sure-fire recipe for high scale populations.
Fertilizer applications should be guided by soil tests with nutrient deficiencies corrected by selecting products that only provide the specific element(s) found to be lacking. Using “general fertilizer” products with nitrogen benefits soft scales and other phloem-sucking tree pests more than trees.
Plant selection is also an effective cultural approach to pest management. As noted above, our native magnolia scale has a strong affinity for non-native magnolias and associated hybrids.
2. Mechanical Management
Soft scales are weakly attached to the bark surface. Thus, it’s easy to physically remove them using a dish scrubber or soft-bristle scrub brush.
A campus project titled, “Scrubbing Scales, Saving Trees, Engaging Students” was published in the American Entomologist in 2019 and describes how students were armed with toilet brushes and directed to scrub the soft scale, calico scale (Eulecanium cerasorum), from trees on the University of Kentucky campus. The approach was highly effective.
Here is a link to the paper: https://entomology.ca.uky.edu/files/rieske_et_al._2019_living_laboratory_scale_scrub_ms_am_ent_65_43-49.pdf
Although scrubbing away soft scales is best suited to small trees, it can be highly effective in reducing burgeoning scale populations. However, timing is important. Eggs should soon be hatching, and the small, flattened 1st instar nymphs may escape the scrubbing.
3. Biological
As with all native insects, magnolia scale population dynamics is heavily influenced by the 3-Ps: Predators, Parasitoids, and Pathogens. Indeed, in 2021, I observed Signate Lady Beetle (Hyperaspis signata) munch a heavy infestation down to zero in one season. I captured the decimation in a BYGL Alert titled, “Magnolia Massacre.”
Signate lady beetles have white wool-coated larvae that are wolves in sheep's clothing. The larvae look almost exactly like mealybugs. Of course, mealybugs spend most of their development stuck to their hosts, while the lady beetles are highly mobile. If you spot “mealybugs” crawling over a scale-infested magnolia, they are lady beetle larvae.
4. Insecticides
A cornerstone of Integrated Pest Management (IPM) is to avoid using one tactic at the expense of another. The graphic below illustrates that cultural and biological tactics should be used first, with chemical tactics held in reserve.
This approach to using IPM can limit possible negative environmental impacts as well as reduce the selective pressure that produces pesticide resistance. Of course, these two concerns played a significant role in the development of the IPM concept in the first place.
For example, while topical applications of pyrethroid insecticides (e.g., bifenthrin) targeting 1st instar magnolia scale crawlers can be effective, this chemical class of insecticides is non-selective meaning they can kill bio-allies. Multiple applications may also be required to cover an extended egg hatch which further reduces help from the “biological” corner of the IPM triangle.
Systemic neonicotinoids offer an effective option that minimizes impacts on beneficial insects. Products based on the active ingredients imidacloprid, dinotefuran, or thiamethoxam are effective against magnolia scale if used to target 1st instar crawlers.
The insect growth regulator (IGR) insecticides, pyriproxyfen (e.g., Distance IGR) and buprofezin (e.g., Talus), are also effective against 1st instar crawlers and will likewise have a limited impact on beneficials. The same is true of insecticidal products based on the active ingredient azadiractin, which behaves as an IGR. Keep in mind that although azadiractin is found in the neem tree (Azadirachta indica), it’s only found and extracted from neem seed kernels. It is not found in neem oil.
Of course, as with any pesticide, it’s critical to read and closely follow product label directions. The label is not only “the law,” it also provides information that maximizes efficacy while minimizing environmental impacts.