Magnolias are a common plant species in southern US landscapes, as they are evergreen and deciduous trees and shrubs. Native to Asia and the Americas, magnolia species are popular trees because of their attractive flowers, foliage, aesthetic value, requirements for low maintenance, and adaptability to the southern US climate and soil conditions. Magnolia scale (Neolecanium cornuparvum (Thro); Family: Coccidae; Fig. 1), native to the eastern US, is a specialist, serious pest of native and non-native magnolias. The magnolia scale is found in 29 US states. In the US, the magnolia scale is one of the largest scales, reaching the size of our thumb. It exclusively feeds on magnolias found in ornamental landscapes

Description and lifecycle
Magnolia scale completes one generation per year in the north (Fig. 2). Adult females have a diameter of ~12 mm (~1/2 inch) and are smooth, elliptical, and convex. The females give birth to young ones (referred to as crawlers) in the fall and overwinter as first instar nymphs. Crawlers (Fig. 3) often aggregate in masses on the underside of 1 or 2 year-old twigs. They develop through nymphal stages and molt into adult males and females (Fig. 2). In the summer of the following year, crawlers will emerge again. Crawlers are small (< 1/32 inch), mobile, 6-legged scales with no protective cover on their bodies. Once settled on the bark, they lose all their legs and become immobile. Gradually, they develop a white waxy covering over their bodies and increase in size. A magnifying glass is not needed when their size increases. As they develop, females change their color to dark brownish-purple and harden their exoskeleton (covering) in the summer. Older females are brown. Males are smaller than females, approximately 1/8 inch long, and appear as gnats. Once mated, males die. Although the adult female dies after giving birth to crawlers, the waxy covering will remain on the stem for many weeks, giving the impression that they are all alive.

Damage symptoms
Similar to other scales, magnolia scales possess piercing and sucking mouthparts. As a soft scale, they ingest photosynthates (sap) from the phloem vessels and weaken trees by depleting essential nutrients. This causes reduced growth, yellowing of leaves, premature leaf drop, and increased susceptibility to other pests and diseases. Infested trees may exhibit reduced growth and vigor, appearing generally unhealthy. They ingest more sugars than they need and excrete excess sugars as honeydew (Fig. 4). The honeydew excretion coats the leaves and stems, making the surface sticky where the black sooty mold fungus develops (Fig. 5). The sooty mold fungal covering reduces photosynthesis by physically screening sunlight. The honeydew also draws ants, wasps, and flies seeking sugars for nutrition (Fig. 6). Sometimes, removing infested trees is the best option to stop honeydew dripping from the tree to reduce the damage it causes to cars and buildings. Heavy infestations of magnolia scales can lead to branch dieback.




Host plants
Magnolia scale primarily targets magnolia species, such as southern magnolia (Magnolia grandiflora), star magnolia (M. stellata), saucer magnolia (Magnolia × soulangeana), cucumbertree magnolia (M. acuminata), lily magnolia, (M. liliiflora) and many magnolia hybrids.
Dispersal
Magnolia scale is primarily dispersed through plant trade between nurseries. Because females are immobile and crawlers do not typically move further away from females, they disperse locally. Crawlers can hop on the feet of birds and ants and are actively transported from plant to plant or canopies.
Management
Magnolia scales can be managed through integrated control tactics, such as cultural, biological, and chemical control. Regularly monitoring magnolia trees, especially during late summer and early fall, will help detect adults or early signs of infestation, such as honeydew or sooty mold fungus. Removing and destroying heavily infested branches to reduce the population size and prevent spread are advised. Adequate irrigation, mulching, and fertilization will help trees withstand and recover from infestations and maintain tree vigor and growth. Planting resistant magnolia varieties, such as M. grandiflora ‘Little Gem’ and M. virginiana, to reduce infestation is advised. Adults and larvae of lady beetles(Hyperaspis signata), syrphid larvae (especially Ocyptamus costatus), lacewings, and encyrtids and eulophid parasitic wasps help reduce magnolia scale infestation. Because broad-spectrum insecticides (such as neonicotinoids) can harm naturally occurring predators and parasitoids, it is advised to use them if all other alternative options are exhausted or provided limited control.
Horticultural oils applied during the winter as dormant sprays can reduce scales that overwinter. Systemic insecticides (such as neonicotinoids, dinotefuran, imidacloprid, etc.) applied as bark sprays or soil or stem injections can reduce magnolia scale problems. Because neonicotinoid insecticides are implicated in harming pollinators, such as bees, these insecticides must be used according to label instructions. Because of the waxy layer on their bodies, adult scales are often shielded from chemicals. Application of contact insecticides, such as pyrethroid insecticides (such as bifenthrin and permethrin) and insect growth regulators (such as pyriproxyfen), can be timed in the summer to target the crawler stage. Please thoroughly read the label instructions before using insecticide, as the label is the law!
References
Herms, D. A., & Nielsen, D. G. (2004). The magnolia scale: biology and management of a key pest of magnolia. https://kb.osu.edu/dspace/handle/1811/71940
Knox, G. W., Klingeman, W. E., Paret, M., & Fulcher, A. (n.d.). Management of Pests, Plant Diseases and Abiotic Disorders of Magnolia Species in the Southeastern United States: A Review. Retrieved July 18, 2024, from https://dx.doi.org/10.24266/0738-2898.30.4.223
Vanek, S.J. and D.A. Potter. (2009). Host plant resistance among Magnolia spp. and Quercus spp. to soft scale pests. UK Nursery and Landscape Program Overview – 2009. Accessed July 19, 2024. http://www2.ca.uky.edu/agcomm/pubs/pr/pr602/pr602.pdf
Whittaker, A. (2022). Neolecanium cornuparvum (magnolia scale). CABI Compendium. https://doi.org/10.1079/cabicompendium.119071