Magnolia scale (Neolecanium cornuparvum) is the largest soft scale insect found in North America. This pest weakens its host by feeding on the tree’s internal fluids, causing noticeable symptoms and substantial damage to ornamental trees. However, the insect poses no physical danger to people or common household pets.
Is Magnolia Scale Toxic to Humans or Pets
Magnolia scale is purely a plant pest and does not bite or sting mammals. Its feeding habits focus exclusively on the host tree’s sap. The insect does not carry or transmit any diseases pathogenic to people or pets, nor does it contain toxic compounds.
Pets may brush against an infested tree without risk of illness or injury. The primary concern is the insect’s impact on the tree’s health and the mess it leaves behind.
Damage to Magnolia Trees
The harm caused by this pest is directed entirely toward the host tree. The scale feeds by inserting needle-like mouthparts into the phloem tissue, siphoning large quantities of sugary sap. This constant draining of the tree’s primary energy source reduces its overall vigor and causes stress.
Symptoms of a heavy infestation include yellowing leaves and premature leaf drop (defoliation). Sustained sap loss leads to branch dieback, and if left untreated, a severe infestation can result in canopy thinning, stunted growth, or the death of smaller trees.
Sooty Mold and Honeydew Nuisance
A secondary problem associated with infestation is the excretion of honeydew, a sticky, sugary liquid. Honeydew is the excess sap the scale insects process and discharge as a waste product. This clear, viscous substance coats the leaves and branches, often dripping onto surfaces beneath the canopy, such as patios or parked vehicles.
The sweet residue serves as a substrate for the growth of sooty mold, a harmless black fungus. Sooty mold colonizes the honeydew, turning affected surfaces an unsightly black color. While the mold does not infect tree tissue, a heavy coating blocks sunlight and interferes with photosynthesis, further stressing the plant. Honeydew also attracts other insects, including ants, wasps, and flies.
Safe Control Methods
Management should focus on methods effective against the pest while minimizing risk to the environment, people, and pets.
Mechanical Removal
For small, localized infestations, mechanical removal is a safe option. This involves gently scrubbing adult scale insects off the branches or pruning out small, heavily infested twigs.
Horticultural Oils and Soaps
Horticultural oils and insecticidal soaps are low-toxicity options that kill the scale through contact by smothering them. These treatments are most effective when timed to target the vulnerable “crawler” stage, generally occurring from late summer through early fall. Dormant oil can be applied in late winter or early spring before the tree breaks dormancy to smother overwintering nymphs.
Systemic Treatments
Systemic insecticides are an alternative for severe infestations, but they are often best applied by a professional arborist to ensure proper timing and placement. Regardless of the product chosen, careful adherence to label directions is necessary. Healthy tree maintenance, including proper watering and mulching, also helps the tree naturally withstand and recover from pest stress.