My goodness! Magnolia Scale!

Magnolia scale feeds on magnolia trees. Star magnolia, saucer magnolia, and many magnolia hybrids are most commonly and severely affected. The Magnolia Scale refers to a soft scale (family Coccidae) that can affect magnolia trees, particularly the Magnolia grandiflora. Coccids are small soft scale, sap-sucking insects that can impact the health of the tree. The females are hidden beneath a helmet-like, soft, leathery covering that provides some protection. Here are some key points regarding Magnolia Scale:

Magnolia scale is the largest soft scale insect found in Ohio, with adult females reaching up to 1/2" in diameter. This is the time of year when the females mature and become most noticeable.

On small trees, magnolia scale can infest all stems. On larger trees, they usually remain on the branches but can also be found on woundwood on the main trunk.

All scale insects possess sucking mouthparts and feed on tree sap. Soft scales, such as Magnolia scale, specifically consume sap from the phloem tissues. They can extract substantial amounts of sap, which stresses the host tree. Typically, trees can handle small scale populations. However, extensive feeding by a larger population often results in leaf yellowing and twig dieback. Over time, an untreated magnolia scale infestation may cause the tree to decline.

Soft scales release their waste as honeydew, which is sticky and can coat plant parts, often dripping onto surfaces beneath the tree. A black fungus known as sooty mold can grow on the honeydew, though it causes minimal harm to the plant. The sticky honeydew and black sooty mold are usually noticed before the insects themselves. Honeydew may also attract other insects, such as ants and wasps, to the tree.

Types of Magnolia Scale

• Soft Scale: This scale is well-known for generating large amounts of sticky, dripping honeydew. This sugary substance can lead to heavily infested trees buzzing with insect activity, as flies, bees, and wasps are attracted to the sweet treat. A significant proportion of these flies often belong to the blow fly family, Calliphoridae. While their maggots may be drawn to decaying flesh, the adults prefer sweets.

• Armored Scale: smaller and has a harder outer shell and may be more difficult to control but can cause similar damage.

Symptoms of Infestation

• Yellowing leaves

• Stunted growth

• Honeydew accumulation on leaves and surrounding surfaces

• Sooty mold on leaves

Black Sooty Mold grows on the Honeydew

Life Cycle

• Overwintering: Scales spend the winter as small, dark nymphs on twigs. 

• Spring Activity: Nymphs resume feeding and begin to grow in the early spring. 

• Summer Maturation: By mid-summer, females swell and develop their characteristic white, waxy coating. 

• Crawler Stage: In late summer and early fall, the females give birth to live young called crawlers. These mobile young then settle on twigs to overwinter, starting the cycle again. 

Management and Control

• Stressed trees are more susceptible to scale infestations. To keep trees healthy, ensure proper watering, mulching, and pruning of dead or infested branches. Small magnolia scale populations might be managed manually. If the insects are confined to a few branches, pruning those branches may suffice. Additionally, small populations can be carefully removed from branches by hand.

• Scale insects are particularly vulnerable during the crawler stage when the young are seeking feeding sites. Adult scales are typically shielded from chemicals due to their waxy covering. Application timing is crucial. Chemical sprays should be applied when crawlers emerge. Insecticidal soaps and horticultural oils can effectively target the crawler stage when sprayed on the tree, but they generally do not affect adult scales. These products require thorough coverage and must directly contact the crawlers to be effective. Multiple applications may be necessary since they do not have residual activity. Dormant oil applied to overwintering nymphs in early spring can also be effective. This treatment should be done before the buds open in spring. Insecticidal soaps and horticultural oils are preferable as they have minimal impact on beneficial insects, such as ladybugs, that may prey on magnolia scale. Systemic insecticides can be injected into the tree by our certified arborists.

• Regular Monitoring: Keep an eye on magnolia trees for early signs of scale to manage infestations promptly.

• As a Side note: Be careful when parking your vehicle next to a magnolia tree, the sticky, disgusting honeydew can easily come into contact with your car and be difficult to get off.

Prevention Tips

• Regular pruning is recommended for airflow and improved water/nutrient allocation. 

• Maintain tree health through proper watering and fertilization.

• Avoid overcrowding of plants to improve air circulation.

• Regularly inspect plants for early detection of pests.

  
  

• By understanding and managing Magnolia Scale, you can help ensure the health and longevity of your magnolia trees.