Midlands Magnolia Owners – Be on the Lookout for Magnolia Scale!
Prized for their beautiful, fragrant flowers, and large waxy leaves, magnolias add dramatic presence to any lawn or garden. Generally, these are fairly robust plants that do not suffer from major infestations – however magnolia scale (Neolecanium cornuparvum) has increasingly become a problem in the Midlands.
Left unchecked, magnolia scale can cause a general decline in your tree’s health, compromising its beauty and longevity. In this article, we’ll be learning how to recognize magnolia scale, learn what causes it, and some common treatment methods.
For minor infestations and small trees, this may be a DIY project, but we recommend working with an ISA-certified arborist for more severe infestations and infestations of large trees.
Which trees are affected by magnolia scale?
The name is a bit of a giveaway – magnolia scale is an insect infestation of magnolia trees! However, not all magnolias are equally susceptible to infestation. Severe cases of scale are most common in small species like star magnolias, saucer magnolias, and magnolia hybrids.
How to Identify Magnolia Trees
Magnolia trees are easily identifiable – particularly the large evergreen examples – which stand out for their showy flowers and large waxy leaves that persist throughout the winter.
However, the species of magnolia which are most susceptible to scale are actually deciduous varieties – meaning that they lose their leaves in the fall.
Identifying Star Magnolias (Magnolia stellata)
Flowers:
- Star magnolias produce many-petaled, star-shaped flowers that are usually white but can also be pale pink.
- The flowers bloom early in the spring, often before the leaves appear.
Leaves:
- Star magnolia leaves are smaller than those of other magnolias, typically 2–4 inches long.
- They are oblong, smooth-edged, and turn yellowish-brown in the fall.
Growth Habit:
- Star magnolias are typically small trees or large shrubs, typically less than 15–20 feet tall and similarly wide.
Identifying Saucer Magnolias (Magnolia × soulangeana)
Sometimes called the tulip tree, saucer magnolias produce large pink, white, or even purple flowers that emerge before their leaves. The result is visually striking and quite recognizable.
Flowers:
- Saucer magnolias are known for their large, tulip-shaped flowers, which can be
pink, purple, or white. - Flowers often appear in mid to late spring and are quite large, reaching 5–10+
inches across.
Leaves:
- The leaves are broad and oval-shaped, growing up to 8 inches long.
- They are dark green during the growing season and may turn a yellow-brown in autumn.
Growth Habit:
- Saucer magnolias grow up to 25 feet tall with a similar spread.
Identifying magnolia scale
When magnolia scale shows up, it is easy to tell that something is wrong… although many people aren’t sure what. Scale can appear as fluffy white patches, causing it to be frequently misidentified as mold. In fact, these patches are insects which are covered by a waxy protective coating.
Other noticeable symptoms include sticky honeydew secretions covering the tree and surrounding surfaces. Honeydew attracts insects like ants, wasps, and hornets, and can encourage sooty black mold to grow.
The life cycle of magnolia scale
Neolecanium cornuparvum, or magnolia scale as it is commonly known, is a species of scale insect. There are thousands of species of scale insects, but N. cornuparvum is one of the most destructive for magnolias and these insects use their piercing mouthpieces to feed on plant fluids. Scale infestations cause yellowing leaves, twig dieback, and in severe cases death.
Magnolia scale have several distinct life stages. The adults are easiest to see – although are not immediately recognizable for the insects that they are as they are stationary. These creatures resemble waxy, brownish purple lumps, up to ½ inch in length, which develop a fuzzy white coating in August or September.
The females lay their eggs beneath them, making it appear that scale babies are ‘born’ instead of ‘hatched’ as the live young emerge from beneath their mothers in the fall.
Image Credit: https://mortonarb.org/
After hatching, N. cornuparvum are in their mobile form called crawlers. Crawlers spend the winter on new growth, and become active again in the spring. Male magnolia scale insects mature into gnat-like creatures which mate with the females in late spring and then die. The females will themselves transform again into their sedentary scale form and the process begins anew.
How to treat magnolia scale
There are several methods for treating magnolia scale, and the correct one to use will depend on the severity of your infestation as well as the time of year that you are beginning your treatment.
The simplest method, which is best for young, small magnolias, is to simply brush or pick off the scale insects.
There are a variety of chemical control methods available, although we recommend working with an ISA-certified arborist for any spray pesticide applications. These pesticides can be dangerous if misused. Adult scale insects are resistant to spray applications – and so the optimal time for spraying is August and September when the crawlers are active.
Horticultural oils are another good option for treating scale insects and are generally slightly safer to use. These oils should be applied starting in late summer, and will need reapplication in the fall before the first
Image Credit: https://mortonarb.org/
frost, and again in the spring before the flower buds have begun to swell.
Finally, a very effective treatment method is the application of a systemic insecticide. These treatments are applied by arborists directly to the tree’s roots and then are absorbed into the tree sap. When the scale insects feed on the tree they ingest the insecticide, killing them. This type of treatment is best performed in the spring, a couple weeks before the crawlers have had time to become active.
Preventing magnolia scale
While magnolia scale is not entirely preventable, healthy, happy trees are less likely to get infested and more likely to survive an infestation. It is important to have an arborist regularly check your trees’ health to keep avoidable illnesses at bay.
Magnolia scale is more common in under-watered or over-fertilized trees. It is important to strike the right balance to prevent your trees from becoming stressed and susceptible to disease.
Don’t Let Scale Harm Your Magnolias
In general, magnolias are low maintenance plants but from time to time they need our help. If you spot signs of magnolia scale, such as purple, brown, or fuzzy lumps, or sticky black soot, then you need to take action.
If caught early, scale insects can simply be removed from the plant, ending the infestation. However, in many cases the infestation is too advanced for this low-tech solution and your best bet is to contact an ISA-certified arborist. They have the training necessary to pick the best treatment method to eliminate the scale before it causes more harm to your tree.
