Does a magnolia tree produce sap my car is parked under it and it has splashes all over it every morning?

Answer 1

The tree is not dripping sap, but the sticky substance you took for sap is known as honeydew, a polite term for the excrement produced by the insects feeding on your tree. The bees (and probably flies and ants) are there to consume this sugary substance.

The tree is infested with magnolia scale. It is a common pest of saucer magnolia (Magnolia soulangiana), star magnolia (M. stellata) and cucumbertree magnolia (M. acuminata). You may not have noticed the insects on the smaller twigs -- they look like little white bumps. It is understandable that gardeners have a hard time believing these "bumps" are living insects because they do not move. Once the maturing scale insect inserts its mouthparts into a twig or small branch, it spends its entire life in the same place. Magnolia scale (Neolecanium cornuparvum) is the largest scale insect in the United States.

Magnolia scale resides on trees year-round, but goes unnoticed until it starts producing large amounts of honeydew. Soft scale insects insert piercing-sucking mouthparts into the portion of a plant's vascular system responsible for transporting the carbohydrates and sugars produced by photosynthesis. Honeydew can be a real annoyance when it drips on the lower leaves and anything unfortunate enough to be under the magnolia. It also attracts nuisance insects such as yellow jackets, ants and flies. To make matters worse, a black sooty mold fungus often grows on the honeydew. Although it is unattractive, sooty mold does no real damage to the tree. It is simply growing on the carbohydrate-rich honeydew.

It is helpful to understand this pest's life cycle to control it effectively. Magnolia scale warrants control, not only because of the mess it creates, but also because it can cause severely infested branches to die. It does not take long for a sizable population to build up. Adults are covered with a waxy covering that makes them quite impervious to insecticide applications, so you have a narrow window of time when the young nymphs (immature insects) are susceptible. Newly hatched nymphs are also known as crawlers because it is the only point in their life cycle when they are mobile. There is one generation of magnolia scale a year in our climate.

Control is a two-step process. First, apply a horticultural oil spray just before the tree leafs out in spring to kill the overwintering nymphs. They are quite small and difficult to see as small, gray dots on smaller twigs. They are visible to the naked eye when you know what you are looking for, and you may find it helpful to look with a magnifying glass. Horticultural oil suffocates the pests rather than poisoning them, and it will greatly reduce the number of young produced in late summer. Horticultural oil is more refined and lighter than dormant oil (Volck oil), and there is less chance of burning tender new foliage if you mistakenly spray as the tree begins leafing out in the spring.

The timing for the second step is critical because the newly hatched crawlers are very susceptible to insecticide applications, including environmentally friendly products such as insecticidal soap. Magnolia scale is in its crawler stage in late August and early September in our area. Of course, insects do not live by the calendars that govern our lives; their development is based on temperature and moisture.

It is always best to check to make sure you see active crawlers before applying insecticide sprays to control them. The crawlers are quite small but can be seen upon careful inspection with a hand lens or magnifying glass. They will appear as small, moving, reddish specks. Begin checking your magnolia in late July. Make your first insecticide application when you first see the crawlers moving around.

Sevin (carbaryl), Bayer Advanced Power Force Multi-Insect Killer (cyfluthrin), horticultural oil, Bayer Advanced Garden Tree & Shrub Insect Control (imidacloprid), insecticidal soap, BioNeem (neem), and malathion are all registered for control of magnolia scale crawlers. Depending on the insecticide, you may need to make repeat applications at the intervals recommended on the product label.