Magnolia scale

What is magnolia scale?

Magnolia scale is a native soft scale. UW-Madison calls it the commonest insect problem on magnolias in Wisconsin. The adult females look like oval bumps on the twigs. They have no visible legs and can be mistaken for buds or a fungus.

The scales suck sap from twigs. Feeding cuts down on leaves and flowers and can cause twig and branch dieback; Penn State says heavy infestations can seriously injure or kill trees. They also give off large amounts of honeydew, which grows black sooty mold and draws ants, bees, wasps and yellowjackets.

There is one generation a year. The best times to act are the dormant season, with oil on the twigs, and late summer, when the newborn crawlers are out.

People and pets: Honeydew attracts stinging insects such as wasps, bees and yellowjackets (UMass, Penn State).

Signs and damage

• Large, oval, white-coated bumps up to 1/2 inch on young twigs in summer
• Sticky honeydew on leaves, cars, patios and furniture under the tree
• Black sooty mold on leaves and branches
• Ants, bees, wasps and yellowjackets visiting the tree
• Fewer leaves and flowers, twig and branch dieback

Magnolia scale identification: what to look for

• Adult: Female: smooth, oval, convex, up to about 1/2 inch, pinkish-orange to brown under a white waxy coating. Males are small fly-like winged insects.
• Larva: Crawlers are flat, oblong, yellow to reddish-brown. Overwintering nymphs are dark slate-gray with a red-brown ridge down the middle.
• Damage: Honeydew, sooty mold, fewer leaves and flowers, twig dieback. UMass says the scales turn a deep purple by June, before the white wax covers them.
• Timing: In PA, adults mature late July to early August and crawlers appear in August and September.

Life cycle

One generation a year. Young nymphs spend the winter on one- and two-year-old twigs. They start growing in spring and mature by late July to early August, when the small winged males mate with the females. The females give birth to live crawlers in late August and September. Crawlers settle on new twigs, where they spend the winter.

When to look: Dormant oil: early spring before buds open. Honeydew and sooty mold show by July. Crawlers: late August into September.

Magnolia scale look-alikes

A few things get mixed up with it:

• Tuliptree scale (Toumeyella liriodendri): Also attacks magnolia, but it is usually under 3/8 inch and its waxy cover has a crimped, flanged edge (UMass).

How to control magnolia scale

Cultural control

• On light infestations, brush or scrape scales into soapy water in July, before crawlers come out, using light pressure so the bark isn't hurt.
• Prune out heavily infested branches if it won't ruin the tree's shape.
• Keep the tree well cared for; UW-Madison notes infestations often decline over a few years as natural enemies catch up.
• Watch crawler timing with tape wrapped sticky side out around a branch; crawlers show up as small dark spots (UW-Madison).

Biological control

• Lady beetles, including multicolored Asian lady beetle adults and signate lady beetle larvae, feed on the scale and give some late-summer control.
• Parasitic wasps also attack it. These enemies usually can't stop a major outbreak alone, and sprays can kill them.

Chemical control

Dormant season: horticultural oil on 1- and 2-year-old twigs in early spring, after freezing nights end but before buds open (Penn State, UMass). Crawlers: Penn State says to apply a registered insecticide in late August through September; UW-Madison suggests a repeat 10 to 14 days later. UW-Madison names insecticidal soap, horticultural oil and pyrethrins as lower-risk contact options with short residual activity (pyrethrins can also harm beneficial insects), and malathion and pyrethroids as conventional options that typically last one to two weeks. UW-Madison names imidacloprid as a spring root-zone drench after bloom; UMass also lists dinotefuran and other systemics. Use only products labeled for this use; the label is the law. Have an ISA Certified Arborist or licensed applicator treat large trees. Muthler Landscaping does not treat trees or apply pesticides; see our pesticide applicator license guide.

Use only products labeled for this pest and this site; the label is the law. For trees, work with an ISA Certified Arborist. If you hire someone to apply pesticides, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Prevention

• Inspect magnolias each summer for white, waxy bumps on young twigs.
• Expect honeydew and sooty mold to soil cars, patios and furniture under infested trees (UMass).

When to call a pro

Call an ISA Certified Arborist if a magnolia has heavy scale year after year, branch dieback, or is too big to treat from the ground.

Related guides: Tree database: mature size and planting distance · Pennsylvania tree identification · Firewood rules by state · All pests and diseases

Questions about magnolia scale

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