Magnolia and tuliptree scale
Click for larger image Mature magnolia scale (Hemiptera) in mid-September on magnolia twigs with sooty mold growing on the honeydew excreted by the scale insects

Magnolia scale (Neolecanium cornuparum) is one of the largest soft scale insects in North America, the female magnolia scale can reach up to ½ inch in diameter.  This scale is shiny tan-brown and smooth.  As the scales grow they are often covered with a white mealy wax.  They lose the wax at the time that the crawlers emerge. Tuliptree scale (Toumeyella liriodendri) is a similar appearing scale. Both are native to eastern United States. Their ocurance in the St. Louis area has increased in recent years. Heavy infestations can cause twig and limb dieback. Repeated heavy infestations can weaken or kill small trees.

Symptoms and Diagnosis

Magnolia scale attacks primarily magnolia plants but will also infest daphne and Virginia creeper. Tuliptree scale infests tuliptrees (Liriodendron sp.) as well as magnolias, basswood, and redbud. Scales have “syringe-like” mouthparts and suck tree sap.  Excess sap is excreted by the scale and is called honeydew.  Honeydew is then a growth medium for black sooty mold.  The mold reduces sunlight reaching the plant and reduces the vigor of the plant.  Also, the honeydew is a food source for ants, flies, wasps and bees, which then become pests.

Scale are identified by their body covering, which normally appears as a colored raised area on the leaf or stem of the plant that can be flicked off with the point of a knife or a fingernail.

Life Cycle

Soft scales have a single generation.  The adult scale gives birth during late August and may continue to produce young during September.  The young larvae are called “crawlers”, and they spend the winter on one- and two- year old twigs.  When the weather warms, the scale starts to eat sap —eventually, it settles in permanently.  The best time to kill scale is when it is in the crawler stage. After they produce their hard covering they are much more difficult to kill without the use of systemic insecticides.

Integrated Pest Management Strategies

1. Obtain pest-free plants  Most magnolia scale comes with the new plant.  Inspect the branches when you buy them.

2. Natural controls. Lady beetles and squirrels may eat some scale, but do not count on them.  You can, also, scrape the scale off.  The mouthparts break off and the scale is no longer a threat.

3. Maintain plant vigor.  A healthy plant will try to resist insects.  Water when needed (1” a week), fertilize, give it well draining soil, supply enough sunlight and air movement.

4. Use summer and dormant season horticultural oils.  These oils smother the crawlers and the adults.  Summer weight oil can be applied in the warm summer months.  Wet down the stems and leaves.  Dormant oil can be applied in October and November and again in March to kill the crawlers--do this before the buds have started to swell in the spring.

5. Use insecticidal soap. These soaps can also be effective against crawlers. They have no effect on mature adults. You can monitor crawler emergence by applying double sided sticky tape around the branches- for magnolia scale look for tiny, yellow specks (fried eggs), for tuliptree scale look for dark red crawlers. Apply as directed and be sure to thoroughly soak the stems and leaves to cover all the crawlers.

6. Other chemical insecticides. Malathionbifenthrin and pyrethrins can be used according to label directions. Malathion is very toxic to bees. Do not apply when plants are in flower or bees are present.  Imidacloprid is a systemic insecticide that can be used as a soil drench. It is taken up by the tree’s roots and kills insects feeding on the sap.  Imidacloprid is also highly toxic to bees but using a soil drench greatly reduces the chance that bees will come in contact with the insecticide. Read and follow label instructions on all pesticides.

Organic Strategies

Strategies 1, 2, and 3 are strictly organic approaches. For an organic approach to Strategies 5 and 6, consult the Organic Materials Review Institute (OMRI™) for appropriate insecticidal soap and pyrethrin products.

More images:

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Magnolia scale (Hemiptera) on magnolia (Magnolia)
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Magnolia scale (Hemiptera) on magnolia (Magnolia)
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Magnolia scale (Hemiptera) on magnolia (Magnolia)
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Magnolia scale (Hemiptera) and sooty mold on magnolia
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Sooty mold growing on the honeydew excreted by magnolia scale (Hemiptera) wrapped around a magnolila twig
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Large mature magnolia scale (Hemiptera) on magnolia twigs
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Immature tuliptree scale (Hemiptera) possibly overwintering 2nd instar on tulip tree (Liriodendron)
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Immature tuliptree scale (Hemiptera) on tulip tree (Liriodendron)
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Magnolia scale (Hemiptera) dropped honeydew onto the concrete beneath the tree. Sooty mold then grew on the honeydew, turning the sidewalk black.
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This European paper wasp (Hymenoptera) was attracted to the honeydew exuded by magnolia scale
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Magnolia scale (Hemiptera) on magnolia (Magnolia) with sooty mold growing on the honeydew that has dropped on the leaves