The magnolia scale, Neolecanium cornuparvum (Thro), is one of the
largest and most conspicuous scale insects known to occur in Ohio.
Adult females may reach nearly 1/2-inch in diameter when fully grown.
The scale is shiny tan-brown and smooth. As the scales grow, they are
often covered with a white mealy wax. This wax is lost at the time
that the crawlers emerge.
Plants Attacked
As the name implies, this insect is primarily a pest of various
species of magnolia. Saucer, star, lily and cucumbertree magnolias are
the most common trees attacked. It has also been reported to feed on
Daphne and Virginia creeper.
Damage
Magnolia scales have sucking mouthparts and when heavy infestations
completely encrust branches, the branches often die. Badly infested
branches and twigs are weakened and growth is retarded. Leaves may
also be under-developed. Under a continuous and heavy attack trees may
be killed. Like most soft scales, the excess plant sap is excreted as
a sweet, sticky material called honeydew. The honeydew drips onto the
foliage and branches. A dark fungus, called black sooty mold grows on
the honeydew which results in the leaves becoming blackened. This
greatly detracts from the plant's normal ornamental value. The
honeydew also attracts a ants, bees, wasps and flies which feed on it.
Description and Life Cycle
The magnolia scale spends the winter on one to two year old twigs as
tiny, dark-colored nymphs. As temperatures warm in the spring, the
scales begin to suck sap and have molted once by early May. At this
time two distinct forms can be found, males and females. The males
remain small, about 1/8-inch, and soon turn a translucent white. Soon
after the males turn white, they emerge as tiny, pink to yellow gnat-
like insects with two long waxy threads extending from the tip of the
abdomen. The females continue to expand and by early June, they have
turned a brownish-purple color. This is also the time that they
produce excessive amounts of honeydew. By July the females are covered
with a powdery, white waxy coating and are turning more of a yellow-
tan color. By late July and August the adult females begin to give
birth to their young known as crawlers. The tiny, mobile crawlers move
around until they find a suitable feeding site on which they settle
down, feed, and remain through the winter.
Control Hints
Though there are several predators and parasites known that attack
this scale, they rarely do an effective job of control, especially on
smaller magnolias.
Strategy 1: Obtain Pest Free Plants - Most of the magnolia scale
infestations come with the plants, so carefully inspect the branches
of plants being considered for purchase. The large scale exoskeletons
often remain from the previous season. Any plants with these remains
should be avoided.
Strategy 2: Summer and Dormant Oils - Horticultural oils (often called
summer oils) at 1.5-2.0% applied after the crawlers have settled in
late August can be very effective in reducing the scale population. Be
sure to thoroughly wet down the stems and leaves. Dormant oils can be
applied in October to November and again in March to kill the
overwintering nymphs located on the stems. Be sure to check the spring
buds as some damage may be caused on the flower buds if they have
begun to swell.
Strategy 3: Standard Chemical Control - Magnolia scale can be
satisfactorily controlled with a variety of insecticides if applied
when the insects are in the freshly settled crawler stage. This is
usually in late August to early September. Sprays applied before the
crawlers are present, or after they have become dormant in the
overwintering stage will have little effect. See Bulletin 504 for
currently registered insecticides.
NOTE: Disclaimer - This publication may contain pesticide
recommendations that are subject to change at any time. These
recommendations are provided only as a guide. It is always the
pesticide applicator's responsibility, by law, to read and follow all
current label directions for the specific pesticide being used. Due to
constantly changing labels and product registrations, some of the
recommendations given in this writing may no longer be legal by the
time you read them. If any information in these recommendations
disagrees with the label, the recommendation must be disregarded. No
endorsement is intended for products mentioned, nor is criticism meant
for products not mentioned. The author and Ohio State University
Extension assume no liability resulting from the use of these
recommendations.
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All educational programs conducted by Ohio State University Extension
are available to clientele on a nondiscriminatory basis without regard
to race, color, creed, religion, sexual orientation, national origin,
gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and
Director, OSU Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-1868
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