Insect
and Disease Fact Sheet Compliments of New Century
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Magnolia Scale and Its Control
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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 |
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As
the name implies, this insect is primarily a pest of various species of
magnolia. Saucer, star, lily and cucumber tree magnolias are the most common
trees attacked. It has also been reported to feed on Daphne and Virginia
creeper.
Damage
Magnolia
scales have sucking mouth parts 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
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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 nave: 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 -
Dormant oils can be applied in October to November and again in March to kill
the over wintering 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 over wintering stage will have little effect.
Information obtained through the
Ohio State University Extension Factsheet HYG-2003-94
Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES