Magnolia Scale
Magnolia scale is common this year in northern Illinois. We have
received numerous requests for information, so this article is being provided
to help answer client questions even though it is still too early to achieve
effective control. Magnolia scale is common in northern Illinois south
through Kankakee County and occurs sporadically in the
rest of the state. It attacks star magnolia, Magnolia stellata;
cucumbertree magnolia, M. acuminate; saucer magnolia, M. soulangiana; and lily
magnolia, M. quinquepeta.
Magnolia scale females can be very large for scales, about
1/2 inch in diameter, but are usually smaller. They range from yellowish to brownish, from
oval to a roundish blob.Magnolia scale produces large amounts of honeydew, resulting
in shiny, sticky leaves,as well as sticky sidewalks and cars underneath infested
trees. Black sooty mold grows on the honeydew, resulting in black branches, foliage, and
sidewalks. Tree sap is very low in nitrogen, so soft scales consume great quantities of
it, separate out much of the water and nitrogen, and excrete most of the remainder as the
concentrated sap, or light syrup, called honeydew.
Mature females produce living young in late September to
early October. These first-stage nymphs, or crawlers, are oval and gray, with a
reddish brown ridge running down the back. Each crawler has two white, waxy
spots, one on each side. Crawlers mass on the undersides of 1- and 2-year-old
twigs for the winter. From the time that they emerge from the female until they
molt to the second nymphal instar in late April or early May, they are
vulnerable to insecticide sprays. In early June, they molt again to the
third-instar nymphal stage and are deep purple.
Heavily infested twigs and branches appear purple and rough
from the high scale numbers. The nymphs then produce white, powdery wax that
covers their bodies, causing twigs to appear whitish in high infestations. As
they mature to adults, the white wax wears away, being heaviest on the edges of
the scale. There is one generation per year.
An insecticidal spray of acephate (Orthene), insecticidal
soap, or summer spray oil in late September into October controls the crawlers. Injection
of acephate (Lepitect) should also control them at that time. The same treatments
at bud break in the spring are also effective. With the insecticidal soap and summer
spray oil, be sure to get good coverage, particularly on the twig undersides, where the
crawlers will be most numerous. As these are contact insecticides, insects not hit directly
with the soap or oil spray will probably survive; so thorough coverage is
essential.
Author:
Phil Nixon