Cottony Maple Scale
Cliff Sadof, Extension Ornamental Entomology Specialist,
The maples in the photos beloware
infested with cottony maple scale. The sap is the excrement of
these sucking insects. The white cotton tufts on the twigs are
egg masses. There has been an increase in these this year. My
guess, based on some recent research papers, is it has something
to do with increased applications of mosquito adulticides killing
the natural enemies of scales.
Right now the scales should be
in the nymphal stage feeding on the undersides of leaves. You
should find them (without cotton) attached to leaf veins. I
suggest you do the following:
Assess the natural enemy population. Inspect the trees for
twice stabbed lady beetles. These black beetles with orange
(red) spots feed on scales. The larvae may also be found in
the egg masses themselves. The larvae resemble mealybugs, as
a way to hide from the ants feeding on the honeydew. Also check
the scale nymphs on leaf undersides. Some may be parasitized
and appear black.
If you can find many natural enemies, then just leave the
problem alone. It should lessen over the next 1-2 years and
be gone by yr 3.
If you find few or no natural enemies, then apply imidacloprid
to the soil in early spring. This will kill the scales next
year. Applications at this time of year may be marginally effective
due to poor uptake by scales who really do not feed much in
the summer. The soil applications should stop the honeydew
dropping at this time.
Please see E-29 for