Pardon our dust; we're 90% done here but will still be compiling
our notes, formatting and posting our images of oak kermes scale
damage and control. 'Tis what winter is for, to learn and be ready
to short circuit the pest before budbreak!
How to identify this scale
Kermes scale crawlers (immature scales) emerge from under adult
scale covers and bark crevices beginning at oak budbreak and
continuing for eight weeks. Adults are small gall-like bumps on
twigs. They lay eggs at the end of summer, up to 3,000 per female.
Eggs hatch by December and the (tiny salmon colored) young
overwinter on the tree (under the adult scale body, near leaf buds,
in bark crevices). (Steven can we possibly get photos of what we
saw in 30x magnifier?)
Damage they can do
These scales feed on sap causing a loss of plant vigor and
growth, as well as twig dieback, reduced tree growth rate, and the
production of sooty mold which grows on the honeydew secreted by
the scales. Tree mortality may occur during heavy infestations,
especially in an oak that's used up its resources battling other
stresses such as severe drought and repeated defoliation. More
often, natural enemies (including a parasitic wasp, scale-eating
caterpillar, and twice-stabbed lady beetle) are usually plentiful
and control is not necessary.
Control of Kermes scale, if needed, is dormant oil treatment in
spring as leaves begin to grow. Avoid using insecticides with
residual activity since parasites normally control this pest and
will be killed as collateral damage. In fact, in tests of that
strategy, multiple insecticide applications resulted in an
increase in scale population.
Best photos we can find of these scales: In Biology and
Management of Allokermes kingii on Oak by Eileen Buss
Related pubescent kermes scale and pin oak kermes scale with
similar life cycle. Pubescent adults coat themselves with white
fuzz, may adhere along leaf midrib.
(We see this link to download pdf won't work as link. If you copy
and paste the URL to your browser it will then download the pdf
bulletin but we can't yet figure why we can't make that happen with
one click here.)
Below: That's not natural hairiness where the veins join the
midrib. It is one sign of a different scale insect and may mean we
have not oak Kermes scale on this tree but pubescent Kermes scale,
or both. Control will likely be the same or similar but
consequences to and involvement of nearby plants may be different
as that scale has a different host range.