Oak kermes scale

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

Similar insects

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.
www.entomology.umn.edu/cues/Web/191PubescentLeafKermes.pdf‎ (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.