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Problem: Kermes Oak Scale - Kermes spp.
Hosts: Primarily pin and bur oaks but other oaks may be affected.
Description: There are two different oak kermes species that are common in Kansas.
Bur Oak Kermes: This one has been commonly seen on bur oak. Overwintering nymphs attack newly expanding leaves in April and cause the mature leaves to be distorted. New crawlers appear in June.
Pin Oak Kermes: The oak kermes scale commonly found on pin oak has a bit different life cycle. Eggs hatch in September rather than June. This kermes scale appears to cause much more damage than the one on bur oak. Terminal growth can be killed outright or the union between terminal growth and last year’s growth may be weakened so that July winds can cause terminal growth to break off.
Recommendations: Recommendations differ depending on the oak kermes species present. Insecticidal sprays should target the crawlers before the form their protective "shell."
Bur Oak Kermes: Insecticides may be sprayed in April as overwintering nymphs become active and/or in June when crawlers are active.
Pin Oak Kermes: Insecticidal sprays should be applied in September when the crawlers are active.
Biorational sprays such as an ultra fine oil or an insecticidal soap can also be used when the crawlers are active. These sprays have a low to moderate impact on natural enemies of scales such as parasitic wasps. You can also use malathion or acephate (Hi-Yield Acephate Systemic Turf, Tree and Ornamental Spray or Ortho Systemic Insect Killer).
References:
1. Insects and Mites Associated With Shade Trees and Woody Ornamentals, K-State Research and Extension Pub S-85, pg 35
2. Life Histories of Common Insects, Mites and Nematodes Infesting Ornamental Plants in Missouri, Missouri Department of Agriculture, pg D-9
3. Scale Insects on Shade Trees and Shrubs, Purdue University Cooperative Extension Service, Publication E-29
4. Horticulture 2004 Newsletter, No. 33, K-State Research & Extension, http://www.oznet.ksu.edu/hfrr/hnewslet/ksht0433.htm
5. Garden Insects of North America, Princeton University Press, pg 342
Last Update: 08/23/2004
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