A northern red oak showing symptoms of drippy blight disease.
Figure 2. Bacterial exudates covering second instar kermes scales feeding at the junction of new and one-year-old growth.
This research describes the emergent disease complex, known as drippy blight, which affects red oak species in Colorado. To determine the causal agent of drippy blight, studies were conducted on red oak saplings including pin, northern red, and Shumard oaks to determine if the bacterium isolated from cankers and exudates was causing the disease. Furthermore, tree surveys were performed in order to determine the extent of damage throughout the community, document the identifying characteristics of the disease, and note interactions with plant feeding insects.
Drippy blight disease is caused by a plant pathogenic bacterium in the family Enterobacteriaceae, Lonsdalea quercina subsp. quercina, in association with the kermes scale insect, Allokermes galliformis.
We confirmed the bacterium as the causal agent, because the red oak species inoculated with the bacterium all showed symptoms of drippy blight, and the bacterium was recovered from these inoculated oaks.
The bacterium consistently exudes from kermes scale feeding sites on the newer branch growth throughout the upper canopy, lending to the name “drippy blight.”
The disease symptomology includes twig abscission, leaf drop, and branch dieback; after successive years of infection whole-limb dieback is observed.
Sitz, R.A., Zerillo, M., Snelling, J., Ibarra Caballero, J., Alexander, K., Nash, K., Tisserat, N.A., W.S. Cranshaw, and Stewart, J. 2017. Drippy blight, a disease of red oaks in Colorado produced from the combined effect of the scale insect Allokermes galliformis and the bacterium Lonsdalea quercina subsp. quercina. Accepted manuscript. Journal of Arboriculture and Urban Forestry.