Oak bacterial necrosis

The causative agent of the disease is the bacterium Lonsdalea quercina, formerly classified as Brenneria quercina. It is a gram-negative, rod-shaped bacterium responsible for inducing necrotic lesions in the bark and underlying sapwood of host trees. This pathogen is recognized as a significant threat to the health of oak populations in various temperate climates.

The primary host for Lonsdalea quercina is the oak tree (Quercus genus). The pathogen acts as an opportunistic invader, typically entering the tree through wounds, bark cracks, or galleries created by wood-boring insects. Once inside, the bacteria multiply rapidly within the phloem and cambium tissues, disrupting the transport of nutrients and water.

Symptoms of the infection manifest as localized areas of bark necrosis, where the tissue becomes depressed, discolored, and eventually dies. In many cases, a dark, viscous bacterial exudate leaks from the cracks in the bark, leaving dry residues upon drying. As the disease progresses, the tree crown shows signs of decline, including leaf chlorosis, premature wilting, and canopy dieback.

The development of the disease is heavily influenced by environmental factors such as high humidity and moderate temperatures, which favor bacterial survival and reproduction. Spread of the pathogen occurs primarily through rain splashes, wind-blown moisture, and insect vectors that transfer bacterial cells from infected lesions to fresh wounds on nearby healthy trees.

Management and prevention of oak bacterial necrosis focus on maintaining tree vigor and minimizing wounding. Silvicultural practices, such as thinning overstocked stands and removing heavily infested trees, are essential to reduce inoculum levels. Additionally, keeping the bark intact and treating any necessary mechanical wounds with appropriate antiseptic agents can significantly lower the risk of successful bacterial colonization.