Crown Gall on Oak: Bacterial Tumor with a Biotech Legacy

The large, woody swelling at the base of an oak is crown gall, caused by Agrobacterium tumefaciens. The bacterium transfers a snippet of its DNA into the tree, triggering uncontrolled cell growth—essentially plant cancer.

Remarkably, this natural genetic engineering inspired modern crop biotechnology: ‘Flavr Savr’ tomato, ‘Roundup Ready’ soy, and ‘Bollgard’ cotton all trace their gene-insertion method to crown gall biology.

The gall may weaken the trunk or impede water flow, but many trees coexist for decades. Woodworkers prize burled wood, but it’s common and low-value. Best advice: leave the tree as a landscape conversation piece.