Cause The bacterium Agrobacterium tumefaciens enters plants through wounds, either natural or caused by pruning, grafting, mechanical injury, chewing insects, or the emergence of lateral roots. Pruning or cutting tools that cut through galls can become contaminated with the bacteria and spread them to cut surfaces of subsequently pruned plants. Galls can also occur at sites of lateral shoot removal or pinching of terminals. The bacteria can be systemic in plants.
