Cottonwood Crown Gall: Agrobacterium Management

Massive Bark Blisters = Crown Gall

The huge blisters/galls on your Eastern cottonwood (Populus deltoides) are crown gall caused by Agrobacterium tumefaciens—a soil bacterium that genetically engineers plant cells to produce tumors.

Disease Facts

• Enters through wounds (roots, crown, lower trunk)
• Stimulates uncontrolled cell division → galls
• Galls: spongy/light young → hard/rough/fissured old
• Host range: 600+ species, 90+ families (cottonwood highly susceptible)
• Persists in soil 2+ years without host; decaying galls extend this

Management (Difficult)

1. Remove severely galled trees — they're inoculum sources
2. Sterilize tools between cuts (10% bleach, flame) — prevents spread
3. Don't replant cottonwood on site for 5+ years
4. Resistant alternatives: Populus hybrids with resistance, or non-host species

Structural Risk

Galls weaken wood at infection site. Large galls on main trunk = breakage hazard in storms. If near structures/targets, removal is prudent.

No Chemical Control

Biological control (A. radiobacter K84) only prevents infection of new plants—doesn't cure existing galls.