Controlling Rose Gall

Tis the season in Rosedom to cut things! Some of you in the southern hemisphere will be pruning for summer flush. Some of you in the northern hemisphere will be digging for transplant. Some will be ordering bareroot roses through the mail. And some will even be performing your annual pruning in preparation for spring. All of you will be cutting stems or roots and making wounds on your roses. And as you might expect, these wounds provide an entry point for bacterial infection - not the least of which is gall.

How Galls Get Started:
Bacterial galls are tumors caused by a critter called Agrobacterium.

• Crown galls, those tumors which attack the root crown of the plant near the soil's surface, are produced by A. tumefaciens.
• Cane and stem galls are produced by A. rubi.

These bacteria live in the soil and can survive long periods of adverse conditions in soil debris or within the systemic fluids of the plant. When the plant is wounded, the bacteria enter the tissues and form a soft, spongy tumor. The bacteria proliferate on the outer surfaces of the tumor. As the gall hardens, some of these outer tissues are sloughed to the ground carrying with them more bacteria which then re-infect previously non-infected, wounded areas of the plant.

Susceptible Soil Conditions
If you have acidic soil, consider yourself lucky. A. tumefaciens does not do well in acidic soil. The bacteria is most prevalent in late spring when soils are moist.

How Plants Get Wounded
The wounds can be caused by pruning, digging, freeze injury, improper fertilization or irrigation causing cracked stems, and even pest insect damage.