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.
Here are some common scenarios and precautions:
A deal too good to be true: The wounds can be caused by pruning, digging, freeze injury, improper fertilization or irrigation causing cracked stems, and even pest insect damage. Here are some common scenarios and precautions.
Pruning with improperly maintained equipment: The use of dull shears or shears with misaligned blades can cause damage to stems and canes; preventing a "clean" cut. Tissue damage or die-back areas are prime entry points for pest bacteria. Be certain your pruning equipment is sharp and the "business end" is working correctly.
Pruning with infected equipment: If pruning lots of plants, the bacteria can be passed from infected plants to a non-infected plants. Sterilize shears and saws between shrubs.
Transplanting: Digging plants for transplanting causes many damaged roots. Prune away damaged and broken roots before replanting.
Purchasing bareroot plants: Roots and stems can be damaged or broken in shipment. Prune them cleanly before planting.
Freeze damage: After severe winters, plants can experience die-back or chafing due to canes rubbing together. Prune it away.
Stem cracks: After heavy rains or feedings, cracks in stem tissues can appear. Prune it away.
Plant chewing pests: Critters of all types like to chew on the succulent foliage and stems. Prune away damaged areas and apply repellents to discourage them from returning.
If you find galls on your plants, don't despair. At the worst, gall infection will cause stunted plant growth, poor fruit development, and reduced nutrient and water uptake. Often, the top the the plant will appear normal.
Root galls are hardest to detect and sometimes go unnoticed until a seemingly unresponsive plant is dug for transplant or removed. Prune away the gall and that portion of the root to which it is attached. Dip the cut into a solution of Agrobacterium radiobacter strain 84 (commonly sold as Galltrol-A or NOGALL) to prevent reinfection.
Crown galls are hardest to remove. They frequently form on the grafting union of modern hybrid roses. Prune away the infected area to the best of your ability, and spray on a solution of A. radiobacter to prevent reinfection.
Stem galls are the easiest to notice and remove. Prune away infected stems and canes and spray with A. radiobacter to prevent reinfection.
Note: A. radiobacter will not eliminate existing galls. It is a naturally occurring biological control bacterium - the natural counterpart - to A. tumefaciens and A. rubi.
If planting or replanting in the infested or potentially infested soil, spray the plant's roots and stems in a solution of A. radiobacter to prevent infection. I perfer to dig out the old soil and replace with new uninfected soil.
