Impact
Bacterial ring rot (BRR) is caused by the bacterium Clavibacter michiganensis subsp. sepedonicus. BRR is a serious disease of potato. Presence in seed will result in rejection of lots for certification. The bacteria overwinter mainly in infected seed tubers. BRR is capable of surviving more than five years in dried slime on the surfaces of crates, bines, burlap sacks, and harvesting and grading machinery. Survival is possible even if exposed to temperatures well below 0 degrees F. BRR survives longest under cool, dry conditions. BRR occurs sporadically in the San Luis Valley.

Bacterial ring rot foliar symptoms.		Bacterial ring rot tuber symptoms.

Descriptions and Symptoms
	Foliar symptoms usually appear late in the growing season. Cultivars differ greatly in their expression of the disease
	Symptoms include: early dwarfing, rosetting of upper leaves and general wilting of the plant with chlorosis and necrosis of the leaves.
	Stems of plants, when cut at the base, produce a milky exudate upon squeezing. Commonly, only one or two stems develop symptoms.
	Infected tubers often develop a creamy yellow to light brown rot in the vascular ring.
	BRR readily spreads between tubers during seed cutting and handling.
	Tubers and plants may be symptomless even though they are infected with BRR.
Integrated Management
	Plant certified seed potatoes.
	Never plant contaminated seed lots.
	Avoid cutting seed tubers and using pick-type planters.
	Maintain strict sanitation aimed at eliminating BRR from all production surfaces. A complete sanitation program involves thoroughly washing all surfaces with a detergent applied by a high-pressure washer, rinsing with clean water and sanitizing with a suitable disinfectant for a minimum of 10 minutes under ideal conditions.
	Undertake a thorough cleanup and santitation of any farm with confirmed BRR in potato stocks to reduce risk of carryover into next year's crop. Dispose of infected tubers and cull piles as soon as possible.
	Salvage a commercial crop with a low level of BRR by an integrated managemetn approach involving delayed harvest, careful grading to remove any decayed tubers when the crop is placed in storage, and proper storage management. Do not save seed to replant. Market potatoes as soon as possible.
	No resistant cultivars and pesticide control are available.

This material is based on work supported by the San Luis Valley Water Quality Demonstration Project Best Management Practices Advisory Committee, Colorado State University Cooperative Extension, Farm Service Agency, Natural Resources Conservation Service, and the U.S. Department of Agriculture under authorization as 1991 U.S. Department of Agriculture Water Quality Demonstration Project.