Ring Rot
Beginner
Scientific Name
Clavibacter michiganensis subsp. Sepedonicus
Identification
Zero tolerance control measures are in place against this disease.
The seed potato regulations in Canada indicate that upon finding bacterial ring rot, all lots under cultivation by the grower are rejected for certification.
One of the characteristics of this disease is that the expression of foliar symptoms and the type of symptoms expressed vary depending on the variety. In addition, infected plants may not show symptoms if the weather is cool and wet. Thus, all potato cultivars are potential symptomless carriers and may spread the disease extensively as latent infections. Latent infections in tubers may be secondarily infected by soft rot.
In hot, dry seasons, ring rot develops rapidly. The first symptoms in the field usually appear on the lower leaves about mid-season.
Foliage: The yellowing of interveinal areas and curling and browning of leaf edges are distinct symptoms of ring rot. Yellowing is followed by wilting. Lower leaves usually wilt first. Eventually, necrosis kills the leaflets
Russet Burbank may develop the dwarf rosette symptom early in the season. Dwarf rosette symptom is caused by shortened internode length in the terminals. These bunchy or rosetted terminals are a darker green than the rest of the plant.
Stems: One or more stems in a hill may show symptoms while the rest appear normal. When affected stems are cut at the ground line and squeezed, a creamy white mass of bacteria may ooze from the water-conducting tissue.
Tubers: Infected tubers usually develop star-shaped cracks in the skin
A creamy, yellow-brown, cheesy, odourless rot develops in the vascular ring. Corky tissue surrounds hollows in the vascular ring.
When secondary bacteria invade infected tubers, a foul smelling rot may occur, and tubers may be completely destroyed.
Often Confused With
Soft
rot
Period of Activity
Throughout the season
Scouting Notes
- Scouting should start before the rows close.
- Fields should be monitored at least twice a week.
- When walking fields, stop at many sites as possible and check plants at random.
- If incidence of ring rot is suspected, CFIA must be notified immediately.
- Strict sanitary measures are in place when entering suspicious fields:
- Wear disposable spraying suits, and disposable vinyl gloves.
- Disinfect boots before entering and when exiting suspicious fields.
Thresholds
If one infected plant is found in the field CFIA must be notified immediately.
Advanced
Scientific Name
Clavibacter michiganensis subsp. Sepedonicus
Identification
Zero tolerance control measures are in place against this disease.
The seed potato regulations in Canada indicate that upon finding bacterial ring rot, all lots under cultivation by the grower are rejected for certification.
One of the characteristics of this disease is that the expression of foliar symptoms and the type of symptoms expressed vary depending on the variety. In addition, infected plants may not show symptoms if the weather is cool and wet. Thus, all potato cultivars are potential symptomless carriers and may spread the disease extensively as latent infections. Latent infections in tubers may be secondarily infected by soft rot.
In hot, dry seasons, ring rot develops rapidly. The first symptoms in the field usually appear on the lower leaves about mid-season.
Foliage: The yellowing of interveinal areas and curling and browning of leaf edges are distinct symptoms of ring rot. Yellowing is followed by wilting. Lower leaves usually wilt first. Eventually, necrosis kills the leaflets
Russet Burbank may develop the dwarf rosette symptom early in the season. Dwarf rosette symptom is caused by shortened internode length in the terminals. These bunchy or rosetted terminals are a darker green than the rest of the plant.
Stems: One or more stems in a hill may show symptoms while the rest appear normal. When affected stems are cut at the ground line and squeezed, a creamy white mass of bacteria may ooze from the water-conducting tissue.
Tubers: Infected tubers usually develop star-shaped cracks in the skin
A creamy, yellow-brown, cheesy, odourless rot develops in the vascular ring. Corky tissue surrounds hollows in the vascular ring.
When secondary bacteria invade infected tubers, a foul smelling rot may occur, and tubers may be completely destroyed.
Often Confused With
Soft
rot
Biology
The ring rot bacterium is extremely infectious. It overwinters mainly in seed tubers, but can survive for up to 2 years as dried slime on cutting knives, storage bins, planting and harvesting equipment, burlap bags, paper and plastic. The bacterium is not killed by freezing.
Ring rot spreads primarily from infected seed pieces to healthy tubers during seed cutting and planting. Contaminated seed-cutter knives and pick planters are excellent disseminators of bacterial ring rot because fresh wounds provide a means of entry for the bacteria into the tuber. Ring rot may be spread in the field by direct contact between diseased and healthy plants. The bacteria may also be carried by farm equipment or by insects such as the Colorado potato beetle, the potato flea beetle or the green peach aphid.
Plants and tubers of some varieties may be infected with ring rot bacteria without showing symptoms.
Period of Activity
Throughout the season
Scouting Notes
- Scouting should start before the rows close.
- Fields should be monitored at least twice a week.
- When walking fields, stop at many sites as possible and check plants at random.
- If incidence of ring rot is suspected, CFIA must be notified immediately.
- Strict sanitary measures are in place when entering suspicious fields:
- Wear disposable spraying suits, and disposable vinyl gloves.
- Disinfect boots before entering and when exiting suspicious fields.
Thresholds
If one infected plant is found in the field CFIA must be notified immediately.
Management Notes
- Use only certified seed potatoes.
- Plant whole, single-drop seed. Avoid using picker planters because the pick spreads disease.
- Disinfect cutting knives at least three times a day when cutting a single lot of potato seed. Always disinfect before cutting a new seed lot.
- Disinfect storage bins, tools, trucks, and other equipment frequently during cutting and planting operations.
Always clean extensively before beginning seed handling operations at the start of the season.
