• Aerial stem rot & tuber soft rot
• Black leg begins from a contaminated seed piece
• Stem bases - an inky-black to light-brown decay, extend up the stem from less than an inch to more than two feet
• These enlarge into a soft, mushy rot that causes entire stems to wilt and die
• Leaves - roll upward at the margins, become yellow, wilt & often die
• Potato tubers with soft rot have tissues
  • very soft and watery
  • have a slightly granular consistency
  • tissue is cream to tan-colored
  • black border separating diseased from healthy areas
• In the early stages, soft-rot decay - odorless
• Later a foul odor and a stringy or slimy decay usually develops as secondary decay bacteria invade infected tissues

Identification of pathogen:

Blackleg: Erwinia carotovora subsp. atroseptica

• Carried by contaminated seed tubers
• Usually dormant and do not cause disease unless environmental conditions are favorable

Aerial stem rot: Erwinia carotovora subsp. Carotovora

• Contained in infested soil or introduced to the crop by irrigation water, wind-blown rain, and insects

Tuber soft rot

• Caused by either of these soft-rot bacteria
• Maggot flies (Hylemyia spp. and Phorlin spp.) - spread the black leg and soft rot

Epidemiology

• High soil temperatures and bruising of seed tubers favor seed-piece decay
• RH - 94 to 100% & temp - 21 to 29°C

• Plant only certified, disease-free seed tubers
• Seed treatment
• Temp - just above 0°C
  • Agallol-3(0.25%) for 5 min
  • Streptomycin sulphate 0.1 % for 10 min
  • Streptocycline ( 100 ppm) and copper sulphate ( 40 ppm) for 30 min
• Harvest tubers only after the vines are completely dead to ensure skin maturity
• Precautions to minimize cuts and bruises when harvesting and handling tubers
• Storage - 55-60 F with 90-95% relative humidity for the first 1-2 weeks to promote wound healing