pythium leak
Beginner
Scientific Name
Pythium ultimum
Identification
Initial tuber symptoms are grey to brownish lesions with a water-soaked appearance. These lesions usually develop around wounds, cuts or bruises. Infected tuber tissue is cream-coloured. On exposure to air, the cream rot turns brown. A dark line is present at the margin of the rot. With time, the rot turns inky black. A clear, brownish liquid is readily released by the rotted tissue when the tuber is pressed.
Often Confused With
Late
blight
Pink
Rot
Period of Activity
Pythium may cause seed decay and poor crop emergence if planting conditions are warm and wet. Also, infection may occur in the field prior to harvest or at harvest, especially in hot, humid weather.
In storage the disease may spread from infected to healthy tubers.
Scouting Notes
Leak usually develops at harvest. Assess disease incidence prior to washing and bagging potatoes.
Thresholds
Pythium is a soil borne fungus. The disease is usually detected before harvest, at harvest and in storage. A dig test can be performed to determine the level of disease incidence.
Advanced
Scientific Name
Pythium ultimum
Identification
Initial tuber symptoms are grey to brownish lesions with a water-soaked appearance. These lesions usually develop around wounds, cuts or bruises. Infected tuber tissue is cream-coloured. On exposure to air, the cream rot turns brown. A dark line is present at the margin of the rot. With time, the rot turns inky black. A clear, brownish liquid is readily released by the rotted tissue when the tuber is pressed.
Often, the entire inside of the tuber rots, leaving a thin outer shell. This is known as shell rot.
Often Confused With
Late
blight
Pink
Rot
Biology
The Pythium leak fungus is widely distributed in soils. It also attacks the underground parts of many other crops.
The fungus cannot penetrate tubers directly, but enters through bruises and wounds, which usually occur at harvest. Harvesting the crop in hot, humid weather or exposing the tubers to heat for several hours after harvest creates ideal conditions for leak. Infection may also occur in the field prior to harvest.
Leak development is very rapid, and can cause serious losses in storage, in transit and on the market. When infected potatoes are stored, juice from rotten tubers drips down through the pile.
Pythium may be responsible for the decay of seed tubers if conditions are warm and wet immediately after planting.
Period of Activity
Pythium may cause seed decay and poor crop emergence if planting conditions are warm and wet. Also, infection may occur in the field prior to harvest or at harvest, especially in hot, humid weather.
In storage the disease may spread from infected to healthy tubers.
Scouting Notes
Leak usually develops at harvest. Assess disease incidence prior to washing and bagging potatoes.
Thresholds
Pythium is a soil borne fungus. The disease is usually detected before harvest, at harvest and in storage. A dig test can be performed to determine the level of disease incidence.
Management Notes
- Avoid harvesting under hot, humid conditions.
- Avoid mechanical damage at harvest
- Maintain good air circulation and keep the storage temperature as low as possible.
