Description

Alternaria leaf blight is caused by Alternaria panax. This disease is very common and causes premature defoliation which results in decreased root weights. Alternaria can blight the shoots, stems, fruits and leaves.

Symptoms

This fungus causes tan yellow/lesions or spots that may have a dark margin. In the initial stages of the disease, the leaf lesions look water-soaked or oily. When these spots expand and merge, large areas of the leaves become blighted and
die. These lesions may look a bit “velvety”as the disease progresses especially under wet conditions. Stems may become riddled with the lesions, which will cause the plant to
fall over. Roots are not normally affected.

If Alternaria leaf and stem blight is not controlled, it can reach epidemic proportions within a month after the plants have emerged in the spring, destroying all of the foliage. This loss of foliage retards root growth in maturing crops, resulting in reduced root yields at harvest. Also, defoliation of young plants makes them more susceptible to winter kill. Repeated outbreaks in subsequent years can reduce yields further. The loss of yield reported by Wisconsin growers when the disease is uncontrolled range from 50 to 100%, with the majority of those surveyed reporting losses of 75 to 100% (Drilias, 2002). In addition, Alternaria leaf and stem blight can damage or destroy the seed crop normally harvested from 3-year-old ginseng gardens.

Management Strategies

  • Cultural control
    • Plant spacing
    • Proper airflow
    • Minimize prolonged leaf wetness
    • Sanitation of diseased material
  • Chemical control
    • Garden size is limited to enhance air flow and movement to reduce the environmental
      conditions that favor disease development.
    • Monitor the environment and treat preventively when environmental conditions favor disease
      development.
    • Rotate crops to avoid pathogen buildup.

Refer to the Pesticide Bulletin for treatment recommendations.

DISEASE FACT SHEET CLICK LINK BELOW

ALTERNARIA

Leaf infected with Alternaria Blight

Leaf infected with Alternaria Blight