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Ministry of Agriculture, Food and Rural Affairs

Verticillium Wilt

Initial symptoms on lower leaves Symptoms on young leaves Plant infected with verticillium wilt Flagging symptoms on infected plant Early dying due to Verticillium and root lesion nematode
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Beginner

Scientific Name
Verticillium dahliae

Identification

  • The first symptoms usually appear immediately after flowering in the lower leaves. The area between leaf veins begins to yellow. Later, the symptoms move upward to the younger leaves. Initially one side of the leaves turns yellow and wilts. Later, the entire leaf turns yellow.
  • Leaf yellowing is followed by browning and necrosis.
  • In early stages of the disease, not all the stems from the same plant show symptoms.
  • Infected plants wilt during the day but recover at night.
  • Infected and dead plants stand up higher than the other plants in the field, a condition called flagging.
  • The vascular area of infected stems turns brown.
  • In tubers, the vascular ring turns brown. This brown vascular discolouration starts at the stem end of the tuber and it does not usually extend more than halfway through the tuber.
  • The crop senesces early, 3–4 weeks before reaching maturity. As a consequence, tubers do not size and serious yield losses occur.

Often Confused With
Black dot and wilts caused by excessive soil moisture.

Period of Activity
Usually disease symptoms develop immediately after flowering.

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 you find wilted plants, check for brown discoloration of the vascular area of stems. This symptom is easily seen if the stem is cut close to ground level with a long, slanting cut.
  • Take soil samples from areas where infected plants are found. Soil analysis is a useful method to detect the level of Verticillium infestation in the soil

Thresholds
Soil analysis is useful to determine the amount of inoculum (microsclerotia) in the soil.  The risk of potato crop infection is closely related to the number colonies formed by the fungus when grown in special media in the laboratory.  The results are expressed in number of colonies per gram of soil.

Low risk                0-5   colonies
Moderate risk       6-12  colonies
High risk               >12   colonies

Advanced

Scientific Name
Verticillium dahliae

Identification

  • The first symptoms usually appear immediately after flowering in the lower leaves. The area between leaf veins begins to yellow. Later, the symptoms move upward to the younger leaves. Initially one side of the leaves turns yellow and wilts. Later, the entire leaf turns yellow.
  • Leaf yellowing is followed by browning and necrosis.
  • In early stages of the disease, not all the stems from the same plant show symptoms.
  • Infected plants wilt during the day but recover at night.
  • Infected and dead plants stand up higher than the other plants in the field, a condition called flagging.
  • The vascular area of infected stems turns brown.
  • In tubers, the vascular ring turns brown. This brown vascular discolouration starts at the stem end of the tuber and it does not usually extend more than halfway through the tuber.
  • The crop senesces early, 3–4 weeks before reaching maturity. As a consequence, tubers do not size and serious yield losses occur.

Often Confused With
Black dot and wilts caused by excessive soil moisture.

Biology

The Verticillium fungus persists in the soil for many years as tiny propagules called microsclerotia. In the presence of a susceptible host plant, microsclerotia germinate, and the fungus penetrates the plants through the roots and spreads upwards in the vascular tissue infecting stems, petioles and leaves.

The disease is favored by crop stress induced mainly by heat, drought, nutrient deficiencies and insect damage.

The premature vine death and declining yields caused by Verticillium are called potato early dying syndrome.

Short crop rotations, especially in sandy soils with susceptible varieties, tend to increase the population of Verticillium to damaging levels. The fungus infects many other crops and weed species. High soil temperatures favour disease development.

The root lesion nematode has been associated with this syndrome because it enhances the incidence and severity of Verticillium wilt.

Period of Activity
Usually disease symptoms develop immediately after flowering.

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 you find wilted plants, check for brown discoloration of the vascular area of stems. This symptom is easily seen if the stem is cut close to ground level with a long, slanting cut.
  • Take soil samples from areas where infected plants are found. Soil analysis is a useful method to detect the level of Verticillium infestation in the soil

Thresholds
Soil analysis is useful to determine the amount of inoculum (microsclerotia) in the soil.  The risk of potato crop infection is closely related to the number colonies formed by the fungus when grown in special media in the laboratory.  The results are expressed in number of colonies per gram of soil.

Low risk                0-5   colonies
Moderate risk       6-12  colonies
High risk               >12   colonies

Management Notes

  • The best cultural management of Verticillium wilt is maintaining plant vigor with good fertilization and irrigation practices.
  • Resistance to Verticillium wilt varies among cultivars. Most varieties express tolerance to Verticillium when there is no crop stress during the growing season.

Rotate potatoes with a resistant crop such as corn. Mustards have been reported to reduce Verticillium infestation.