Cause Verticillium dahliae and Verticillium albo-atrum, soilborne fungi that affect a wide range of herbaceous and woody plants. Once V. dahliae makes its way into a soil, the microsclerotia it produces in affected plant tissues can survive for a number of years in soil, thus V. dahliae is the more common species of the two and it is widespread in Oregon. Asymptomatic weedy hosts can also perpetuate the pathogen population. These fungi enter through the root system and progress primarily through the vascular system. Maritime provinces in Canada report wilt problems caused by the second species, V. albo-atrum. This species can cause disease in cooler soils and survives as resistant mycelium as it does not produce microsclerotia. Plant-parasitic nematodes in the presence of Verticillium can result in severe disease.
Symptoms Infected plants' growth is stunted and leaves, beginning with lower leaves, yellow and roll in. Wilting may be obvious. When the stem is cut open in cross-section, the vascular system is distinctly discolored at the soil line.
Cultural control
- Do not leave crop remains on the field or add them to the compost pile; this encourages future infections.
- Rotating to nonsusceptible grass and grain crops is of value; 4- to 5-year crop rotation intervals should be followed in order for pathogen populations to drop as infected plant residues decompose.
- Avoid tomato and potato in any rotation. They are very susceptible hosts.
Chemical control
- Metam sodium (Vapam HL) at various rates. Soil fumigation is recommended in the Hermiston, OR area. See label for details. Restricted-use pesticide.
- OSO 5% SC (Group 19) at 3.75 to 13 fl oz/A on 7- to 14-day intervals. Can be applied the day of harvest. 4-hr reentry. O
Biological control
- Bexfond at 7 to 28 fl oz/A. O
- Stargus at 6 to 8 fl oz per 1,000 ft row as an in-furrow treatment, or 3 to 4 quarts/A as a soil drench (drip or chemigation) on 10- to 21-day intervals. Preharvest interval is 0 days. 4-hr reentry. O