Cause Macrophomina phaseolina is a soilborne fungus that is favored by dry and warm soil conditions and has an extensive host range including beans, brassicas, clovers, corn, cucurbits, grape, lettuce, peppers, onion, strawberry, tomato, tree fruits, and conifers. Disease development is enhanced by high temperature, soil water deficit, and sandy soils. The fungus produces microsclerotia for long-term survival and dispersal in the soil. Microsclerotia in the soil infect susceptible plants each season. The microsclerotia are produced in the host tissue and released into the soil as the infected storage root decays.
Symptoms Plants show wilting of foliage, drying and death of older leaves, plant stunting, and eventual collapse and death. When plant crowns are cut open, internal vascular and cortex tissues are dark brown to orange brown. May look similar to Fusarium or Verticillium wilt.
Cultural control
- Use long crop rotation of grasses for seed in the rotation.
- Anaerobic Soil Disinfestation may be helpful even in the PNW. First rice bran is incorporated into the soil followed by irrigated to near field capacity. Then place clear, oxygen-impermeable plastic (such as anti-condensation film) on the prepared ground. This summer treatment needs to reach soil temperatures of 90°F. Use in combination with other techniques.
- Do not plant parsnip on land with a recent history of this disease.
Chemical control Preplant fumigation.
- Dominus at 10.8 to 17.1 gal/A. Apply as a shank injection to an entire field when soil temperatures are above 60°F but not greater than 90°F. 5-day reentry.
- Telone C-17 at 10 to 30 gal/A broadcast on mineral soils. Allow 2 to 3 weeks between application and planting or until odor leaves the soil. Do not treat extremely heavy soils. 5-day reentry. Restricted-use pesticide.