This soil-borne fungus can attack roots, stems or fruit in contact with the soil. On seedlings, black, sunken cankers may appear on hypocotyls at the time of emergence. These cankers may develop a concentric ring pattern, stunt affected plants and cause wilt. When older plants are attacked, runners and crown leaves may turn yellow and die. Typically, a water-soaked lesion will occur at the soil level and extend several centimeters up the stem. Brown, water-soaked lesions are also symptomatic of fruit infection. Amber-colored droplets of exudate may form within the affected area. Eventually, the lesion dries up, turns light tan and microsclerotia form.
CONDITIONS FOR DISEASE DEVELOPMENT
Macrophomina phaseolina is seed-borne and can be seed-transmitted. Infection and disease development are favored by high temperatures. High soil salinity, drought stress and heavy fruit load can predispose plants to infection. Microsclerotia in infected host tissue and in soil are the primary propagules and survival structures. Microsclerotia reside in the top 0–20 cm of soil and are able to survive from 2–15 years, depending on environmental conditions.
Manage irrigation to avoid drought stress. If soil salinity is high, leach to reduce salt buildup. Drip irrigation may result in higher soil salinity compared to furrow irrigation if salinity of the irrigation water is moderate to high. Destroy or deep-plow all plant debris at the end of the season. A three-year rotation out of cucurbits to a non-host species may be beneficial. However, this strategy is not as effective at controlling Macrophomina phaseolina as it is with other pathogens due to its wide host range and the longevity of the microsclerotia.