Fusarium oxysporum f. sp. cucumerinum (cucumber)
Fusarium oxysporum f. sp. melonis (cantaloupe)
Fusarium oxysporum f. sp. niveum (watermelon)
These fungi can infect host species at any stage of plant development. Pre-emergence rot and damping-off can occur when soil temperatures are cool [18–20ºC (64–68ºF)]. However, infection of older plants is most common. Wilted leaves may exhibit chlorosis and later, interveinal necrosis. Initially one or more runners wilt and later the entire plant wilts. In some cases, sudden collapse occurs without any chlorosis of the foliage. Mature infected plants with high fruit loads are prone to plant collapse. White mycelial growth may be visible on the stem at the base of infected plants. Vascular discoloration can be seen in both the roots and stems. In advanced stages, the roots begin to decompose, which may lead to plant death.
CONDITIONS FOR DISEASE DEVELOPMENT
Fusarium wilt is favored by warm soil temperatures. Wilting of the lower leaves occurs at warm temperatures [25–28ºC (77–82ºF)] and the leaves recover under cooler temperatures. The fungus survives as chlamydospores in the soil and in plant debris. The chlamydospores are readily disseminated in soil and in debris during cultivation of fields, in irrigation water, by wind-blown soil and workers.
For all cucurbit species, grow resistant varieties when available.
Open Field: Graft onto resistant rootstock (e.g., Cucurbita ficifolia). Soil solarization has been shown to be beneficial in light to moderately infested fields. Maintaining a soil pH of 6.5 and use of a NO3 nitrogen source can help reduce disease incidence and severity. Implement an equipment and worker sanitation program to control movement of the pathogen between fields. Crop rotation out of cucurbits for a minimum of five years may provide control in some cases, although is not always an effective strategy due to long-term persistence of chlamydospores in many soils.
Protected Culture: Implement a strict sanitation program for workers, tools, equipment and structures. Produce crops in artificial substrate and do not reuse substrate. Graft crop species onto a resistant rootstock (e.g., Cucurbita maxima, Cucurbita ficifolia). Collect and remove pruning debris from site or destroy by burning or burying. Remove infected plants upon recognition. Crop production during cooler months may reduce disease incidence and severity since Fusarium wilt is not favored at lower temperatures.