Susceptibility and Yield of Kale Horticultural Types and Cultivars Affected with Black Spot Caused by Alternaria brassicicola and Alternaria japonica

Curly kale (Brassica oleracea var. sabellica), lacinato kale (B. oleracea var. palmifolia), Portuguese kale (B. oleracea var. costata), and Siberian kale (Brassica napus var. pabularia) are produced with conventional and organic practices in the southeastern United States. The foliar disease black spot, caused by the fungi Alternaria brassicicola and Alternaria japonica, may reduce yields of curly kale, but its effects on other kale types are unknown. The objectives of this study were to determine which kale cultivars had the lowest percentage of symptomatic leaves (disease incidence) and greatest yield of healthy leaves when grown with conventional and organic practices in fall and spring. Single-row plots of 14 kale cultivars were inoculated on the ends with one Alternaria sp., which then spread to noninoculated plants in the center of the plot. Season, production, pathogen species, harvest, and inoculation affected cultivar performance; season had the largest effect. In general, Portuguese kale was the most susceptible kale type, followed by curly kale. Black spot incidence was greater at the second harvest of cropped plants than at the first harvest. Siberian kales yielded more than curly and lacinato kales, although green curly kale cultivar Winterbor had yields similar to the best-yielding Siberian kales.