Alternaria Leaf Spot Of Brassica Crops: Disease Incidence And Sustainable Management
Alternaria leaf spot (ALS) is a fungal disease that affects all cultivated brassicas, causing small black spots that grow into large lesions with characteristic concentric rings on leaves, stems and heads. The disease is of growing concern to NYS cabbage growers because of decreasing efficacy of chemical fungicides to control the disease. Concurrent with the decline in efficacy of fungicides there has been a 406% increase in organic cabbage production in NYS between 2008 and 2011, indicating that research on organic alternatives for ALS management in NYS is warranted. The goals of the studies presented in this thesis were to answer basic questions of population structure in NYS, and to investigate disease management strategies suitable for use in organic cropping systems. A disease survey was conducted and samples of plants showing ALS symptoms were collected from different host crops and from farms across NYS. All isolates collected were identified as Alternaria brassicicola using DNA-based methods, indicating that disease is not or is rarely caused by the closely related species, A. brassicae, which is also known to infect vegetable brassicas. Furthermore, cultural and biological disease control strategies were investigated in two field studies. First, two soil organic matter amendments and several fungicides approved for use in organic cropping systems were evaluated for their efficacy in controlling ALS in cabbage. None of the treatments evaluated had significant effects on disease severity, but further study under different application conditions is warranted. Secondly, the effects of mulches on kale growth and disease incidence were tested in a field contaminated with ALS-infected crop residues. Results of this study indicate that mulch increases plant growth while reducing disease incidence, and highlights the potential of cultural practices to reduce ALS disease severity in organic cropping systems. Further research is necessary to confirm these results, and additional studies on epidemiology and pathogen population structure will aid in the continuing development of successful ALS management strategies for NYS growers.
Alternaria leaf spot; Alternaria brassicicola; Brassica oleraceae
Dillard, Helene R
Smart, Christine Durbahn; Reiners, Stephen
M.S. of Plant Pathology
Master of Science
dissertation or thesis