Alternaria Black Spot
Alternaria brassicae and A. raphani causes black spot to occur on
leaves, stems, and pods every year, although low levels of black spot
are found in most canola fields but cause little damage. Severe
infection will cause premature ripening and pod shattering and resulting
in yield loss. Shriveled, shrunken seeds result in grade loss.
Symptoms: The symptoms vary depending on environmental conditions. Under moist conditions leaf spots will appear grey, and under drier conditions the leaf spots will appear grey with a purplish or black border. These lesions will often show circular zones of brown and dark brown, surrounded by a chlorotic halo. The spots that appear on the stems and pods will begin show brown to black specks that will change color as they grow, and will then become entirely black or have dark-bordered with a greyish white centre. The leaves that are severely diseased will wither and drop.
Disease Cycle: The Black spot fungus overwinters in/on the seed, crop debris and on weeds. From the spores that are produced in the infected plants and crop debris, they are spread by wind and rain. Seed maybe be contaminated through lesions on the pods or by spores in the combine.
Disease Control: Bury the infected stubble with tillage and control volunteer canola and other weeds to reduce inoculum. Use clean, disease-free seed with a high germination and free from shrunken kernels to reduce seed transmission. Seed treatment fungicides will reduce the seedling infection. Follow a three-year crop rotation and also maintain any nearby crops to help reduce any air-bourne inoculum from crop residue.
Symptoms: The symptoms vary depending on environmental conditions. Under moist conditions leaf spots will appear grey, and under drier conditions the leaf spots will appear grey with a purplish or black border. These lesions will often show circular zones of brown and dark brown, surrounded by a chlorotic halo. The spots that appear on the stems and pods will begin show brown to black specks that will change color as they grow, and will then become entirely black or have dark-bordered with a greyish white centre. The leaves that are severely diseased will wither and drop.
Disease Cycle: The Black spot fungus overwinters in/on the seed, crop debris and on weeds. From the spores that are produced in the infected plants and crop debris, they are spread by wind and rain. Seed maybe be contaminated through lesions on the pods or by spores in the combine.
Disease Control: Bury the infected stubble with tillage and control volunteer canola and other weeds to reduce inoculum. Use clean, disease-free seed with a high germination and free from shrunken kernels to reduce seed transmission. Seed treatment fungicides will reduce the seedling infection. Follow a three-year crop rotation and also maintain any nearby crops to help reduce any air-bourne inoculum from crop residue.