Notes on Raspberry Diseases: Spur blight
Spur blight infections begin on the edge of older leaves and cause brown v-shaped lesions. The infection advances to the mid vein and then into the bud that forms at the base of the leaf in the leaf spur. A dark brown v-shaped lesion develops at the base of the buds. Overwintering lesions become silvery grey. Spur blight infection causes weak or delayed growth from infected buds and increased winter injury.
Spur blight symptoms on raspberry primocane
Period of Activity
Primary spores (ascospores) are discharged from May to August. Inoculum comes only from old fruiting canes. Secondary spores (conidia) are also produced. Conidia splashed about in July and August probably cause the most damage. The lowest leaves and spurs are infected first then infections move up the cane as the season progresses.
Check primocanes for spur blight in mid-late summer as older leaves begin to senesce. Infections on the lower leaves are less serious than infections on the middle portion of the cane where crop losses can be greater.
Keep rows narrow and control weeds to improve drying in the row. Early fungicides are important to reduce overwintering inoculum. Fungicides used for control of botrytis fruit rot may also help to suppress spur blight. Field resistance to spur blight has been reported in Boyne.
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