Notes on Raspberry Diseases
Spur blight
Identification
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.
Monitoring
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.
Management notes
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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