Reason for Concern:
1) Cane blight can weaken fruiting canes, wilt plants, and reduce yield.
2) It enters new canes through wounds so there is greater potential for damage where mechanical harvesters are used.
3) The disease is usually most severe during wet growing seasons.

Identification/Symptoms:
Dark brown to purplish cankers can form at wounds or injuries on new canes. As cankers enlarge and extend down canes, lateral shoots can suddenly wilt and die. Wilting death may also occur on the side shoots of second-year canes. Early cane blight infections may resemble spur blight. However, cane blight usually covers the whole stem and is not confined to the leaf node areas as with spur blight. During the late summer, infected canes turn grayish and may be confused with winter injury or anthracnose.

Disease Cycle:
The causal fungus survives over winter on infected or dead canes. The following spring, spores are released and carried by splashing rain (or overhead irrigation) and wind to nearby primocanes. Under moist conditions, the spores germinate and penetrate pruning wounds, insect punctures, fruit stem breaks and other wounds. After entry the fungus rapidly invades and kills bark and other cane tissues. Fungal fruiting bodies are formed in older cankers and complete the disease cycle. Dead canes continue to produce spores and remain a source of infection for several years. Wet weather causes spores to ooze from the fruiting bodies, and spores can be spread on the wind. Young canes are most susceptible. Infection may occur at any time during the growing season, but often occurs at harvest when canes are wounded.

• WSU Raspberry Manual
  
• Oregon State University Online Plant Disease Manual
• Ohio State University Fact Sheet
  

• In the northwest cane blight spores most often enter raspberries via water splashing into the wounds on the primocanes created by the harvester catcher plates.
• Cankers develop on the canes and the following year, appear as brown to purple lesions.
• The vegetative buds on and above the canker area of the cane die and don’t flush out in the spring.
• When the cankers girdle the stem, it wilts and dies.
• Post harvest and again in late winter, select rows dispersed across the field, monitor 2-3 locations in row, look for lesions/wounds, especially weak hills in the spring.
• Pay particular attention or increase sampling where new drivers, hard springs on catcher plates, auto steer on machine harvester, and particularly wide rows.
• Scrape the lesion/wound and above on cane with knife; there will be brown discoloration of the vascular tissue (vertical striping) under the bark.
• Record number of plants with infection.

• Remove infected canes.
• Prune black raspberries in dry weather to force lateral growth so wounds will dry.
• Prune close to the ground; the fungus overwinters on cane stubs.
• Minimize or adjust irrigation so plants are not wet for long periods Use drip/trickle irrigation instead of overhead irrigation.
• Irrigate in the early morning to minimize the period that plants remain wet.

For information about chemical controls, check with our Pesticide Guide.