Notes on Raspberry Diseases: Phytophthora root rot

Identification

Plants infected with phytophthora root rot grow poorly. Primocanes often wilt. Foliage on fruiting canes dies back, especially when drought or the demands of cropping stress the plants. Fewer primocanes emerge each spring.

Phytophthora symptoms in the field

Phytophthora symptoms in the field

Phytophthora - distinct reddish brown discolouration beneath bark

Phytophthora - distinct reddish brown discolouration beneath bark

Period of Activity

A soil-borne fungus causes Phytophthora root rot. The fungus produces spores that swim in water and infect roots and crowns when soil conditions are very wet. Infections can take place whenever soil temperatures are over 10ºC and the soil is wet, but most frequently in spring and fall.

Monitoring

The disease frequently develops on plants grown on heavy, compacted or poorly drained soil. Confirm diagnosis by digging up plants and scraping away the outer tissue of diseased crowns. Phytophthora infections cause a reddish discoloration just beneath the bark of the infected crown. Certain varieties are very susceptible to phytophthora and are much more likely to develop the disease than tolerant varieties.

Management notes

Phytophthora root rot can be partially managed by the use of fungicides but crop management practices are more important for the prevention and control of this disease.

  • Select fields with excellent drainage and avoid low-lying areas. Consider the use of raised beds to keep the water table below the plant roots.
  • Some varieties of raspberries are very susceptible to phytophthora while others are fairly resistant. See Table 1. Field Resistance of Red Raspberry Varieties to Phytophthora Root Rot.
  • Avoid growing susceptible varieties, especially in heavier soil types or on soils prone to floods.
Table 1. Field Resistance of Red Raspberry Varieties to Phytophthora Root Rot
Partially Resistant Susceptible Very susceptible
Latham1
Killarney1
Boyne1
Prelude2
Anne2
Nova2
Caroline2
NY2582
Heritage1
Taylor1
Newburgh1
Royalty1
Josephine2
Titan1
Canby1
Ruby1
Lauren2
Encore2
Polana2
NY2532

Source:
1 W. Wilcox and M. Pritts
2 Courtney Weber and Jeremy Pattison 2003, Cornell University

Learn more...


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca