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Fungal root and crown diseases of raspberry plants

Note Number: AG0236
Mark Whattam and Cheryle Copes, Knoxfield
Updated: March, 1995

This Agriculture Note describes the symptoms of phytophthora root rot and white root rot and disease control in raspberry plants.

Introduction

Raspberry plants are affected by a number of soil-borne fungal pathogens which cause root and crown rots. These include Phytophthora spp. (Phytophthora root rot), Verticillium dahliae (Verticllium wilt) and Vararia spp. (white root rot).

Phytophthora root rot

Phytophthora root rot affects a wide range of plants and is caused by a number of Phytophthora species. The fungi produce abundant spores which can remain viable in the soil for many years. When conditions are favourable (ie. warm temperatures and high soil moisture) the spores germinate and produce structures which release swimming spores that infect the roots and crowns of plants.

Symptoms

The fungi rot the roots and crowns of plants, particularly plants growing in low lying areas. Symptoms are more obvious during hot, dry weather and include:

  • wilting of foliage and death of the growing tips
  • laterals often fail to develop
  • leaves are small and chlorotic (yellow)
  • plants generally lack vigour

Verticillium wilt

Verticillium wilt is caused by the soil-borne fungus, Verticillium dahliae. The pathogen survives as small microsclerotia (a hard mass of fungal threads) in the soil which can remain viable for long periods. The microsclerotia produce very tiny filaments (hyphae) that penetrate plant roots through cuts and wounds. Factors favouring disease development include heavy soils and cold, wet weather.

Symptoms

Symptoms of Verticillium wilt are most prevalent during the summer months and include:

  • pale yellow interveinal discolouration of leaves, followed by marginal necrosis (blackening) of leaf margins
  • wilting and cane dieback

White root rot

White root rot is caused by a Vararia species and unlike the other root rotting pathogens, the disease is most severe when the soil moisture is low. Although Vararia can be a serious and persistent pathogen of raspberries in Victoria it is not common and has a limited host range.

Symptoms

White root rot causes similar symptoms to those caused by Phytophthora and Verticillium spp.

  • yellowing of foliage followed by wilting and tip dieback
  • a dense, white mycelial mat is sometimes seen on the roots and crowns

Control

  • Use pathogen-tested stock when establishing new plantings.
  • Good drainage is essential. Heavy soils and excessive irrigation favour disease development. Therefore, attention to site drainage is required. Avoid planting in low lying areas. Planting on a slope and using a raised bed system can help reduce waterlogging.
  • To prevent spread of the fungus, soil movement, particularly from infected areas, should be avoided.
  • Soil fumigants can provide effective control, although it is important that this process is thorough and steps are taken to avoid recontamination of the site.
  • It is essential to remove and destroy any infected material immediately to reduce contamination.
  • Phytophthora root rot is most serious on red raspberries. Plantings of Willamette, Skeena, Chilcotin, Comox and Heritage, which are particularly susceptible, should be avoided in areas which are known to be infected with the pathogens. Meeker, Chilliwack and Autumn Bliss show some field resistance.

For effective pest and disease control, correct diagnosis is essential. A commercial diagnostic service is available at the Institute for Horticultural Development. For further information, contact the Diagnostic Service. Phone: (03) 9210-9222 or fax (03) 9800 3521.

The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.