Phytophthora root and collar rot, black butt, gummosis

Phytophthora root and collar rot, black butt, gummosis
Phytophthora spp.

In wattle, Phytophthora causes “black butt”, also referred to as “gummosis” and mottling cankers, affecting trees of all ages.

Symptoms in Eucalyptus spp. include basal cankers, root and collar rot.

Symptoms in wattle are visible as necrotic lesions on the trunk, from the collar to the upper portions, with or without gum exudation (Roux et al. 1995; Roux & Wingfield 1997). Root rot can also lead to wilting and death of trees (Bose et al. 2019).

In eucalypts, cankers, root and collar rot can lead to wilting and may result in reduced growth (and subsequently reduced yields). Trees may also be more prone to windthrow due to reduced root systems. Death can occur in susceptible host species, particularly cold tolerant eucalypts, where collar lesions lead to girdling (Wingfield & Knox-Davies 1980; Maseko 2001; Bose et al. 2019).

The species of Phytophthora causing disease in South African forestry are soil borne pathogens. They are well adapted to diverse plant hosts and environments, and produce several types of structures that are specialised for survival, dispersal or infection. They persist in soil and plant tissue for extended periods of time, by the formation of thick-walled resting spores including oospores (sexual spores) and chlamydospores (asexual spores). Infection requires moist conditions. In the presence of water, resting spores germinate to form sporangiophores, which bear sporangia. These release short-lived, motile zoospores. When these arrive on a suitable site (root or collar), they encyst and infect the plant cells via hyphae. Once the plant is infected, more chlamydospores, oospores, and/or sporangia are produced, thus completing the life cycle. Under water-logging conditions, rapid girdling of collars can occur. Symptoms, however, are often only observed following hot, dry periods when trees suddenly wilt as a result of reduced water uptake capacity.

1931 (Doidge & Bottomley 1931)
All provinces where forestry is undertaken in South Africa
Several species of Phytophthora have been implicated in diseases of wattle and eucalypts in South Africa. While the origin of a number of these remains unknown, it is likely that some are indigenous to South Africa, while others are known to be invasive alien species (e.g. P. cinnamomi, SE Asian origin).


Acacia mearnsii gummosis
Eucalyptus smithii collar rot
Eucalyptus smithii deaths
Collar lesion of Eucalyptus caused by P. cinnamomi
Rapid die back of Eucalyptus fastigata caused by Phytophthora root rot
Young Eucalyptus fastigata dying due to infection at base and root by P. cinnamomi
Phytophthora causing fine root rot

Bose T, Roux J, Burgess TI, Shaw C, Wingfield MJ. 2019. Susceptibility of Eucalyptus grandis and Acacia mearnsii seedlings to five Phytophthora species common in South African plantations. Forest Pathology 49: e12560.

Doidge EM, Bottomley AM. 1931. A revised list of plant diseases occurring in South Africa. Botanical Survey of South Africa 11: 1-78.

Maseko B, Burgess T, Coutinho T, Wingfield M. 2001. First report of Phytophthora nicotianae associated with Eucalyptus die‐back in South Africa. Plant Pathology 50: 413-413.

Roux J, Kemp GHJ, Wingfield MJ. 1995. Diseases of Black Wattle in South Africa - A Review. South African Forestry Journal 174: 35-40.

Roux J, Wingfield MJ. 1997. Survey and virulence of fungi occurring on diseased Acacia mearnsii in South Africa. Forest Ecology and Management 99: 327-336.

Wingfield MJ, Knox-Davies PS. 1980. Observations on diseases in pine and Eucalyptus plantations in South Africa. Phytophylactica 12: 57-63.