pink root
Beginner
Scientific Name: Phoma terrestris
Identification
- Light pink to yellowish-brown discolouration on roots that becomes dark pink/red and eventually purple in advanced stages of the disease
- Severely infected plants appear stunted, exhibit tip dieback and produce undersized bulbs
Often Confused with
Drought stress
Period of Activity
Infection occurs when soil temperatures become warm (24-28°C). Root infections are greatly reduced or may even cease altogether when soil temperatures cool down (16-20°C). Phome terrestris can infect a variety of host plants including many broadleaf weeds.
Scouting Notes
Severely infected plants appear stunted, exhibit tip dieback and produce undersized bulbs. The weakened leaves often become infected with other opportunistic pathogens such as Alternaria porri, which causes purple blotch.
Thresholds
None established.
Advanced
Scientific Name: Phoma terrestris
Identification
- Light pink to yellowish-brown discolouration on roots that becomes dark pink then red and eventually purple in advanced stages of the disease
- Severely infected plants appear stunted, exhibit tip dieback and produce undersized bulbs
Often Confused with
Drought stress
Biology
The fungus can infect many host plants (including other allium species) and broadleaf weeds. Pink root commonly occurs on onion roots of mature plants; however, if soil temperatures are warm enough in the spring, the pathogen can infect the roots of young plants resulting in severe losses.
Diseased roots eventually shrivel, become brittle and die. Although plants will attempt to compensate for the loss by producing new roots, these new roots often become infected and die. The pathogen does not infect the basal plate of onion bulbs. However, basal plate rot caused by Fusarium oxyspoum often occurs on plants with pink root when both pathogens are present in the soil.
Period of Activity
Infection occurs when soil temperatures become warm (24-28°C). Root infections are greatly reduced or may even cease altogether when soil temperatures cool down (16-20°C).
Scouting Notes
Severely infected plants appear stunted, exhibit tip dieback and produce undersized bulbs. The weakened leaves often become infected with other weak opportunistic pathogens such as Alternaria porri, the causal agent of purple blotch.
Thresholds
None established.
Management Notes
- Significant yield losses often occur under hot dry weather conditions
- Three to five year crop rotation with a non-host crop can significantly reduce the soil borne pathogen population levels of P. terrestris
- Resistant cultivars have been developed and should be planted in fields that have high soil population levels of the pathogen.
- Many of the early Japanese varieties appear to be very susceptible to this disease and should be avoided in heavily infested fields. Soil fumigation can also be used to reduce soil population levels.
