Disease/Disorder Collection – Phytophthora Root Rot
Name of Disorder: Phytophthora Root rot.
Scientific name of pathogen causing disease: Phytophthora spp.
Type of disorder: Fungus
Cause: Phytophthora spp. fungus
Host plant where found: Rhododendron
Horticulture situation or host range where this disorder is typically found: Affects broad range of plants; from trees, ornamentals, native plants, fruit trees and vegetable crops.
Plant symptoms: Wilting leaves with brown tips and margins during early stages. Brown tissue under bark on stem at ground level. Plant has reduced root system with black/brown, rotted outer areas.
Spread: By water, zoospores spread in surface drainage water. Windblown contaminated dust. Through soil by means of contaminated tools, machinery, equipment etc. Movement of infected plants. Infected propagation material. Numerous animals may spread the disease by disturbing infected soil.
Conditions favouring: Stress, such as root damage, continuous cropping of susceptible crops. Long wet periods or excessive irrigation. Poorly draining soil, warm moist aerated soil. Poor soil structure and soils low in organic matter and micro-organisms.
Control options suitable for this situation: Remove dead plant; treat remaining Rhododendrons and Azaleas in shrub bed with a fungicide such as Phospot. Improve irrigation practices by managing when and how much water is applied to bed.
Identification Reference(including page no): Plant protection 3, p K28; Plant protection 1, p 364 – 370
The above information was kindly donated by Werner (Horticulturalist)
