---
title: Phytophthora
canonical: https://fernland.com.au/problem-solver/phytophthora/
dateModified: 2026-08-07 09:45:11
summary: "Phytophthora is a soil- and water-borne pathogen causing root, collar and stem rot in nursery, landscape and turf plants, especially in wet, poorly drained conditions."
type: article
keywords: [Phytophthora, Phytophthora spp.]
---

# Phytophthora

> Phytophthora is a soil- and water-borne pathogen causing root, collar and stem rot in nursery, landscape and turf plants, especially in wet, poorly drained conditions.

*Phytophthora spp.*

Phytophthora is a genus of water mould (oomycete) pathogens, not a true fungus, though it is managed similarly. It survives in soil and water as thick-walled resting spores (chlamydospores and oospores) that can persist for years in the absence of a host. Under wet conditions it produces sporangia which release swimming zoospores; these move through free water in the soil profile to infect roots, root crowns and lower stems, and can also be splashed onto foliage and fruit in some hosts.

On affected plants there are no distinctive spore masses visible to the naked eye in the way many leaf-spot fungi show; instead the diagnostic sign is internal. Cutting into the collar or root crown of an affected plant typically reveals a reddish-brown to dark brown discolouration of the tissue just under the bark or epidermis, often with a sharp margin between healthy white/cream tissue and the diseased area. Fine feeder roots are commonly rotted, dark and slough off easily, leaving a stringy central core when gently pulled through the fingers.

Phytophthora species are widespread across Australian nursery, landscape, turf and orchard situations. Disease pressure rises sharply after heavy rain, overhead irrigation, or in any situation where soil stays saturated for extended periods — poorly drained garden beds, overwatered pots, compacted turf, and low-lying areas prone to waterlogging. Warm to mild temperatures combined with free water are the key drivers; disease can appear at any time of year given the right moisture conditions, though outbreaks are most common in warmer wet seasons.

Management is based on avoiding the conditions that favour the pathogen: improving drainage, avoiding over-irrigation, raising root crowns above grade, using clean potting media and hygienic propagation practices, and avoiding movement of infested soil or water between sites. Resistant rootstocks and species selection are useful where available. Chemical control is preventative or suppressive rather than curative once significant rot has occurred, so early detection and cultural correction of wet-soil conditions are the priority.

## How to identify

- **Above-ground decline:** wilting, off-colour or sparse foliage, poor vigour, dieback of shoot tips or branches, and sudden collapse of otherwise healthy-looking plants, often appearing out of proportion to any visible leaf disease.
- **Collar and root symptoms:** dark, sunken or water-soaked lesions at the soil line, bark that lifts or peels easily from the collar, and a foul, poorly drained smell from affected root zones.
- **Root system:** feeder roots are brown to black, soft or slimy, and easily pulled apart, in contrast to healthy roots which are white to cream and firm.
- **Turf:** irregular patches of thinning or yellowing turf that do not respond to fertiliser, often in low or poorly drained areas; peeling back affected turf shows rotted, discoloured root and crown tissue rather than the intact white roots of healthy turf.
- **Field check:** cut through the collar or a root cross-section — a sharp brown-versus-white margin between diseased and healthy tissue is a strong indicator of Phytophthora; confirmation requires laboratory isolation or a diagnostic test, as field symptoms alone cannot distinguish Phytophthora species from each other.
- **Lookalikes:** Pythium causes similar damping-off and root rot but tends to produce softer, more watery root decay without the distinct discoloured margin; waterlogging or salt injury alone can cause similar wilting and root browning without any pathogen present, so persistent wet soil with no drainage issue corrected should raise suspicion of Phytophthora rather than abiotic stress alone.

## Registered products we stock

- [Banrot 400WP Fungicide](https://fernland.com.au/banrot-400wp-fungicide/) — ICL
- [Agri-Fos 600 Systemic Fungicide](https://fernland.com.au/agri-fos-600-systemic-fungicide/) — AgriChem
- [Phytoclean Specialised Disinfectant Cleaner & Sanitiser](https://fernland.com.au/phytoclean/) — Phytoclean
- [Copper Oxychloride Fungicide](https://fernland.com.au/copper-oxychloride-fungicide/) — Amgrow Specialty Agriculture
- [Phosfusion 600 | Fungicide](https://fernland.com.au/phosfusion-600-fungicide/)
- [Root Rot Systemic Fungicide](https://fernland.com.au/root-rot-systemic-fungicide/) — Searles
- [Banrot 80G Fungicide](https://fernland.com.au/banrot-80g-fungicide/) — ICL
- [Magellan 800WG Systemic Fungicide](https://fernland.com.au/magellan-800wg-systemic-fungicide/) — Adama

## Image credits

- [Photo: Don Ferrin, Louisiana State University Agricultural Center, Bugwood.org via Wikimedia Commons (CC BY 3.0)](https://commons.wikimedia.org/wiki/File:5411484-PPT-Phytophthora_blight_(Phytophthora_capsici).jpg)
- [Photo: Jerzy Opioła via Wikimedia Commons (CC BY-SA 4.0)](https://commons.wikimedia.org/wiki/File:Rhododendron-Phytophthora_Root_Rot_(2).jpg)
- [Photo: Jerzy Opioła via Wikimedia Commons (CC BY-SA 4.0)](https://commons.wikimedia.org/wiki/File:Rhododendron-Phytophthora_Root_Rot_(3).jpg)
- [Photo: Rasbak via Wikimedia Commons (CC BY-SA 3.0)](https://commons.wikimedia.org/wiki/File:Prei_papiervlekkenziekte_Phytophthora_porri_on_Allium_porrum.jpg)