Divisi
Phytophthora root rot
Phytophthora cinnamomi · Fungal
Photo: Scot Nelson from Honolulu, Hawaii, USA · CC0
Phytophthora root rot (Phytophthora cinnamomi) is a soil-borne water mould — think of it as a mould that swims. It lives in wet, poorly drained soil and rots the fine feeder roots of trees like avocado, macadamia, citrus and pineapple, so the tree slowly starves of water and food even while standing in wet ground. It spreads in run-off water, mud on boots and tools, and in infected nursery plants, and once it is in your soil it stays for years.
Why it matters
This rot attacks the fine roots that feed your trees, so a tree can be dying of thirst while its feet sit in wet soil. On a badly hit, waterlogged block it can take your whole crop — up to 100% of the trees can decline and die. It is so hard to beat because it hides underground where you cannot see it, it survives in the soil for years, and by the time the leaves show it the roots are already badly damaged — so stopping the wet and catching it early is everything.
When to act
First trees showing unexplained canopy thinning or dieback on wet ground; investigate roots and act on drainage before spread
This guidance is general, compiled from published agronomic references including FAO and CABI. Thresholds and timing shift with your crop, your variety and the season.
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The full phytophthora root rot field guide
- Identify it
- Scout for it
- Control it
13 field-guide sections in the app
The full guide to phytophthora root rot — every symptom to check, how and when to walk your field looking for it, and the controls that actually work, ranked. Built into your crop plan, so you are told to look before it costs you a harvest.
Crops it affects
Frequently asked questions
How do I identify phytophthora root rot?
What you see first (above ground): the top of the tree tells you before the roots do. The canopy thins out and the leaves go small, pale and yellow-green, then hang and wilt even though the ground is wet. Fruit stays small and the tree looks 'hungry' no matter how you feed it.
When should I take action against phytophthora root rot?
First trees showing unexplained canopy thinning or dieback on wet ground; investigate roots and act on drainage before spread
How do I control phytophthora root rot?
Prevent it — keep the feet dry (your strongest tool): this mould needs wet soil to live and swim, so drainage is your best defence. Plant new trees on well-drained ground or raised mounds/ridges, cut drains to carry water away, and never over-irrigate or let water pond around the trunks. Dry roots starve the mould before it starts.
Which crops does phytophthora root rot affect?
Among the crops covered here: Avocado, Pineapple.
Catch it before it costs you a harvest
Divisi builds scouting into your crop plan — it tells you when to walk your field, what to look for at that stage, and what to do when you find it. Free for farmers, works offline.
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