Organism
Phytophthora species
Water moulds of wet soils that cause collar and crown rot in apple trees and rot fruit lying on wet ground, and the reason orchard drainage is a disease measure.
Also called collar rot, crown rot, water mould.
- Kind
- Mould
- Binomial
- Phytophthora spp.
- Role
- Spoilage
What it does
- Produces motile zoospores that swim in free soil water, so infection depends on waterlogging and the disease is a direct consequence of drainage rather than of weather alone.
- Rots the bark and cambium at the collar and crown of the tree, girdling it below ground where the damage is invisible until the canopy declines.
- Rots fruit lying in contact with wet ground, giving the firm, brown, leathery rot that appears on windfalls in a wet autumn.
- Persists in soil as resting structures, so an infested site remains infested and replanting decisions have to account for it.
Conditions it works in
What the organism tolerates and what suppresses it. These are the levers a maker actually has: temperature, acidity, air, alcohol and sulphite.
| Condition | What is recorded |
|---|---|
| Temperature | Active from roughly 10 °C to 30 °C depending on species, with cool wet springs and warm wet autumns both favourable. |
| Oxygen | Aerobic, but dependent on free water for zoospore movement — the defining requirement. |
Faults it causes
Faults this organism is implicated in. Several are faults only against a particular expectation — the same activity is a signature elsewhere.
Mould taint
Musty, earthy, cellar-damp or rotten-fruit character carried in from mouldy fruit or from mouldy equipment, and a marker that the patulin question needs asking.
Microbial haze
Cloudiness caused by a growing population of spoilage organisms, and therefore a symptom of something worse rather than a clarity problem in itself.
Where in the process it appears
Soil and drainage
Assessing and correcting soil depth, structure, pH and water movement so that orchard roots get both water and air across a wet winter and a dry summer.
Site selection
Choosing the ground an orchard will stand on, weighing frost drainage, exposure, soil depth and season length decades before the first full crop is picked.
Orchard planting
The establishment operation itself — tree quality, timing, planting depth, support and protection — which decides whether a young orchard grows away in its first two seasons or never catches up.
Rootstock choice
Selecting the root system a cider cultivar is grafted onto, which fixes tree size, how soon it crops, how long it lives and what soil and orchard system it will tolerate.
Pest and disease management
Keeping scab, canker, rots and the main insect pests to a level the orchard can carry, at a cosmetic standard well below dessert fruit but without allowing rot into the crop.
Windfall management
Deciding which fruit that has reached the orchard floor can be used, and getting the rest out of the crop before it becomes a patulin problem.
Fruit sorting
Taking rotten, mouldy and damaged fruit and foreign material out of the crop before it reaches the mill, which is the primary control on patulin in cider.
Replanting and orchard renewal
Replacing an orchard at the end of its life or filling its gaps as they appear, and dealing with the specific problem of planting apple where apple has already stood.
About Phytophthora species
Phytophthora is not a true fungus. It belongs to the oomycetes, a lineage more closely related to brown algae than to the moulds it superficially resembles, and CiderHQ groups it under `mould` because the entity model offers no closer category rather than because the classification is correct. Its biology follows from that difference: it produces swimming zoospores and needs free water to move them, which is why Phytophthora diseases are diseases of wet ground.
In an orchard the main damage is collar and crown rot. The fungus attacks the bark at and below soil level, girdling the tree out of sight, and the first symptom a grower sees is usually a tree in decline for no visible reason. Rootstock choice matters here — susceptibility differs between rootstocks — and so does the fundamental decision about where to plant. A heavy, poorly drained site is a Phytophthora site.
Its second relevance is at harvest. Fruit collected off wet ground, particularly in a wet autumn on a heavy soil, carries Phytophthora fruit rot along with soil, other rot organisms and the acetic acid bacteria that colonise damaged tissue. This is one of the practical arguments for shaking and collecting promptly rather than leaving windfalls lying, and for sorting whatever is collected.
What people ask next
Questions readers ask about the things this page mentions. Each one goes to the section that answers it rather than to a page written to receive the question.
- What makes a good site for a cider orchard — Frost drainage first, then soil depth and water. A hollow that traps cold air on a May night can lose a crop at blossom, and no later decision recovers it.
- Can you use windfall apples for cider — Traditional cider making relies on fruit gathered from the ground, and there is nothing wrong with it if it is sound. Rotten fruit is a different matter: brown rot carries patulin into the juice and should be discarded, not pressed.
- What rootstock should i use for cider apples — Rootstock sets tree size, how soon it crops and how long it lives. Traditional standard orchards used vigorous or seedling stocks for large, long-lived trees; modern bush orchards use semi-dwarfing stocks that crop early and can be machine-harvested.
- Do you need to sort apples before pressing
- What is mould taint in cider
- What is microbial haze
Where to go next
- All organisms — Grouped by what each does in the ferment, and by what kind of organism it is.
- Compounds — The chemistry this microbiology produces.
- Troubleshooting — Work from the symptom in the glass back to the organism.
Sources
What this page rests on. Where a source is marked as registered rather than read, CiderHQ is recording that the body is authoritative on the subject without claiming to have worked through the document itself. See our evidence policy for what each state means.
NIAB (incorporating East Malling Research)
NIAB · research institute · retrieved 2026-08-24
East Malling developed the M-series apple rootstocks that determine tree size in essentially every modern orchard, cider orchards included. The authority CiderHQ uses for rootstock behaviour.