Gummosis / foot rot (citrus)
Bark rot at the trunk base and collar oozing gum, girdling the trunk and rotting the roots — a wet-soil Phytophthora that declines and kills the tree.
- Pathogen
- Phytophthora (soil-borne, fungus-like)
- Spreads by
- Soil & splashing water; wet trunk base
- Favoured by
- Waterlogging; low graft union; wet trunk
- Main risk
- Bark & root rot; tree declines and dies
Overview
Gummosis (foot rot / collar rot) of citrus is caused by soil-borne Phytophthora, and is one of the main causes of citrus tree decline. It rots the bark at the base of the trunk and the root collar, often near the graft union; the affected bark turns dark, dies and cracks, and a characteristic gum (resin) oozes out from the cracks and runs down the trunk. As the rot girdles the trunk, and as Phytophthora also rots the feeder roots, the tree is progressively cut off from water and nutrients.
Above ground the tree shows the signs of a girdled, root-rotted plant: yellowing, sparse foliage, leaf and fruit drop, twig dieback, poor growth and, in severe cases, death. It is strongly driven by wet, poorly-drained soil, waterlogging around the trunk, and by planting the graft union too low so the susceptible scion bark sits near the soil. Because it is soil- and moisture-driven, management combines a resistant rootstock and high grafting/planting, good drainage, keeping the trunk base dry, and treating affected bark with copper.
How to identify it
- Dark, dead, cracked bark at the base of the trunk and root collar, often near the graft union.
- A characteristic gum (resin) oozing from the cracks and running down the trunk.
- Rotted feeder roots and a trunk being girdled by the spreading bark rot.
- Above ground: yellowing, sparse foliage, leaf and fruit drop, twig dieback and decline, and sometimes death.
What causes it and when
- Soil-borne Phytophthora, which rots the bark at the trunk base/collar and the feeder roots.
- Spread and splashed by soil and water, and favoured by wet, poorly-drained soil and waterlogging around the trunk.
- Made much worse by planting the graft union too low, so the susceptible scion bark sits near wet soil.
- Worst in the wet season and in heavy, poorly-drained or over-irrigated orchards.
Cultural & organic control
- Use a Phytophthora-resistant rootstock and plant with the graft union well above the soil (high planting/grafting).
- Ensure excellent drainage, avoid waterlogging, and keep irrigation water away from the trunk base (no basin against the trunk).
- Keep the trunk base dry and clean, avoid injuries, and avoid heaping soil or mulch against the trunk.
- Remove and destroy severely affected trees, and avoid moving infested soil/water into clean areas.
Chemical control
- On an early lesion, scrape out the dead bark to healthy tissue and paint the wound and trunk base with a copper (Bordeaux) paste/fungicide.
- Apply recommended Phytophthora fungicides (e.g. copper-based, metalaxyl or phosphonate as advised) to the trunk base and root zone where recommended.
- Combine any chemical with fixing drainage and the trunk-base moisture — chemicals alone will not overcome waterlogging.
- Confirm the current rootstock choice and fungicide package for your area with your local KVK.
Prevent it coming back
- Establish orchards on resistant rootstocks with a high graft union and excellent drainage.
- Keep the trunk base dry — irrigate away from the trunk, no soil/mulch heaped against it — and avoid injuries.
- Scrape and treat early lesions promptly, and manage soil moisture through the wet season.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
My citrus trunk base has dark cracked bark oozing gum, and the tree is declining. What is it?
Dark, dead, cracked bark at the trunk base and collar oozing gum, with rotted roots and a yellowing, declining canopy, is gummosis / foot rot (Phytophthora). It is driven by wet, poorly-drained soil and a low graft union. Scrape the dead bark to healthy tissue and paint with copper paste, fix drainage and keep the trunk base dry, and replant on a resistant rootstock with a high graft union. Severe trees are best removed.
Why does planting the graft union high help against gummosis?
Because gummosis is a rot of the susceptible scion bark at the trunk base, and it is worst where that bark sits near wet soil. Planting so the graft union is well above the soil keeps the vulnerable scion bark up and dry, out of the zone of splashing water and waterlogging where Phytophthora attacks. Combined with a resistant rootstock (whose bark resists the fungus), good drainage and keeping the trunk base dry, high grafting is one of the most effective preventive steps.
How is gummosis linked to drainage and irrigation?
Very closely — Phytophthora is a water-loving, soil-borne organism, so waterlogged, poorly-drained soil and water standing against the trunk strongly favour the bark and root rot. Orchards with poor drainage, heavy soils or basins that wet the trunk base suffer far more. Ensuring excellent drainage, irrigating away from the trunk (not in a basin against it), and keeping the trunk base dry are therefore central to control — chemicals alone cannot overcome a constantly wet trunk base.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.