citrus root and foot rot

Symptoms

Dark gummy lesions on trunk base, yellowing leaves.

Plants affected

• sweet orange
• mandarin

Easily confused with

• Mal secco

  How to tell them apart: Plenodomus tracheiphilus (mal secco) is a vascular wilt: look for sudden dieback starting at the shoot tips and one-sided 'flagging' of branches, with leaves turning yellow then dropping while the petiole often stays attached. The diagnostic sign is internal — cut a wilting twig and you see a pink-to-salmon or orange discoloration of the wood under the bark; new shoots emerging from the trunk also show this stain. Phytophthora citrophthora attacks the base, not the canopy first: look at the trunk crown and major roots for dark, water-soaked bark that oozes amber gum (gummosis), with the bark cracking and peeling away to reveal a brown, rotted, sour-smelling inner layer at the soil line. Mal secco's damage runs from the top down through the vascular system; Phytophthora's runs from the soil line up, and the wood under a mal-secco twig is stained pink whereas a Phytophthora trunk shows surface gum and rotted bark.

• citrus tristeza virus

  How to tell them apart: Citrus tristeza virus (CTV) decline shows up in the canopy first, with no rot at the trunk base: leaves turn pale and yellow with vein-clearing or vein-yellowing, the foliage cups and thins, and on susceptible sour-orange rootstocks the whole tree wilts and collapses suddenly (quick decline). Peel back bark just above the bud union on such trees and you see honeycomb-like pitting and a brown line of dead tissue at the graft, while the trunk base stays firm and dry. On grapefruit and some sweet-orange wood you also find stem pitting: long narrow grooves under the bark on twigs and branches. There is no gum, no soil-line lesion. Phytophthora citrophthora attacks from the soil and trunk base: look for dark, water-soaked bark cankers at the crown/foot that ooze amber-brown gum (gummosis), with the bark drying, cracking and sloughing off to expose dead brown wood right at or just below soil level. Scrape the feeder roots and they are blackened and rotten with a sour smell, and after rain you may see brown rot lesions on low-hanging fruit. The yellowing canopy and dieback here are a downstream consequence of the rotted roots and girdled trunk, so the tell-tale damage is low (collar, roots, soil line), not in the bud-union wood. No honeycomb bark pitting.

Common questions

How do I recognise citrus root and foot rot on sweet orange?

Dark gummy lesions on trunk base, yellowing leaves.

Do I have to report citrus root and foot rot?

No. citrus root and foot rot is not a notifiable organism, so there is nothing to report to an authority. Treat it as a normal garden problem.

How is citrus root and foot rot treated?

Mainly with biological and cultural measures — removing affected material, changing the conditions that favour it, and treating with agents approved in your country. The exact steps and their timing depend on the plant, the season and where you live: Dr. Phyto works them out in a free diagnosis.