Collar rot usually occurs on the trunk close to ground level causing bark to flake and wood to rot.

At first, you may notice exuding gum followed by damp, soft bark. Later the bark in this area may become dry and flake off. Badly affected trees will fail to produce new growth and will eventually die.

Lemons are the most susceptible, but all citrus trees can be affected. Many citrus trees are grafted on disease-resistant rootstocks; when planting make sure the graft union is well clear of the ground and organic material is clear of the trunk.

Control:
Treat by cutting away damaged bark to expose healthy bark and clean wood. Paint with a paste of an approved chemical.