Citrus canker
A bacterial disease of lemon and lime that causes raised, corky spots with yellow halos on leaves, twigs and fruit.
Also known as: Xanthomonas canker
Symptoms and identification
Small, raised, rough brown spots surrounded by a yellow halo on both sides of leaves, on young twigs and on fruit. Severely affected leaves and fruit drop early, and fruit is blemished.
Causes
Xanthomonas bacteria spread by wind-driven rain, pruning tools and infected plants. Leaf miner tunnels give the bacteria easy entry.
Organic treatment
Prune out and burn or bin infected twigs during dry weather. Spray a copper-based fungicide after pruning and before the monsoon, repeating every 3–4 weeks in wet weather.
Prevention
Buy healthy, certified plants, control leaf miners on new growth, and disinfect pruning tools between trees.
Chemical treatment (use with care)
Copper oxychloride combined with streptocycline (where approved) is widely recommended; follow local agricultural guidance and the label.