Symptoms:The disease appears on leaves, branches and fruits. The damage is particularly severe in young trees that may flush many angular shoots, resulting in significantly retarded growth or sometimes death of the affected plants.
On young leaves small yellowish water soaked spots develop first on the lower surface and then on the upper surface. In the beginning, these spots are small and scattered. These later turn brown, corky, hard and raised with a yellow halo around them. These spots increase in number and size. The diseased areas become dead and sometimes drop out leaving holes in the leaves. Similar diseased spots (without yellow halo) develop on twigs and fruits. Fruit fall is also common.
Causal organism:Xanthomonas axonopodis pv citri
The disease enters a garden through diseased nursery plants or through small bits of diseased material, which is carried by wind from the neighbouring diseased gardens. The causal organism remains in the diseased material and becomes active under favourable conditions of temperature and moisture especially after rains. The dissemination takes place by splashing rain as well as by contact. Leaf miner and injury by thorns are also potent agents, aiding in the dissemination of the pathogen.
The disease is favoured by mild (20-30 °C) and wet weather. Presence of free moisture for at least 20 minutes is essential for successful infection.
Control:
- Use of healthy nursery plants.
- Removal and burning of diseased plant portions.
- Windbreaks should be set around the citrus groves.
- Periodic spraying of insecticide to control citrus leaf miner.
- Spray of Bordeaux mixture or any other copper compound or streptomycin compounds during the active growth of new shoots (from January to May) and rosin Bordeaux mixture in July and September.
