Canker is one of the most widespread and serious diseases of citrus in India. This disease is a major constraint in citrus, especially in Acid lime (nimboo) cultivation. Sometimes it becomes difficult to locate acid lime orchard completely free from canker infection.

The diseased plants are characterized by the occurrence of conspicuous erumpent lesions that develop on leaves, twigs and fruits. Canker lesions start as pinpoint spots and attain a diameter of 3-10 mm. In leaves, a yellowish halo often surrounds the lesion. Severe infection results in defoliation, dieback and premature fruit drop.

Loss

Canker cause fruit losses from abscission and non-marketable quality due to lesions. In fact, the canker-affected fruits do not attract the consumers on large scale and fetch very little price in the fresh market.

The disease is caused by the bacteria Xanthomonas axonopodis pv.citri (= X. campestris pv.citri). It is a short, rod shaped, motile and gram negative bacterium.

The bacteria survive in lesions in leaves, twigs and branches which constitute the source of inoculum to spread the disease from season to season. Bacteria from the canker lesions are disseminated mostly by wind splashed rains. Other means of short-distance dissemination include insects (e.g. leaf miner), contaminated pruning and harvesting tools. The long-distance dissemination takes place through diseased planting material. Infection by the bacteria occurs primarily through stomata, other natural openings and wound formed due to strong winds and insects.

The disease is most severe in hot, wet cloudy climate, particularly during rainy season. Temperature between 25-30˚C with evenly distributed rains is most suitable for the disease.

Severity of canker infection varies with the species and varieties of citrus and the prevailing climatic conditions. In our country, citrus canker infestation is relatively more on acid lime (nimboo) and less common on mandarin (santra) and sweet orange (mosambi).

1. Use of canker-free nursery tree.
2. Pruning and destruction of infected twigs.
3. Three to four sprays with copper oxychloride (COC) 0.3% + streptocycline 100 ppm at monthly intervals after the onset of monsoon.

1. After pruning, the tools (secateur etc.) should be disinfested with 1.5% Sodium hypochlorite solution or 5% Formalin.
2. Pruned twigs should be burnt immediately.
3. New flush of the tree should be sprayed properly.
4. Sanitary measures like cutting of grasses, clean cultivation should be undertaken.
5. Additional spray should be given during unseasonal, intermittent rains.
6. There should be restricted movement of plant material from canker-infested to non-infested areas.