Citrus canker has become one of the most devastating diseases of citrus orchards in Pakistan, threatening both local fruit supply and export potential. Caused by the bacterium Xanthomonas citri subsp. citri, it affects leaves, stems, and fruits of nearly all citrus varieties. The disease is recognized by its corky, raised lesions surrounded by yellow halos, which severely downgrade fruit quality and reduce yield.
Pakistan is globally known for its delicious Kinnow mandarins and other citrus varieties. Yet, this valuable industry now faces growing losses every year due to citrus canker. Farmers in major citrus zones such as Sargodha, Mandi Bahauddin, Toba Tek Singh, and Sahiwal report increasing cases of infection, particularly during humid and rainy seasons.
Impact on Pakistan’s Citrus Industry
The citrus sector contributes significantly to Pakistan’s rural economy, with citrus covering more than 200,000 hectares of land, mostly in Punjab province. The Kinnow variety alone accounts for more than 80% of citrus exports.
However, citrus canker is now one of the primary reasons for export rejections in international markets because many importing countries enforce zero-tolerance quarantine policies against the disease. Even a few visible canker lesions can disqualify a shipment, leading to heavy financial losses.
Climatic conditions in Punjab like warm temperatures, high humidity, and frequent monsoon rains are favorable for the survival and spread of Xanthomonas citri. The bacterium easily spreads through wind-driven rain, pruning wounds, leaf miner injuries, and infected nursery plants. Once established in an orchard, complete eradication is nearly impossible, making preventive and integrated management essential.
Symptoms of Citrus Canker and Disease Development
The first signs of citrus canker appear as small, water-soaked spots on leaves that later become corky and raised, surrounded by distinct yellow halos. On fruits, these lesions appear rough, scabby, and brown, often leading to fruit drop. Twigs may develop similar lesions that cause dieback and reduce flowering.
The bacterium survives on infected debris, fallen leaves, and nursery stock. It enters through natural openings (stomata) or wounds, and disease outbreaks are typically worse after heavy rain and strong winds. In Pakistan, the disease peaks from August to October and again during the spring flush when new tender growth is abundant.
Integrated Management Practices
Effective management of citrus canker in Pakistan relies on a combination of preventive, cultural, and chemical control measures. Relying on any single method, especially chemical sprays alone, often leads to temporary results and potential bacterial resistance. An integrated disease management (IDM) approach ensures long-term control.
1. Orchard Sanitation
Use only certified, disease-free nursery plants. Prune and destroy all infected leaves, twigs, and fruits away from the orchard. Always disinfect pruning tools with 10% sodium hypochlorite or 0.5% copper sulfate solution after every use. Keeping orchards clean significantly reduces bacterial inoculum.
2. Cultural Practices
Avoid overhead irrigation that splashes water on leaves and spreads bacteria. Instead, use drip or furrow irrigation. Establish windbreaks (such as poplar or eucalyptus trees) along orchard borders to limit wind-driven spread.
Balanced fertilization helps, as too much nitrogen promotes tender growth susceptible to infection. Managing leaf miner infestations is also vital because their feeding damage opens pathways for bacterial entry.
3. Chemical Control in Citrus Orchards
Chemical sprays are crucial for controlling citrus canker, especially during vulnerable growth stages. The main objective is to reduce bacterial populations and protect new flushes from infection. Regular sprays during humid or rainy periods are highly recommended.
1. Copper-Based Bactericides:
Copper compounds remain the backbone of citrus canker control. Commonly used products include Copper Oxychloride (50% WP), Copper Hydroxide (77% WP), and Bordeaux Mixture (1%).
- Dose: 2.5–3.0 grams per liter of water
- Interval: Every 15–20 days during the growing season
- Combination: Often mixed with Mancozeb (2 g/L) to improve effectiveness and reduce copper accumulation
Copper provides protective coverage on leaves and fruits but should not be overused, as excessive application can cause phytotoxicity and soil buildup. Rotation with antibiotics like Kasugamycin and Streptomycin is recommended for better results.
2. Kasugamycin:
Kasugamycin is among the most effective bactericides for controlling citrus canker. It inhibits bacterial protein synthesis, reducing lesion formation and spread.
- Formulation: Commonly available as Kasugamycin 2% AS or 3% SL
- Recommended dose: 0.2–0.3 grams per liter of water
- Timing: Spray during new flush emergence and after pruning; repeat every 15–20 days
- Compatibility: Can be safely tank-mixed with copper sprays for extended protection
Kasugamycin has shown excellent results in field trials in Punjab and Sindh, where it significantly reduces active lesions and prevents new infections. It is currently one of the most reliable bactericides for citrus canker management under local conditions.
3. Streptomycin Sulfate:
Streptomycin is another highly effective antibiotic against Xanthomonas citri. It is best used alternately with Kasugamycin or copper to avoid resistance development.
- Formulation: Streptomycin Sulfate 17% WP
- Dose: 0.5–1.0 grams per liter of water
- Interval: Every 15 days during active growth or after rainfall
This bactericide is particularly useful during high-humidity periods and provides strong protection for young leaves and fruit surfaces. However, responsible use is essential as overuse can lead to bacterial resistance and residue concerns.
Note: Ensure uniform coverage of both leaf surfaces and fruit and avoid spraying during extreme heat to prevent phytotoxicity.
Table 1: Recommended Spray Schedule for Pakistani Orchards
| Stage | Chemical | Dose (per L of water) | Purpose |
|---|---|---|---|
| Early flush | Kasugamycin + Mancozeb | 0.25 g + 2.0 g | Prevent early infection |
| 15 days later | Copper Oxychloride | 2.5–3.0 g | Protective cover |
| After rainfall | Streptomycin + Copper Hydroxide | 0.75 g + 2.0 g | Control renewed infection |
| Ongoing | Rotate Kasugamycin and Copper | every 20 days | Maintain protection |
Future Outlook and Research Directions
Long-term citrus canker management in Pakistan requires more than just chemicals. Researchers are working to develop canker-resistant citrus varieties using traditional breeding and modern biotechnology tools like CRISPR/Cas9 gene editing. Biological control using beneficial bacteria such as Bacillus subtilis and Pseudomonas fluorescens also shows promise for sustainable management.
Government initiatives should focus on certified nurseries, grower training programs, and strict quarantine enforcement to prevent disease spread through plant material. Collaboration between research institutions like the Citrus Research Institute (Sargodha) and private sector nurseries can strengthen national citrus health programs.
Conclusion
Citrus canker remains a persistent challenge for Pakistan’s citrus industry, causing heavy yield and export losses each year. However, the disease can be effectively controlled through integrated management i.e. by combining Kasugamycin (0.25 g/L), Streptomycin (0.75 g/L), and Copper-based sprays (2.5–3.0 g/L) with good orchard hygiene and preventive practices. Protecting citrus orchards from canker is not just a farmer level responsibility; it is essential for maintaining Pakistan’s global citrus reputation and ensuring the livelihood of thousands of growers who depend on this golden fruit.
Contributing Author:
1. Usama Ahmad (Department of Plant Pathology, University of Agriculture, Faisalabad. Email: [email protected])
