Hass avocado farming has grown significantly in Kenya due to high local and export demand. However, successful production depends not only on good agronomic practices but also on effective disease management. If left unchecked, diseases can drastically reduce yields, quality, and even wipe out entire orchards. This article highlights the major diseases that affect Hass avocado plants, their symptoms, causes, and practical control measures.
1. Anthracnose (Colletotrichum gloeosporioides)
Symptoms:
- Black, sunken lesions on ripening fruits.
- Leaf spots and twig dieback.
- Fruits may rot during storage or transport.
Causes:
- Caused by a fungal pathogen that thrives in warm, humid environments.
- Spread by rain splash, wind, or contaminated tools.
Control Measures:
- Prune trees to improve air circulation.
- Apply copper-based fungicides during flowering and early fruit development.
- Remove and destroy infected plant parts.
- Harvest fruits carefully to avoid injuries.
2. Root Rot (Phytophthora cinnamomi)
Symptoms:
- Yellowing and wilting of leaves.
- Stunted growth and poor fruit production.
- Root system appears dark, decayed, and brittle.
Causes:
- Caused by a water mold (oomycete) present in poorly drained soils.
- Excessive watering and flooding favor its spread.
Control Measures:
- Plant in well-drained soils or raised beds.
- Use disease-free planting materials.
- Apply phosphonate-based fungicides.
- Avoid overwatering and improve drainage systems.
- Graft onto Phytophthora-resistant rootstocks like Duke 7.
3. Powdery Mildew (Oidium spp.)
Symptoms:
- White or grey powdery coating on leaves, stems, and flowers.
- Flower and fruit drop in severe cases.
Causes:
- Caused by fungal spores that thrive in dry, warm environments with poor air circulation.
Control Measures:
- Regular pruning to allow better airflow.
- Apply sulfur-based or systemic fungicides.
- Monitor regularly, especially during dry seasons.
4. Sunblotch Viroid
Symptoms:
- Yellow or white streaks on leaves and fruits.
- Cracking and scarring on fruits.
- Stunted tree growth and yield reduction.
Causes:
- Caused by a viroid (sub-virus-like agent) transmitted through infected propagation material or contaminated tools.
Control Measures:
- Use certified, virus-free seedlings and scions.
- Sanitize tools between tree pruning or grafting.
- Remove and destroy infected trees to avoid spread.
5. Cercospora Spot (Pseudocercospora purpurea)
Symptoms:
- Small brown or purple spots on leaves, fruits, and stems.
- Lesions enlarge over time, leading to fruit blemishes and early drop.
Causes:
- Fungal disease that thrives in humid conditions.
Control Measures:
- Spray fungicides (like Mancozeb or copper-based products) during fruit development.
- Improve orchard hygiene by removing fallen leaves and fruits.
- Space trees adequately for airflow.
6. Armillaria Root Rot (Armillaria mellea)
Symptoms:
- Yellowing of leaves and dieback.
- White fungal mats under the bark near the base.
- Tree collapse in advanced stages.
Causes:
- Caused by soil-borne fungi that infect tree roots, especially in previously forested areas.
Control Measures:
- Avoid planting Hass avocado in sites with known Armillaria presence.
- Remove infected stumps and roots before planting.
- Improve drainage and avoid root injuries.
7. Scab (Sphaceloma perseae)
Symptoms:
- Dark, corky scabs on immature fruit, leaves, and twigs.
- Deformed fruits and premature drop.
Causes:
- Fungal disease spread by rain, wind, and insects.
Control Measures:
- Prune infected branches and destroy affected plant parts.
- Apply preventive fungicides early in fruit development.
- Ensure good orchard sanitation.
Best Practices for Disease Prevention
To reduce the impact of diseases on Hass avocado farms, farmers should adopt the following integrated disease management strategies:
- Use Certified Planting Materials: Always source seedlings from reputable nurseries that provide disease-free, grafted avocado plants.
- Proper Spacing and Pruning: Ensure adequate spacing to reduce humidity and improve airflow.
- Regular Monitoring: Early detection helps prevent the spread of infections.
- Sanitation: Clean tools, remove infected plant parts, and maintain orchard hygiene.
- Fungicide Application: Apply recommended fungicides at key stages, especially during flowering and early fruit set.
- Water Management: Avoid waterlogging and ensure proper drainage to prevent root diseases.
Conclusion
Diseases are a major threat to Hass avocado production in Kenya, but with early detection and proper management practices, they can be effectively controlled. Farmers should be proactive, monitor regularly, and seek professional agronomic support when symptoms appear. A healthy avocado tree is the foundation for a profitable orchard and successful export business.
