Litchi downy blight

Litchi downy blight is a devastating fungal-like disease caused by the oomycete Phytophthora litchii. This pathogen is considered one of the most serious threats to litchi production worldwide, specifically impacting orchards in humid tropical and subtropical climates.

The infection targets all aerial parts of the litchi tree, with the most noticeable damage occurring on fruits and panicles. Initial signs present as water-soaked lesions that rapidly expand and turn brown. Under high humidity, a dense, white, downy mycelial growth emerges on the surface of the lesions.

Disease progression is highly dependent on environmental conditions, particularly high humidity, rain, and temperatures ranging from 20°C to 28°C. The pathogen produces sporangia that release motile zoospores, which are easily disseminated by wind-blown rain and splashes across the canopy.

The economic impact of Phytophthora litchii is severe, often resulting in significant crop losses. Infested fruits undergo rapid decay, making them unsuitable for export or local markets. Furthermore, the destruction of flower panicles directly reduces the yield potential of the trees for the entire season.

Effective disease management strategies include:

• Strict sanitation practices, such as pruning and removing infected twigs and mummified fruits.
• Improving canopy ventilation through proper pruning to reduce humidity levels around the fruits.
• Application of targeted fungicides, such as copper-based products or systemic metalaxyl-based treatments.
• Implementing regular orchard scouting to detect initial infection sites before widespread outbreaks occur.