Raspberry leaf spot

The fungus overwinters primarily as mycelium, pycnidia, and pseudothecia within infected leaf litter and on raspberry canes. As temperatures rise in spring, the pathogen begins its infection cycle, releasing spores that are spread by rain splash and wind to healthy foliage.

The disease primarily impacts raspberries and blackberries. By infecting leaves and petioles, the fungus disrupts the plant's ability to photosynthesize. This leads to reduced plant vigor, poor cane maturation, and increased susceptibility to winter injury.

Severe infestations result in premature leaf drop, which significantly lowers fruit yield and quality. Weakened canes often fail to produce a sufficient crop in the following year, threatening the overall economic sustainability of the plantation.

Infection begins in early spring when primary spores are released. Throughout the growing season, secondary spread occurs via conidia during wet weather conditions. High humidity and moderate temperatures provide the ideal environment for the pathogen to thrive.

The disease peaks during seasons with frequent rainfall and foggy conditions, which facilitate the rapid spread of the fungus. Proper spacing and site management are crucial to reducing the humidity levels that favor spore germination and infection establishment.

Initial symptoms appear as small, circular, reddish-brown spots on the leaves. As the lesions mature, the centers turn gray or white, while the margins remain dark brown or purple, creating a distinct "halo" effect around the necrotic tissue.

Close inspection of the infected spots reveals tiny, black, pimple-like structures known as pycnidia. In heavy infections, these lesions coalesce, causing large portions of the leaf to die and drop, which leads to early defoliation of the raspberry canes.

Effective control requires an integrated approach starting with sanitation. Removing and destroying fallen leaves and diseased canes is essential to reduce the primary inoculum source within the field for the upcoming growing season.

• Prune canes to ensure proper airflow and light penetration, reducing moisture on leaves.
• Apply copper-based fungicides or other approved chemical treatments during the early growth stages.
• Ensure balanced nutrition to boost plant vigor and tolerance against fungal infections.
• Use certified disease-free planting material and select cultivars with known resistance to leaf spot diseases.