Hop sphaerulina leaf spot

Hop Sphaerulina leaf spot is a fungal disease caused by Sphaerulina socia, which affects common hop plants. It is a foliar pathogen that compromises the plant's ability to perform photosynthesis efficiently by damaging the leaf tissue. Although often considered a secondary concern compared to downy mildew, its presence can negatively impact the overall vigor of the hop yard.

The host plant for this pathogen is the common hop (Humulus lupulus). The disease manifests mainly on the foliage, with a preference for older leaves located in the lower parts of the canopy where humidity remains higher for longer periods. If left uncontrolled, the infection can spread upwards, leading to premature leaf loss.

Symptoms initially appear as small spots on the leaf blades, which later develop into distinct necrotic lesions. As the fungus matures, it produces numerous small, black fruiting bodies known as pseudothecia within the dead tissue. Severely infected leaves turn yellow, become brittle, and eventually drop off, causing a noticeable thinning of the hop vine foliage.

The development of Sphaerulina socia is heavily dependent on moisture. Rainfall, high relative humidity, and cool to moderate temperatures create optimal conditions for spore production and dissemination. The fungus overwinters primarily on infected leaf litter and crop debris, making sanitation a critical aspect of disease control in the subsequent growing season.

• Removal and destruction of fallen leaves and crop residues in autumn.
• Promoting air circulation within the hop yard through proper pruning and training.
• Application of preventative fungicides during the active growth stages.
• Selecting resistant hop cultivars whenever possible for new plantings.
• Regular scouting and monitoring to detect the first signs of leaf spotting.