Kernel spot

Kernel spot is a specific fungal disease caused by the yeast-like fungus Nematospora coryli. This pathogen significantly impacts the internal quality of nuts, leading to necrosis and decay of the kernel, which renders the harvest unacceptable for the market.

The primary host for this fungus is the hazelnut (Corylus). The disease is unique in its dependence on transmission vectors. The fungus enters the developing nut primarily through puncture wounds caused by hemipteran insects, most notably stink bugs (Pentatomidae), which carry the spores on their mouthparts.

The symptoms are internal and only visible upon cracking the shell. Affected kernels exhibit dark, sunken, or spongy lesions. These necrotic areas often turn black and are associated with a bitter taste and an unpleasant odor, which completely ruins the culinary quality of the nuts.

Environmental conditions that favor the proliferation of stink bugs and high humidity also accelerate the spread of the infection. The pathogen thrives in warm, moist environments, which assist in the colonization of the kernel tissue after the insect has introduced the spores into the nut during feeding.

Effective prevention and control measures focus on integrated pest management. Key strategies include:

• Monitoring and controlling stink bug populations using targeted insecticide applications during the nut development stage.
• Sanitation practices, such as removing fallen nuts and infested plant material from the orchard.
• Promoting overall tree health to improve resilience against secondary infections.