Eyespot of wheat

Eyespot of wheat is a fungal disease caused by the pathogen Oculimacula yallundae (formerly Pseudocercosporella herpotrichoides). This pathogen primarily targets the base of the stems in small grain cereals, including winter wheat, barley, and rye, leading to significant structural weakening of the plants.

The disease is most prevalent in areas with mild, wet autumns and winters, which facilitate the survival of the fungus on crop residues. Infection occurs when spores are splashed by rain from the soil surface or lower plant parts onto the leaf sheaths of young seedlings during cool, moist conditions.

Symptoms become visible as characteristic oval lesions on the lower leaf sheaths, which eventually penetrate into the stem base. These spots often feature a light, necrotic center with a darker brown margin, frequently described as an «eyespot» lesion. Severe infection causes the stem tissue to become soft and brittle, which significantly reduces the plant's structural integrity.

The disease development is highly dependent on environmental conditions, with prolonged periods of high humidity and temperatures between 5°C and 15°C promoting infection. Dense crop canopies and high nitrogen application rates exacerbate the problem by maintaining a humid microclimate at the base of the stems, which is optimal for fungal proliferation.

Economic damage is primarily driven by lodging, which complicates harvesting and causes substantial yield losses. The loss of straw strength interferes with water and nutrient transport to the grain, leading to pinched kernels and reduced test weight. Effective management requires a combination of strategies, including the use of resistant varieties, extended crop rotations, optimized sowing dates, and targeted fungicide applications during the early stages of tiller development.