Maize eyespot, caused by the fungal pathogen Aureobasidium zeae, represents a significant foliar disease that can undermine the structural integrity and photosynthetic capacity of corn plants. This pathogen thrives in environments characterized by high humidity and moderate temperatures, often proliferating during the extended dew periods common in late-season corn-growing regions. The disease initially manifests as small, circular lesions with a distinctive tan or gray center and a dark brown to purple margin, a visual signature that allows for rapid identification in the field.
Disease Cycle and Favorable Conditions
The lifecycle of Aureobasidium zeae begins with mycelium and conidia surviving in corn residue left on the soil surface after harvest. When conditions become favorable—specifically during periods of high moisture and temperatures ranging between 18°C and 28°C—the fungus produces new spores. These spores are dispersed by wind, rain splash, and agricultural equipment, initiating new infections on healthy leaves. The continuous presence of free water, often from frequent rainfall or irrigation, is critical for spore germination and the penetration of the leaf cuticle.
Visual Identification and Scouting Techniques
Accurate identification is paramount for effective management. The lesions of maize eyespot are often confused with other foliar diseases, but the purple border and the gray-tan center are diagnostic hallmarks. Under humid conditions, a grayish-purple fungal growth may become visible on the underside of the lesion. Scouting should focus on the lower leaves early in the season, progressing upward as the disease advances, with a particular emphasis on tracking the progression past the ear leaf.
Impact on Yield and Plant Health
The primary economic consequence of maize eyespot is the premature death of leaf tissue, which directly reduces the plant's photosynthetic area. When lesions coalesce and girdle the leaf, the flow of carbohydrates to the developing ear is impeded, potentially leading to kernel abortion or reduced grain weight. Furthermore, the disease can predispose the plant to stalk rot pathogens by compromising the integrity of the rind and internal pith, creating a dual threat to standability and harvest efficiency.
Integrated Pest Management Strategies
Managing maize eyespot requires a multifaceted approach that combines cultural practices with resistant genetics. The most effective long-term strategy involves the rotation of corn with non-host crops such as soybeans or small grains to reduce inoculum levels in the residue. Tillage practices that bury infected debris can further diminish overwintering fungal structures, although no-till systems must rely heavily on resistant varieties and vigilant scouting.
Fungicide Application Timing
When disease pressure is high, fungicide applications become a critical component of an integrated management plan. Systemic fungicides from the QOI (strobilurin) and SDHI (succinate dehydrogenase inhibitor) classes are most effective, as they provide both curative and protective activity. The optimal timing for application is typically during the VT (tasseling) to R1 (silking) growth stages, coinciding with the period of maximum ear susceptibility and physiological stress.
