Glomerella graminicola

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Glomerella graminicola is a fungus that causes corn anthracnose, mainly in maize but also in other grasses and cereals such as sorghum, ryegrass, bluegrass, barley, wheat and some fescue varieties. It has two life forms: the sexual stage Glomerella graminicola and the asexual stage Colletotrichum graminicola, with the asexual form usually responsible for the disease.

The disease appears mainly as leaf blight and stalk rot. It is common in fields where crop residues stay on the soil surface and where crop rotation is limited or absent.

Early-season symptoms show on lower leaves as oval, water-soaked spots about 25 mm long and 13 mm wide. These lesions are light brown with darker edges and can develop small black fruiting bodies in the center. If the infection spreads, the leaf tissue may die and turn yellow. In mid-season, infection can cause top die-back of the plant if many parts are affected. Late in the season, stalk rot may develop, shown as a dark stripe along the stalk internodes and can make stalks soft enough for plants to lodge in wind or rain.

Life cycle and how it spreads: In spring, structures called acervuli form on corn residue and produce banana-shaped conidia (asexual spores). These spores travel by wind and rain splash and infect young plants through the epidermis or stomata. The disease spreads fastest in warm, humid conditions; conidia can germinate in 6–8 hours in very humid air, and necrotic lesions can appear within about 72 hours. Infected lower leaves can produce more spores, causing secondary infections on upper leaves and stalks. The fungus can also invade the plant’s vascular system through wounds, such as those made by stalk-boring insects, leading to vascular wilt, top die-back or stalk rot. In autumn, the pathogen survives on corn residue as a saprophyte, with certain secretions helping conidia survive harsh conditions. This residue acts as the main source of new infections in the spring.

Conditions that favor infection and spread include warm temperatures (roughly 25–30°C or 77–86°F) and long periods of wet weather or high humidity, along with overcast conditions that reduce sunlight. Cultural practices that worsen the problem include continuous planting of the same crop and no-till farming, which leave large amounts of residue on the soil surface. Management strategies focus on reducing the primary inoculum: rotate crops for at least a year, plow and bury corn residue to disrupt the saprophytic stage, and avoid leaving residue on the surface. Using resistant hybrids can help, though resistance may not protect against stalk rot later in the season. Biological control options exist but are not widely used. Maintaining healthy plants and controlling other pests also helps. This disease is found worldwide and has caused significant losses in North America since the 1970s, especially in corn production.

In short, Glomerella graminicola is a two-form fungus that causes corn anthracnose, with leaf blight early on and stalk rot later. It survives on crop residue and spreads under warm, humid conditions, making crop rotation, residue management, and resistant varieties key parts of control.