Type
Healthy Maize
Description
Healthy corn also called maize usually has no form of deformity or discoloration on the leaf or cob. The Leaf or cob are usually free from any form of disease and pest infestation.
Disease
Common Corn Smut
Causative Agent
Fungus
Description
Corn smut is a troublesome disease of corn plant disease caused by the fungus Ustilago maydis throughout most of the world. The disease reduces corn yields and can cause economic losses. Corn smut galls can develop on both the aboveground part and beneath the soil surface when the apical meristem of the corn.
Damage Pattern
Symptoms are localized to the site of infection. Corn smut galls are initially firm to spongy and are covered with a glistening, greenish-white to silvery-white membrane. As the gall ages, the interior turns dark, and the membrane eventually ruptures to expose a mass of powdery, dry, black, sooty fungal spores (teliospores). Galls on leaves are usually small, hard, and dry, and often do not rupture. The early signs of an attack are whitish galls that later rupture to release dark spores capable of infecting other corn plants. The galls vary in size from less than 1 cm to more than 30 cm (0.4-12 inch) in diameter and are found most frequently on ears, tassels, stalks, nodal shoots, and mid-ribs of leaves.
Mode of Transmission
- Contact of healthy corn with infected ones.
- Through the activities of insect pests and rodents.
- Through mechanical injury to plants during cultivation.
- Through carrying infected corn from one farm to another.
Management
- Plant corn where common smut has not previously occurred or has not occurred for several year
- Phytosanitary harvesting (prompt removal of galls before they mature) and burning them in a designated place.
- Practice crop rotation
- Planting of resistant varieties
- Avoid mechanical injury to plants during cultivation, or any other practice that may wound plants. In seed production fields, avoid detasseling during wet weather.
- Provide balanced fertilization. Excessive N tends to increase the incidence and severity of common smut
Disease
Common Rust
Causative Agent
Fungus
Description
Common rust is caused by the fungus Puccinia sorghi. Rust occurs every growing season. and is favored by high humidity with night temperatures of 65-70°F and moderate daytime temperatures.
Damage Pattern
Early symptoms of common rust are chlorotic flecks on the leaf surface. These soon develop into powdery, brick-red pustules as the spores break through the leaf surface. Pustules are oval or elongated, about 1/8 inch long, and scattered sparsely or clustered together. The leaf tissue around the pustules may become yellow or die, leaving lesions of dead tissue. The lesions sometimes form a band across the leaf and entire leaves will die if severely infected. As the pustules age, the red spores turn black, so the pustules appear black, and continue to erupt through the leaf surface. Husks, leaf sheaths, and stalks also may be infected. Common rust can be differentiated from Southern rust by the brown pustules occurring on both top and bottom leaf surfaces with common rust.
Mode of Transmission
spores are carried long distances by wind.
Management
- Planting of resistant varieties
- Application of recommended Foliar fungicides especially if applied early when few pustules have appeared on the leaves.
- Timely planting of corn early during the growing season may help to avoid high inoculum levels or environmental conditions that would promote disease development.
Disease
Gray Leaf Spot
Causative Agent
Fungus
Description
Gray leaf spot, caused by the fungus Cercospora zeae-maydis, occurs virtually every growing season. If conditions favor disease development, economic losses can occur.
Damage Pattern
Symptoms first appear on lower leaves about two to three weeks before tasseling. The leaf lesions are long (up to 2 inches), narrow, rectangular, and are yellow to tan to brown in color. They look very similar to those of other diseases, except that they often have a faint watery halo which can be seen when held up to the light. Later, the lesions can turn gray. They are usually delimited by leaf veins but can join together and kill entire leaves.
Management
- Plant resistance hybrids
- Crop rotation and clean plowing are effective at reducing in-field inoculum buildup.
- Use recommended fungicides and apply fungicides early in the season before significant leaf damage occurs. Check fungicide labels for appropriate timing of fungicide application.
Disease
Northern Corn Leaf Bright
Causative Agent
Fungus
Description
Northern corn leaf blight caused by the fungus Exerohilum turcicum can cause yield loss if it develops before or during the tasseling and silking phases of corn development
Damage Pattern
Symptoms usually appear first on the lower leaves. Leaf lesions are long (1 to 6 inches) and elliptical, gray-green at first but then turn pale gray or tan. Under moist conditions, dark gray spores are produced, usually on the lower leaf surface, which give lesions a "dirty" gray appearance. Entire leaves on severely blighted plants can die, so individual lesions are not visible. Lesions may occur on the outer husk of ears, but the kernels are not infected.
Management
- Select Resistant Hybrids
- Practice crop rotation and tillage
- Timely planting
- Use recommended Fungicides at appropriate quantity and timing
Disease
Southern Corn Leaf Bright
Causative Agent
Fungus
Description
Southern corn leaf blight is caused by the fungus Bipolaris maydis.
Damage Pattern
Lesions are generally from 1/8 to 1/4-inch-wide by 1/8 to 1-inch long tan in color rectangular to oblong in shape usually found on leaves variable, making identification more difficult than for other diseases. Its lesion type depends on hybrid genetics Lesions usually develop first on lower leaves and work up the plant
Management
- Select Resistant Hybrids
- Practice crop rotation and tillage
- Use recommended Fungicides at appropriate quantity and timing
Disease
Northern Corn Leaf Spot
Causative Agent
Fungus
Description
Northern corn leaf spot, also known as Carbonum leaf spot, is caused by the fungus Bipolaris zeicola. It is occasionally seen in the lower canopy during periods of high humidity and moderate temperatures.
Damage Pattern
Symptoms of northern corn leaf spot usually appear at the time of silking or at full maturity. It consist of circular tan to brown lesions (1/8 to ½ inch) running in a line along the leaf vein. These lesions are often described as looking like a "string of pearls."
Management
- Select Resistant Hybrids
- Practice crop rotation and tillage
- Use recommended Fungicides at appropriate quantity and timing
