Untitled Quiz

Corn Diseases and Management

• Brown Spot (Physoderma maydis): Symptoms appear on leaf blades as chlorotic spots in alternating bands of healthy and diseased tissue. Spots on midribs are circular and dark brown. Severe infections can cause stalk rotting and lodging. The disease is prevalent in areas with abundant rainfall and high mean temperatures.

• Buggy Whip (Abiotic): A characteristic symptom is the fusion of the top portion of the plant into a tight tube, encompassing leaves and tassel. Heavily lignified tissues result in a appearance similar to a buggy whip or an onion leaf. It may be caused by certain volatile herbicides, like 2,4-D, and can be particularly severe in warm conditions.

• Common Rust (Puccinia sorghi): Characterized by large, circular to elongated pustules, displaying brown or cinnamon brown color. The disease is favored by moist, cool temperatures and high humidity; hot, dry conditions slow disease progression. The fungus survives on brassica weeds in crop debris or soil for months without a host.

• Corn Stunt (Helicotylentus spp): A noticeable symptom is plant stunting. The disease occurs frequently in heavy soils and less frequently in sandy soils.

• Curvularia Leaf Spot (Curvularia lunata): Initially, small necrotic spots with a light colored halo appear. Fully developed lesions reach around 0.5 cm in diameter. High humidity and heat areas often experience a severe infection, resulting in yellowing.

• Diploida Rot (Stenocarpella macrospora): On stalks, lesions appear as oval or irregular shapes with pale cream-brown centers and indeterminate darker borders. Diamond-shaped brown lesions are common on leaves. The disease is influenced by several factors, such as unbalanced fertility (low K), poor drainage, mechanical and insect damage, and planting density.

• Downy Mildew (Peronosclerospora philippinensis): Initial symptom is chlorosis (yellowing) or chlorotic stripes on young leaves. White downy growth (conidia and conidophores) develops on both upper and lower leaf surfaces under conducive conditions. Tassels often become malformed, producing less pollen. The disease thrives in warm, humid regions and frequently occurs in areas prone to flooding. Seedlings are more susceptible to infection than mature plants.

• Gray Leaf Spot (Cercospora zea-maydis): Lesions begin as small, necrotic spots, potentially with or without chlorotic halos. They elongate and grow parallel to leaf veins, creating a rectangular shape with sharp edges. Favorable temperatures and moisture conditions increase infection.

• Mosaic (Sugarcane Mosaic Virus): Infected plants display a mosaic pattern in their leaves with broken linear stripes between veins, leading to necrosis or ring spots. Plants commonly display stunting. This disease is transmitted mechanically via aphids and seeds.

• Northern Corn Leaf Blight (Exerohilum turcicum): Long, gray-green, and elliptical or cigar-shaped lesions form on older, lower leaves. As the disease advances, paler gray to tan lesions develop. Husks are susceptible to infection; however, the disease doesn't typically spread to the ear section. Conditions like moderate temperatures, heavy dews, and frequent rain, plus black spores in wet weather that spread, support this infection.

• Southern Corn Leaf Blight: Symptoms vary by pathogen race. Race 0, prevalent in warm and humid regions, displays tan lesions with brown borders. Lesions start small and diamond-shaped, elongating and widening to a rectangular form within veins, remaining confined to the leaves. The overall dimensions of the lesions can fluctuate from 2 to 6 mm wide and 3 to 22 mm long. The fungus winters in corn debris and seeds, with wind and splashing water spreading the spores rapidly.

• Bacterial Stalk Rot (Erwinia chrysanthemi): Internodes turn tan or brown and become water-soaked, soft, and slimy, causing the plant to collapse. Affected tissues often exhibit a foul odor. Rotting might be evident at the whorl base. The pathogen enters through openings, wounds in leaves, stalks, roots, insect damage, and weather-related injuries. This disease frequently occurs after pollination, and the impact is worsened by high humidity, high temperatures, significant rainfall, and excessive irrigation, resulting in the disease's propagation.

• Corn Smut (Ustilago maydis): Ear and tassel infection appears during development. Galls featuring white membranes form on tassels and ears, but rarely on leaves. Infection thrives in dry conditions with 78° to 95°F temperature, and in soils deficient in nitrogen, as well as with excessive manure presence.

Management and Control Strategies

• General Recommendations: Use resistant varieties whenever possible. Crop rotation with non-host plants is critical to reduce inoculum, and proper field sanitation and removal/burning of infected plant matter are essential.

• Specific Fungicides: Various fungicides might be employed, including but not limited to: mancozeb (e.g., Dithane®, Manzate®), chlorothalonil (e.g., Daconil®), maneb (e.g., Maneb®), pyraclostrobin+dimetomorph (e.g., Cabrio®), propiconazole (e.g., Bumper®, Tranzole®), azoxystrobin (e.g., Amistar®). Other methods of control include; using fungicide-treated seeds, avoiding excessive use of nitrogenous fertilizers, and providing adequate potassium fertilization. Consider use of reflective mulches to help reduce aphid populations and implement good drainage practices for corn fields.

• Other Strategies: Avoid mechanical injury and maintain balanced fertility; remove infected plants when symptoms emerge to limit the pathogen's dispersal, and cultivate the field thoroughly to bury residues and diminish inoculum.