Although growers produce hybrid plants specifically to be more resistant to disease than their heirloom parents, hybrid plants may still develop some diseases. Like all plants, hybrid plants may become diseased if they are weakened from bad weather or poor cultural practices such as lack of care or improper practice of crop rotation.
Crazy Top is a corn disease that affects both hybrid and heirloom plants. The disease primarily affects corn that is planted in wet, boggy areas. The wet conditions provide a fertile breeding ground for mold and downy mildew. The pathogens that cause Crazy Top cannot infect corn in dry areas, because it may take nearly two days for the pathogen's swimming zoospores to invade corn stalks. Once Crazy Top penetrates a stalk of corn, it invades tissue and prevents growth in some areas, which leads to the corn's deformed appearance. Symptoms of Crazy Top include excessive leaf deformity and "tillering," which is lateral growth of branches on low nodes.
Seed rot is a disease that primarily affects the saved seeds of plants including corn. Various hybrid forms of seed are more resistant to seed rot than heirloom varieties, but farmers frequently treat hybrid seed with fungicide to increase their resistance. Seed rot affects seed after it has been planted in the ground. Stricken seed typically fails to germinate and produce new sprouts. The seed is usually infected with fungus in the soil once it has been planted. Affected seed is typically planted in wet, compacted soil in low-lying areas.
Leaf Blight and Anthracnose
A plant's resistance to leaf blight and anthracnose varies depending on the hybrid and the conditions. Hybrids are less resistant in warm, wet weather than they are in dry weather. These conditions become more present in soil and vegetation left in the ground over time. Rotating crops will help prevent hybrid plants from contracting these diseases. Both leaf blight and anthracnose appear as lesions on the leaves of a plant. The severity of the lesions may vary among hybrids.
Rust lives in the soil from year to year in the presence of spores left by other plants that suffer from rust. Infected plants exhibit reddish brown pustules over the surface of plant leaves. Although rust can appear severe, it will not dramatically affect crop production. Rust is more prevalent in the subtropical regions of the South, where warm weather provides a more habitable environment for the disease.