The potential for corn seeds and plants to become infected with a disease is greatly determined by genetics, use of fungicidal seed treatments, environmental conditions, time in the growing season, and the presence of casual agents (fungal or bacterial pathogens, viral vectors, and nematodes). The warm, humid southern environment is very favorable for the development and propagation of many corn diseases.
Newly planted seeds are immediately subjected to pathogenic fungi and bacteria that inhabit the soil. In general, these pathogens have a greater potential for causing damage when soils are wet and cold; however, some pathogens prefer warm conditions. Infected seedlings may show signs of damping-off or rotting, stunting, yellowing leaves or loss of color, and deformities.
Susceptibility to diseases depends largely on the level of genetic resistance to a disease. Some seed products can have nearly complete resistance while others are very susceptible. When selecting seed products for planting, the historical disease presence should be considered, and seed selections made accordingly.
Foliar fungal diseases may become apparent anytime during the season depending on the presence of the pathogen. Many fungal pathogens can overwinter on or in infected residue and can contact plants via splashing rain or wind. Pathogens that are unable to overwinter in the southern areas of the United States can be carried in from Mexico, the Caribbean Islands, and South America on wind currents. Hurricanes have been known to bring diseases into new areas. Depending on the disease, foliar fungicides may provide control.
Bacterial diseases can also overwinter on infected residue. The bacterium can contact plants through water movement in the soil, splashing rain, wind-driven rain, and mechanical means such as cultivating when plants are wet. Infection occurs when bacterium enter the plant through wounds or natural tissue openings such as stomates.
Viral diseases rely on a vector such as aphids or thrips to infect a plant. As the vector feeds, infected juices are injected into plant tissue. Scouting for insects that have the potential to vector viral diseases and applying a timely insecticide may help protect plants from becoming infected via insect feeding. Caution should be taken not to spray insecticides without proper identification as many beneficial insects can be killed.
Additional harvest-time diseases include stalk and ear rots. Stalk rots can result in lodging that can diminish harvest speed, increase harvesting equipment wear and tear, decrease grain quality, and increase the potential for personal injury. Ear rots can affect grain quality, test weight, and marketability. Some ear rots produce toxins that can be harmful or even lethal to livestock and humans.
Nematodes are often discussed under the disease umbrella; however, they are microscopic parasitic worms that live outside (ectoparasitic) or within (endoparasitic) corn roots. Nematode infestations may go unnoticed, particularly under favorable growing conditions, or cause stunting, nutrient deficiencies, and create entrance wounds for other pathogens.
Click below on Seed and Seedling, Foliar, Viral, Stalk, Ear Rot, or Corn Nematodes to identify and learn about the corn diseases on your farm.
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Web sites verified 9/10/2019. 1010_G3