MDMV – Maize Dwarf Mosaic Virus
Type: Virus - Potyvirus
Maize Dwarf Mosaic Virus is a world-wide virus disease that affects the growth of corn. Symptoms include yellowing of the leaves, then red streaks or blotches appear later in a mottle or a mosaic pattern. Plants show stunting after the infection is established. Ear formation and development may slow, which can cause substantial yield loss. The disease is spread by aphids. The disease is favorable when night temperatures are consistently around 60 F. Plan on using a 3 year crop rotation and avoid planting in the same location, year after year. Insecticides for aphids are of limited value to control the disease. Controlling Johnson grass with herbicides may be beneficial in the management of the disease. The best option is to use disease resistant varieties.
NCLB – Northern Corn Leaf Blight
Scientific Name: Exserohilum turcicum
Type: Fungus
Northern Corn Leaf Blight is a fungal disease that affects the growth of corn. Northern corn leaf blight occurs commonly in the Midwestern regions of the United States. Symptoms are cigar-shaped or elliptical shaped gray-green lesions on the leaves that range from 1 to 7 inches long. Lesions begin on the lower leaves and then spread to upper leaves. Severe symptoms can progress rapidly, resulting in blighted leaves. Lesions can also be found on the husk of ears or the leaf sheaths. It can cause significant yield loss in corn. Losses are greater and more severe when plants are infected at the early stage of growth. The disease will spread by rain or wind. The disease is favorable when temperatures are 64-81 F and usually occur when moisture and humidity are very high. Plants usually become infected when water is present on the leaf surface for 6 to 18 hours. Plan on using a 3 year crop rotation and avoid planting in the same location, year after year, as the disease can survive in over winter on corn leaf debris. Proper tillage practices may be helpful in managing the disease. Fungicides can help manage the disease. The best option is to use hybrid disease resistant varieties.
R - Rust
Scientific Name: Puccinia asparagi, Puccinia sorghi
Type: Fungus
Rust, also known as Common Rust, is a world-wide soil borne disease that affects the growth of asparagus, cantaloupes & melons, corn, and lettuce. It is one of the most destructive disease in growing asparagus in the United States. The disease affects the ferns on asparagus. Lesions develop and turn cream-orange color, then turn a reddish-brown color, then eventually turn a brick red or rust color. During the winter the lesions will turn a black color. Severe infestation stunts or kills young asparagus shoots. The infected plants should be removed to avoid further infestation. When corn is infected the disease affects the upper and lower leaf surfaces, where small specks appear on the leaves, then develops into small tan spots, and distinguished by cinnamon-brown pustules. These pustules blister and turn dark brown to black late in the season. Corn stalks are weakened and stalk rot potential increases. Significant damage to upper leaves results in significant yield losses. Common rust spreads by windblown spores. The disease is also favorable cool and moist conditions when temperatures are 68-72 F, and usually occurs when there is nine hours of wet weather. The best option is to maximize air movement between the plants and to use disease resistant varieties.
SW - Stewart's Wilt
Scientific Name: Erwinia stewartii
Type: Bacterium
Stewart's Wilt is a disease that affects the growth of corn. Stewart's wilt is common throughout the eastern regions of the United States. The disease is transmitted to corn plants during feeding by adult corn flea beetles. These beetles overwinter in the soil and upon emergence in the spring, commence feeding on the plants, and contaminates corn seedlings. An entire field of corn may become infected in a relatively short period of time. Some or all of the plants may die, and severe yield reductions result. The bacteria is carried in the digestive tract of the corn flea beetle. Beetles feeding on infected corn tissue acquire the bacteria and spread it further. Wilting of foliage is often associated with the infection, plants may be stunted, and in severe cases, death may result. When seedlings and young plants are infected, they will wilt and the main stalks may die. Symptoms include lesions on the leaves. The lesions appear as long wavy streaks that turn yellow and eventually brown. Entire leaves may die if the disease is severe and the stalks may develop fungal rot and become weaken. The disease can cause substantial yield loss due to leaf damage and weakened plants resulting from stalk rot. The infestation year to year depends largely on winter temperatures, and how many beetles carrying the disease survive the winter. Mild winter temperatures favor survival of the beetle, thus the disease can be greater the following spring. When winter temperatures are greater than 24°F during a two month period, a moderate to high risk of Stewart’s wilt is possible. Beetles carrying the bacteria that survive the winter could infect corn plants next spring. Insecticide treatments helps reduce flea beetle populations. The best option is to use hybrid disease resistant varieties.