Additionally, leaf diseases are often accompanied by stalk rot therefore, it also will be important to monitor stalk quality and opt for a timely harvest if leaf diseases occur. Scouting for foliar diseases will be critical in corn-on-corn fields to ensure that fungicide applications are applied in a timely manner, and the ear leaf and leaves above the ear are protected from infection and extensive blight development during grain fill. Therefore, as the season progresses, and provided environmental conditions are conducive to disease development (moderate temperatures and high moisture), the disease moves up the plant from the lower canopy to the upper canopy. Lesions develop and produce more spores that are spread to and infect the upper leaves. Under moist conditions, the fungi produce spores that are either rainsplashed or blown by the wind onto susceptible corn leaves and infection occurs. This means that in corn-on-corn fields, inoculum pressure will be considerably greater, especially in those fields where foliar diseases were a problem the previous season.
Research has shown that disease severity is directly associated with the amount of surface residue. Apart from the rusts, which are windblown from the South each growing season, the fungi that cause these diseases survive in infested corn residues left on the soil surface. The most common foliar diseases of corn in Iowa include anthracnose leaf blight, gray leaf spot, northern leaf blight, common and southern rust, and eyespot. Seed treatments will continue to be necessary to ensure a healthy stand. Thus, corn-on-corn fields, in particular those with crop residues left on the surface, will be more prone to seedling diseases due to higher inoculum pressure and cooler, wetter soils. Although several of the seedling pathogens can attack both corn and soybean, there are others that are specific to corn and their populations will increase under continuous corn. When soil temperatures are below 55 ☏, germination and emergence are greatly retarded. Corn germinates and emerges quickly at soil temperatures above 68 ☏. Seedling susceptibility to infection increases the longer the seed sits in the ground, and the more stress germinating corn undergoes. Cool (<55 ☏), wet soils favor the development of seedling diseases.
They survive in crop residue and the soil.
All these fungi are common microbial inhabitants of corn fields. Numerous fungal species in several genera ( Fusarium spp., Rhizoctonia spp., Pythium spp., Diplodia spp., Penicillium spp., Trichoderma spp.) cause seed rots and seedling blights in corn. Weather conditions during the growing season will still significantly impact disease severity.Īnticipated disease problems that might occur in corn-on-corn fields in Iowa include the following. However, do not forget the disease triangle (below). Thus, the risk of increased disease severity is higher when corn follows corn. Many of these diseases are caused by pathogens that survive in crop residue or in the soil. If dry weather returns, infected plants may recover and make a good crop.Corn is vulnerable to the following infections by plant pathogens throughout the growing season under favorable environmental conditions: seed rots and seedling blights soon after planting, foliar diseases in mid-season, and stalk and ear rots toward the end of the growing season. Managing Outbreaks:Ĭlip off affected leaves and dispose of them in an active compost pile.
Avoid places near trees, fences, or low pockets where dew is heavy and slow to dry. Leaves that dry rapidly after rain or heavy dew are unlikely to develop problems with leaf blight, so grow corn at proper spacing to make sure sunlight reaches all the leaves. These fungi can overwinter in soil, so always rotate sweet corn so that it is not grown in the same spot more often than once every three years. However, plants may be weakened and yields may be low when many leaves are lost to leaf blight. Damage:Ĭorn leaf blight diseases may cause plants to lose their lowest leaves, while the top part of the plant continues to make new growth. The spots become numerous and run together, often causing the whole leaf to wither. The leaf spots caused by Southern corn leaf blight are smaller, usually less than two inches long, and outbreaks are triggered by persistent warm rains, with temperatures between 70 and 90F (21-32C). A disease of wet weather, northern corn leaf blight is most severe when temperatures are between 66 and 80F (18-27C), with constant moisture from rain or fog. Northern corn leaf blight causes large spots to form on corn leaves, which begin as gray-green areas several inches long and one-half inch wide. Worldwide, wherever sweetcorn or maize is grown in temperate climates Description: On Crops: All types of sweetcorn and maize Where Found:
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