Under hot humid conditions, spores of the fungus can infect susceptible corn, and symptoms can be observed within 3-4 days. Rust spores can be rubbed off of the leaves and leave a brown or orange stain on fingers or clothing. The early symptoms of Southern corn rust include small circular-to-oval shaped lesions which are oftentimes accompanied by a light green to yellow halo. Foliar diseases ultimately reduce carbohydrate allocation to developing ears, thereby reducing yield. Early infections especially in irrigated corn can be devastating. More on the Diagnosis of Southern Rust of Corn With corn now beyond the R4 growth state in most fields, there is really nothing you can do about southern rust in terms of fungicide application. As the disease can spread rapidly, this is a crucial component of prevention with a fungicide application. Most rusts have an alternate host to complete its life cycle. Figure 1. Early symptoms of common rust are chlorotic flecks on the leaf surface. During summer months, however, the fungus which causes southern rust, Puccinia polysora, often moves into southern areas of the U.S. Pustules contain thousands of small orange spores. New infection can occur within 7 to 14 days. Entomology Image Gallery > Plant Diseases and Damage > Corn > Southern Rust. If common rust is severe, a foliar application of an approved fungicide is recommended to prevent yield loss. To manage common rust during the growing season, it is advised to regularly scout corn to detect it early. brown, circular to oval and densely scattered on the upper leaf surface. These do not likely play a major role for disease in the United States, and the urediniospores are carried north from tropical regions. Like common rust, it does not overwinter in Kansas, but blows in from southern corn production areas. Information for resistance to southern rust is limited. Remember that fungicides provide approximately three weeks of protection. Southern rust is caused by the obligate fungal pathogen Puccinia polysora. Southern rust pustules are often numerous and tightly clustered in patches. Southern Rust Southern rust is caused by the fungus Puccinia polysora. Puccinia polysora produces fuzzy, raised structures called pustules on leaves and stalks of corn. Southern rust prefers warmer temperatures of 77-88°F (25-31°C). These lesions will be found on both the upper and lower surfaces of the leaves or leaf sheaths and are scattered across the leaf surface. Symptoms. Read our Additional Resources can be found at the Crop Protection Network. Pustules are mostly found on the upper leaf surface, which can help distinguish it from the less damaging common rust. 2). Symptoms. Common rust usually appears to some degree in the southern United States and the Corn Belt every year. In contrast, common rust produces brick-red to brown spores on both the top and bottom of the leaves. The disease can cause significant yield loss in susceptible hybrids if it becomes severe, so producers and … Small, cinnamon-brown, powdery, circular-to-elongated pustules occur on upper and lower leaf surfaces often in bands across leaves (Figure 2). The severity of disease in the upper canopy is increased by wet conditions (frequent rain) during the season. Symptoms also may appear similar to Physoderma brown spot (Figure 4). The uredia are small, 0.2-2.0 mm long nad circular to oval in shape (4). Southern rust is more orange or reddish-orange in appearance, while common rust is red or cinnamon-brown. The alternate hosts for common rust are several Oxalis spp. Most spores are produced in raised rust pustules on the upper leaf surface. As the growing season progresses, dark brown to black teliospores develop within the lesions. southern rust may possibly kill the corn plant while common rust seldom does. Cooperative Extension is based at North Carolina's two land-grant institutions, NC State University and NC Early and frequent scouting of fields are beneficial if corn rust is found nearby to prepare for potential fungicide applications. Lesions that appear on both lower and upper leaf surfaces Primary distinguishing characteristics of southern rust include: 1. Pustules appear oval to elongate in shape, are generally small, less than 1/4 inch long, and are surrounded by the leaf epidermal layer, where it has broken through. Pustules contain thousands of small orange spores. This summer, southern rust has been observed in at least 11 Indiana counties. Southern Corn Rust can occur in major regions for corn production in the US and Canada despite being a tropical disease. Very early symptoms of southern rust or some other diseases may begin as tiny yellow flecks making early diagnoses difficult. 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