By Pierce Paul, Ohio State University Extension
This July has been one of the wettest on record, and with the extra moisture, comes concerns about diseases. Gray Leaf Spot (GLS) and, to a lesser extent, northern corn leaf blight (NCLB), have already been reported in some fields, well before tasseling in some cases. Such early disease development could impact grain yield, especially if it continues to be wet and the hybrid is susceptible. GLS is favored by warm temperatures (70 and 90 F) and high relative humidity. NCLB is also favored by wet, but slightly cooler (64 and 80 F) conditions, than GLS. Over the last several days, we have had temperatures within the favorable range for both diseases, and if they continue to spread and damage the ear leaf before grain fill is complete, yield losses could be high.
A warm, wet start to the growing season led to a decent start for the 2021 corn crop in central Kentucky; however, we all now know disease development can devastate a good crop. One disease particularly on the farmerâs radar this year is Southern Rust because of the devastating losses it caused on late planted corn in past years.
Southern rust, caused by Puccinia polysora, made an appearance in Kentucky the last several years, turning many combines and silage choppers orange during harvest because of the large number of orange-colored pustules present on the leaves.
Although the fungus that causes southern rust is not able to overwinter in Kentucky, it has been found in corn fields in northern Arkansas and Mississippi. This pathogen will move north during the season, but remember, timing is everything. If the disease is found in Kentucky corn fields prior to the milk stage â R3 growth stage â then yield losses may occur.