Gray Leaf Spot of Corn
Gray Leaf Spot (GLS) of corn is a regular disease in the United States and can have significant affect on crop yields. This disease is caused by the fungus Cercospora zeae-maydis and has been growing in economic importance since the 1990s.
Gray leaf spot can be identified by its rectangular lesions. These narrow lesions are brown to gray in color and have a yellow halo when held up to light. Single lesions are restricted by leaf veins, which gives the lesions their blocky shape, but in heavy infections multiple lesions can coalesce into large areas of dead tissue. Infection begins on lower leaves and moves up the plant with successive generations. Once the infection moves above the year, yield impacts can become significant.
The fungus that causes GLS can easily over winter throughout the United States in crop residue. When temperatures warm in the summer, wind and rain spread the spores to young plants and infection can begin. Conditions that are optimal for infection include temps above 76˚F along with high humidity and prolonged leaf wetness. Disease progression may stall during very hot or very cool dry weather but then pick up again when conditions become favorable.
There are many ways to manage GLS in corn.
- Hybrid Tolerance – GLS tolerance is available in many commercial corn hybrids but varies between each hybrid. Choose higher levels of tolerance for fields with a history of the disease or fields that have more suitable environments for infection such as those that catch a lot of morning dew.
- Residue Management – Since the GLS pathogen over winters in corn residue, we can manage future infections by burying or taking away infected residue.
- Use Foliar Fungicides – Applying fungicides at or just after tassel when disease is present in lower leafs and conditions are favorable and greatly reduce overall infection. Using fungicides with multiple modes of action can also enhance control and reduce the risk of disease resistance.
Wise, K. (2010, June). Diseases of Corn – Gray Leaf Spot. Purdue University Extension. https://www.extension.purdue.edu/extmedia/bp/bp-56-w.pdf
Crop Protection Network. Gray Leaf Spot of Corn. Crop Protection Network. https://cropprotectionnetwork.org/resources/articles/diseases/gray-leaf-spot-of-corn