Corn Diseases and Fungicide Considerations
In Kansas, we are entering the time window where corn producers should be scouting fields and assessing the need for a foliar fungicide application.
Common Rust is caused by the fungus Puccinia sorghi. It blows in from southern corn production areas. Moderate temperature, frequent rains, heavy dews, and fog encourage disease development and can occur under relatively dry conditions since a short amount of moisture on the leaf is required for spores to germinate and infect. Symptoms include a variation in the number of pustules(often appearing in a band) and dark-brown reproductive spores. Pustules develop on both the upper and lower leaf surfaces.
Southern Rust is caused by the fungus Puccinia polysora. It blows in from southern corn production areas, with development encouraged by temperatures above 80 with relative high humidity. Symptoms resemble those of common rust but the pustules are usually smaller and circular to oval with a diameter of 0.2 to 2.0mm. They typically are densely scattered on the upper leaf surface. They have light-brown to orange spores which are lighter compared to common rust. Normally first reported in mid-July in Kansas.
Gray leaf spot is caused by the fungus Cercospora zeae-maydis. It overwinters on corn residue, especially when the residue is on the soil surface. Gray leaf spot develops between 70-85 degrees F and can thrive in even the hottest of Kansas summers if morning dews or fog is present. Symptoms include rectangular lesions that are 1-2 inches in length and cover the entire area between the leaf and veins. Early lesions are small, necrotic spots with yellow halos that gradually expand to full-sized lesions. They are usually tan in color but may turn gray during wet conditions. Scouting for this should begin in corn about two weeks before the expected tassel emergence.
Tar spot is caused by the fungus Phyllachora maydis. This pathogen can survive in crop residue. Tar spot is favored by mild temperatures, high relative humidity, and a prolonged leaf wetness period. Symptoms include black lesions, that are raised and have a round or elliptical shape. Irrigated corn may be at a higher risk for yield or silage loss.
Management recommendations:
Each corn foliar disease has its own developmental characteristics which may be wet or dry growing conditions, cool or warm temps, survivability on or in crop residue, and crop stage of growth when the infection is most critical. Knowing the characteristics of each disease and field histories are important when considering management options.
-Avoid highly susceptible hybrids
-Introduce crop rotation
-Manage irrigation
-Scout early and often
-Fungicide applications
Fungicides don't increase yield, but they can protect the yield potential of the crop in the presence of fungal diseases. Without prudent applications of the correct fungicide at the right time, your corn fields may not reach their yield potential.
See article (and pictures) from the latest KSRE Agronomy eUpdate "Fungicide considerations for corn diseases in 2023" here.
More information here:
Why You Should Apply Fungicide on Corn This Year - Farm Progress
Corn Rust Identification and Management in Kansas - KSRE
Corn and Soybean Disease Management with Foliar Fungicides
Contact Tyree Ag offices or your salesman today to discuss your fungicide options.
866-897-3324
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