Fungal Disease Scouting Crucial for Corn in Kansas

As corn fields in eastern Kansas approach the V14-VT development stage, it becomes crucial for corn producers to scout for fungal diseases and assess the need for foliar fungicide application. This article provides essential information about the common fungal diseases affecting corn in Kansas and outlines key factors to consider when determining the necessity of fungicide treatments.

The following fungal diseases should be monitored during the scouting process:

Southern Rust:

• Typically reported in mid-July
• Pustules appear on the upper leaf surface
• Pustules are scattered, with orange spores that rub off
• Severe infections may be visible on leaf sheaths

Gray Leaf Spot:

• Begin scouting approximately two weeks before tassel emergence
• Rectangular lesions between leaf veins
• Lesions start as small necrotic spots with yellow halos, gradually expanding
• Lesions usually tan, but may turn gray in foggy or rainy conditions

Tar Spot:

• Detected in various counties in Kansas during the 2022 corn season
• Black, raised lesions with a round/elliptical shape
• Higher risk for yield or silage loss in irrigated corn

Factors Influencing Fungicide Application:

Corn Hybrid Susceptibility:

• Seed companies provide information on hybrid susceptibility
• More susceptible hybrids show greater response to fungicides

Previous Crop:

• Fields with a history of gray leaf spot and tar spot should be closely monitored
• Southern rust blows in from the south each year

Weather:

• Rainy and humid conditions favor gray leaf spot
• Southern rust prefers warm days, high humidity, and temperatures above 80°F
• Tar spot thrives in mild temperatures, high humidity, and prolonged leaf wetness

Field locations in river bottoms, low areas, or surrounded by trees may have higher disease severity.

Based on corn hybrid susceptibility and disease symptoms, consider the following guidelines:

• Susceptible Hybrids: Apply fungicide if disease symptoms are present on the third leaf below the ear or higher on 50% of the plants examined.
• Intermediate Hybrids: Apply fungicide if disease symptoms are present on the third leaf below the ear or higher on 50% of the plants examined, and the field has a history of foliar diseases, the previous crop was corn, there is 35% or more surface residue.
• Resistant Hybrids: Fungicide applications are generally not recommended.

Timing of Fungicide Application:

• Research suggests the best time for gray leaf spot control is from VT to R1
• Fungicide applied at VT and R1 can provide suppression of southern rust and tar spot
• Consider late-season pressure and efficacy when deciding on application timing

Corn producers in Kansas can make informed decisions about foliar fungicide application by scouting for fungal diseases and considering factors like hybrid susceptibility, crop history, and weather conditions. Timely and appropriate management practices promote healthy corn yields.

Photo Credit: GettyImages-klosfoto