The economic loss from late-season diseases can be hard-hitting. Even with proactive planning and preventative management, disease can develop when a susceptible host with the right pathogen in a favorable environment as shown by the disease triangle.

When discussing late-season soybean and corn diseases with growers who are considering a fungicide application and the right timing, it is important to first consider with them if fields are at high risk for disease development. This includes conversations about cropping history, disease history, the current environment in the field and weather conditions as they all play a part in risk for disease. Hot and humid weather or dry conditions can play different roles in disease development and spread.

Next, it is important to talk to growers about the levels of disease resistance in the varieties they’ve planted. Each variety has a different level of disease resistance or susceptibility, so understanding the current level of protection will help to determine if fungicide is needed.

Late-Season Diseases

When disease does appear, it can be difficult to quickly identify it and decide whether a fungicide application is needed. Iowa State University has developed guidelines to help retailers and growers determine when to use fungicide to prevent yield loss in their crops.

Consider a fungicide application if:

1. The variety is rated as susceptible or moderately susceptible AND:
   1. 50 percent of the plants in a field have disease lesions present on the third leaf below the ear leaf or higher prior to tasseling
2. The variety is rated as moderately resistant AND:
   1. 50 percent of the plants in a field have disease lesions present on the third leaf below the ear leaf or higher prior to tasseling
   2. Additional factors or conditions that favor disease development are present (residue present, favorable weather conditions)

Maximizing Fungicide Application

When selecting a fungicide, it is important to consider disease management best practices, timing of application, the pros and cons and how to use them. It is also important to consider the use of an adjuvant to ensure the application is effective.

The below adjuvants from CHS Agronomy can help to ensure that each fungicide application is effective by increasing droplet size and uniformity. The larger the droplet size, the further into the canopy a fungicide will penetrate. This is especially important for disease that starts lower in the canopy and works its way up the plant.

Petrichor® is a soy-enhanced drift and deposition agent unique to CHS. It offers enhanced performance, storage stability and mixability as a result of less impurities found in refined soybean oil. It reduces fine droplets and holds spray pattern in more uniform larger droplets at a low use rate of 3 oz/A.

Cerium® Elite is a surfactant that can be used to replace traditional oil adjuvants. It is designed for use with herbicides, fungicides, insecticides, defoliants, desiccants, plant growth regulators, and any other crop protection product where an oil concentrate, nonionic surfactant and/or improved deposition is required or recommended. Cerium Elite provides the convenience and simplicity of a low use rate replacement for many oil concentrates that are typically used at 2-4 times the use rate of Cerium Elite.

For more information about Petrichor or Cerium Elite, contact your local CHS Agronomy representative or visit CHSAgronomy.com