Plant Pathology Department


Date of this Version



Chapter in 2017 Guide for Weed, Disease, and Insect Management in Nebraska, University of Nebraska–Lincoln Extension, Institute of Agriculture and Natural Resources (EC130), pp. 233-265.


Copyright © 2017 The Board of Regents of the University of Nebraska.


Fungicides are an important component of the pesticide program for some Nebraska fields. While not all fields of corn, dry bean, sorghum, soybean, sugarbeet, sunflower, and wheat will require a fungicide application, it’s critical that you know the correct product for the disease in your field when you do need it.

Identification. The first step with any disease management program is to make sure you have correctly identified the problem. Identification is critical as there are many bacterial diseases with symptoms similar to fungal diseases, and fungicides will have no activity on them. For help identifying crop diseases, visit the Plant Disease section of UNL’s CropWatch at http://cropwatch.

Timing. The second step is to ensure accurate timing of the application. With some diseases it is critical to apply the fungicide before there is significant disease development.

Fungicides are plant protection compounds but have some of the same restrictions as many other pesticides, such as preharvest intervals and post-application field reentry restrictions. Read and carefully follow all label directions.


The use of pesticides, including fungicides, has resulted in the development of organisms that are resistant to their effects. Currently, the only major field crop pathogen with known resistance is Cercospora sojina (Frogeye leaf spot of soybean) with resistance to the strobilurin (QoI) fungicide group. This has been identified in other parts of the United States and not in Nebraska as of 2016. Misuse of products may result in the development of other resistant populations and jeopardize the benefits that are provided by those products and other closely related fungicides.

Resistance can develop after the repeated use of products with the same modes of action, particularly with single-site modes of action. Also, organisms vary in their ability to become resistant and the frequency that they develop resistant strains. The Fungicide Resistance Action Committee (FRAC) is responsible for ranking the risk for resistance development in fungal pathogen populations. FRAC assigns codes to each fungicide class based on its mode of action (MOA) and likelihood that its use could lead to the development of resistant strains. Rotating the use of products with different or mixed modes of action and avoiding repeated applications can help prevent the development of resistant populations. It’s important to carefully read and follow the directions described in the most recent version of the product label in an attempt to avoid the development of resistant populations.

Using this Resource

When crop diseases become a problem, use the following section to assist with the decision-making process for fungicide applications.