The newly updated K-State publication Foliar Fungicide Efficacy Ratings for Wheat Disease Management, 2015, EP130, is now available. This publication focuses on the most widely marketed fungicides in Kansas and examines how effective these products are at controlling the most common leaf diseases. This publication can be found at: http://www.ksre.ksu.edu/bookstore/pubs/EP130.pdf
In recent years, I have received a lot of questions about the length of residual activity of the different fungicide products and questions about the nature of the fungicidal activity of the products. Below are some thoughts to consider when evaluating the product options.
Residual life of fungicides
The research that I have reviewed indicates that fungicides listed in the publication Foliar Fungicide Efficacy Ratings for Wheat Disease Management 2015 will generally provide 21 days of good protection against fungal diseases. This includes products with the active ingredient tebuconazole that is listed in the table as the product Folicur but is also marketed in a number of generic formulations. The diseases will often begin to recover and there are differences in residual life after this 21-day period.
The residual life of the fungicide is influence by many factors, including the rate at which the product is applied, the targeted disease, the level of disease pressure, and weather conditions. Fungicides applied at the full-labeled rate will generally have longer residual life. Fungicides will generally provide longer residual life against rust diseases (often more than 21 days) than leaf spot diseases. Some of the products may provide additional residual life but this extra residual does not always translate into more grain yield.
The chart below is just one example of the type of data that supports the 21-day residual activity for the various fungicide products.
Pre- and post-infection activity
The comparison of fungicide products often includes a discussion of terms like preventive vs. curative activity. These terms have confused a lot of people and I think we should be discussing the fungicides in terms of pre-infection or post-infection activity.
Both the triazole fungicides (Prosaro, Caramba, Tilt, and Folicur) and the strobilurin fungicides (Headline, Aproach, and Evito) prevent new infections from developing on healthy plants and are best applied when disease is at low levels. We might consider this pre-infection activity. The triazole fungicides are generally considered to provide some post-infection activity as well. This means that they can stop the development of fungi during the early stages of the infection process when the fungus begins to invade and colonize the plant. Because the strobilurin fungicides lack this post-infection activity, they are often combined with triazoles in mixed mode of action fungicides such as Quilt Xcel, Stratego YLD, and Twinline.
The bottom line is that producers have a lot of excellent fungicide options. A little time spent up front evaluating the options and their costs will help make you make a good decision later. In my experience, based on the all the data I have seen in research trials in Kansas and other states, correctly identifying when fungicides are needed, or not needed, is more important than which product you use.
Erick De Wolf, Extension Plant Pathology