UW Soybean Plant Health
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| Fungicides |
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Sentinel plot in Brazil. |
A major decision will be whether the potential for rust merits the application of a fungicide. There are several factors to consider in making a spray decision to manage soybean rust. It is expected that although soybean rust will affect soybean production throughout the continental U.S., it will be endemic in some areas, and seasonal in others. Disease epidemics are also likely to vary from season to season. Thus, decisions will focus on the need to spray, timing of application, and the number of applications required for a specific field. The need for fungicides will likely be different from region to region and season to season.
Decision starting points
Growers and advisors have several starting points for the decision making process. The first is to monitor rust activity to the south of Wisconsin. A second approach is to monitor the information from the sentinel plots in Wisconsin.
Sentinel plots involve planting early-maturing soybean varieties about 3 weeks before the commercial crops are planted. Spray warnings are given once soybean rust is found in the sentinel plots. Since soybean rust is usually first observed on plants of more advanced growth (beginning flowering (R1) or later), the sentinel plantings provide an opportunity to observe the first signs of the disease before the disease gets a foothold in production fields.
Read more on state and national soybean rust monitoring»
Read more about fungicide timing»
Possible Fungicide Interactions with Soybean Aphids and Two-Spotted Spider Mites
When considering the use of foliar fungicides, attention must be given to their ability to control the disease as well as to economics. Crop advisors must also consider their effects on entomopathic fungi. Entomopathic fungi are naturally occurring and can significantly lower arthropods populations if environmental conditions are favorable.
Results from a 2005 foliar fungicide efficacy test at the West Madison Agricultural Research Station indicated a possible interaction with these fungi because some fungicide treatments had a significantly lower yield with the presence of two-spotted spider mites. Similar results are known to exist with aphids in potatoes as well as other cropping systems.
Information from this site can be copied and distributed for educational use. Please credit the source with our name and URL: University of Wisconsin-Madison, Departments of Agronomy, Entomology, and Plant Pathology at www.plantpath.wisc.edu/soyhealth.
Last update 3/07