Managing foliar soybean diseases and fungicide applications
Often we are asked for the appropriate fungicide application timing for managing soybean diseases. Interestingly enough, that is a question that will be followed by additional questions from the plant pathologist. The reason for asking for more information is simple, but the answer might not be so cut and dry.
Those questions might be:
Which disease(s) are you concerned about?
What is the variety? (Is it susceptible to the pathogen of concern?)
Have you grown this variety before?
Was this disease present the last time you grew that variety?
What is the current growth stage of the crop?
Are you seeing symptoms of the disease at present or are you concerned about preventing an anticipated problem?
Is the field irrigated?
Have you used fungicides on this crop this season?
There could be others depending on the individual situation. Why are these questions asked? Because all of this information is important in answering the original question. A direct answer to the original question without additional information would be inappropriate.
Let us begin with the facts. Plant diseases may cause yield and quality losses in the soybean crop, but not all diseases are equal in importance. Disease management systems vary from one grower/region to another, but integrated approaches to management should be the norm. Integrated approaches include, disease resistance, cultural practices that might reduce disease development, and the use of fungicides.
No soybean variety has resistance to all diseases, but variety choice should include any available resistance to the main diseases of the geographic area where the crop is grown if the variety also possesses agronomic and yield characteristics desirable to the grower. Often fungicides are needed to protect yield and quality of the crop.
Current Considerations and Basic Principles
If a fungicide application is warranted, there are many considerations before choosing a product. Many fungicides are labeled for use in soybean. Basically, producers have five chemistry types from which to choose based on modeofaction. The Group 11 fungicides, or strobilurins (“strobies”), include but are not limited to products such as Aproach, Quadris, Headline, and Gem. The Group 7 fungicides, or SDHIs, include Endura, Vertisan, Priaxor, and others.
Group 3 fungicides, or triazoles, include products such as: Domark, Proline, and Topguard. A single Group 1 fungicide, thiophanatemethyl, is available to producers in several products (Topsin, Incognito, and Cercobin). A Group M5 fungicide, chlorothalonil, is available to producers in three products: Bravo, Echo, and Equus. All of the above-mentioned chemistry types are available in a number of premixes containing two different modesofaction.
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