There is a wide range of soybean planting dates and maturity groups planted across the area.
Fungicide applications began a few weeks ago and will continue through this month on chosen acres. Dr. Carl Bradley, Extension plant pathologist with the UK Grain and Forage Center for Excellence at Princeton, compiled the following comments about making decisions regarding fungicide use on soybean fields. Beginning pod developmental stage, R3, is generally the stage to consider an application of a foliar fungicide for protection against foliar diseases.
Areas that have received frequent rainfall have a greater risk of foliar diseases. In addition to rainfall, the risk of foliar diseases is also determined by other factors, such as the soybean variety planted and the cropping history in a field.
The primary foliar diseases of concern in Kentucky are frogeye leaf spot, Septoria brown spot, Cercospora leaf blight and target spot. Of these diseases, frogeye leaf spot has been the most important in terms of causing yield reductions in Kentucky. The incidence and severity of frogeye leaf spot are influenced greatly by the soybean variety being grown. Some varieties are highly resistant to frogeye leaf spot, while others may be susceptible; therefore, it is important to be aware of the disease ratings of the varieties planted in your fields.
In general, Septoria brown spot often is not an economic concern, as symptoms are typically only on leaves in the lower canopy. However, in years with frequent rainfall throughout the season, spores of the Septoria brown spot pathogen may splash to the upper canopy and cause some upper leaves to prematurely defoliate.
When this happens, some yield loss can be attributed to Septoria brown spot. Although target spot and Cercospora leaf blight may occur in Kentucky, the appearance of these diseases generally has been later in the season, which has often been too late to cause yield reductions.
A soybean disease scorecard titled "Know Your Disease Risk in Soybeans: What's Your Score?" is available in the resources section of the Take Action website. This scorecard can be used on a field-by-field basis to help determine what the risk is for foliar disease development and can help make fungicide application decisions.
If the decision is made to apply a foliar fungicide, it is important to choose a product that has efficacy against the spectrum of diseases that might affect your field. It is also important to choose a product that contains multiple modes of action to help manage the potential of fungicide resistance. Isolates of the frogeye leaf spot pathogen and the Septoria brown spot pathogen that are resistant to strobilurin (group 11) fungicides are present in Kentucky, and isolates of the Cercospora leaf blight pathogen that are resistant to strobilurin fungicides have been confirmed elsewhere in the U.S., so fungicide resistance is an important consideration.
To help make a decision on which fungicide products might work best for the diseases you intend to manage, the "Fungicide Efficacy for Control of Soybean Foliar Disease" publication on the Crop Protection Network can provide information that will help with that decision.
Corn, Soybean and Tobacco Field Day
The University of Kentucky's Corn, Soybean and Tobacco Field Day is tomorrow at the UK Grain and Forage Center of Excellence at Princeton. Registration begins at 7 a.m. CDT. Tours begin at 7:50 a.m. and will offer producers in-depth, educational options related to grain crops, tobacco production, and ongoing research projects at the station.
Participants will have time to attend two of the three tours given by UK Grain and Tobacco Extension Specialists. Discussion topics include dicamba stewardship, cover crop management systems, soybean cyst nematode management, and disease management in burley and dark tobacco.
Certified crop advisers can receive two continuing education credits per tour. Pesticide applicators can receive two general hours and one specific hour in categories 1A, 10, and 12 per tour. The field day concludes with lunch provided by the Kentucky Corn Growers Association, Kentucky Soybean Promotion Board, Gallatin Redrying and Storage Company, and Hail and Cotton International Group. The UK Research and Education Center Farm is at 1205 Hopkinsville St. in Princeton.