Published on Tuesday, March 10, 2020
Manganese (Mn) is important in a soybean plant for its role in the activation of enzymes and in the process of photosynthesis. Additionally, Mn is known to regulate potassium (K) uptake. Mn deficiency can be characterized by interveinal yellowing of soybeans. Early on, it can be confused with iron deficiency and can be referred to as “yellow flash.” This deficiency is often found in higher pH soils, dry soil conditions, depressed areas of the field, and soils high in organic matter, sand, peat, or muck. A combination of any of these can amplify Mn deficiency. A lack of moisture causes Mn to be present in a form that is not plant available. A rain event can alleviate Mn deficiency in cases where Mn is present in the soil but not available to the plant.
Fungicide applications are often made to prevent disease from entering a soybean field. Once a disease has set in, it is likely that yield has been lost, but the amount can be unclear. University and industry research alike has shown a synergistic effect with the combined use of fungicides and insecticides however, specific yield gains will vary from one year to the next. In a meta-analysis done at the University of Wisconsin, a 0.5 to 1.0 Bu./A. advantage was noted in various Midwestern states. Additionally, we know that the damage caused by insects can further promote diseases and therefore justifies the combined application.
Many soybean fungicides are recommended at an R3 application. What does R3 look like and why is it important? The R3 growth stage in soybeans is identified by having at least one pod that is 3/16 in. long at one of the four uppermost nodes (as demonstrated to the right). Because R3 is the start of pod development, it's also the best time to control diseases and insects. A majority of yield (about 60%) comes from nodes 7 to 13. An R3 application would add protection to those nodes, which might explain the positive yield response.
Seven-year PFR data has shown a $17/A. ROI advantage from an R3 application of fungicide and insecticide with a breakeven soybean grain price of $5.75/Bu. If soybeans are sprayed at R2, our per bushel price to breakeven rises to $11.50/Bu. By missing the application by a single growth stage (R4), the breakeven rises to $10.91/ Bu. Essentially, missing the R3 timing results in a cost of roughly $5/Bu.
Both university and PFR data have shown that foliar applications of Mn are recommended to provide the crop with additional Mn in a plant available form. PFR results showed Versa Max™ Mn and MAX-IN® Ultra Manganese to be PFR Proven in 2016. When applied between V3 and V4 at 2 qt./A., Versa Max Mn has shown an average yield increase of 5.2 Bu./A. MAX-IN Ultra Manganese is also applied at a 2 qt./A. rate between V3 and V4, and has averaged a yield increase of 4.3 Bu./A.
Data from The Ohio State University has shown yield advantages when applying MAX-IN Ultra Manganese at R3, providing an increase of 8.0 Bu./A. in sandier locations. This yield advantage was present in fields where the control plots did not show deficiency symptoms.
Author: Jim Schwartz
Categories: Agronomy, Agronomy Talk