Fungicide seed treatment for soybeans has been thought necessary ever since the soybean production system in the Mid-South changed from traditional May and later plantings to early soybean planting systems. Ensuring against stand failure in early plantings has been thought to be worth the cost of seed treatment even though proving yield increases and greater net returns has been difficult.

Finally, there is proof that treating soybean seeds before planting provides increased economic return. A study conducted in Arkansas and published in the Agronomy Journal by senior author Paul Poag and his colleagues is the first to provide results that place an economic worth on fungicide seed treatment.

According to sources cited in their report, soybean seedling diseases in Arkansas caused an estimated loss of $32.4 million in 2003. Also, they state that there is no feasible instrument to economically test for the presence of seed and seedling pathogens, or to predict resulting yield losses at time of planting. That is why it has been difficult to objectively prove the worth of fungicide seed treatments for soybeans.

The data for their study were obtained from experiments conducted at Stuttgart and Keiser over a three-year period. They used high- and low-quality seeds planted at high and low seeding rates in April, May, and June.

To ensure that conditions were conducive to pathogen development, they applied simulated rainfall when seedlings were emerging.

They used contact, systemic, and contact plus systemic combination fungicides applied to seeds before planting to compare their effect to untreated seeds. Since the cost of the different seed treatments used in their study was relatively minor (<$2 per acre for product) compared to other production costs, the economic impact of the different seed treatments was mainly driven by yield differences.

Their results are striking. According to their analyses, profitability was increased by an average of nearly $18 per acre when high-quality seeds were treated with a systemic fungicide (<$3.50 per acre cost for pretreated seed). This finding was true across locations, planting month, and soil moisture conditions.

Their data revealed another important point. Using high-quality rather than low-quality seeds when both were properly treated increased producer returns by an average of over $26 per acre. When low-quality seeds were used, a seed treatment product containing both systemic and contact fungicides was sometimes superior.

Another conclusion can be drawn from their results, based on the following two points.

First, the cost difference between the systemic fungicide and the product containing both contact and systemic fungicides used in their study was only 27 cents per 50 pounds of seed. (Similar cost differences exist today.)

Second, the use of a product with both systemic and contact fungicides was sometimes necessary to achieve the best results in their study. Therefore, since the cost difference between a systemic product and a combination product is small, it makes economic sense for producers to use one of the myriad products that contain both systemic and contact materials to ensure the best possible results from the application of fungicides to soybean seeds for planting.

My next column will provide a list of combination products that are labeled for soybean seeds.

Larry G. Heatherly is a retired USDA-ARS research agronomist and current crop consultant. e-mail larryheatherly@bellsouth.net