When to treat soybean seeds for no-till

Spring brings questions about when to use chemically treated soybean seeds for no-till. Make the decision based on the risk level of seedling diseases. Using fungicide to treat seeds is beneficial only when risk of seedling diseases is high. The risk level of seedling disease in a field is associated with the following factors:

1. If there is a history of stand reduction for a field in the past few years, there is a high disease risk in the field.

2. Use of low quality seeds increases disease risk.

3. Planting early at soil temperatures lower than normal increases disease risk.

Of the three factors, the history of stand reduction is the most important in assessing disease risk. A history of stand reduction means that the disease is in your field. If your no-till fields had seedling diseases in recent years, you didnt have high quality seeds, and you planted soybeans early, seed treatment may insure your profitability. Weather also affects the occurrence of seedling diseases. A cold, wet spring, such as the spring of 1993, increases disease risk.

To effectively manage seedling diseases, you must know the causal agents to select the right chemicals. Studies at Iowa State University, which were supported by the Iowa Soybean Promotion Board, found that last years soybean seedling diseases were caused by Pythium, Phytophthora, Rhizoctonia, and Fusarium in Iowa. Pythium and Phytophthora accounted more than 50 percent of total infection, and Rhizoctonia accounted for about 30.

Updated 04/14/1994 - 1:00pm