Tools of the Trade: Soybean seedling issues

David Kee is the director of research at Minnesota Soybean and can be reached at dkee@mnsoybean.com or 507-388-1635 for questions.

Like a freight train in a tunnel on a dark night, there are a few things you can see coming. We know, from years of experience and research, traffic on wet soils leads to soil compaction.

Well, between rain and snow, it feels like we have been wet since September. We had rutted fields from combining, and little opportunity to correct this situation since. It has also been frustratingly damp, or frozen, this spring. We will wait to work the fields, to the last minute, but the clock is ticking and our optimal window for planting is narrowing.

One of the results from soil compaction is reduced water infiltration, which results in wet (moist) soil. Moist soils are associated with increased soybean seedling disease. Planting into moist soil increases risk for slow emerging seedlings; another opportunity for seedling disease infestation. The most recommended management practice for soybean seedling disease management is to plant into a well-drained, non-compacted soil with soil temperature 55^oF or higher. However, three weeks of sunny, warm (>80^oF) weather is not in the forecast.

As previously stated, the optimal window for planting soybeans is getting narrow. What are our options?

First, identify the problem. There are four common Minnesota soybean seedling disease pathogens: Pythium spp., Phytophthora sojae, Fusarium spp. and Rhizoctonia solani. Fusarium and Rhizoctonia are true fungus; the other two are fungal likes. Consequently, the management practices available are not equally effective in treating these soil borne pests. In a corn/soybean rotation, a single year of corn does not effectively reduce the pathogen to prevent disease. Once you notice a problem, the links below will help diagnose the seedling disease.

Growers should optimize what they can.

Use high quality seed, plant uniformly, manage your nutrients, practice good weed control;
Give the bean seed as much opportunity to outgrow disease infestation;
Use resistant varieties (but variety resistance is only available for Phytophthora;
Use a crop rotation;
Optimize drainage;
Limit soil compaction; and
Do your best to create an environment optimized for the soybean and adverse for the pathogens – all of which should have been accomplished prior to now.

What are your options, today?

Optimal planting in a well-drained, non-compacted soil may be problematic this year. If the site hosted the disease the past two years, pathogen loads may be problematic. This close to planting, seed treatment may be the most viable tool available for growers to use. Below is a table of diseases, soil conditions and effective active ingredients for seed treatments from Minnesota soybean checkoff supported research.