Fungicide seed treatments offer protection from seedling diseases that can reduce soybean stands and yields in Arkansas, says John Rupe, University of Arkansas Division of Agriculture plant pathologist.

Three years of research data can help producers know which fungicides are most effective for seed treatments, Rupe says.

Three groups of pathogens cause seedling diseases in Arkansas: Pythium, Rhizoctonia and Fusarium. Five different species of Pythium cause disease in the state. University of Arkansas scientists are still identifying the Fusarium species responsible for disease. Only one Rhizoctonia species, Rhizoctonia solani, is known to cause disease in Arkansas.

Division of Agriculture scientists have tested nine commercial fungicides at three planting dates in April, May and June. The tests were conducted at three locations in northeast, east-central and southwest Arkansas. Both high-quality and low-quality seeds were included in the tests, Rupe says.

Test plots with treated seed showed significantly better seedling stands than untreated control plots at some or all of the planting dates at each of the research sites.

The research demonstrates that fungicide seed treatments can improve stands — and often, yields — with both high- and low-quality seed that's planted in a variety of environments and locations, Rupe says. This is especially important if growers reduce the seeding rate to reduce planting costs.

“The improved stands and yields were seen mostly in seed planted in April or June,” Rupe says. “Plant stress from being planted in soil that's either too cool or too hot seems to be having an effect on the results.”

BROAD-SPECTRUM fungicides that control multiple pathogens were more consistently effective in varying environments than fungicides that control specific diseases, Rupe says. “This suggests there are a number of different pathogens causing seedling diseases in these locations,” he says.

Low-quality seed benefited more often from fungicide treatments than did high-quality seed, Rupe says, though both high- and low-quality seed saw improved stands, yields or both in many plots.

“The longer it takes a plant to emerge from the ground after planting, the more vulnerable it is to diseases,” Rupe says. “High-quality seed gets out of the ground faster.”

In ongoing research, Rupe and graduate student Valeria Avanzato are trying to narrow down which specific pathogens are attacking the plants at the various planting dates, environments and soils. Rupe is also working with University of Arkansas soybean breeder Pengyin Chen to screen cultivars and breeding lines for resistance to Pythium.

“When we started this study three years ago, we believed Pythium was the most important seedling disease we were dealing with,” Rupe says. “In the seed treatment studies, broad-spectrum fungicides were more effective than fungicides that specifically treated Pythium, indicating that other pathogens were also at work in Arkansas fields.”

Rupe and Chen found one soybean variety that has resistance to Pythium, and are taking a closer look at some others that they believe may also have resistance.