Farmers have more important things to worry about than soybean rust. That message was conveyed consistently on June 1 at a Syngenta field day just outside Ames, IA. It was not an “all-clear” signal on the dreaded disease for 2005. But company experts and university agronomists at the event were generally in agreement that rust, while lurking on the southern fringes, isn't here in the Midwest yet. Farmers would be better served, they said, by focusing on other fungal diseases and pests that have been established in Midwest fields for many years. Pythium, Fusarium, Phytophthora and soybean aphids ranked high on their list of yield-robbing threats.
Syngenta, which offers the fungicide Quilt as a Section 18 preventative or rescue treatment for rust, sees far more need for its soybean seed treatment Cruiser Maxx Pak, which provides protection against early-season fungal diseases and insect pests. The company believes that this year’s cool early growing season, which favors fungi and soil insects, will show especially good yield improvements for treated seed in 2005.
Because soybean rust is capable of turning a soybean field into a total loss, growers in the upper Midwest are still well advised to remain vigilant against rust. However, they can breathe a little bit easier with each passing day that a soybean rust outbreak isn’t reported in the South. The southern soybean-growing season is well under way, and the entire country is on full alert for rust. But the disease triangle (host, disease presence and favorable conditions) hasn’t been stacking up to soybean rust’s liking so far. Signs are few that rust could reach epidemic proportions as far north as Iowa this year. For the 2005 growing season, only one volunteer soybean plant in Georgia and some spores collected in Texas rain gauges have shown themselves to confirm that rust still exists as a potential threat in the Corn Belt.
So what should soybean growers be most concerned about? Iowa State University’s Palle Pedersen expressed particularly strong concern that Pythium in the spring and soybean aphids later in the season could reduce soybean yields on fields planted with untreated seed.
“Farmers need to balance risks and opportunities. Early planting can boost yields and help reduce the risk of soybean aphid damage,” Pedersen said. “But cool soils favor Pythium, which can reduce stands and limit individual plant yield potential. The only good way to prevent Pythium in early-planted soybeans is with an antifungal seed treatment. A seed treatment also allows the farmer to plant lower seed populations, which becomes more important as the price of soybean seed increases and seed companies move toward pricing by seed count rather than weight.”
Pedersen also pointed out that systemic insecticidal seed treatments provide some, but not complete, protection against aphids. “Unchecked, soybean aphids can multiply tenfold in a week,” he said. “A lot of damage can be done before the farmer is able to spray. A seed treatment insecticide won’t stop the aphids completely, but it will slow them down enough to give you time to scout and get the sprayer into the field.”
For more information about soybean pest control and plant populations, visit extension.agron.iastate.edu/soybean.