Picking a planting date isn’t always an easy decision for soybean growers. Planting too early in cool or wet soils can result in replanting. Waiting too late can lower yields and invite diseases.

Boyd Padgett, LSU AgCenter plant pathologist, is working with AgCenter soybean specialist David Moseley to conduct date of planting research to determine a sweet spot for different soybean varieties.

Padgett said they are evaluating six planting dates and 12 varieties in three maturity groups at the Dean Lee Research and Extension Center near Alexandria. He and Moseley plant two sets of plots for each variety and planting date.

“I don’t spray my variety plots with a fungicide, but he does so we have a comparison,” Padgett said. “This will provide producers with the performance of each variety with and without a fungicide.”

They started planting in March and planted approximately every two weeks until July 1. The wet and cool conditions in spring and early summer did affect their ability to plant on specific dates.

Throughout the growing season Padgett will look to see if disease pressure varies by planting date. He said available fungicides don’t offer complete control of Cercospora leaf blight.

“There is no silver bullet,” Padgett said. “We are kind of strapped with the tools we have.”

He is hopeful that planting date can be used to avoid disease severity on the crop.

“If, for example, we may find that planting the first week of April results in less Cercospora, then a fungicide may be more beneficial or not be needed,” he said.

Padgett said soybean rust appears to be more of an issue on later-planted soybeans, so an early planting date might help growers avoid that disease.

Padgett and Moseley are also conducting an official variety trial at Dean Lee and Central research stations. They planted two identical trials each of 125 varieties of soybeans on the same day. Like the planting date study, one plot will be treated with a fungicide, and one will not. All other pest control applications and cultural practices will be the same for both trials, Padgett said.

“A grower can see if a variety benefited from a fungicide or not,” Padgett said.

The results from these tests are published in the AgCenter’s Soybean Variety Yields and Production Practices guide. Armed with that information, growers can make planting decisions and perhaps choose a variety that doesn’t require a fungicide application.

Padgett is also working with AgCenter plant pathologist Trey Price to determine how effective fungicides are against different soybean diseases. Price said they have fungicide trials at several AgCenter research stations and work with growers to conduct trials in their fields.

“Some problems growers have in their fields you can’t replicate on the station,” Price said.

Both researchers are working to determine how to control fungicide-resistant aerial blight that has cropped up in rice-growing areas of south Louisiana.

“We are looking at new fungicides that aren’t commercially available yet but are showing promise and may be effective against resistant aerial blight,” Padgett said, adding that they are watching soybeans in neighboring parishes where resistance has been documented to see if it is spreading.

Price also is looking at fungicides that can fight taproot decline. They have multiple seed treatment and in-furrow fungicide efficacy trials at the AgCenter Macon Ridge Research Station that specifically target taproot decline. Price said a few promising compounds have been identified, and the researcher is currently generating more data on which to base future recommendations.

“We’ve also installed a variety trial in the field at Macon Ridge to manage taproot decline,” Price said. “We inoculate varieties with the fungus, record reactions and provide data for stakeholders on an annual basis.”

He is trying to determine which varieties show resistance to the disease and recommend those varieties to growers.

Price said ultimately the best way to manage any disease is through resistant varieties.

Boyd Padgett, LSU AgCenter plant pathologist, inspects a field of soybeans used in his date of planting study at the LSU AgCenter Dean Lee Research and Extension Center on July 16. Photo by Tobie Blanchard