Good planning can help soybean yields, drop risk

PAINTER, Va. — Selecting the correct planting date, maturity group and seeding rate for soybeans can increase yields and reduce risk, explained David Holshouser, Extension soybean agronomist, at the virtual Eastern Shore Agricultural Conference. Research on fungicides and sulfur also was reviewed.
Holshouser’s research identified three principles to maximizing yields: Position beans for the most efficient water, light and nutrient use and the least temperature stress; grow more leaves and reproductive nodes; and protect and maintain leaf area.
He noted that maximum yield potential comes with earlier planting. But, he said, “There is little yield loss up to a certain planting date then yield just falls rapidly.”
One reason for the fall in productivity, he said, is that the plants intercept less sunlight.
“Gaining maturity theoretically gives a slight yield increase,” he said, “but I haven’t always seen that.”
He cautioned that planting too early a maturity group and too early planting date can cause sharp yield reductions because it pushes critical plant development periods to hotter, drier times of the year.
With good soil or high rainfall and correct maturity, “you can keep yields up pretty well even into relatively late planting date,” he said.
His general rule of thumb is “if you’ve got a late planting date or a less-productive soil, go with later maturing variety.”
He stressed that with poor land or low rainfall, planting date becomes more critical.
“Later maturing varieties and somewhat later panting dates — before mid-June, not real late — can help solve poor soil problems.”
He also recommended later maturing varieties for less productive soils “because you push critical growth stages beyond hot and dry times of the year.”
Holshouser said low seeding rates will decrease yields but, “I have found occasionally we have been able to correct low yields with higher seeding rates as the planting date gets later.” He cautioned however that higher seeding rates “are not always cost effective.”
Four years of seeding research has demonstrated “the earlier the maturity group, the higher seeding rate you’re going to need,” he said.
Plant pathologist Dr. David Langston discussed timing and selection of soybean fungicides. He said, “Applying fungicides between the R3 and R5 stages can be the most effective time for improving disease control and yields in soybeans. We recommend you spray these fungicides during that time only when conditions are cool, wet or humid and favorable for disease development.”
He analyzed data on the degree of fungal control achieved by a wide range of fungicides. While responses varied, he concluded, “Most fungicides reduced disease severity compared with the untreated check.”
In one study, three premium fungicide premixes “performed very well at suppressing disease compared to stand-alone products Quadris and Domark,” he reported. They were Priaxor+Domark, Quadris Top SBX and Miravis Top.
Langston said, “Most R3 sprays really didn’t improve yield much over the untreated check with the exception of Quadris Top SBX.
Sprays applied at R5 or two sprays applied at R3 plus R5 did improve yield more consistently compared to spraying at just R3.”
He recommended not using Strobilurin alone due to fungicide resistance. Tetraconazole (Domark) “is generally effective and inexpensive and a consistent performer in fungicide trials,” he said. Quadris Top SBX has proven to be the most consistent premium product, he added.
Keren Duerksen, a Virginia Tech PhD candidate reviewed research on sulfur applications for soybeans. Until recently, she said, acid rain has provided needed sulfur for soybeans, but the Clean Air Act has resulted in “less free sulfur in the air and less being deposited to our crops.”
Duerksen has studied rate, timing and sources of sulfur including ammonium sulfate, gypsum, elemental sulfur and ammonium thiosulfate.
At a Suffolk, Va. research site, one of four such sites in eastern Virginia, ammonium sulfate and elemental sulfur improved soybean yields over the zero control; there was no effect noted at three other sites.
The studies found no significant differences in yield regardless of whether sulfur was applied at planting, at the R1 growth stage or divided between the two.
Likewise, she reported no significant difference in yield response based on the rate of application for three test sites.
At the Suffolk site however, applications at both the 10- and 30-pound rates “yielded significantly higher than the zero-rate control,” she said.