How could Group 3 soybeans fit in Louisiana crop systems?

The Mid-South's move to earlier soybean varieties continued in 2006. While Group 4s currently make up more than half of Louisiana's soybean acres, Group 3s are increasingly attractive. Is that warranted?

“A few years ago, when we first began growing (Group 4s) in central Louisiana, out of about 20 varieties or so, two or three were well-adapted,” said Steve Moore, LSU AgCenter researcher at the recent crop demonstration meeting at the Dean Lee Research and Extension center in Alexandria, La. “I noticed those that got above 20 bushels per acre were Group 4.5s or later.

Three years ago, Moore began getting questions about Group 3s. At that time, some farmers had cut high yields with Group 3s and other producers wondered if they might follow suit. Among those interested were members of the Louisiana Soybean and Grain Research and Promotion Board, which funded a Moore study on the variety group.

“When we began this work two years ago, I was a bit skeptical. But the results we've seen since, coupled with the disease cycles that have hit Louisiana, have caused me to look at Group 3s in a different light.”

The Group 3s allow farmers to get out of the field very early in the fall.

In August, when Groups 3s are typically harvested, there are often more favorable soybean prices.

But the biggest factor driving producers to early-season soybean production is disease.

“Cercospora and Asian soybean rust are beginning to rule the roost. They're threatening to govern the future of soybean production in the state — particularly in central and southern Louisiana.”

For the past five to seven years, Cercospora has been growing in incidents and severity.

“It's getting worse and worse. This year, though, it boiled over the top. Here (on the Dean Lee Research Station), we're seeing numerous tests planted after mid-May coming up with empty pods. We're blanketed with Cercospora. I believe we're even beginning to see some effects of the disease where you don't see the foliar symptoms but it's still in the crop early-season in the pod.

“To me, Cercospora in soybeans is becoming like aflatoxin in corn. It's becoming the dominant disease that drains our economics in producing soybeans.”

And, also knocking loudly at the door is Asian soybean rust. “ASR has been around for several years. This year, it sprang up and took off — in late September and into October it really came on.”

Moore was holding out hope ASR would strictly be a late-season disease. Every time he saw ASR, it was in R6, or later, soybeans.

But the week of Oct. 9, during ASR collection with the USDA, Moore and colleagues found the disease in R1 and R2 soybeans.

“I hope it remains a late-season disease, but it can jump on early beans too. Regardless, late-season disease pressure could force early planting and harvest to obtain good yields.”

Before ASR arrived in Louisiana, Moore found early-planted soybeans escape perennial aerial blight better than later-maturity groups. He wondered if the ASR/maturity group connection would show the same.

“You could rate aerial blight in the variety test and as you moved from Group 4s, 5s, 6s and even 7s, you'd see an aerial blight increase in the late maturity groups. But the Group 4s had matured and were harvested before aerial blight became a factor.”

If ASR similarly remained a late-season disease, the early-season soybeans could be the best method for escaping pressure.

“So we began looking at the Group 3s and Group 4s at multiple planting dates at the Dean Lee station and the Macon Ridge Station.”

In 2005 and 2006, early Group 3 tests were planted at both stations.

In 2005 in Alexandria, “we planted on March 30 and May 2. The March 30 field yielded 22 bushels per acre. The May field saw a yield increase to 38 bushels per acre. We gained about 3 inches in plant height — I thought we'd see more.”

And even though there was a month difference in planting date, there was only about 11 days difference between harvests.

This year in Alexandria, Moore and colleagues planted on March 27 and April 28. The earlier beans yielded 27 bushels per acre. On the later beans, they again saw a yield increase of about 16 bushels to 43. This year, the later beans gained over a foot in plant height compared to the early.

As for the Macon Ridge tests, in 2005 the tests were planted on March 30 and April 30. The earliest beans had a respectable yield for March Group 3s at 35 bushels. There was an 11-bushel yield gain for the later beans and a 3-inch plant height difference.

Again, even though there was a month difference in planting date, there were only 11 days between harvest times.

This year, the Macon Ridge tests were planted on March 28 and April 20. The March beans yielded 27 bushels per acre. The April beans yielded 20 bushels more at 47 bushels — “that's very good yield for Group 3s.”

Plant height increased 6 inches. Again, there was an 11-day gap between harvests.

How do these compare to other maturity groups? For 2005 tests at Alexandria, the Group 4s were also planted early and late. The early Group 4s yielded 42 bushels and the late Group 4s yielded 45 bushels.

“Notice that when you compare this to the Group 5s and Group 6s, the late date was very competitive. That's even though the Group 4s did much better than the Group 3s.

“If you can plant early and cut down on some fungicide and insecticide sprays, there's an advantage to planting Group 3s.”

Another test was conducted on a top Group 3 variety. “We planted it in two replications on 38-inch row spacings here in Alexandria. We began on March 31 and were able to plant every week for seven weeks.”

On the March beans, researchers harvested 19 bushels per acre. The second week yielded 20 bushels and the third, 27 bushels. Then, in the third week of April, the yield made a big jump to 38 bushels per acre. The next two weeks saw yields of 40 and 41 bushels. After that, yields began falling off.

“Now, admittedly, we need more data than this. More extensive studies are being conducted. But based on what we know now, there's an advantage to delaying planting of the Group 3s. Using this data alone, I'd guess the best date to plant would be from mid-April to April 25.”

Points to consider:

Late-planted Group 3s performed well in both 2005 and 2006.

March planting appears to be detrimental to Group 3 production.

In the tests, there was about a 35 percent yield increase in favor of the late-planted beans.

“Any company developing Group 3s and Group 4s for the Deep South needs to focus on selecting for good agronomic adaptations that fit our environment. Mainly, the focus needs to be on dry-down and shattering. The pod needs to be toughened up.”

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