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One week makes difference in soybean harvest

One week to 10 days may not seem like an incredibly long time, but to your soybean crop that span of time could be the difference between bin-busting yields and a near disaster.

In August 2001, much of the Delta's soybean crop was decimated by seed decay brought on by extreme warm, wet, and humid weather conditions, which in turn, triggered the soybean disease phomopsis.

“We received nearly 10 inches of rain in Stoneville, Miss., during the Aug. 11-Sept. 3 (2001) period and we had extreme seed rot problems. I've been here 27 years, and I've never seen anything like it in my life, and I don't want to see it again. Had we been out of the field when that rain period occurred we would have had the yield and not had the seed rot,” USDA soybean agronomist Larry Heatherly told growers attending the 2002 Delta Research and Extension Center's rice and soybean field day.

Spared from the crop disaster were those growers who planted shorter-maturity soybeans in an early soybean production system.

The opposite was true in both 1999 and 2000 when much of the Delta experienced severe drought conditions in late summer, yet in all three years one extra week in the field meant the difference between very low yields and respectable yields.

“In our 1999 soybean research we had a 10-day difference in planting dates, but a 20-bushel difference in yield,” Heatherly says. “Both 1999 and 2000 were the driest Augusts I've ever seen. We had one-third inch of rain in August 1999 and none in August 2000. We had extreme drought, and in that kind of scenario a seven- to 10-day difference means the difference between extremely low yields — in the low teens — and respectable yields in the low 30s.”

Ongoing research by USDA's Agricultural Research Service in Stoneville, Miss., could improve growers' odds of harvesting high-yielding soybeans, no matter what hand Mother Nature deals them.

Heatherly is looking for a 120-day-maturity soybean plant (90 days from bloom to maturity) for his ultra-early-season production system in order to stay in the field as little as possible, and still maintain high yields.

“A growing season seven to 10 days shorter is very important to soybean production in this region for what has become our normal weather pattern of extremely hot and dry late July and early August,” he says. “We hope not to see the extreme of last year again, and it's certainly not normal for our region of the country. Our main goal is to get out of the field seven to 10 days earlier to avoid the effects of drought. So, our ultra-early concept hopefully will be very useful once we determine what maturity groups we need to plant at this latitude or other latitudes so that we shorten our growing season by seven to 10 days.”

With the early soybean production system, however, comes the inherent problem of seed decay.

Contributing to the problem, says USDA researcher Alemu Mengistu, is the fact that many early-maturing varieties are produced and bred in the Midwest and have not been evaluated under Mid-South phomopsis disease pressure. “There is no resistance to phomopsis seed decay at present, so we have to integrate the list of genes from plant introductions into the adaptable cultivars for this region.

“Many of the varieties used in the early soybean production systems in the South are bred and adapted to the northern region of the United States. They were not bred for the Mid-South region, and so the breeders with USDA and Mississippi State are working together to breed the necessary genes into more adapted varieties for this region,” says Mengistu, a plant pathologist with USDA's Agricultural Research Service in Stoneville, Miss.

In the meantime, he says, we need to assess the impact of the phomopsis fungus on the early soybean production system, and determine what effect the environment, particularly moisture, plays in its development.

To determine what, if any, differences in yield are caused by of the presence of this disease under various environmental conditions, Mengistu's ongoing research includes three irrigation regimes, including a non-irrigation treatment, season-long irrigation, and irrigation applied only after soybean plants begin blooming.

“What we have discovered already is that the phomopsis fungus can be present in the plant before exhibiting any symptoms. It can stay latent in the plant and then take over at the end of the season when the environment is very conducive to its growth,” he says. “It stays there just waiting for the right environment to cause an epidemic in your soybean field.”

Diverting another disaster, Heatherly says, may lie in combining his ultra-early soybean production system with disease resistance development.

e-mail: [email protected].

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