By DOUG SCHMITZ
Iowa Correspondent

IOWA CITY, Iowa — While ideal planting time for soybeans is the same as for corn – late April to early May – delayed planting may actually hold advantages for farmers, according to an Iowa State University extension field agronomist offering advice when soybean planting must be delayed because of weather or soil conditions.

“The yield potential doesn’t decline as rapidly for soybeans (as with corn) with delayed planting,” said Jim Fawcett, who oversees several eastern Iowa counties. “If most of the soybeans can be planted by May 20, there may not be much of a decline in yield potential.

“I think it is still possible that most of the planting can be done by around May 20, but it will obviously depend on the weather in the next couple of weeks. One potential advantage of the delayed planting is that it might reduce sudden death syndrome (SDS) and bean leaf beetle problems.”

Despite widespread problems last year with SDS in southeastern Iowa, Fawcett said it was virtually nonexistent on the ISU research farm in Crawfordsville, since they weren’t able to get soybeans planted until late last year.

The Iowa Soybean Assoc. (ISA) stated while soggy and cool conditions have kept farmers out of the field, the optimal planting dates for soybeans – April 25 in southern Iowa and May 1 for the northern half of the state – have already “come and gone.”

The average rainfall in the state this April was five inches, or about 1.36 inches above normal, the ISA said. By comparison, in April 2008, the second wettest April recorded, the precipitation totaled 5.88 inches, or 2.55 inches above normal.

Although spring 2011 planting is off to a slow start because of the cool, wet weather, Fawcett said there were a few fields planted before the rains came on April 14. In fact, most farmers waited for the cold snap that was forecast for Iowa at that time to pass “and it was probably good that they did,” he said.

“Some got back in the fields on April 30, and planters were going strong over most of the area by May 2,” which he added may further stave off disease. “We were thinking that there was a potential for more bean leaf beetle problems this year since the winter temperatures were not as extremely cold as the past few years, but if planting is delayed, that will reduce beetle problems.
“It forces the overwintered beetles to survive on alfalfa until the soybeans have emerged; they do not reproduce well when they feed on alfalfa.”

Fawcett is also somewhat concerned about northern corn leaf blight, “since we have had two bad years in a row and it appears that there may have been a race shift in the fungus, so the resistant varieties are not as resistant as they used to be.

“A lot will depend on the weather,” he added. “If things turn dry, diseases may not be the main concern.”

Looming threats of plant diseases aside, it’s unlikely farmers will get soybeans planted early enough to maximize the growing season, said David Wright, ISA director of contract research and strategic initiatives. he said farmers can expect to lose 0.3-0.7 bushels per acre per day due to delayed planting, with yield loss more prevalent in fields planted after May 10.

“Even though planting has been delayed, don’t rush and mud it in, if our current rainfall pattern continues,” he said. “The extra couple of days waited will have benefits later on in the growing season. The biggest risk in mudding-in is sidewall compaction, which limits soybean growth and root development.”
Wright added soybeans need a healthy, vigorous root system to take up water and nutrients, “and for later in the season when rainfall may be less abundant.
“It’s the number of roots that matters during the critical seed-fill period because water and nutrients are taken up into the root just behind the root tip,” he said. “More root tips equals greater stress tolerance and yield potential.”

Like Wright, Mark Licht, ISU extension field agronomist covering the counties in central Iowa, said farmers need to consider soil conditions at planting time.
“Farmers must be patient by not rushing in to plant in wet soil conditions,” he said. “Waiting for suitable soil moisture and warmer temperatures will result in faster, more uniform emergence. Warmer, drier soils also reduce the risk of soil-borne pathogens that can infect the plant, such as Pythium.”

While many are comparing this planting season to the spring of 2008, Wright said more farmers are using seed-applied fungicides this year, which, he added, may help reduce root infection by soil-borne pathogens.

Licht said a fungicidal seed treatment may be one of the more profitable input costs because of the risk of soil-borne pathogens for the 2011 season.
Although seed-applied fungicides won’t reduce the negative impact of soil compaction in the seed zone, Wright said “2011 will be a good test of performance of fungicide seed treatments.

“Good weed management will continue to be critical, especially in later-planted fields,” he said. “Farmers should get a good pre-emergent herbicide down if they can.”

But if farmers can’t use a preemergent herbicide or rely on post-emergent herbicide, Wright said they need to apply it in a timely manner to reduce weed competition.

“Weeds are constant competitors for the water and nutrients soybeans need for fast growth and development,” he explained. “Iowa is predicted to plant 9.4 million acres in 2011, with the capacity to plant a million acres a day.
“Farmers should consider first the best soil conditions to get their crop off to a good start,” he added. “Patience will pay off.”