Soggy, cool conditions have kept farmers out of the field, and the optimal planting dates for soybeans, April 25 in southern Iowa and May 1 for the northern half of the state, have come and gone. The average rainfall in the state of Iowa for April 2011 was 5 in. – about 1.36 in. above normal. In April 2008, the second wettest April recorded, the precipitation totaled 5.88 in. – 2.55 in. above normal.

In addition to rain concerns, Iowa State University (ISU) Extension Climatologist Elwynn Taylor says the strong shifts between cool and warm weather will continue through the spring and summer since La Niña is the strongest it has been in 50 years.

“The National Weather Service forecasts the rest of spring to be on the cool side of average,” Taylor says. “We expect equal shifts from one extreme to the next every couple of weeks, which is not favorable for crops. Yields are expected to be below normal due to La Niña conditions.”

David Wright, Iowa Soybean Association (ISA) director of contract research and strategic initiatives, says it’s unlikely farmers will get soybeans planted early enough to maximize the growing season. Farmers can expect to lose 0.3-0.7 bu./acre/day due to delayed planting. Yield loss may be more in fields planted after May 10. However, Wright warns against rushing the process.

“Even though planting has been delayed, don’t rush and mud it in if our current rainfall pattern continues,” Wright says. “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 explains early root development is critical to provide healthy roots and rapid vegetative growth.

“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. More root tips equals greater stress tolerance and yield potential.”

Mark Licht, field agronomist for ISU, agrees with Wright that a major factor is considering soil conditions at the time of planting.

“Farmers must be patient by not rushing in to plant in wet soil conditions,” Licht says. “Waiting for suitable soil moisture and warmer temperatures will result in faster, more uniform emergence. Warmer, dryer soils also reduce the risk of soil-borne pathogens that can infect the plant, such as Pythium.”

What to do with fungicides and herbicides

While many farmers and climatologists are comparing this spring to spring 2008, Wright says more farmers are using seed-applied fungicides this time, which may help reduce root infection by soil-borne pathogens. However, seed-applied fungicides will not reduce the negative impact of soil compaction in the seed zone.

“2011 will be a good test of performance of fungicide seed treatments,” Wright says.

Licht agrees, “This year a fungicidal seed treatment may be one of the more profitable input costs due to the risk of soil-borne pathogens.”

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

However, if farmers are unable to put down a pre-emergent herbicide and relying on post-emergent herbicide, Wright says it’s important to apply in a timely fashion to reduce weed competition.

“Weeds are constant competitors for the water and nutrients soybeans need for fast growth and development,” he says. “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. Patience will pay off.”