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Difficult to determine what weather will have on yields

By Staff | May 5, 2017

Mark Licht, assistant professor and Iowa State University Extension cropping systems specialist, checks plant growth for corn at the Field Extension Education Laboratory field near Ames.

AMES – With the unseasonably cold, rainy weather most of the state experienced over the weekend and earlier this week, many producers are wondering what the effect will be on those acres that have already been planted into corn.

Mark Licht, assistant professor and Iowa State University Extension cropping systems specialist said it’s most likely too early to tell what, if any, yield robbing issues the cool, wet weather may have caused.

“It’s hard to say how, with anytime we get these cold blips, what the true impact is going to be,” said Licht. “It’s also hard to say what other things may factor into yield loss as we continue throughout the growing season.”

Typically, Licht said cold weather could potentially bring a 5 to 10 percent yield penalty along with wet conditions.

“This might be one of those years where we look back and we say anything that was planted in April dropped yield potential just because of the cold weather conditions we had in April,” said Licht. “This is going to be one of those years that May planted corn is probably going to have a little bit better yield potential than April planted corn.”

Admittingly, Licht said, this particular situation does go against the expert’s recommendations of achieving higher yields with earlier planted corn.

“We do generally say that earlier planting has better yield potential than late planting, but weather trumps everything,” he said.

Crop conditions

Licht said for those acres that have corn that has emerged could be in better shape than the corn that is trying to start to germinate.

“I think the stuff that got planted on the early side, that emerged before this recent cold spell, there could be less of a yield penalty compared to those acres that got planted last Thursday before all of this started.”

Licht said to use the various tools available to help detect heat units in order to be able to track where your corn is at.

“Corn should emerge in 90 to 120 heat units,” he said. “Obviously, this cold weather, we are not accumulating anything. It will take more days to emerge just because of that.”

When the corn that has been planted eventually hits that 120 heat unit mark, Licht said is a good time to get out in the field, and start digging to check for conditions and perform stand assessments.

“At this time, we can start looking at the plant and seeing if it is getting close to emerging or not because that would be a pretty good indicator as to just how much of an impact the cold had,” he said. “We simply need to wait and have emergence occur and then do some stand assessments and look at what the established stand is. If we have plants emerging three, four or five days later, there’s probably more of an impact of a loss in stand than if they have emerged all together or within a day or two.”

Licht added, that if we have seeds that do not emerge because they leafed out underground and started that germination elongation process, but lost vigor before emergence, there will definitely be a direct impact on yield.

“Generally, if it leafs out underground, it’s not going to make it to emergence,” he said. “It occasionally can, but generally not.”

Corkscrewing of the plant is also common in these recent wet, cool conditions, Licht said.

“If we get some nice, warm weather, those that have corkscrewed can still penetrate and emerge,” he said. “Naturally, it is going to be delayed a little bit, but it can still reach emergence and still be a productive plant, but most likely there will be less yield potential, less vigor with that.”

In extreme conditions, Licht said the corn seed may become saturated, begin to germinate and not grow.

“The seed can absorb that water and if it gets cold enough it can kill the seed, or kill that plant from further growth, but that is pretty extreme,” said Licht. “I don’t think we have gotten to that point, at least here in Iowa. But there could be parts of the Corn Belt that could be close to that.”

Seed treatments, Licht said, are helpful, but only to a certain point.

“With a lot of moisture, the chemical used to treat that seed can become diluted, so the more rain we obviously get, the less effective they become,” he said.

The longer it takes for the seed to emerge, Licht said, the more yield penalty or more risk there is for disease pathogens to affect the seed, he added.

“We have a risk of disease pathogens affecting the mesocotyl and the coleoptile,” Licht said. “Those seedling disease might not be truly visible until we get out there to check the plant at the V1 to V2 stage of growth.”

That stage of growth, he added, may show that there also could have been some underground herbicide injury.

“Around that stage we can also look and see if the mesocotyl have some pinching associated with herbicide injury,” he said. “There tends to be a little more risk prone to happen the longer it sits in the ground as well. But again, those are things we have to wait a little bit longer on, to truly be able to identify and see.”

Licht said in order to asses a stand, a grower needs to wait for emergence.

“We can do some early digging and see how that mesocotyl is doing and get some of those early indicators of any cold injury, but in order to make any management decisions, we really have to wait for emergence, at that V1 timing. Unfortunately that moves it to another week or so, but that management decision will have to come later.” he said.

When to plant

When it comes to making the decision whether to plant of not, Licht said there are a few variables to consider.

“You can get yourself in trouble if you look at soil temps alone,” he said. “You need to look at the soil temp, soil moisture and conditions and also, look at that three to seven day forecast. I think that forecast is a key component of when it is the right time to plant.”

In the meantime, Licht said there is still plenty of time to get the corn in to the ground in a productive way.

With the warmer, drier conditions in the forecast, Licht said that should be bring the planters out in full force and with today’s mechanization, planting can be done pretty quickly.

In fact, Licht said he has looked at USDA-NASS numbers in the past and that is where planting progress can really be seen, when it is put into numbers.

“It never fails, toward the middle to the end of the corn planting season, we can get up to a million acres of corn planted day,” he said. “It’s phenomenal what we can truly get planted once we get the good conditions.”

At this stage, we have a good two weeks left of that ideal planting window and fortunately, warmer, drier conditions are in the forecast.

“Be patient, hope the weather turns warm,” he said. “Warmer weather and a little patience is where we need to be right now.

“We’re not sitting in a horrible position right now. We do have time.”

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