Cooler temps just what crops need

Farmers in southeast Iowa have had a very frustrating planting season, but the recent heat wave and the current cooler temperatures are just what is needed to help the corn crop catch up to historic development norms, according to Iowa State Extension Field Agronomist Rebecca Vittetoe.

Agronomists measure the development of corn using a calculation based on a formula which measures the number of growing degree days (GGD). The historic accumulation of GGD for July 1 is 1,175 GDD but GDD accumulation in Washington County for 2019 was only at 1,000 GDDs, or 175 GDDs behind. The heat wave seen during the Washington County Fair week (July 14-19) helped to close that gap, and the area is now fewer than 25 GDDs behind the historic average.

The cooler temperatures that have set in after the fair are ideal for corn pollination as excess heat can cause stress on corn and can deter the pollination process, Vittetoe said. The cooler temperatures, ensuring less stress during pollination, are a welcome sign for farmers.

But not all fields are equal across the region. The spring rains, which seemed to keep coming, delayed planting longer in some areas than others. In general, the crops look pretty good given the year, Vittetoe said. The corn that was planted earlier is pollinating but corn planted later won't reach that stage until early August, she said. The early-planted corn handled the recent heat wave better than the later-planted corn, Vittetoe said.

Josh Michel, Iowa State University Extension and Outreach field agronomist covering southeast Iowa including Jefferson County, said there are practically two distinct corn crops this year – one planted before the May rains and one planted after. The rains came at exactly the time farmers were trying to work in the field. Michel said corn is usually planted in late April or early May, while soybeans are planted in late May to early June.

'The April planted corn is looking pretty good; it's got a good root system,” Michel said. 'Most of it has tasseled or is tasseling. That corn will do OK, even though we've had less than average precipitation for the past two to three weeks.”

The June planted corn, on the other hand, shows signs of heat and moisture stress. Michel said the June corn is rolling up its leaves and looks like a tropical fruit, which is why it's sometimes called 'pineapple corn” in its current condition. He said the leaves roll up as a way to conserve moisture.

'The June corn was not able to get a deep root system because of the excessive soil moisture we got before it was planted,” Michel said. 'The roots didn't have to grow deep to find moisture. Unfortunately, that means the roots are shallow, and now that it's gotten hotter, we see they are under more moisture stress.”

The fate of this year's soybean crop will be no different, tied very much to when it was planted. Beans planted earlier are in full bloom, but some late-arriving beans haven't started to flower yet, Vittetoe said. Beans in general seem to be smaller and shorter than usual this year.

One pest that has been more prevalent this year across the state is thistle caterpillar, which can cause defoliation in soybean fields. The treatment threshold for defoliation of soybeans is if 20 percent or more of the field is defoliated.

Michel concurred with Vittetoe in observing that the thistle caterpillar has been reported much more this year than prior years.

'I don't know if it's because of the temperature, but the number we're seeing is definitely above average,” Michel said. 'Actually, Jefferson County has seen fewer of them compared to some other areas.”

Michel said the main diseases afflicting corn this year have been gray leaf spot and common rust. The main insect pest has been the Japanese beetle.

Michel said soybeans look good for the most part, though the beans planted in June are pretty far behind their older cousins. He said many of them are still in a late vegetative state (a pre-reproductive phase) and have not put out pods.

'By this weekend (Aug. 10-11), we hope to see those plants start to put on their first flowers, which is where their pods will develop,” he said. 'The timing of planting all depends on the individual farm, whether the ground is ready, and the machinery the farmer has. Some farmers might even plant soybeans before corn depending on the varieties they're using. It varies a lot across the board.”

For most crops, moisture in the soil has been fine. Vittetoe said the United States Department of Agriculture Crop Progress Report indicates topsoil in southeast Iowa is short to adequate leaning toward adequate and subsoil moisture is adequate.

Earlier this spring, the moisture content of the soil was more than adequate – too much, even, preventing them from getting in their fields. Farmers had to worry about meeting the June 15 federal crop insurance deadline for soybeans. For those who decided their fields were too wet to plant at all, their federal crop insurance payment was a welcome relief. However, the payment doesn't fully reimburse the farmer for their lost revenue in most years.

According to a Journal/News story from early June, Iowa was not the only state where farmers were facing this crisis of whether to risk planting or cut their losses and opt for crop insurance payments. Ryan Drollette, a farm management specialist for Washington County, said states like Ohio, Illinois and Indiana were well behind schedule for planting, and that they all had fields resembling swimming pools. The more fields underwater, the greater the pressure for other farmers to plant because the diminished supply will push up the price.

In June, Henry County farmer Alan Miller told The Journal/News about something else farmers must consider. Farmers assume greater risk the later they plant, because those crops tend to yield less. He said the saving grace this year was the good planting weather during the last week in April. The fields were dry and warm, and many were able to plant a substantial amount of corn. In fact, some of the most fruitful planting done this season across the Midwest was done in that pivotal week.

'We haven't done any planting since April 25,” Miller told The Union. 'I did finish with my corn at that time, but some will have to be replanted. All this rain is taking its toll.”

That late week in April made sure that a large amount of corn was planted, but the last couple wet weeks of May undid a lot of that progress. Many farmers were met with delayed crop-heads that forced them to question what their plan was for the season.

Since then, the month of June was drier than May and the month of July much drier still. Michel said the next two to three weeks of weather will have a lot to say about the quality of this year's harvest.

'It's still too early to tell what kind of harvest we'll have,” he said. 'My crystal ball is pretty cloudy.”

- Carter Melrose contributed to this story.