homepage logo

Late planting options and considerations for corn and soybeans

By Staff | Jun 3, 2019



As we bid a farewell to May and conditions in many parts of the state remain too wet to plant, is it time for producers to begin thinking of switching maturity or even possibly crops?

Iowa State University Extension and Outreach field agronomists Virgil Schmitt and Rebecca Vittetoe shared some of their recommendations and expertise during a delayed and prevented planting webinar last week.

During the webinar, they discussed what can be expected for late planted corn and soybeans as well as an agronomic perspective on prevented planting.

Late planted corn

“Yields do tend to drop regardless of the maturity we are planting at that point after May 20,” said Schmitt.

With a 111 day hybrid, in the northern tier of Iowa, Schmitt said there are some spots, at this time, where we could be pushing the limits and suggests considering backing down a few days of maturity after June 1.

“Come June 13, even a 104 day hybrid does not get matured before being frosted off. At that point, even a 95 day is probably not going to make it, particularly in northern Iowa,” he said.

When considering what maturity to plant later in the season, Schmitt said to look at the average frost dates.

“As we think about maturity considerations with later planting, we do need to remember that the later plantings do have a higher risk of frost before reaching physiological maturity,” he said. “We may also have higher grain moisture at harvest which may increase drying costs.”

In the last 30 years, the northern half to two-thirds of the state of Iowa, has an average killing frost date that occurs in late September to early October. Further south, the average killing frost dates are further into the fall, happening in late October.

Both Schmitt and Vittetoe recommend staying with a well-adapted, full season hybrid until June 1

Vittetoe said a general rule of thumb is to shorten corn maturities one day for every two days after June 1, but to be sure to understand the hybrid you are planting.

“Thinking about how good maturity is, is one thing, if we do switch to an earlier maturity, it is also still good to consider the yield potential of that hybrid, what is the disease package on that hybrid and just other overall tolerances to stress,” she said. “You shouldn’t just be thinking about maturity, but all of the other things you consider when picking out hybrids to plant.”

Weather should also be taken into consideration.

Schmitt said when looking at the seasonal outlook from the National Weather Service, for the months of June, July and August, there could be a potential for below average temperatures and a higher chance of above average precipitation.

“So, for many of us here in Iowa, it looks like it is going to be a little bit cool and wet throughout the growing season,” he said. “With that, we need to remember cooler than normal temperatures will provide us a slower than normal corn maturity.”

Is switching to a completely different crop like soybeans an option?

“The answer is, maybe,” said Schmitt. “One of the questions we have to ask is, do we already have some corn herbicides down that would prohibit that? If we have something down that is an atrazine product, for instance, then we would have some issues there.”

If herbicides have not been applied, another factor to consider is the reason why we don’t raise soybeans following soybeans.

“That is simply because they tend to not do as well and the reason they tend not to do as well is we have a lot of disease issues out there we start to build up, so we need to make sure we look at good yields for those soybeans, but the other thing we need to be thinking about, is it also needs to have a very excellent disease package,” he said.

Late planted soybeans

“Just like corn, our soybeans will adjust to being planted later,” said Vittetoe.

Soybeans are photo-period sensitive and they will adjust to being planted later. Some research that has been conducted at seven of the ISU research farms, Vittetoe said, showed the same soybean maturity planted 40 to 60 days a part matured within seven to 10 days of each other.

“That just shows how the soybeans will adapt to being planted later,” she said.

When looking at different maturities, from .5 to 1.0 maturity group spread, Vittetoe said the soybeans had a three to five day difference in maturing.

Preventive planting

With preventive planting as a potential option, Vittetoe and Schmitt said, through an agronomic perspective, producers need to think about weed management and soil health.

“Weed management is going to be important if you do decide to take preventive planting,” said Vittetoe. “We don’t want to let more weeds go to seed and contribute to that weed seed bank.”

Not only will putting those acres into a cover crop help with weeds, it will also help to prevent fallow syndrome.

Preventive planting rules state that there is no grazing or haying of a cover crop planted on preventive planting acres until after Nov. 1.

“If we are thinking about haying or grazing, what is the condition of that cover crop going to be on or after Nov 1,” said Schmitt.

One option of a cover crop on those acres is soybeans. Schmitt recommends planting them at 60,000 to 80,000 seeds an acre – about half of a normal rate.

“Basically we looking for something to protect the soil and hold the nutrients in place,” he said. “And because we want to have that quick canopy, there we suggest planting them in 15-inch rows or less. You may, if weather permits, broadcast the soybeans and disk them in.”

Using soybeans as a cover crop, Schmitt said is fairly inexpensive and will work especially well if soybean herbicides have been applied. Soybeans will also winterkill, so there will be no need for termination of that cover crop in the spring.

There are disadvantages of planting soybeans as a cover crop. Schmitt said they don’t provide as much cover and are not a nitrogen scavenging crop.

Corn is another potential cover crop.

“This one again is fairly inexpensive and you can use bin-run corn for example,” he said.

Corn will also winter kill, but a disadvantage is it will provide less of a canopy than soybeans.

Oats are another option. Schmitt said plan for one bushel to the acre if they are drilled and one and a half bushels if they are broadcasted. Oats will also winter kill and won’t be a hindrance come next spring.

Some disadvantages to using oats as a cover crop:, oats are very sensitive to herbicides and are hard to broadcast from a plane. Schmitt said many pilots do not like to broadcast oats and would prefer spring barley.

“Spring barley would be a good substitute, but it would cost a little bit more,” he said.

Cereal rye, a popular cover crop in Iowa, can also be used on preventive planting acres.

“Again, this is something inexpensive,” Schmitt said. “If we have herbicides applied, I’m not making any guarantees, but cereal rye is probably the most forgiving of any herbicides we have out there. It does an excellent job of protecting the soil and also scavenging for nitrogen in the fall and spring.”

“You need to have a plan in place for weed management on those preventive planting acres,” added Vittetoe.

Please Enter Your Facebook App ID. Required for FB Comments. Click here for FB Comments Settings page