Unlike years' past, the early 2018 growing season wasn't fraught with fields of waterhemp or marestail. The bigger problem, at least for many fields in eastern Nebraska, was volunteer corn – in some cases, multi-stacked resistance volunteer corn.
The factors that led to this year's volunteer corn woes are well-documented by this point: 50-mile-per-hour winds combined with weak ear shanks last fall resulting in higher-than-normal amounts of downed corn. In some cases, fields had as much as 30 bushels left on the ground. Despite growers' best efforts to clean up these fields this year has seen widespread issues with volunteer corn.
That said, here are a few takeaways on this year's volunteer corn problems:
1. Yield impact depends on density. Much like any weed, the impact on yield depends on the density of volunteer corn, and the crop it's infesting.
"Based on UNL's research, it tends to be worse in soybeans than it is in corn," said Jenny Rees, Nebraska Extension educator. "The general hypothesis is that it's due to the different architectures in the soybean plant. Data shows with high amounts of volunteer, you could lose anywhere from 40 to 60 bushels per acre, depending on the density of volunteer corn. It's really competitive with soybeans."
University of Nebraska-Lincoln research shows volunteer corn has a bigger yield hit on soybeans than on corn. This research shows volunteer corn densities of 3,500 plants per acre led to a 10% yield reduction in soybeans, while doubling the density to 7,000 plants per acre led to a 27% yield reduction.
Meanwhile, clumps of volunteer corn led to even greater yield losses, because they were more competitive than individual plants. In this case, a density of 3,500 clumps per acre brought a 40% yield reduction. A recent UNL study found the greatest yield reduction in soybeans happened when volunteer corn was left uncontrolled or when controlled too late at the R2 growth stage.
In corn, the yield reduction is less severe. UNL's research found a volunteer population of 3,500 plants per acre brought a 2% yield reduction in corn, while 7,000 plants per acre brought a 5% yield reduction, compared to a density of 7,000 clumps per acre, which brought a 14% yield loss.
2. Options for control. The good news is, soybeans have more options for control of volunteer corn compared to corn-on-corn. So, the first recommendation, if it looks like there will be a lot of ears on the ground, is to plant soybeans, said Amit Jhala, Nebraska Extension weed management specialist.
"If it's Roundup Ready corn, there really aren't many herbicides that can effectively control volunteer corn. The only option would be Enlist corn, which is resistant to 2,4-D choline, glyphosate and a group of graminicide, or a grass herbicide known as FOPs [arloxyphenoxypropionate]," explains Jhala. "You can use those herbicides to control your glyphosate or LibertyLink volunteer corn in Enlist corn."
This year was the first year Enlist corn was commercially available. If growers planted Enlist corn this year, and it seems likely volunteer corn could be a problem again next year, it's a good idea to rotate with soybeans.
"Then you can use the remaining group of graminicide, known as DIMs, like Select Max and Poast, so you're able to control Enlist volunteer corn in soybeans," Jhala said. "If you planted Enlist corn, then in year two you can't control volunteer Enlist corn because it's also resistant – and you can't use graminicides like Select Max or Poast in corn."
There is NO selective herbicide in corn that can control volunteer corn, especially when volunteer corn is resistant to glyphosate (Roundup) plus glufosinate (Liberty), leaving growers with the one option left for control: inter-row cultivating.
3. Plan ahead. While it's impossible to tell for certain how widespread volunteer corn will be, there are a few things to watch for. Volunteer corn is a problem every year, but last year, weak ear shanks and high winds were the primary cause of widespread issues However, it's often the case that stalk rot plays a role in down corn. While stalk rots are more of a problem in years with strong fungal disease pressure, it can potentially be a problem in years like this where corn plants experience rapid growth due.
That's why it's recommended to watch fields before harvest and test stalks for stalk strength. Nebraska Extension advises growers to harvest fields affected by stalk rot first.
"We're again going to have to watch stalk strength. It's getting hot again, and we're getting close to tassel in the next week or two," Rees said in late June. "High heat during pollination can change the diameter of the ear shank, and we may be setting up for that again this year, although it's hard to tell at this point."
"As you walk a field, you can still see beautiful ears on the ground and corn hasn't germinated from it yet," Rees added. "It's amazing even at this point in the season how much corn is on the ground."