Iowa farmer John Hanson of Gowrie finds himself in a situation akin to nearly all farmers in the state over the last few months.
“We’re dry,” Hanson says. “We had some snow this winter, but it all melted and our tile lines aren’t running at all. The creeks are already dry.”
This winter’s lack of moisture combined with a multiyear drought has created spring planting concerns, says Angie Rieck-Hinz, Iowa State University Extension agronomist. Although drought plagued much of Iowa last year, crops still yielded well in some of those areas.
The difference between 2023 and 2024, though, is that adequate soil moisture sustained crops for many weeks last year. “A large part of Iowa does not have that luxury going into the 2024 growing season,” she says.
What to do?
University of Nebraska research shows that tilling soil can trigger a 0.5- to 0.75-inch loss of soil moisture per tillage pass. This can worsen moisture losses in soils that are already dry, and lead to non-uniform germination and emergence. A joint research project completed by University of Minnesota and North Dakota State University shows soil moisture differs with various tillage practices, Rieck-Hinz says.
Here are some tillage tips from Rieck-Hinz to consider this spring:
Do a little. If fall tillage left a rough field surface, do spring tillage to provide an adequate seedbed for planting. Till as shallow as possible to obtain a good seedbed. Tillage also should be done as closely to planting as possible.
Check soil surface. If fall tillage left an adequate soil surface and seedbed, you may not need to do any spring tillage. You can easily plant into existing conditions by adjusting your planters to manage residue. Leaving residue intact will reduce evaporation from the soil and lessen soil particle detachment when rain does fall. When rainfall occurs, it will also reduce soil crusting and allow more water to infiltrate.
Plant directly. If you didn’t do any fall tillage, you may plant directly into existing residue. This allows existing residue to reduce evaporation from the soil by acting as a mulch. This may require adapting your planter to manage the residue. More information is contained in the ISU Integrated Crop Management blog, Considerations for No-Till and High Residue Fields in a Predicted Dry Season.
Cover crop termination may also be earlier this year. Favorable temperatures have spurred cereal rye and other overwintering cover crops to break dormancy earlier this year. This means they’re actively growing and pulling up soil water. Consider terminating cover crops earlier than originally planned to conserve soil water, she says.
“Once terminated, the decaying cover crop will serve as a mulch or barrier and reduce soil evaporation,” she adds.
For more information on terminating cover crops, visit the ICM blog, Cover Crop Termination Review for 2023.
Other issues of concern
Drought can also impact the following areas:
Weed control. Preemergence herbicides continue to helpful in preventing early weed flushes. However, drought complicates their effectiveness.
“Some of these active ingredients have certain water requirements for activation,” says Andrew Penney, a Bayer technical agronomist. “Unfortunately, if we don’t get rain, weeds can’t take in the [herbicide] product. This makes it challenging in really dry climates to maintain efficacy with preemergence products.”
Some preemergence products are encapsulated, but that doesn’t help during drought, Penney says. Encapsulation, instead, enhances herbicide performance under soils that are wet and saturated.
Even so, it’s still advised to use preemergence herbicides in a weed management program. “Start with a foundation [preemergence] herbicide,” says Ron Geis, a market development specialist for Corteva. “That will give you four to six weeks of activity. As that starts to wane, you will get other [weed] flushes. That’s when you want to come in with a postemergence residual herbicide to take it [the soybean crop] to canopy.”
Drought nixes preemergence herbicides’ effectiveness due to lack of activation. However, the good news is drought also slows waterhemp germination. This can play into early soybean planting strategies, where preemergence herbicides are also applied earlier.
“Waterhemp normally germinates [in Iowa] about May 15,” Geis says. “But if it hasn’t rained by May 15, there’s a good chance that waterhemp has grown little due to dry weather.”
When rainfall finally occurs and incorporates the earlier applied preemergence herbicide, some activity will remain to partially control waterhemp until a postemergence residual herbicide can be applied to take the soybeans to canopy, Geis says.
Herbicide carryover. In some drought years, herbicide stays too long and carries over into the next year.
“There were parts of Iowa that were dry into the growing season a year ago and definitely had some herbicide carryover issues,” says Matt Vandehaar, a Pioneer field agronomist. “If you look at weather patterns in certain parts of Iowa, it’s replicating what it did a year ago where it didn’t rain much and didn’t allow for the breakdown of some herbicides after those applications.”
Unfortunately, there is little that can be done now to deter it. However, farmers should watch for reduced stands triggered by herbicide carryover and resulting replant decisions, Vandehaar says.
Group 27 — including HPPD inhibitors such as mesotrione, such as Callisto, and isoxaflutole, such as Corvus — was the main herbicide class that carried over in affected parts of Iowa in 2023. Carryover is most likely to occur when late applications were made in corn, Vandehaar says.
“If that’s the case, you need to be out watching those fields this year, particularly if it was dry after application,” he says. However, it’s important to watch all fields for carryover, as carryover can also occur when earlier applications are made, he says.
Corn rootworm. Dry weather also exacerbates the chances of high corn rootworm populations later this year. Although it’s difficult to predict populations, several factors point to potentially high numbers. Due to drought, large soil cracks developed late last summer and early fall.
“Adult rootworm beetles were able to lay eggs deep into moisture,” Vandehaar says. “We also didn’t have a lot of cold weather to kill off a lot of those eggs.”
However, don’t sweat your corn being overrun by rootworm beetles just yet. “We have a long way to go before actual hatch,” he says. “We certainly could have some June rains that could drown out those eggs and larvae. But right now, it’s a concern because we haven’t had any conditions to decrease populations.”
Traits, soil-applied insecticides and crop rotation are all ways to manage corn rootworm. However, all those decisions have been made for 2024. This summer, though, is a chance to prepare for your 2025 corn rootworm management program.
Plan on scouting cornfields later this summer to monitor adult beetle populations that will later lay eggs, Penney says. Root digs this summer also enable farmers to assess root damage, he adds.
“If we continue to have dry situations, we will have to be vigilant about monitoring rootworm pressure in fields,” Penney says.