Research HighlightsManaging the unplanted
By Daniel Lemke, photos by Daniel Lemke and Wanbaugh Studios
Saying that farmers across North Dakota and nationwide faced challenges during the 2019 growing season is an understatement. Wet conditions through much of the Corn Belt resulted in an estimated 19.4 million acres of prevented planting according to the USDA Farm Service Agency (FSA). The FSA reported over 830,000 prevented planting acres in North Dakota alone.
Just because farmers were unable to plant crops in those areas doesn’t mean management stops. In fact, unplanted areas require additional attention for weed control and nutrient management.
Unplanted acres can be the perfect environment for weeds to grow un-checked. If the fields are dry enough to allow implements in, farmers could manage weeds by spraying, tilling and establishing cover crops.
“A lot of prevent plant acres in North Dakota have been tilled,” says Joe Ikley, North Dakota State University (NDSU) Extension weed control specialist. “If that tillage was done in late July and fields were not worked again or planted to cover crops, there will likely be some weed management issues.”
Weed management experts have long advised farmers to watch for weed trouble spots or escapes while fields are harvested. Noting the type of weed and the location can help growers formulate next year’s management plan. That practice is still recommended for planted and unplanted fields.
“Be aware of what weeds went to seed to prepare for next year,” Ikley says. “What goes to seed will be an issue next year.”
“Prevented planting provides the perfect conditions for certain weeds to enjoy a good seed bed,” explains crop consultant Sarah Lovas. “If those weeds, like waterhemp or ragweed, are difficult to control or are herbicide resistant, areas where farmers took prevented planting provide the perfect conditions for them to grow.”
Spreading the Word
Ikley participated in a series of meetings across North Dakota to help farmers address concerns with prevented planting acres. He says that the main thing farmers need to understand is what weed species have gone to seed.
“The biggest thing is to know the weeds that have seeded and then be strategic. If it’s waterhemp, that weed is easier to control in corn than in soybeans,” Ikley says, “so it’s important to know what’s in the seed bank because it could affect next year’s rotation.”
Ikley says that waterhemp is likely the main weed concern, but there could be other weeds that farmers will need to control, such as ragweed or kochia. He recommends using post-harvest down time to plan for next year based on what farmers learned about their weed populations this fall.
Lovas adds that there could be rotation issues with herbicides and other management options, so farmers should keep that in mind when planning for next year’s crop. Growers also need to pay attention to field edges and the areas around prevented planting acres.
“Check the edges because weeds can creep in from field edges,” Lovas says.
Where possible, getting a cover crop established on prevented plant-ing acres is the preferred management option. If those acres don’t have a cover crop established, they’ll be most likely to be prevented planting again next year.
Planting cover crops helps to suppress weeds. Ikley says that, if grasses such as cereal rye are established, there is a good scenario for controlling broadleaf weeds. Broadleaves are easier to control in the fall, so spraying 2-4D or dicamba herbicides will kill most weeds without harming the rye.
Established cover crops will do more than manage weeds. The crops also utilize some of the excess water that kept farmers from getting the crops planted in the first place.
“Cover crops are a good management tool for both water usage and weed suppression,” Lovas says. “Those acres that were wet this year typically will be the last ones planted again next year, so using up that water is critical.”
“Without that cover crop to utilize the excess soil moisture, the possibility of prevent plant could arise again, especially if the snowmelt and rainfall we receive next spring is close to normal,” says Angie Johnson, the NDSU Extension agent for Steele County.
Getting a cover crop established on prevented planting acres, especially in areas with high water tables, can be helpful to manage soil salinity, Johnson says.
“Salts can be an issue in prevent plant acres as well. In areas with high water tables, salts move through capillary rise up towards the topsoil, causing challenges to raising a crop,” Johnson says. “Lowering your groundwater table by incorporating cover crops on can be an option to help utilize water and keep the salts down in the soil profile.”
According to Johnson, another consideration that gets overlooked with prevented planting acreage is soil micro and macro activity. With no live cover, the soil has no roots present to help create pore space for water to infiltrate into the soil profile (instead of ponding on the surface). Macro activity, such as earthworms, also create pore space for water movement down the soil profile, and earthworms need plant material to feed on in order to survive.
“Our good microorganisms also start to show a decline when there is reduced plant life present in our soils,” Johnson explains. “This can be visually assessed by looking at your soil aggregates.”
Fallow Syndrome Concern
Lovas says that farmers need to be on the lookout for the potential to have fallow syndrome in prevented planting acres. Mycorrhizae form a symbiotic relationship with plants and help the plants take up phosphorous. Not all plants host the soil mycorrhizae, so fallow syndrome can occur following a non-host crop, such as sugarbeets, or if the land was not planted at all.
Symptoms of fallow syndrome can be corn plants that look purple because they’re not getting the needed nutrients from the soil.
“If farmers plan to plant corn into prevented planting acres next year, they will need a good fertilizer program, and they may need to add phosphorous and zinc,” Lovas says.
Lovas explains how growers will need to manage their phosphorous program so that the nutrient is available for crops right away in the spring. While fallow syndrome is most common in corn, Lovas says that small grains can suffer from it, too, and may require additional fertilizer.
Using cover crops can also help manage fallow syndrome. Lovas says that getting cover crops planted early in the summer gives the seed time to become established, giving the roots a chance to explore the soil. A diverse cover crop mix is best to help develop those mycorrhizal relationships.
Visit with your local NDSU Extension agent if you have questions or want additional information.
Published: Dec 4, 2019