The spring planting season is soon upon us. Prevent plant acres, or fields which were too wet to be planted to a cash crop last year, may need some special attention this season. As final preparations are made for planting, suggested strategies will depend on how these areas were managed in 2019.
In fields where a cover crop was planted, be sure to have a termination plan for cover crops which overwintered, such as cereal rye. To protect yield, a general guideline is to terminate the cover crop 10 to 14 days prior to planting the cash crop — particularly if planting corn, since an overwintering cover crop can create a “green bridge” for insect and disease pests. This timing can be less stringent for soybean, although it is recommended to terminate the cover crop prior to planting to minimize risk.
If a non-winter hardy cover crop was planted like oats, the cold temperatures of winter should have taken care of termination. Sometimes, however, some radish or turnips can survive the winter, or seeds will germinate in the spring instead of the previous year. Check fields for survivors and apply an appropriate burndown herbicide around planting time as needed to ensure these plants do not compete with the cash crop.
If an herbicide is used for termination, apply when the cover crop is actively growing and use an appropriate rate for the cover crop growth stage.
For more details on spring management of cover crops and termination tips, see https://extension.umn.edu/cover-crops/spring-management-cover-crops.
As far as planting into cover crop residue this spring, most planters are well equipped to handle moderate levels of residue. Be sure to check for good seed-to-soil contact, planting depth, seed placement and any other issues, and be prepared to make adjustments if necessary. Useful tips for planting into higher residue situations can be found at https://crops.extension.iastate.edu/encyclopedia/equipment-maintenance-planters.
If you used cover crops for the first time in a prevent plant situation, but like what you’re seeing in terms of soil conditions, 2020 could be a year to expand your experiment to different species or planting methods. The Midwest Cover Crop Council and University of Minnesota Extension have cover crop recipes and a species selector tool to help you make a plan for cover crops in 2020 (http://mccc.msu.edu/).
Fallow syndrome is a risk in fields where there was little to no plant growth last year. Fallow syndrome occurs when populations of “good fungi,” called vesicular-arbuscular mycorrhizae (VAM), are dramatically reduced because VAM fungi need actively growing roots to survive. VAM fungi assist in the uptake of phosphorus, zinc and other nutrients with limited mobility in the soil.
Corn is at the greatest risk of yield loss due to fallow syndrome, while soybean is at low risk. If you are planning to plant corn in a field at risk of fallow syndrome, the best course of action is to band phosphorus and chelated zinc directly on the seed as a starter at planting. A normal application of 10-34-0 at a rate of five gallons per acre should be sufficient. Be sure to not apply too high of a rate directly with the seed due to risk of root damage to corn (and especially soybean).
For more information on preventing fallow syndrome in corn see https://blog-crop-news.extension.umn.edu/2020/03/how-to-prevent-fallow-syndrome-in-corn.html
In fields or areas where management was not possible (e.g. too wet, inaccessible with equipment) and weeds took over, a tremendous contribution to the weed seedbank was likely made. Although tillage would help bury weed seeds, burial can help enhance survivability of weed seeds and subsequent tillage operations will bring weed seeds back to the soil surface. Leaving seeds on the soil surface by avoiding tillage this spring will leave them more susceptible to predation and decay, thus lowering weed seedbank levels.
A burndown herbicide may be needed in these areas to target early-emerging weeds, and an application of a preemergence herbicide at the full labeled rate is recommended. Be sure to scout these fields and utilize a layered approach where you apply another preemergence herbicide with the postemergence herbicide application about 30 days after planting, as needed. Apply to small (less than 3 inches), actively growing weeds, and ensure you have good coverage where weed populations are thick. Be sure to check herbicide labels for recommended rates and application restrictions.
The University of Minnesota and North Dakota State University have compiled pre-emergence and post-emergence diversification strategies for key problem weeds. They can be found at https://drive.google.com/file/d/1QorYainbBjIac9PtTo2VfK5a3TDS2HtR/view.