Phyllis Bongard, Content development and communications specialist, and Jochum Wiersma, Extension small grains specialist
Dr. Jochum Wiersma, Extension small grains specialist joined Extension Educator Nathan Drewitz to discuss these and other small grain topics in the March 1st Strategic Farming: Let’s talk crops session.
Winter cereals can provide many benefits. Their fibrous roots help hold soil in place to reduce erosion. The biomass that they produce can help suppress weeds and add organic matter to the soil. They can also scavenge nitrate from the soil profile, though depending on planting and termination dates, this benefit may be minimal.
Research conducted at the University of Minnesota’s SWROC studied nitrate reduction in tile lines for four winter rye seeding dates ranging from September 15 to October 30. The earliest seeding date was the only one of the four treatments where nitrates were reduced in the tile lines during the fall. Winter rye in the other three seeding date treatments didn’t produce enough biomass after October 1 to make a difference in nitrate uptake.
By the end of April, the earlier seeded rye had enough biomass so that it reduced the amount of nitrate leaching to the tile line by about 30%. However, the greatest nitrate reductions would be expected between the end of May and into June, a time when the winter cereal would be competing with corn. As a result, winter rye is typically terminated before it can significantly reduce nitrate leaching, unless it is established by mid-September.
Small grains grown as cover crops
Winter cereals
Winter cereals – rye or wheat - are often used as cover crops in corn and soybean rotations. Winter rye, for example, is very winterhardy, relatively inexpensive, and easy to establish, making it an attractive option when wanting to provide ecosystem services.Winter cereals can provide many benefits. Their fibrous roots help hold soil in place to reduce erosion. The biomass that they produce can help suppress weeds and add organic matter to the soil. They can also scavenge nitrate from the soil profile, though depending on planting and termination dates, this benefit may be minimal.
Research conducted at the University of Minnesota’s SWROC studied nitrate reduction in tile lines for four winter rye seeding dates ranging from September 15 to October 30. The earliest seeding date was the only one of the four treatments where nitrates were reduced in the tile lines during the fall. Winter rye in the other three seeding date treatments didn’t produce enough biomass after October 1 to make a difference in nitrate uptake.
By the end of April, the earlier seeded rye had enough biomass so that it reduced the amount of nitrate leaching to the tile line by about 30%. However, the greatest nitrate reductions would be expected between the end of May and into June, a time when the winter cereal would be competing with corn. As a result, winter rye is typically terminated before it can significantly reduce nitrate leaching, unless it is established by mid-September.
Choosing to raise the winter rye or winter wheat as a grain crop, however, completely changes this picture as both winter wheat and winter rye will take up most of their nitrogen during the month of June, right as the potential of nitrate leaching is the greatest.
The Hessian fly is one of the earliest invasive species in North America. It has two generations each year with the later one overwintering as pupae in winter cereals. Its cycle will be broken if adults can’t find a suitable host – such as winter wheat or winter rye - to lay eggs on. In addition to growing resistant varieties, following Hessian “fly-free” seeding dates are recommended to help break the green bridge for this pest, unless small grains are not in the crop rotation. The current guidelines for Minnesota’s fly-free dates are September 30 for south of I-90, September 25 for US-12, September 20 for MN-28 (Morris, Glenwood), and September 7-10 up to the Canadian border. It’s possible these dates have shifted with warming temperatures, but new research is needed to find out whether that is the case.
While technically not a green bridge situation, winter cereals used as cover crops can attract the first flights of true armyworms in the spring. Armyworm adults, which are carried up from the south with weather fronts, look for green, grassy areas in the spring for egg laying. If that lush area happens to be a cover crop, the armyworm larvae will feed on it until it’s terminated, then move into a corn or even soybean crop. Several cases were reported last season where corn had to be replanted due to armyworm infestations that began in winter rye.
Thanks to the Soybean Research and Promotion Council and the Corn Research and Promotion Council for their generous support of this program.
Concerns and challenges
The ecosystem services provided by winter cereals don’t come without risks, particularly when they are planted early and when small grains are in the crop rotation.Avoid the “Green Bridge”
Winter wheat and winter rye are alternate hosts to several disease and insect pests. When winter cereals overlap with volunteer spring wheat or another host, a “green bridge” is created for pests to continue their life cycle. One such pest is the Hessian fly.The Hessian fly is one of the earliest invasive species in North America. It has two generations each year with the later one overwintering as pupae in winter cereals. Its cycle will be broken if adults can’t find a suitable host – such as winter wheat or winter rye - to lay eggs on. In addition to growing resistant varieties, following Hessian “fly-free” seeding dates are recommended to help break the green bridge for this pest, unless small grains are not in the crop rotation. The current guidelines for Minnesota’s fly-free dates are September 30 for south of I-90, September 25 for US-12, September 20 for MN-28 (Morris, Glenwood), and September 7-10 up to the Canadian border. It’s possible these dates have shifted with warming temperatures, but new research is needed to find out whether that is the case.
While technically not a green bridge situation, winter cereals used as cover crops can attract the first flights of true armyworms in the spring. Armyworm adults, which are carried up from the south with weather fronts, look for green, grassy areas in the spring for egg laying. If that lush area happens to be a cover crop, the armyworm larvae will feed on it until it’s terminated, then move into a corn or even soybean crop. Several cases were reported last season where corn had to be replanted due to armyworm infestations that began in winter rye.
Be mindful of herbicide restrictions
Preemergence herbicides are an essential tool in today’s era of herbicide resistant weeds. However, they are more likely to injure sensitive cover crops, particularly under dry conditions. Be sure to carefully read herbicide labels for rotation restrictions, preharvest intervals and grazing restrictions if the cover crop will be used for forage.The argument for widening crop rotations
Wiersma encourages growers to think about winter wheat and winter rye not just as a cover crop and an expense, but as an actual crop to generate income. There are advantages to including small grains in the crop rotation. Most crops other than corn - including soybeans -need a minimum of a two-year break to fully exploit the benefits of a crop rotation. . As weed control continues to become more expensive and complicated, a systems approach with a widened rotation may make more sense.Oats
Oat is a good alternative to winter cereals as a cover crop. Because it doesn’t have a vernalization requirement like the winter cereals, it will reach stem elongation and produce biomass in the fall. This biomass is a good source of forage, an attractive option for a livestock operation. Even if the forage is harvested, the remaining stubble will prevent wind and water erosion.Other cover crops
Could flax be a good alternative to small grains as a cover crop? Flax has a very fine seed, so requires very shallow seeding. As a result, establishing it in the fall and getting good growth is likely more difficult than any other cover crop.Spring outlook
Drought and winter rye seed production
Last fall, a lot of winter rye was seeded into dry soils. How might that affect seed production? First, check to see if the seed germinated. Look for the radicle (first root) and coleptile shoot. Even if the shoot didn’t reach the surface, the seed should have started to vernalize during the fall and it should make it. If, on the other hand, the seed stayed dry through the winter, it’s unlikely that the winter rye would accumulate enough cold units - soil temperatures between 32 and 50 degrees F. – to produce seed.Drought and seeding depth
In a drought situation, how deep can small grains be seeded to try and reach moisture? To help answer this, Wiersma is characterizing coleoptile lengths for varieties for each of the small grain species. Generally, oats can be planted deeper than wheat which can be planted deeper than barley. Likewise, taller varieties can be planted somewhat deeper than shorter varieties. If needed, oats can be planted to a 3-inch depth and wheat to about 2-1/2 inches. Seeding depth limits are trickiest to determine for barley, since it requires an early and uniform emergence.Disease outlook
How do the drought conditions of 2022 change what we should watch for this season? Since it was relatively dry, the risk for Fusarium head blight may be reduced. However, that is still a field-by-field and in-season decision. The risk for rust may also be reduced, since Nebraska and Kansas - the area that the spores come from - are also in a drought. If conditions become favorable, watch the residue-borne diseases, like tan spot, Septoria, and Fusarium head blight.Insect outlook
Grasshoppers were a major issue last spring in northwestern Minnesota. After the dry fall, it’s possible that there could be another outbreak this spring.Join the webinar series
University of Minnesota’s Strategic Farming: Let’s talk crops! webinar series, offered Wednesdays through March, features discussions with specialists to provide up-to-date, research-based information to help farmers and ag professionals optimize crop management strategies for 2023. For more information and to register, visit z.umn.edu/strategic-farming.Thanks to the Soybean Research and Promotion Council and the Corn Research and Promotion Council for their generous support of this program.
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