Strategic Farming: Let's Talk Crops Focused On Small Grains

Phyllis Bongard, Content development and communications specialist, and Jochum Wiersma, Extension small grains specialist

Small grains are versatile since they can be grown as a profitable crop in the crop rotation or grown as a cover crop to provide ecosystem services or forage.

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. 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. 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.

Source: umn.edu