How much is weed suppression worth to you in your cropping system? Is it worth enough to change up crop rotations? That’s a question many producers ask themselves as they face tough weed challenges and herbicide-resistant weeds that are extremely difficult and expensive to control.

At a recent University of Nebraska Crop Production Clinic, Nevin Lawrence, Nebraska Extension weed management specialist, noted that adding small grains to a crop rotation can affect weed pressure.

“Small grains like rye, triticale and wheat are the best crops or cover crops at suppressing or preventing weed emergence,” Lawrence said. “This is because they emerge before most summer annual weeds germinate. They are planted close together to not allow a lot of space for weeds to germinate. And they grow quickly to block sunlight from reaching the soil surface.”

All small grains have weed suppressing properties. “Cereal rye might be a little better than wheat or oats, but the differences are slight,” Lawrence said. “Generally, winter cereals are a better option for suppressing summer annual weeds because they would be larger and more competitive at the time summer annual weeds germinate.”

Depriving sunlight

Just like all other seeds, weed seeds need sunlight to germinate. Those weed seeds are able to tell if direct sunlight is hitting the soil, or if there is another plant already established.

“If there is another plant already established, the weed seeds will wait to germinate at a time when no plants are growing above them,” Lawrence added, “so that is why early weed control is essential.”

When corn crops canopy, the ability of weed seeds to germinate is greatly curtailed. “When you are trying to manage a particular weed, it is ideal to have a fully established crop that closes rows before the weed would germinate,” Lawrence explained.

“With kochia or a pigweed in corn or soybeans, the weed emerges at the same time as the crop, and it would not be possible to completely suppress emergence by shading the soil. With a cover crop or small grain crop planted in early spring or fall, you can completely shade the soil and prevent a lot of weed seeds from germinating.”

Cover crop strategies

Simply adding wheat or another small grain to the crop rotation would have weed suppression benefits, but if wheat prices are low, it might not be profitable. “Another option is to include some small grain in rotation as a cover crop,” Lawrence said.

“In western Nebraska, this is difficult at times. Planting wheat after dry beans is not difficult and is a common strategy for many farmers. But corn is grown on a lot more acres, and by the time corn is harvested, it is too late in the year to plant a winter cover crop.”

Lawrence said that he is conducting research on the feasibility of planting a cover crop in the late winter, around early March, but the results of these trials are still pending.

In 2021, research projects that are related to small grains and cover crops will look at cover crops before both sugarbeets and dry beans. Lawrence also is in his second year of a project looking at relay cropping — growing dry beans and winter wheat on the same piece of ground in the same year.

For more information on how small grains and cover crops can suppress weed pressure, email Lawrence at [email protected].