Barnyardgrass is a vigorous summer weed that thrives in rich, moist soils and can even withstand partial submergence. It’s often found in open, sunny areas such as cropland, pastures, marshes, roadsides and in wet ditches across the United States. It can also quickly drain soil of important nutrients such as potassium, nitrogen and phosphorus.
Favorable Conditions for Prolific Weed Seed Production
Barnyardgrass flourishes in moist, compact soils where there is plenty of sunlight and temperatures range from 75° to 90° F. If left untreated, the weed can grow to 5 feet in height. Barnyardgrass is versatile enough to survive dry periods, but growth and seed production are greatly reduced, reducing its threat during drought.
Nutrient Loss: Important nutrients such as potassium, nitrogen and phosphorus can be quickly taken up by barnyardgrass. About 60 to 80 percent of soil nitrogen can be robbed by barnyardgrass in an impacted crop area.1
Emergence Timing: Plants emerging from July through September will only be a fraction of the size of those germinating in March and April. These late arrivals pose little threat to crops, as barnyardgrass is susceptible to crop shading.
The greatest threat? Barnyardgrass weeds that appear in early spring.
- At emergence, barnyardgrass has a reddish color. The first true leaf is smooth and wide with a rounded tip. Rolled in a bud, the seedling will turn green and grow to about ¾ inch tall. Seedling leaves are without hairs, distinctly flat, and tinted a dark red at the base.
- Barnyardgrass is one of the few grasses without auricles or ligules at the junction of the leaf blade and sheath. The leaf sheath is also rolled into a bud and is open but compressed.
- Mature leaves range in length from 4 to 20 inches and have a thick white midvein. They are rough to the touch on both sides, but the leaf collar is smooth and the stem is flat.
- Weeds grow in clumps by rooting and branching at the lower joints. A single plant can grow as many as 15 tillers, creating a patch-like look in the field. Expect to see denser tillering in areas of high soil fertility.
- The root system is dense and fibrous, and one plant can cover a 30-inch diameter with roots that reach only 2 to 6 inches below the soil surface.
- Flowering takes place from July to October. The dense, erect, branched flower head can be 2 to 8 inches long. About a dozen pencil-shaped purple and green side branches, each ¾ to 2 ½ inches long, develop individual spikelets containing seeds.
- The unique seedhead is green to purple in color. It has a 2- to 8-inch densely packed bristle with pale yellow, 1/8-inch seeds that are flat on one side and round on the opposite.
Known Resistance to Barnyardgrass
Barnyard grass is resistant to many classes of chemistry, including ACCase (1) and ALS (2) inhibitors. Many barnyardgrass control programs have used glyphosate (9) as the foundation. While there is no documented barnyardgrass resistance to glyphosate, higher rates may be needed for control as field conditions indicate possible resistant populations.
How Do I Manage Barnyardgrass?
Because barnyardgrass does not handle shade well, early-season field crops will be good competitors. In cultivated fields, prevention is important, so start early with a pre-emerge followed by a timely post when weeds are still small.
Because of regional crop differences, a range of management practices can help manage barnyardgrass, including:
- Avoid mowing; the plants will quickly regenerate.
- In the South, use a soybean-rice rotation.
- For the best coverage and efficacy, use full herbicide rates and manage the timing of post-emergence herbicide applications.
- Using a disk harrow will eliminate young plants before they grow seeds.
- Plow in the fall or use a shallow tillage program to allow germination so weeds can be eliminated before planting. The risk of erosion becomes too high on sloping ground, so only use these practices on flat ground.
Bayer Solutions for Barnyardgrass
Bayer offers growers season-long weed control options starting with the decision to purchase LibertyLink® soybeans. LibertyLink soybeans are widely available in many brands including Credenz® soybeans. This year’s soybean herbicide program allows growers to start and finish clean with the inclusion of a full lineup of residual products combined with the powerful control of Liberty® (10) herbicide.
Liberty is the pre-eminent weed management system, with a unique chemistry and novel site of action to offer superior control of a broad spectrum of resistant and tough-to-control weeds in LibertyLink soybeans. In fact, it is the ONLY non-selective post-emergence herbicide that still effectively handles grasses and broadleaf weeds, including barnyardgrass.*
To learn about proper application tips, visit S.T.O.P. weeds with Liberty for maximum control.
Remember: Not every product is suitable for every situation, and use of the correct application technique will ensure the best results. A well-thought-out herbicide program, using multiple sites of action, should be implemented to sustainably manage weeds. Before applying any herbicide, please read the entire label for the best possible results and to confirm that the product is effective on the weeds you wish to control.
To learn more about products Bayer offers to help control weeds in soybeans as part of an integrated weed management program, contact your local Bayer representative.
*The active ingredient in Liberty is a Group 10 herbicide, which is the only broad-spectrum herbicide that effectively controls grasses and broadleaf weeds, and it has no known resistance in U.S. broadacre crops.