Grasses can have a significant economic impact on crops. They compete for water, light, space and nutrients, all factors which can reduce yields. In order to manage their farms for maximum profitability, farmers must be able to first identify and understand the biology of common grasses and then design effective integrated weed management programs to control them.
Tricky Grass Identification
Many common grasses share similar characteristics that make them difficult to identify. One example is the group of similarities shared by fall panicum, Johnsongrass and barnyard grass. Fall panicum is often mistaken for Johnsongrass or barnyard grass prior to the formation of a seedhead. Johnsongrass, however, has a thin membranous growth from the blade, known as a ligule. Unlike fall panicum, Johnsongrass seedlings lack hairs on their lower leaf surfaces. Additionally, barnyard grass does not have any ligules, and barnyard grass seedlings sometimes only have hairs near the leaf base.
Fall panicum, a summer annual that can reach 7 feet in height, is found throughout most of the United States. Its zigzag growth pattern, which it exhibits by bending at the nodes of its large, round, smooth sheaths, is a primary identifying characteristic. In addition to being mistaken for barnyard grass and johnsongrass at the seedling stage, fall panicum can easily be confused with green foxtail until the differences become more evident in fully grown plants.
Barnyardgrass is a summer annual with thick stems that can grow up to 5 feet in height. Found throughout the United States, Canada and Mexico, it is one of the few grass weeds that lacks ligules, a feature that helps distinguish it from most other grasses in both the seedling and mature stages of growth.
Johnsongrass, which originally made its debut in the United States as a forage crop, is now one of the most prevalent and troublesome weeds of crop fields, hay fields, pastures, roadsides and ditches. This perennial weed has a thick mass of jointed white rhizomes that can reach 9 feet in height. It is capable of rapidly colonizing in various environments because of the large amount of seed and mass of rhizomes it produces. To identify Johnsongrass, look for leaf blades without hairs on both sides; however, some hairs might appear at the base of the leaf blade. The ligules are 3 to 4 millimeters in length, membranous and often toothed at the end. This membranous ligule is distinct from fall panicum or barnyardgrass. Seedheads are large, open and often have a purplish hue. The seedlings and mature plants of Johnsongrass also share some of the same characteristics as shattercane, but shattercane lacks the mass of tough rhizomes characteristic of Johnsongrass.
Shattercane is an annual weed that looks and grows like Johnsongrass and grain sorghum. It has even been known to hybridize with cultivated Johnsongrass and sorghum. This grass is usually without hairs and has very long, flat leaves that are 1 to 2 feet long and 1 to 2 inches wide. The leaves have a distinct midvein. The membranous ligule is 1 to 2 millimeters long, and the seedhead is quite compact, unlike Johnsongrass.
Several varieties of foxtail – yellow, giant and green – can cause problems in agronomic fields. All foxtail weeds are clump-forming summer annuals with seedheads that resemble a fox’s tail. They can be found throughout the United States, particularly in areas with fertile soil. Long, silky hairs appear at the base of the leaf blades, which can reach 12 inches in length and 7 to 12 millimeters in width. There are no auricles (outgrowths on the leaf collar), and the ligule has a fringe of hairs reaching 2 millimeters in length. Stems are erect, hairless and often flattened with a reddish tint at the base.
To identify yellow foxtail, look for the characteristic foxtail-like seedhead, which yellows upon maturity, and leaves with long, silky hairs, which appear only at the base. Conversely, the leaf blades of giant foxtail have many short hairs on their upper surfaces, as does green foxtail. Giant foxtail is also typically larger and has a seedhead that droops – or nods – when mature, unlike the other foxtail species.
Pesky Pair: Goosegrass and Crabgrass
Another commonly confused pair of common grass weeds that are typically treated postemergence are goosegrass and crabgrass. Goosegrass is a summer annual with flattened stems that radiate outward from a distinctive white or silver center, even on seedlings, which distinguishes this weed from most other grasses. Leaf sheaths are flat and smooth. Plants often appear compressed or flattened against the soil . On mature plants, leaf blades are 2 to 14 inches long and 3 to 8 millimeters wide, without hairs or only sparsely hairy, and folded along the midvein. This weed might be confused with smooth crabgrass, but the leaves of goosegrass are folded in the bud, while those of smooth crabgrass are rolled in the bud.
Crabgrass has two varieties: smooth and large, which is also referred to as hairy crabgrass. They are summer annual grasses with ascending growth habits, but smooth crabgrass has hairless sheaths and stems that do not root at the node. Leaf blades are 2 to 8 inches long, and seedheads are composed of four to six spikes at the top of the stems. Seedlings or mature plants often have a reddish tint at the base.
Other Common Grass Weeds
Wooly cupgrass is an erect summer annual weed with relatively robust seedlings and wide leaves that are covered with very short hairs. Seedlings often have a red tinge at the base. The leaves have rough margins, no auricles and a small ligule with a fringe of hairs. Prairie cupgrass is similar in appearance, but its flower head is not covered with hairs.
Field sandbur is an annual grass widely distributed across the southern United States, particularly in sandy sections of fields. Its distinctive seedhead, which is approximately 5 to 7 millimeters wide, has many round, spiky, somewhat hairy burs. Leaves are rolled in the shoot and do not have auricles. Leaf blades, which are hairy on top and smooth underneath, can grow to 8 inches in length and 6 millimeters in width. The ligule has a fringe of hairs approximately 1 millimeter long. Overall, this weed grows about 20 inches in height.
Best Management Practices (BMPs) to Control Grasses
Farmers can keep common grass weeds from affecting their bottom line by using well-designed best management practices. Herbicide programs should consist of a fall and spring burndown treatment to ensure the field is clean at planting, as well as spring-applied residual herbicides to control weeds after planting. An integrated approach combining different sites and modes of action along with cultural practices, such as cover crops and equipment maintenance, can protect your fields now and prevent resistance in the future.
Crop Science has a broad portfolio to combat tough-to-control and resistant weeds. A well-thought-out herbicide program, using multiple modes 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. Not every product is suitable for every situation, and use of the correct application technique will ensure the best results.
The following Crop Science solutions are valuable tools to consider for your program.
Bayer Solutions for Corn
When managing corn crops for high yields, remember it’s always best to start with a clean field. Start with an Autumn™ Super (2) application in the fall, and the following spring use Corvus® (2, 27), a pre-emergence residual herbicide which has overlapping modes of action to control early season problem weeds. Corvus pre-emergence herbicide from Crop Science is the only corn herbicide to offer burndown, residual and reactivation. Residual activity prevents new weeds, while reactivation controls late weeds.
The multiple modes of action in Corvus deliver consistent, broad-spectrum control of grasses and broadleaf weeds, including weeds resistant to glyphosate-, ALS-, PPO- and triazine-based herbicides.
A wide application window allows for application from pre-plant to early postemergence at V2, making it an effective, long-lasting first pass herbicide in a two-pass system. Depending on the weed spectrum in your field, such as fields without heavy Palmer amaranth and waterhemp pressure, Corvus may still be a great one-pass option.
A recommended two-pass program starts with a pre-emergence application of Corvus herbicide. The second pass should include a postemergence product such as Laudis® herbicide (27). If using Laudis following an application of Corvus, add another effective herbicide with a different mode of action, such as DiFlexx® (4) herbicide or atrazine, to ensure you are using multiple modes of action in your weed control. DiFlexx DUO® from Bayer also provides growers with powerful post-emergence control of the toughest weeds, and offers multiple sites of action for built-in resistance management.
Another pre-emergent herbicide Bayer offers corn growers is Balance® Flexx (27). Follow a pre-emergent application of Balance Flexx with a postemergence herbicide to control multiple weed flushes. Balance Flexx has the unique power to reactivate with as little as a half-inch of rain to control late-emerging weeds. It controls glyphosate-, triazine-, PPO- and ALS-resistant weeds, including resistant marestail, common ragweed, waterhemp and Palmer amaranth. Balance Flexx even controls tough grasses, such as woolly cupgrass.
Balance Flexx fits into many cropping systems. Its superb weed control power combined with state-of-the-art crop safety innovation enables growers to readily rotate from corn to other key crops with little or no delay.
Capreno® herbicide (2, 27) is a post-emergence herbicide option for corn from Bayer. It has the longest-lasting residual of any post product on the market. With multiple modes of action, Capreno controls more than 65 grasses and broadleaves, including those resistant to glyphosate, PPO, ALS, dicamba and triazines.
Learn more about products Bayer offers to help control weeds in corn as part of an integrated weed management program.
Bayer Solutions for Wheat
Huskie® Complete herbicide (2, 27, 6) is available to wheat growers in Colorado, North Dakota, South Dakota, Minnesota, Montana, Wisconsin and Wyoming. This all-in-one wheat herbicide is a combination of Huskie plus thiencarbazone that provides grass control. Together, these modes of action provide good control of green and yellow foxtail along with 50 grass and broadleaf weeds.
Another herbicide solution is Wolverine® Advanced, (1, 6, 27) which controls 69 grass and broadleaf weeds in wheat, thanks to three modes of action in a single product. Wolverine Advanced provides the same unique broadleaf control found in Huskie with the addition of ACCase grass chemistry to control green and yellow foxtail and barnyardgrass. This wheat herbicide is an excellent tool to consider as grass chemistry rotation partner to manage weed resistance.
Wheat growers also have the option of a second new herbicide, Varro® (2) which controls grass weeds and is available in Colorado, North Dakota, South Dakota, Minnesota, Montana and Wyoming. Green and yellow foxtail as well as barnyardgrass are controlled by Varro. Just as important, Varro provides excellent rotational flexibility and allows a wide range of choices when it comes to broadleaf tankmix partners—while enhancing the performance of those partners.
Visit our Cereal Experts section for information on additional herbicide products Bayer offers as part of an integrated weed management program for wheat.
Read More About Managing Weeds