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Reviews of weed management strategies in corn and soybean fields during 2023 found that one-pass, pre-only programs controlled an estimated 60–70% of weeds. Two-pass programs were estimated to be more effective, controlling an average of 80–90% of weeds. Either way, we can expect to see some familiar plants emerging in our fields this year, with especially problematic weeds like palmer amaranth (pigweed), giant ragweed, waterhemp and marestail making another appearance.1
📸:@darcymaulsby via Canva/soybean crop interspersed with encroaching weeds.
To help you take a more targeted approach this season, we’ve assembled a guide to some of the most common Midwest weeds in corn and soybean fields. With proper scouting and a proactive weed-control strategy, you’ll have everything you need to manage challenges posed by ever-changing environmental conditions.
The common Midwest weeds at the top of this list share some similarities. They all compete for resources in your corn and soybean fields, limiting yield potential and taking valuable time and money away from other parts of your operation. Many have also developed resistance to at least one herbicide, like glyphosate or PPO inhibitors, meaning they’ll require targeted and intentional management strategies to adequately control.
We recommend first using this library to scout and identify the weeds in your fields. Then reach out to one of our experts for additional information and management strategies.
📸:@Delaware Agriculture via Flickr/Examples of Palmer amaranth aggressively spreading.
Palmer amaranth, also sometimes referred to as a Palmer pigweed, is a broadleaf species that is not native to the northern United States but is steadily demonstrating its ability to survive in a growing number of Midwest corn and soybean fields.
Individual plants have a smooth stem, oval- or diamond-shaped leaves arranged in symmetrical patterns, long leaf petioles and unbranched flowering structures. You can distinguish between Palmer amaranth and similar plants by its lack of hair, the petiole length and look of the seed head structures, which are long and thin and have stiff, sharp bracts that make seed heads feel prickly. While the male plants are smaller in size, female plants can grow to over 10' tall at a rate of over 2" a day.2
Palmer amaranth has a lengthy emergence period that lasts well into the summer season and can even occur after harvest.
Palmer amaranth is an annual weed that emerges and begins outcompeting corn and soybean quickly. In ideal conditions, plants that emerge in May can reach 6' in height by July. Mature plants distribute small seeds that thrive in no-till or minimum-tillage fields, as they prefer to stay within an inch of the soil line.
Palmer amaranth has developed resistance to several classes of herbicides with a variety of modes of action, including glyphosate. It can be difficult and expensive to control, so we urge careful consideration and cooperation with experts. Unchecked growth can cause yield loss as high as 78% in soybean and 91% in corn.3
Zidua® Pro herbicide has three modes of action for outstanding grass and broadleaf weed control. It uses three active ingredients (pyroxasulfone, saflufenacil and imazethapyr) that help maximize your chances of controlling herbicide-resistant weeds like Palmer amaranth. The use rate is 4 to 6 oz/acre, depending on weed pressure and spectrum.
📸:@aloha17 via Canva/Giant ragweed with its clusters of drooping flower heads.
Giant ragweed can stand up to 12' tall on large, erect stems. It has rough leaves with three to five deep lobes. Male flowers have terminal racemes, while female plants flower in auxiliary clusters, and fruits are large, crown-shaped achenes. Growing plants are similar in appearance to cocklebur or sunflower.4 Giant ragweed can grow in large colonies with a dense canopy that can choke out a crop.
Giant ragweed emerges very early in summer. By 150 growing degree days (GDD) from January 1, 10% of seeds have typically emerged. Patterns differ across the region, but there are almost always multiple emergence events throughout the growing season. Due to its large seed size, giant ragweed can emerge from soil depths as great as 6 inches.
Giant ragweed is an annual weed. Seedlings create large, ovate cotyledons that become hand-shaped leaves. As the plants shoot up, they grow into drooping clusters arranged like spikes. Flowerheads face downward on stalks, releasing their infamous pollen into the wind. Giant ragweed’s seeds are relatively large and encased in a crown-shaped husk.5
Beginning in the late 1990s, experts began to document cases of herbicide resistance in giant ragweed. Today, they are widely resistant to group 2 (ALS-inhibitors) and group 9 (glyphosate) herbicide modes of action.
Zidua® Pro herbicide’s three modes of action make it an invaluable tool against weeds like giant ragweed. Always use 6 oz/acre for managing giant ragweed. Other common control methods include group 4 (2–4D) and group 10 (glufosinate) herbicides.6
📸:@ivanastar via Canva/Side-by-side examples of a marestail rosette and a mature stem.
Marestail is a winter annual weed that grows into rosettes after emergence, lies dormant over winter and ultimately bolts up into an elongated stem crowded with lanceolate leaves. Marestail can commonly be found in no-till fields as well as in cultivated areas, in pastures and on roadsides. Marestail contains allelopathic chemicals that can inhibit germination and growth of several other plant species.
Marestail seeds tend to germinate quickly and can emerge in either fall or spring. Seeds that have not emerged yet can lie dormant for extended periods.
Marestail is an annual weed. Most growers first notice Rosettes clinging to the soil line. They are most likely to emerge at soil depths of less than ½", but they can emerge from depths of up to 1". Rosettes appear to be small clusters of club-shaped leaves covered in small white hairs and can be encountered at almost any time of year.
Maturing marestail plants elongate into stems surrounded by grouped leaves that will eventually produce cone-shaped seed heads. One plant can produce an average of up to 200,000 seeds that disperse on the wind. Mature plants can reach heights of 6'.
Marestail is resistant to glyphosate and ALS-inhibiting herbicides, requiring the use of solutions like Verdict® herbicide or Engenia® herbicide.7 Engenia herbicide application resulted in significant reductions of marestail when applied in the rosette stage.
📸:@jj Gouin via canva/Featuring an example of waterhemp growing alongside a row of crops.
Waterhemp is another plant from the pigweed family, like Palmer amaranth. There are several variations of this species, but the type that growers in the Midwest are most likely to encounter is common waterhemp (Amaranthus tuberculatus). Mature plants have oblong, dark-green leaves with prominent veins and a reddish-pink underside. Stems are smooth or occasionally ridged. Note that waterhemp are hairless plants, which can help distinguish them from redroot and some other pigweed species. Fully grown plants can reach heights of up to 8'.
Waterhemp can emerge for several months during the corn and soybean growing seasons, with temperature fluctuations having little effect on germination.
Waterhemp is a summer annual. Seedlings begin with light-green to reddish-pink stems and sit up to 0.2" above the soil line. The plant progresses to oval-shaped cotyledons that develop into the hairless true leaves of the mature plant. Male and female flowers are produced by separate plants, though both are green, petal-less clusters.8
Waterhemp emerges relatively late in the growing season, so early planting can help manage pressure by giving crops a head start at gathering nutrients and creating a canopy. Tillage also helps control waterhemp. Though plants release a massive amount of seeds, they need to remain close to the surface to successfully emerge.
Waterhemp has developed resistance to triazines, ALS inhibitors, post applied PPO inhibitors, and glyphosate. There have also been instances of plants with resistance to growth regulators and VCFLA inhibitors.9
For a flexible solution, try Verdict® herbicide. It can be used as a pre-plant burndown when the tank is mixed with 1 pt/a MSO, or it can be applied after planting but prior to crop emergence. Verdict herbicide is compatible with liquid fertilizer and can be combined for a weed-and-feed application. Speaking of flexibility, Verdict herbicide is also labeled on seed corn, popcorn, sweet corn and soybean. Check the use rates for each crop.
📸: @Susan Vineyard via Canva/Example of henbit blooming.
Henbit is a weed belonging to the mint family and is considered one of the 10 most troublesome weed species in the Midwest. It arises in open areas, waste ground, cultivated fields and many other places. Henbit is a fast-growing plant with rounded, heart-shaped leaves featuring scalloped edges. They grow from a shallow taproot and have a number of weak stems.10
Henbit is a winter annual with most plants germinating in the fall and some in the spring, racing to compete for resources in corn and soybean fields.
Henbit seedlings mature through the growing season, producing many weak stems that sprawl along the soil. Plants can flower in spring or fall, or occasionally even in winter. Plants may be 4" to 15" tall and produce delicate purple flowers. The flowers result in 40 to 200 seeds per plant.
Henbit also threatens corn and soybean acres by acting as an overwintering host for corn earworm, soybean cyst nematode and two-spotted spider mites.
Henbit has exhibited signs of resistance to ALS-inhibiting herbicides since the 2000s. Apply pre-emergence herbicides in mid-September or post-emergence herbicides in late October or early November.
📸: BASF employee/A side by side comparison featuring a close up of emerged Kochia (Left) and a field view of emerged Kochia weed (Right).
Kochia is an invasive weed that can be found in a wide range of climatic regions. It is part of the goosefoot family and thrives in arid environments, but adapts well to rangelands, pastures, roadsides and even cultivated fields. Kochia is an annual plant that reproduces solely from seeds.
Kochia has a bushy appearance with dense clusters of spiky leaves. Stems are round and covered in soft hairs.
Most kochia emerge in a short time frame early in the Spring, with some emergence continuing throughout the summer.
Kochia is an annual weed. Seeds are viable for one to two years with seedlings maturing through the growing season and flowering from July to October. Plants produce several flushes of seeds per year and are extremely drought resistant. Dead plants break off from stems and roll as tumbleweeds.
Early tillage in spring can help control kochia seedlings. Kochia grows rapidly, so preemergence treatment is recommended. These plants have shown resistance to numerous herbicides including glyphosate, sulfonylureas and triazines. 2,4-D or dicamba may be an option for managing weed pressure, and rotating herbicides helps reduce the likelihood of additional resistance.
📸: BASF employee/Featuring a close up shot of common lambsquarters.
Common lambsquarters is a very competitive weed in corn and soybean fields. Just one lambsquarter weed per 1.5" of corn row can result in up to 13% yield loss. Soybeans can see 25% yield loss with less than one lambsquarter weed per foot of crop row. Lambsquarters is a nonwoody plant that grows in disturbed areas like gardens, mulch piles and fields. The plant has a single stem with several branches near the base. Leaves vary in shape but are usually covered with a waxy, white coating that makes them hard to get wet.12
Lambsquarters is a summer annual emerging in early spring, with 10% of seeds resulting in seedlings by 150 GDD after January 1, in soil depths of less than 1".
After emergence, lambsquarters flowers from May through October, creating green clusters in the leaf axils and at the top of the stalk. Flowers do not mature at the same time and have a five-lobed ovary covering a shiny black seed.13
Lambsquarters is difficult to control with post-emergence herbicides in soybean. Because it emerges early, it must be watched to ensure that it does not exceed the maximum height for post-emergence applications. Contact your BASF representative for additional guidance.
📸: BASF employee/Featuring a view of common chickweed on a field.
Chickweed is a winter annual that lies dormant over winter and sets seeds in early spring. It has frail stems and egg-shaped, pointed leaves of a light-green color. It can most easily be identified by these pointed leaves, which are arranged in opposite positions.
Chickweed typically emerges in late summer.
Chickweed is highly variable in form. Plants emerge in tight bundles but quickly begin to branch and spread out, resembling mats of plant material along the ground. As it grows, it develops leaves that are opposite, mostly hairless and oval-shaped to elliptical. In maturity, it creates small clusters of flowers with five green sepals at the base that resemble small leaves. Flowers bloom throughout the year.14
In no-till operations, chickweed is best controlled with a fall burndown or in early spring when plants are small. Chickweed becomes more difficult to control under cool conditions or when plants become large enough to form dense vegetation.
BASF has a full suite of solutions for managing difficult-to-control weeds like Palmer amaranth and giant ragweed. Work with your local extension agent or a representative from BASF to help you select the best herbicide for your field’s weed pressure. Ask about how products like these can help:
📸: @simonkr via Canva/Featuring an crop spayer applying herbicide onto corn.
Interested in learning more about corn and soybean weed management?
Always read and follow label directions. Grow Smart, Verdict, Status, Armezon, Distinct, Engenia, Extreme, Liberty, and Outlook are registered trademarks of BASF. Copyright 2024 BASF Corporation. All rights reserved.
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