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May 06, 2024
Have you ever wondered how all of the troublesome weeds in your fields got there in the first place?
While many weeds are native to North America, some species were brought here accidentally or deliberately by early settlers. In fact, many non-native weeds were first introduced intentionally for medicinal, nutritional, or ornamental purposes. In other cases, weed seeds were introduced in contaminated crop seed lots that early settlers brought to North America.
In this post, we’ll cover:
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Canada thistle (Cirsium arvense) is a perennial weed that invades natural areas, including prairies, savannahs, stream banks, wetlands, and disturbed sites like pastures and hayfields. It can be identified by its clusters of tiny purple or pink flowers and spiny, deep-divided leaves.
Musk thistle, also known as nodding thistle (Carduus nutans), is a biennial weed common in overgrazed pastures and disturbed areas. It begins as a rosette in its first year, then bolts and flowers in the subsequent season. It can be identified by its disc-shaped flower head, which contains hundreds of individual purple flowers. The flower head droops at a 90-degree angle from the stem when the weed matures.
By the 1500s, Canada thistle spread throughout southern Europe and, by the mid-1700s, was common in continental Europe.
Musk thistle is native to Europe and Asia.
Canada thistle was most likely introduced to North America by contaminated imported crop seed in the 1700s.
Musk thistle was accidentally introduced to North America by ship ballast and crop seed contamination in the early 1800s.
Canada thistle quickly spreads in disturbed areas where it has been established. It is a particular threat for grazing pasture livestock, as it reduces the amount of desirable forage for the animals. Canada thistle competes with crops for resources like sunlight, nutrients, and water and serves as a host for agricultural pests such as bean aphids.
Livestock do not eat musk thistle, giving it a competitive advantage over native vegetation in its habitat. Canada and musk thistle are invasive and noxious weeds that require control.
Learn how to manage Canada thistle and musk thistle.
Dandelion (Taraxacum officinale) is a perennial plant in the Asteraceae family, which also includes popular ornamental flowers such as chrysanthemums, dahlias, marigolds, zinnias, coneflowers, and daisies. Dandelions have large, fragrant, yellow flower heads that provide abundant early pollen and nectar for beneficial pollinator species.
Dandelions are native to Asia and Europe and have been used for medicine and cooking as early as the 10th and 11th centuries, according to ancient writings.
Some of the first European settlers brought dandelions to the United States in the 1600s and planted them in gardens for food and medicinal purposes. Settlers ate the dandelion leaves as spring greens. They also used dandelion roots to treat ailments, including heartburn and constipation, while they used the flowers to make tea and wine.
Dandelion can be a threat in forage crops or production systems that use no-till. Once established, the weed quickly captures space and competes for soil moisture and nutrients. Each dandelion plant produces an average of 15,000 seeds, which are easily distributed long distances by the wind.
Learn how to manage dandelions.
Henbit (Lamium amplexicaule) — also known as henbit deadnettle, common henbit, and greater henbit — is a cool season annual or biennial in the mint family (Lamiaceae). It can be identified by its small purple leaves, which sit just above clusters of non-stemmed (sessile) leaves. Henbit has a square stem and is often found in yards, parks, cultivated fields, roadsides, and pastures.
Henbit is native to Europe, western Asia, and the Mediterranean region. It has grown wild in these areas since ancient times.
It’s believed that henbit arrived in North America in the 1700s from ship ballast and livestock feed. However, some legends claim that henbit was intentionally brought to the New World from Europe for chicken feed. In some European and Asian countries, henbit leaves are eaten raw or cooked and have been used as medicinal herbs for centuries.
Henbit grows best in cool, moist areas and is most problematic in fallow gardens, lawns, or crop fields. It is an important early season nectar and pollen source for honeybees and bumblebees. But for cattle, henbit can cause grass tetany, or “staggers,” a metabolic disease involving magnesium deficiency that can occur in ruminant animals, usually after grazing on rapidly growing pastures.
Learn how to manage henbit.
Kochia (Kochia scoparia) — also known as Mexican fireweed, burning bush, and summer cypress — is an annual plant in the goosefoot family (Chenopodiaceae). Its multi-branched stems can reach up to seven feet tall. Leaves are generally green, but transform to yellow, red, and brown as the plant matures and eventually dies.
Kochia is highly adaptable and can grow in areas with limited soil moisture, such as typical cereal-growing regions. The weed is often found in grasslands, pastures, prairies, roadsides, ditch banks, riparian habitats, and cultivated fields. Dry plants break off at the stem and form rolling tumbleweeds that widely distribute the plant’s more than 50,000 seeds.
Kochia is native to southern and eastern Russia.
Kochia was introduced to the United States from Europe and Asia as an ornamental plant in the 1800s. Settlers often used kochia to edge gardens because of the vibrant colors it displayed in the fall. By the 1930s, it had spread across the United States and Canada, primarily by wind-blown tumbleweeds that scattered seeds.
Kochia is considered a noxious weed in several states and serves as a host for fungal pathogens and insects that can limit the potential of cash crops, including:
Sugar beet
Potato
Tobacco
It can be especially challenging for harvesting pulse crops like peas and lentils.
Kochia can have a high forage value at its early growth stages and has another common name — poor man’s alfalfa. Kochia was used extensively as livestock feed during the drought years of the 1930s. While kochia is palatable to all classes of livestock, it can be toxic and may cause death if consumed in large quantities due to its high levels of oxalates, alkaloids, and nitrates.
Songbirds and upland birds benefit from kochia as a nesting material, protection from predators, and as a food source.
Learn how to manage kochia.
Lambsquarters (Chenopodium album) — also known as white goosefoot, wild spinach, and fat hen — is a fast-growing summer annual in the Amaranathaceae family. It can be identified by its ovate to triangular-shaped leaves with slightly lobed edges and white, powdery undersides. Lambsquarters are common in North American row crops, including:
Corn
Soybeans
Sugar beets
Potatoes
Lambsquarters is one of the most widespread introduced weeds in the world, making its origin difficult to trace. Many believe the weed is indigenous to Europe and Asia.
Early European settlers may have introduced lambsquarters to North America as a food crop. Before the introduction of spinach in Asia in the 16th century, lambsquarters was the most predominant leafy vegetable in Europe. It was consumed raw or boiled, and dried seeds were ground into flour. Unused plant parts served as fodder for livestock.
What to Know About Lambsquarters Today
Animals and farm machinery easily spread lambsquarter seeds. They often survive in the digestive tracts of livestock and are a common contaminant of manure.
The weed may compete with row crops for valuable resources and can serve as a host for insects like beet leafhoppers, stalk borers, and green peach aphids.
Young lambsquarters leaves can be used as salad greens, while seeds and dried flower heads may be ground for soups and bread. Plants contain oxalic acid and nitrates, which may be toxic to sheep and pigs if consumed in large amounts.
Learn how to manage lambsquarters.
Marestail (Conyza canadensis), also known as Canadian horseweed and Canada fleabane, is a winter and summer annual broadleaf weed in the Asteraceae family. It can be identified by its erect, bristly haired stem, which can grow up to six feet tall, with clusters of cup-shaped, greenish-white flowers. Marestail is common in row crops, pastures, and rangelands and is an opportunistic weed that can emerge in the fall or spring.
Marestail is native throughout much of North America.
Native Americans and early settlers used marestail leaves to treat dysentery, sore throat, and other ailments.
Marestail has become one of the most troublesome weeds for U.S. farmers to manage. Some weed populations are now resistant to several herbicide classes, including glyphosate, ALS inhibitors (amino acid synthase), and PPO (cell membrane disruption) herbicides. Marestail can be controlled in the rosette stage by using effective herbicides, but it is difficult to control once the weed bolts.
One marestail plant can produce up to 200,000 seeds, so it’s critical to control weeds before seed set.
Learn how to manage marestail.
Palmer amaranth (Amaranthus palmeri) is an annual broadleaf weed in the pigweed (Amaranthaceae) family. It can be distinguished from other pigweed species by its relatively smooth, reddish stem and diamond-shaped leaves that may contain a whitish V-shaped mark on the top surface. Another defining feature is that Palmer amaranth’s petiole is longer than its leaf.
Finally, Palmer amaranth is dioecious, meaning individual plants are either male or female. In contrast, redroot pigweed, smooth pigweed, and Powell amaranth are monoecious, meaning all plants contain male and female reproductive parts and will produce seed.
Palmer amaranth and most pigweed species are native to North America.
Native Americans collected pigweed seeds and consumed them raw or ground into flour. Young pigweed plants were also boiled and eaten.
Although Palmer amaranth is indigenous to the desert regions of the southwestern United States and northern Mexico, it has spread throughout the United States through contaminated hay, feed, and seed lots, on equipment such as custom combining machinery, by wildlife, and via irrigation water. The weed was first reported outside its established native range when it was identified in Virginia in 1915.
Palmer amaranth is a prolific weed that causes significant yield losses in many row crops. It is especially prevalent in:
Cotton
Corn
Soybean fields
Palmer amaranth can hybridize with other pigweed species, and its dioecious reproduction supports genetic diversity that facilitates the spread of herbicide resistance. Several populations across the United States have documented resistance to multiple herbicide classes. Many Palmer amaranth populations are resistant to glyphosate (Group 9). More recently, Palmer amaranth populations with resistance to ALS- (Group 2), Photosystem II- (Group 5), and HPPD-inhibiting (Group 27) herbicides have been identified. Expanded herbicide resistance, a long emergence window, and a rapid growth rate make controlling Palmer amaranth challenging in row crops.
In addition to the economic threats to row crops, Palmer amaranth contains oxalates and nitrates, which may be toxic to livestock when consumed in large quantities.
Learn how to manage Palmer amaranth.
Purple loosestrife (Lythrum salicaria) is a perennial wetland plant with purple flowers arranged in long spikes at the end of the stem. It has long, narrow leaves in opposite pairs that attach closely to the stem. Another distinguishing feature is the weed’s square-shaped stem, which is generally four- to six-sided.
Purple loosestrife is native to Europe and Asia.
Purple loosestrife was first discovered in the United States in Lake Ontario in 1869. It was likely introduced accidentally through contaminated cargo ship ballast or imported raw wool and sheep.
Purple loosestrife was promoted and planted as a decorative ornamental plant for many years. Its flowers were also used as medicine to treat digestive issues and skin infections. However, due to its negative impact on native vegetation and its ability to escape from cultivation, it is now illegal to sell the plant in most states.
Purple loosestrife is a highly undesirable invasive plant species that severely impacts wetland environments. Research suggests that wetlands may lose up to 100% of their native biomass due to purple loosestrife invasions. This noxious weed spreads rapidly and forms dense mats that disrupt the natural habitat of native species such as waterfowl, amphibians, flowers, and other wetland species.
Learn how to manage purple loosestrife.
Velvetleaf (Abutilon theophrasti), also known as elephant ears or buttonweed, is a broadleaf weed commonly found in corn and soybean crops in the eastern and midwestern United States. The weed is easily identified by its large, heart-shaped, velvety leaves. In midsummer, it produces orange-yellow flowers that give rise to large seed pods containing five to 15 flat seeds.
Velvetleaf is native to India and other tropical countries in Asia.
Chinese farmers grew velvetleaf from around 2000 B.C. for its stem’s strong fiber characteristics. The Chinese people also used velvetleaf for medicinal purposes to treat ailments like fevers, dysentery, and digestive issues.
It’s believed that velvetleaf was intentionally introduced to North America from China in the early 1700s to provide fiber for rope, paper, and ship caulk. Due to the demand for fiber, colony farmers cultivated fields of velvetleaf and continued to do so for over 100 years.
Velvetleaf was a significant weed problem in midwest corn and soybean fields from the 1960s to 1980s; however, new herbicide modes of action have significantly reduced its impact on row crop production. However, left untreated, velvetleaf can contribute to yield loss through competition for light and soil moisture. The weed also serves as a host for several corn, cotton, and soybean diseases and insects. It is also known to inhibit the germination of some crop seeds by releasing specific chemicals into the soil.
Learn how to manage velvetleaf.
Native or not, weeds are an unwanted guest in your crop fields. That’s why FBN offers a diverse portfolio of herbicides you can rely on to control tough weeds and keep your operation running smoothly. With 24/7 digital shopping access, direct-to-farm delivery, transparent pricing and savings opportunities, and detailed label information for each product, FBN offers the information and products you need to build an effective herbicide strategy this season.
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May 06, 2024