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Identifying weeds can often feel as challenging as successfully controlling them. Broadleaf weeds are no exception to that rule. These weeds run the gamut of growth habits, leaf arrangements, and flower type (and the list goes on). Since different weed species often require different control methods, identifying the correct culprit is the first step to implementing successful management practices.
In this article, we dig into how to recognize and differentiate seven of the most prevalent broadleaf weeds in corn and soybean crops.
Keeping your eyes peeled for broadleaves emerging in your field is one thing, but identifying which broadleaf is setting up shop is quite another. Below, you’ll find an overview of broadleaf weed species, plus tips on how to identify them, from emergence to maturity.
📸:@Delaware Agriculture via Flickr/Featuring a photo of a mature Palmer amaranth plant.
Palmer amaranth is one of the fastest-growing, most competitive, most aggressive and damaging annuals of the amaranth/pigweed species. It has developed resistance to traditional herbicide control in many regions and has a longer-than-average emergence period. To make matters worse, one mature female plant can produce anywhere from 100,000 to 500,000 seeds.
Palmer amaranth typically emerges anywhere from May through September. Seeds will begin to germinate when surface soil temperatures reach 63 F.It can be challenging to distinguish from related species like redroot pigweed, smooth pigweed and waterhemp.
When scouting for Palmer amaranth, look for the following features:
Seedling:
Mature plant:
📸: BASF employee/Featuring an image of Palmer amaranth growing in a soybean field.
Learn more about Palmer amaranth at Grow Smart® Live:
📸:@JJ Gouin via Canva/Featuring an image of a young waterhemp plant growing in a soybean field.
Waterhemp is generally considered one of the most widespread and detrimental weed species, regularly wreaking havoc on corn and soybean production across the Midwest. Like Palmer amaranth, waterhemp is highly competitive and has developed herbicide-resistance. Waterhemp has a penchant for fast growth, only second to Palmer amaranth. Waterhemp spreads like wildfire, like Palmer amaranth, a mature female Waterhemp plant can produce anywhere from 100,000 to 500,000 seeds.
Waterhemp's peak emergence occurs in mid to late June, but it can emerge anywhere from mid-May to late July. Waterhemp seeds can start to germinate when daily temperatures reach 41 F to 59 F, but peak germination doesn't occur until the mean daily temperature ranges from 68 F to 91 F. When emergence is delayed, waterhemp can avoid earlier weed-control tactics, so thorough and regular scouting is critical.
When scouting for waterhemp, pay attention to the following features:
Seedling:
📸: BASF employee/Featuring early emerged waterhemp (Left), and mature waterhemp (Right).
Mature plant:
Read more about waterhemp at Grow Smart® Live:
📸:@Matt Lavin via Flickr/Featuring a photo of a kochia plant.
Kochia is a summer annual weed common in all western states except Alaska. Non-native to the U.S., this herbicide-resistant weed can significantly reduce crop yield if not effectively controlled. The mature plant spreads seeds when stems at the base of the plant break and the plant essentially becomes a tumbleweed, sprinkling seeds everywhere it goes.
Additionally, kochia contains nitrate, oxalate, sulfates, saponins and alkaloids that can poison cattle and sheep, so be mindful if you spot kochia on land where livestock are foraging. Mature or drought-stressed kochia is more poisonous than early-season kochia.¹
Kochia seedlings typically emerge from early April through July, but seeds continually germinate during the growing season (ranging from early popups in March to the final round of seeds germinating as late as September). This long emergence period is due to kochia’s broad range of ideal germination temperature and little dormancy. Kochia seeds can germinate anywhere from 41 F to 95 F. Germination is only reduced if temperatures exceed 104 F.
When scouting for kochia, be on the lookout for the following features:
Seedling:
📸: BASF employee/Featuring early emerged kochia (Left) and huge mature kochia (Right).
Mature plant:
Read more about kochia at Grow Smart® Live:
📸: @Olko1975 via Canva/Featuring redroot pigweed seedheads.
Redroot pigweed is an annual in the pigweed family, often mistaken for Palmer amaranth or waterhemp. Redroot pigweed is native to North America and is generally not common in cultivated fields in the Midwest as waterhemp and Palmer amaranth have taken its place due to selection by the use of glyphosate. When found, it does have the ability to produce up to a whopping 1 million seeds per plant (and as luck would have it, 95% of redroot pigweed seeds are typically viable).²
Redroot pigweed emerges over a long period of time from late spring to midsummer, so make sure you’re scouting for this weed well into the growing season. Redroot pigweed seeds typically germinate in soil temperatures between 86 F and 104 F.
When looking for redroot pigweed, keep an eye out for the following features:
Seedling:
Mature plant:
📸:@Olko1975 via Canva/Featuring a photo of mature lambsquarter plants with seedheads.
This annual broadleaf is a competitive, herbicide-resistant weed commonly found in corn and soybean crops.
On average, a lambsquarters plant can produce over 72,000 seeds. Lambsquarters seeds are persistent in the soil because seeds from a single plant have varying dormancy requirements and may germinate at different times due to inconsistent burial depth.³ Additionally, lambsquarters seeds can survive the digestive tracts of livestock, meaning manure spread as fertilizer or deposited during rotational grazing can easily distribute lambsquarters seeds.
Lambsquarters typically emerge from mid to late spring. Ideal germination temperatures for lambsquarters range from 64 F to 82 F.
When scouting for lambsquarters, look for the following features:
Seedling:
📸: BASF employee/Featuring early-emerged lambsquarters weed.
Mature plant:
Read more about lambsquarters at Grow Smart® Live:
📸:Howard F. Schwartz, Colorado State University, Bugwood.org/Featuring a nightshade weed escape.
Nightshade species are a toxic, but not necessarily competitive, form of broadleaf. Even though they may not crowd out a crop as aggressively as some weeds, they can be a nightmare for soybean growers at harvest, interfering with the harvest process and lowering crop quality.
Nightshade berries wreak havoc on harvest equipment and crop quality. The juice from crushed berries creates a gum that adheres nightshade seeds and other materials to grain, subsequently clogging implements and potentially delaying harvest. Additionally, nightshade berries are the same size as soybean, which makes them hard to separate from grain. The berry juice can also stain seeds, potentially reducing quality and price. Finally, nightshade berry juice can add moisture that may lead to mold growth and cause bulk flow issues in soybeans.
There are thousands of nightshade species, but the ones that typically interfere with row crop production include eastern black nightshade, hairy nightshade and cutleaf nightshade. Eastern black nightshade is the most common nightshade affecting Midwest growers.
Below you’ll learn how to scout for each of these three species.
📸: @arousa via Canva/Featuring a close up shot of European black nightshade.
Nightshades typically begin emerging in May and continue throughout the growing season. In general, nightshade seeds actually prefer fluctuating temperatures for optimal germination. These temperatures can range anywhere from 9 F all the way to 86 F.
When scouting for nightshade, keep your eyes peeled for the following features:
Eastern black nightshade
Seedling:
Mature plant:
📸: @Tomasz Klejdysz via Canva/Featuring European black nightshade in a field.
Read more about nightshade at Grow Smart® Live:
Hairy nightshade
Seedling:
Mature plant
Cutleaf nightshade
Seedlings:
Mature plant:
📸:@aloha17 via Canva/Featuring an image of giant ragweed flowerheads.
Giant ragweed is an early-emerging weed that easily dominates tilled land. Giant ragweed can produce up to 10,000 seeds per plant, making it easy for this mammoth plant to invade your cropland.
Known for its pesky pollen that is a major cause of hay fever, giant ragweed is generally one of the first summer annuals to emerge, starting in early April. Giant ragweed can germinate during a wide range of temperatures, but peak germination occurs between 68 F to 86 F. Its extended emergence period makes continual scouting necessary.
When scouting for ragweed, look for the following features:
Seedling:
📸: BASF employee/Featuring emerged Giant Ragweed in Seymour, IL.
Mature plant:
Understanding the differentiating characteristics of broadleaf weeds can help you properly diagnose the problem and implement a treatment solution that gives your cash crop sufficient protection (and gives you peace of mind).
Finding the right protection against ever-evolving herbicide-resistant broadleaf weeds in soybean and corn fields can be overwhelming, but experts are available to help you make your decisions. Reach out to your seed retailer, a nearby extension office agent or a seed company professional like your regional BASF representative.
Discover how different weed management practices can help protect your crop.
Always read and follow label directions. Grow Smart is a registered trademark of BASF. Copyright 2024 BASF Corporation. All rights reserved.
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