Weeds

10 Toxic Pasture Weeds: How To Identify and Manage

Fri, 18 Jul 2025 15:11:28 GMT

Not all toxic plants are equally dangerous, and many factors, such as stage of growth, part of the plant consumed and quantity, play a role in whether animals are affected.

With the ongoing weather variability the past few years, pasture conditions have been highly inconsistent. Some are thriving, while others are struggling due to overgrazing, flooding or drought.

“When pastures thin out, they leave space for opportunistic weeds to move in,” Shelby Gruss, Iowa State University Extension forage specialist, says. “While all weeds can compete for light, nutrients and moisture, some pose a greater threat due to toxicity risks for livestock.”

Below is a list of some of the most common toxic pasture weeds in Iowa and the Midwest, with tips on identification:

Poison Hemlock

(Kevin Bradley)

Poison Hemlock (Conium maculatum)
Toxic Part: Entire plant, especially leaves and stems
Risk: Highly toxic to all livestock (and humans); small amounts can be fatal
ID Tips: Finely divided, fern-like leaves; purple-spotted stems; umbrella-shaped white flower clusters
Notes: Often found in ditches and low-lying areas; do not mow when flowering — can release toxins and spread seeds
Common look-a-like: Queen’s Anne Lace/wild carrot

Wild Parsnip (Pastinaca sativa L)

(John Cardina, The Ohio State University, IPM Images)

Wild Parsnip (Pastinaca sativa)
Toxic Part: Sap causes skin irritation when exposed to sunlight (phytophotodermatitis)
Risk: Mainly a risk to humans (and pets) through skin contact; generally avoided by livestock, but ingestion can cause photosensitivity and severe sunburn
ID Tips: Yellow umbrella-shaped flowers; hairy and grooved stems; leaves look like celery or parsley
Notes: Wear gloves and long sleeves when handling; mowing before seed set helps control
Common look-a-like: Queen’s Anne Lace/wild carrot

Common St. Johnswort (Hypericum perforatum L.)

(L.L. Berry, IPM Images)

St. Johnswort (Hypericum perforatum)
Toxic Part: Entire plant
Risk: Contains hypericin, which causes photosensitivity (sunburn-like skin damage) in light-skinned livestock such as sheep, cattle, goats and horses; severe cases can lead to skin sloughing, blindness or death
ID Tips: Upright perennial with small flowers; the flowers have five bright yellow petals that often have black dots on the petal margins; leaves are opposite, oval and have translucent spots when held up to light; woody base; grows 1' to 3' tall in clumps
Notes: Becomes more problematic in overgrazed or low-fertility areas. Most toxic when flowering. Often avoided unless forage is limited

Common Milkweed

(Kevin Bradley)

Common Milkweed (Asclepias syriaca)
Toxic Part: Leaves and stems
Risk: Contains cardiac glycosides; toxic in large amounts, especially to cattle and sheep
ID Tips: Thick oblong, opposite arranged leaves; milky sap; large round pink flower clusters; stems covered with dense pubescence
Notes: Generally unpalatable unless forage is scarce; monitor pasture for adequate forage growth

Johnsongrass

(Kevin Bradley)

Black Cherry (Prunus serotina) / Johnsongrass (Sorghum halepense)
Toxic Part: Wilted leaves (Black Cherry); young regrowth and frost-damaged tissue (Johnsongrass)
Risk: Both produce cyanide (prussic acid), which can be fatal within minutes
ID Tips (Cherry): Tree with shiny leaves, dark bark, and white flowers
ID Tips (Johnsongrass): Tall grass with prominent midrib, purple panicle seeds, spreads rhizomes
Notes: Do not allow livestock access to wilted branches or frosted regrowth; delay grazing after frost or drought
Common look-a-like (Johnsongrass): Sorghum species

White Snakeroot (Ageratina Altissima)

(Ansel Oommen, IPM Images)

White Snakeroot (Ageratina altissima)
Toxic Part: Entire plant
Risk: Causes “milk sickness” in humans through milk from affected cattle; toxic to cattle, goats, horses
ID Tips: Opposite triangular leaves with serrated edges (sharply toothed) with three main veins; white flowers in flat-topped clusters
Notes: Common in wooded pastures or shaded edges; control early; avoid grazing densely infested areas
Common Look-a-like species: bonesets, other snakeroots

Horsenettle (Solanum Carolinense)

(Kevin Bradley)

Horsenettle (Solanum carolinense)
Toxic Part: Berries and leaves
Risk: Contains solanine; can affect the nervous system and digestive tract
ID Tips: Spiny stems and leaves; small, star-shaped purple flowers; yellow berries when ripe
Notes: Toxic when consumed in large amounts; spot spray or dig out to reduce spread; berries are particularly toxic

Cocklebur

(Kevin Bradley)

Cocklebur (Xanthium strumarium)
Toxic Part: Seeds and seedlings
Risk: Toxic to pigs, sheep and cattle; seedlings are especially dangerous
ID Tips: Rough stems with darks pots; sandpaper-like, triangular leaves with serrated leaf edges; hooked burs that cling to fur and clothing
Notes: Can cause liver damage; avoid overgrazing, as seedlings are more likely to be eaten when forage is limited

Pigweed (Genus Amaranthus L)

(Howard F. Schwartz, Colorado State University, IPM Images)

Nitrate Accumulators
Some plants can accumulate toxic levels of nitrates, especially after drought or heavy fertilization:
Common culprits: Pigweed, lambs quarters, Johnsongrass, and thistles
Risk: Nitrate poisoning reduces oxygen transport in blood — can be fatal
Management Tip: Have suspect forages tested before grazing or feeding; elevated risks following fertilization, and following drought breaking rains

Field Horsetail (Equisetum Arvense L)

(John Cardina, The Ohio State University, IPM Images)

Horsetail (Equisetum spp.)
Toxic Part: Entire plant
Risk: Contains thiaminase; can cause neurological symptoms, especially in horses
ID Tips: Hollow, jointed stems; no true leaves; resembles a bottle brush
Notes: Grows in poorly drained soils and along ditches; improve drainage and limit access

“The first step to weed management is identifying the species you have in your field,” Gruss says.

If you’re unsure about a plant in your pasture, contact your local field specialist.

“When in doubt, better safe than sorry — keep animals away until you’ve confirmed safety,” she summarizes. “Typically, animals will avoid toxic species when there is something else to graze, but eliminating the toxic weed species is ideal. If using herbicides, please read and follow all herbicide directions and grazing restrictions.”

More information on common pasture weeds can be found here: Recognizing and managing common pasture weeds .

More information can be found here: 2025 Herbicide Guide: Iowa Corn and Soybean Production for herbicides labeled for grass pasture, hayfield (table 6) and alfalfa and legumes (table 7).

Cut Feed Costs by Improving Pastures: Weed Control and Soil Fertility Strategies for Ranchers

Thu, 09 Apr 2026 12:00:43 GMT

Feed, it’s one of the biggest, if not the biggest, expense for many ranches. So what can ranchers do to reduce feed costs and still meet nutritional requirements of animals?

“The cheapest way to feed cattle is through grazing standing forage,” says Sam Ingram, field scientist for Corteva Range and Pasture. More specifically, ranchers should prioritize the forage resources they already have access to.

Ingram explains, “If we prioritize those forages… we can produce more pounds of beef on that given acre.”

In addition to practicing rotational grazing, implementing weed control and fertilization practices are key components of prioritizing forages.

Weed Control

A few weeds may seem harmless at first, but they have a significant economic impact when the difference in pounds of forage is measured after removal.

“If we remove weeds, we see an increase in forage production,” shares Ingram. “A rule of thumb is remove a pound of weeds and you can get a pound or more of grass.”

Two weed control options are mechanical and chemical. Mechanical options include tillage, hand pulling or clipping weeds, which can be time consuming and labor intensive.

Chemical options involve the use of herbicides to control weeds. A challenge with chemical control is finding a herbicide that controls weeds without harming other beneficial forages such as grasses and legumes.

“In the past, we’ve had producers tell us they won’t spray because they don’t want to sacrifice their clovers and annual lespedeza,” Ingram shares. “Fortunately, producers who had this reservation about herbicide application don’t have to have it now.”

The herbicide NovaGraz is a broadleaf weed control option that doesn’t kill off beneficial legumes such as white clover and annual lespedeza.
Ingram exlains, “It’s a really revolutionary herbicide that we haven’t had on the market to date.”

For those prioritizing hay forages, the nonresidual feature of NovaGraz is also favorable.

“The nice part of a non-residual herbicide … is that it gives producers flexibility,” Ingram says. “They can make a broadleaf application and still have the option to rotate that acre into another crop.”

It gives both the hay producer and buyer confidence.

Soil Fertility

Ingram says creating a plan to focus on fertility starts with soil testing.

“If you don’t have that test to show you what your nutrient levels are, you’re just guessing,” Ingram says. “Pick a time of the year to test and stick with that time because seasonally our nutrient levels can change.”

Next, producers should put those results to use.

“After you get the results, what are you going to do with them,” asks Ingram. “If it makes sense to add fertility, then let’s do that.”

One caveat of adding fertility is that you are not only providing nutrients for those forages and beneficial legumes, but also weeds. Weeds and grasses are in competition for the same nutrients to thrive.

“Some producers have to choose — am I going to do fertilizer this year or weed control,” Ingram says. “Now with UltiGraz, you have one pass with both fertility and weed control.”

UltiGraz combines both weed control and fertility, and it can be done in one pass to save time and input costs.

He says, “We’re controlling the weeds we don’t want, and the fertility is right there for the forages to take off.”

These are two solutions to maximizing forage production, regardless of the methods you use, remember the bigger picture.

Ingram says, “If we can improve forages through grazing management, weed control and fertility, that’s going to benefit producers.”

Listen to the full conversation on the Casual Cattle Conversations podcast. Learn more about weed control at RangeAndPasture.com/CattleConversation s.

Top 5 Tips for Effective Weed Management in Pastures

Wed, 13 Dec 2023 17:30:45 GMT

Undesirable weeds in pastures and hayfields can significantly impact the quantity and lifespan of preferred forage plants. Producers should consider several aspects of weed management to mitigate the adverse effects on forage production.

Tip 1: Start with Soil Health

Soil Assessment: Begin by conducting a thorough soil test to determine nutrient levels and pH status.

Fertility Correction: Correct any deficiencies in soil fertility to create an optimal environment for the growth of desired forage plants.

Tip 2: Use Strategic Grazing Practices

Stocking Rate Management: Implement a stocking rate that prevents overgrazing, ensuring the health of your pasture.

Pasture Rotation Schedule: Establish a rotation schedule to allow for recovery periods, promoting sustained forage growth.

Early Weed Grazing: Leverage livestock to graze on weeds during their early vegetative stage when nutritive values are high, effectively managing weed populations.

Tip 3: Consider Mowing Techniques

Mower Height Adjustment: Adjust mower height to prevent scalping, preserving the integrity of the pasture and leaving adequate stubble.

Weed Seed Reduction: Utilize mowing as a strategic tool to reduce weed seed production, particularly effective for established broadleaf weeds.

Tip 4: Select and Apply Herbicides

Broad-Spectrum Control: Choose herbicides that offer broad-spectrum control, addressing multiple weed species in one application.

Pre-emerge and Post-emerge Application: Apply pre-emerge herbicides like Prowl H2O before weed seeds germinate and post-emerge herbicides on actively growing plants for targeted weed management.

Tip 5: Consider the Surroundings

Pesticide Drift Awareness: Be cautious of pesticide drift, considering factors such as boom height, nozzle type, pressure, and wind direction.

Herbicide Impact on Crops: Select herbicides that won’t harm surrounding crops in case of drift, ensuring the well-being of neighboring vegetation.

Adherence to Restrictions: Strictly adhere to grazing and feeding restrictions specified on herbicide labels, respecting withdrawal periods before slaughter.

By incorporating these comprehensive strategies, ranchers and pasture managers can proactively manage weeds, fostering healthy pastures that optimize forage production while minimizing the impact of undesirable vegetation.

_{*Editor’s Note: This article was restructured using information from the article, “

Weed Control in Pastures and Hayfields

,” by Steve Morgan with the University of Georgia Extension. It was originally published on the Drovers website in April 2019.}

What in the World is Going On With Glyphosate Prices?

Wed, 19 Jul 2023 22:55:24 GMT

An explosion at a Dow Chemical plant in Louisiana isn’t expected to disrupt ag chemical supplies in the U.S., according to Rabo AgriFinance. That’s as the industry seems to be swimming in supplies of key inputs such as glyphosate, forcing suppliers and ag retailers to cut prices in an effort to get rid of unused supply.

An explosion and fire broke out at a Dow Chemical plant in Plaquemine, Louisiana late Friday night. The site produces several different chemicals, including one used as a fumigant in agricultural products. There hasn’t been any information released about a possible cause, but reports indicate at least six explosions occurred Friday night at a Dow manufacturing site that covers 883 acres. The incident caused a large mushroom cloud of smoke.

The plant is one of Louisiana’s largest petrochemical complexes, and the disruption is sparking flashbacks to what happened in 2021 when Hurricane Ida’s direct hit on Bayer’s largest glyphosate plant pushed the manufacturing site offline for nearly two months. The one event sent severe supply shockwaves through the entire agriculture industry.

Sam Taylor, Farm Inputs Analyst for Rabo AgriFinance, says the incident at the Dow Chemical location on Friday shouldn’t impact availability of ag inputs for farmers.

“I’ve not been given that indication that it will. That’s the feedback that I’ve received,” says Taylor.

Why was the hurricane’s impact such a heavy weight on the entire industry? As strict Covid-19 protocols in China continued to restrict production of active ingredients essential to make products like glyphosate, the hurricane compounded already strained supplies.

According to Reuters, Bayer saw herbicide sales jump 44% in 2022 after Hurricane Ida damaged rival producers and constrained Chinese suppliers failed to plug the gap. Farmers felt the impact in terms of pricing and supplies. In the fall of 2021, glyphosate prices were up as much as 300%, but finding the supply was an even bigger problem reported by farmers. As competitors have been able to return to the market this year, prices have been dropping.

Ag Herbicides’ Supply Problem

Taylor says herbicide prices aren’t falling because of demand issues, it’s a supply problem. A major reason is China. AI production coming back online was a huge boost for overall production as the country accounts for 60 to 70% of global production. With such a production monster now back online, Taylor says it’s also led to a significant drop in global benchmark pricing.

“I think that the global pricing, at the moment, is sub $4 a gallon in China. So, you’ve had that drop from about $16 to $17 a gallon in 2022. It’s now about 25% of what it was,” says Taylor. “That’s the main catalyst of it, and that’s why we’ve seen the kind of the cost curve and shift down as Chinese production is back online. They account for about two-thirds of global production.”

Retailers and suppliers continue to cut the price of glyphosate to help offload expensive inventory in preparation for the fall months. While the prices of both generic and PowerMAX glyphosate products continue to vary widely, it’s a sizable decline from even the beginning of the year.

Glyphosate Prices Tank

In May, one major ag company started offering retailers a $5 per gallon rebate just to push more glyphosate inventory onto the farm level. This week, FBN started offering a pricing special on Willowood Glypho 5, a generic glyphosate product. FBN’s promotion is being advertised as “glyphosate stock up,” offering the product at $13.50 a gallon, if pre-purchased by July 31st. The special only applies to product that will be delivered September to October.

Taylor says while wholesale and retail prices vary, he expects wholesale glyphosate and chem prices to stay low throughout the remainder of the year, especially with the supply situation.

“I would also say that I don’t think the issue is going to resolve itself overnight. I think you’re going to see this rumbling through 2023,” says Taylor.

Taylor points out hints of growing input supplies started at the beginning of the year. Several publicly traded companies mentioned inventories in their earnings report saying it was an industry-wide issue. That created the situation today where input suppliers across the U.S. are sitting on inventory that was purchased at a much higher price than where wholesale and retail prices are today.

Bayer’s most recent earnings report in May signaled the company expects its 2023 financial results to come in at the lower end of the targeted range, not only because of inflation, but a slump in prices of glyphosate-based herbicides from last year’s highs. Bayer’s then CEO told investors the company was forced to reduce expectations of what it can command for glyphosate products.

The Industry is Upside Down

It’s an issue companies and retailers of all sizes are grappling with. AgriTalk’s Chip Flory spoke to the Eric Cowling who’s the CEO of Helena Agri-Enterprises, a large U.S. ag retailer that has more than 350 sales locations across the U.S. Cowling told Flory the supply issue is one that’s still impacting the entire industry.

“It’s one of those things you couldn’t predict. It’s really about supply and demand,” Cowling said on AgriTalk. “We’re probably putting together one of the highest input crops that we’ve ever seen, so that is an impact of the supply situation. We had to buy product to take care of customers for the last two years. Now, you heard the term ‘we’re upside down.’ I think the industry is upside down. If anybody could have predicted the decline over the last 12 months, I’d like to have that conversation to know exactly how they predicted that. I think there’s plenty of inventory. I don’t think there’s excessive inventory. And I believe we’re in a good spot to take care of customers for the next six to eight months, but I’m not sure I can say we’re in a spot to do it for 12 months.”

A Global Supply Chain

Just as Taylor points out, the fluctuations in crop protection and input prices for farmers are ones driven by what’s happening on a global scale.

“I tell our teams that it’s become a global supply chain. So we’re reliant on supplies of things we need to produce products globally, some from China, some from other sources like India,” he says. “As their world changes, so does ours. I don’t think there’s any one blueprint today that we could follow to say this is what we do.”

He says the big input suppliers in the U.S. are dealing with the same issues, which then compounds the supply chain issues for retailers such as Helena.

“When their issues are compounded, it compounds our issues, because we’re looking for the same inert ingredients or things that have to be imported,” he says.

Cowling also told Flory he doesn’t think the industry is in the recovery process yet, something Helena thinks will continue to change the way ag retail does business with farmers in the future.

“We’re in a state of turmoil, so we don’t know what the real world looks like today, and I think the way we’ve procured product in the past, I don’t believe we’ll see those days again,” says Cowling. “We have to use more intelligence tools, the AI tools available, to be better predictors of what we’re going to sell.”

Related News:

New Study Shows Glyphosate Ban Would Drive Up Food Prices

EPA: Glyphosate Can Still be Used Through 2026

Bayer to pull Glyphosate from U.S. Lawn and Garden Markets

Dormant Spray For Alfalfa Weeds

Sun, 15 Nov 2020 21:26:58 GMT

Timing is crucial when controlling winter annual weeds in alfalfa.
By: Bruce Anderson, UNL Forage Specialist

Warmer spring weather soon will green up your alfalfa. Before that happens, though, maybe you should do a little weed control.

Weeds like pennycress, downy brome, mustards, cheatgrass, dandelion, and shepherd’s purse are common in first cut alfalfa. They lower alfalfa yields, reduce quality, lessen palatability, and slow hay drydown. Walk over your fields during the next few weeks once snow is gone, especially in areas where these weeds grew last year. They probably will be there again this spring. You should be able to see their small, green, over-wintering growth.

Before deciding to spray these weeds, first consider whether or not they are actually causing economic damage. If you kill these weeds, you may harvest more actual alfalfa but total tonnage at first cutting might be less because you won’t have weeds to add weight. If dairy quality hay is your objective, controlling these weeds might be very important due to their impact on forage quality, palatability, and hay drydown. In some other livestock operations, though, these weeds may not cause serious problems so use of herbicides may not be cost effective.

If your alfalfa is a Roundup Ready variety, you have some flexibility in timing the application of Roundup. Don’t wait too long, though. If weeds get more than three inches tall or alfalfa begins to form a canopy, weed control may not be as effective.

Once conventional alfalfa starts growing, you can’t control these weeds very well without hurting your alfalfa. However, if you treat your alfalfa as soon as possible during this winter’s next spring-like weather, you can have cleaner, healthier alfalfa at first cutting.

Several herbicides can help control winter annual grasses and weeds in alfalfa. Herbicides that are used before alfalfa breaks dormancy include metribuzin (Sencor), Velpar, Sinbar, and Karmex. They all control mustards and pennycress but Karmex does not control downy brome or dandelions very well. Metribuzin usually is the least expensive.

To be most successful, though, you must apply these herbicides before alfalfa shoots green-up this spring to avoid much injury to your alfalfa. During mild winter weather would be a great time. If you wait and alfalfa shoots are green when you spray, your alfalfa growth might be set back a couple weeks.

If it does get late and alfalfa turns green before you can spray, switch your herbicide choice to either Pursuit or Raptor. These herbicides tend to cause less injury to your alfalfa.

Timing is crucial when controlling winter annual weeds in alfalfa. Get ready now, in the next few weeks before alfalfa greens up, to take advantage of nice weather when you get it.