Pigweed control in lawns

Redroot Pigweed Eradication

Hello and thank you for your question.
Pigweed is a very difficult plant to control, and I’m sorry that you are having so much trouble. As much as I wish we had a recommendation that is guaranteed to get rid of it, I’m afraid there is no one magic answer. As far as eradicating the weed, it may not ever completely disappear. Sometimes managing a weed is the best we can do.
Normally weed control is a two-pronged approach where you do your best to control the weed, but you also build up the population of more desirable plants to give competition to the pigweed. You say you are working on a 12 acre area, but I’m not sure if you are using your acreage to grow a crop, or as pasture land for animals, or perhaps something different? In your question, you described the area as a home plot. Here is a link to homeowner information about controlling this weed: http://hortsense.cahnrs.wsu.edu/Search/MainMenuWithFactSheet.aspx?CategoryId=6&ProblemId=2034
We would like to help you get control of the situation if we can, but we might need to talk to you, to get a better idea of what is going on, so we can give you the best solution(s). Depending on what you are doing with your acreage, you might find the right answer on our Small Farms team website. If you click on this link, it will take you to a page with a choices about what you might be doing, such as pasture land, crop production, or forestry. If you click on the one that is the closest match to you, you will find information about weed control in different situations. http://smallfarms.wsu.edu/crops
Our Small Farms Coordinator is Pat Munts, and I’ve copied her contact information: Munts, Pat — Small Farms and Acreage Coordinator
WSU Spokane County Extension, 222 N. Havana, Spokane, WA 99202-4799
Phone: 509-477-2173
Our Master Gardeners can be contacted directly at [email protected] or by calling 509-477-2181.
Another option would be checking out the website for the Spokane County Noxious Weed board which has a variety of weed control strategies that work in the area.
I hope this information helps and we can connect you to the right information to take care of the Redroot pigweed on your acreage. Thank you again for your question.

How to Kill Pigweed

Pigweed (Amaranthus retroflexus) goes by many names, including redroot pigweed, redroot amaranth and many others. Pigweed thrives in garden settings and grows wild in untended fields. Young pigweed can be eaten in salads and its seeds are often used as a flavoring. Small amounts of pigweed can also be ued as an animal feed. Left on its own, pigweed will invade and crowd out almost all other plants. Older pigweed plants are not edible and become true weeds. Pigweed is generally resistant to herbicides such as Roundup. And because pigweed has such a deep taproot it is difficult–but not impossible–to kill.

Dig up pigweed in early spring while plants are small. Dig down and remove as much of the tap root as possible. It will be easy to dig up young pigweeds, but older, established plants will be more difficult.

Recheck the area in two weeks. Dig up as much pigweed as possible, once again digging deep down into the soil to free the taproot whenever possible.

Use a hoe to cut pigweed down to ground level in places where it is not possible to dig out the taproot. Continue cutting pigweed down to ground level every week during the growing season. This will make the roots use most of their energy trying to sprout new growths–and will eventually cause the roots to die.

Search for any mature pigweed plants in fall and either dig down, removing the taproot, or hoe the plant down level with the ground in order to prevent the plants from seeding. Preventing the plants from seeding will prevent the weed from spreading any farther next year and will make your job of destroying new pigweed growth in the following season that much easier.

Growers share resistant pigweed control strategies

The first step is acceptance, and no, we’re not talking about a 12-step program. The name of this game is glyphosate-resistant Palmer amaranth pigweed, and the first step in preventing or battling it is admitting you have a problem.

“Don’t deny it, and don’t say that you’ve got only three or four on your farm, and you’re not going to do anything about it. It’s here and it’s real,” says Patrick Turnhage, a west Tennessee farmer. Turnhage was on a panel of consultants and growers telling of their experiences with resistant Palmer pigweed during a recent meeting in Decatur in north Alabama

Turnhage said it was great to see such a large turnout at the meeting focusing on resistant pigweed. “Five years ago, you couldn’t get two or three people together long enough to talk about it. If someone said resistant pigweed, they’d bust up like a covey of quail. You should treat a farm as if you cannot kill a pigweed. If it gets its head above ground and you treat it, but treat it as if you cannot kill it with anything, you’ll be successful,” he says.

It’s important, he says, to overlap pre-emergence treatments and chemistries by following a calendar rather than by driving out into the field to see if pigweeds are emerging.

“If that pre-emergence has a two-week residual, you need to get out in 10 days and spray. You’ve got to learn how to spray clean ground. It’s hard to do — it’s hard to spray something that is as clean as a concrete parking lot, but you’ve got to try and do it if you want to stay in business,” says Turnhage.

Resistant pigweed is putting farmers out of business, he adds. “We’re talking about bush hogging 80-acre cotton fields and disking up 1,000 acres at a time because they’d be alright,” he says.

Next July, says Turnhage, you can go to the foothills of Missouri, in west Tennessee, and tell exactly to the row where people have applied their pre-emergence, and where people are digging and trying to rescue their crop. “They’re spending more money trying to rescue it than they would have putting out the pre-emergence in a timely manner. My grandfather always said that you should spend money only on the things that make you money, and these pre-emergence treatments will make you money and keep you in business,” he says.

Turnhage farms about 5,000 acres of which approximately 3,000 will be planted in cotton this spring.

“We’ll actually put out herbicide before we do any tillage, because you can’t rely on tillage alone to eliminate that problem. Disking, bedding or chiseling alone won’t do the job. You have to kill pigweed before it gets above the ground.”

Turned off dry

Tunhage says he didn’t receive any significant rainfall after May 31 last year. “We might have received 1 3/10 inch until November — we were burnt up. If you take away the competition, and you’re spraying grass herbicides, the only thing that’ll survive is the resistant pigweed.

“If you’re doing a burndown, you may be using a 2,4-D and Dicamba combination, something with a long residual to get you to planting. When you come out to plant, you’ll think you have a clean field. But you won’t — the pigweeds are there. Spray that clean ground with Gramoxone, and put out another pre-emergence. If you have the capability, put out your herbicides before you disturb the ground. Put out herbicides in front of the planter and put out your pre-emergence behind the planter – it makes a huge difference.”

Tim Roberts, a consultant in west Tennessee and Missouri, says that when a cotton crop is emerged, if you don’t have WideStrike or LibertyLink, then there is no rescue treatment for Palmer amaranth resistant pigweed. “If you hood the middles with Gramoxone, you can try post-directed MSMA and Caparol on the row. We often have dry weather during planting time, but we’re getting pre-emergence out 2 weeks to 30 days ahead of planting, depending on if it’s Reflex or Valor, in the hopes of getting an activating rain prior to planting the crop. The pigweed in our area generally starts to come up at about the middle of April — about the time we plant cotton — and we’ll plant until the end of May.

“If you plant on May 10 and put out your pre-emergence, and then you have no activating rain, and you have an emergence of pigweed, you’re hurt. The way to counter that is to incorporate a yellow herbicide — which works pretty well — or apply an early pre-emergence, always with a burndown and something for marestail if that’s a problem. That should make you clean from the get-go. Then we layer our pre-emergence treatments,” says Roberts.

Growers shouldn’t be scared of resistant pigweed, he says, they should just go after it. “In 2009, we had 10 fields my group consulted on. We probably lost 10-percent yield from those fields due to resistant pigweed. We took an aggressive approach in 2010, and cleaned up the crop. We probably got about 95 percent control. We still had pigweeds in the field. Like boll weevils, you can clean them up, and you can manage them and make a crop,” says Roberts.

Resistant pigweeds can be moved by equipment, but they’ll also show up in the middle of a field, he says.

“Be proactive. We figure we’re spending about $37 per acre on resistant pigweeds, but it’s cheaper than attempting a rescue mission. Do your best to keep it from emerging. Your timeframe for getting control is narrow. The information about controlling resistant pigweed starts to sound repetitive after awhile, but keep listening,” says Roberts.

First noticed along waterways

John Newby, who farms in Alabama and Tennessee, says he first starting seeing pigweed up and down the river and along the creeks on his farms. “We first thought we didn’t have them. We thought maybe we didn’t get glyphosate on them because of the rain. But about four years ago, we decided we had them,” he says.

Pre-emergence herbicides have worked well, says Newby, and the yellow herbicides have been very effective.

“We’ve started putting out more liquid nitrogen, putting out the yellow herbicides, and then incorporating with a Turbo-Till, and that has worked really well for us. Once we get that down, we just keep hammering away at it. One thing we might have made a mistake on is that when we went with Flex, we pretty much threw our hoods in the garbage and didn’t do any layby or anything for awhile.

“But we started going back to that. We’ve taking advantage of the incentive program for hoods, and we try to do a better job with our layby,” he says.

Resistant Palmer pigweed is a “nightmare,” says Newby, and growers should do everything possible to stay ahead of it. “You’ll start out with a small spot. The next year, it’ll be as big as a pickup truck, and the next year it’ll be as big as a trailer. Once you get on it, don’t let up,” he says.

Bill Webster, a consultant in Alabama and Tennessee, says it was about four years ago when he decided he probably had a problem with resistant pigweed. “We had escapes that first year. Then, the next year — about three years ago — we planted cotton, put down Prowl, let it get activated, came back twice with Roundup, and still had pigweed. We killed a few with Staple, but most of them survived and we ended up topping them out. The next year — two years ago — we planted in wheat and then came back with soybeans, double-cropped, and put out the pre-emergence,” he says.

When rain finally did arrive, says Webster, the pigweeds came up. “Once they get any size on them, you’re not going to get rid of them. This year, we noticed that the combines and other equipment spread them to more fields. You can tell where the equipment pulled into the field. There may be a streak of them or they may be scattered in the field,” he says.

Webster says he’ll be advising growers to do more incorporating of yellow herbicides. “We just need to stay on top of them. I don’t think we’ll ever eliminate them,” he says.

[email protected]

By: Killbuck Date:23-Aug-16

Checked my rr bean field 3 days ago. Manually pulled 5 or 6 pigweed plants leftovers from an infestation 4 years ago. Yesterday my son comes in and says I better get on the pigweed. Drove up there this am and found 2 thick patches about 100 square feet each. Wanted to plant something else up there next year but probably still need rr seed or some herbicide that will kill that crap. Any Ideas? Anybody make rr alfalfa?

By: jingalls Date:23-Aug-16

Pat, expensive yes. But factor in your time of trying to take care of regular alfalfa, and the amount of quality feed the animals get…I’m planting RR alfalfa!

By: sticksender Date:23-Aug-16

I assume you’re saying your pigweed has become glyphosate resistant, like it has in a lot of places?

Next year you could try this. Kill the pigweed in late July or early August with 2-4,D then plant a fall crop. Repeat for a couple years until you get it under control.

By: chasin wtails Date:23-Aug-16

I found some generic Flexstar at my local Rural King store. It burned the pigweed back but did not kill it all. I went back and spot sprayed with 24d as that will kill the beans. Luckily so far this year I think I got a handle on it and have been hand pulling any I see now. Hopefully I can get rid of it in the next year or two for good.

By: r-man Date:23-Aug-16

I have never seen the seeds from them, I see them appear in my yard from time to time, I walk the yard with spot sprayer, one touch with gly and gone. How and where is mine comeing from (birds)? Or I cut the root out which is just as easy. Have not seen any resistant to gly here in SC.

By: Bfulldraw Date:24-Aug-16

There are many companies that carry RR Alfalfa. Monsanto provided the technology but there are many breeders out there developing lines. We carry RR alfalfa by Ameristand. The varieties are very good. Price is about $425/50lb. This includes a technology fee which goes to Monsanto. You have to have a Monsanto tech license no. to purchase RR Alfalfa.

By: longbeard Date:24-Aug-16

Does anybody have a picture of pigweed?

By: sticksender Date:24-Aug-16

By: shortstop Date:24-Aug-16

Alfalfa or clover and keep it mowed. IF you have a good alfalfa stand and mow it a few times, shouldn’t have much trouble with any weeds. If so, spot spray them (hand sprayer to minimize damage) with 2,4,D. when actively growing.

By: SouthernILbowhunter Date:29-Aug-16

you can still plant soybeans just get “liberty-link” beans. You can post spray liberty mixed with some select (if you have any grasses) and you will have very clean beans. If you have sprayed round-up previously in your sprayer, rinse very well, as round-up will kill liberty-link beans. Round-up is actually only labeled on weeds 6″ or less, which is one of the reasons we have round-up resistant weeds, guys trying to spray 3 foot tall pigweed and mares tail, all it does is stunt the plant and eventually make it resistant. Do a little research and there are several “pre-chemicals” that can be sprayed and incorporated into the soil that will help prevent weeds such as pigweed and mares tail. If you have an infestation, do not let them go to seed. good luck.

By: joshuaf Date:29-Aug-16

Pigweed on my property in southern Ohio dies quite easily when sprayed with Glyphosate (main ingredient in Roundup). Marestail doesn’t.

By: dm/wolfskin Date:30-Aug-16

A lot of pigweed has become resistant to Roundup. The seed is real small shiny black. One plant can produce thousands of seed.

By: Keef Date:02-Sep-16

Just tried Butyrac on the pigweed two days ago. Initial reaction is that it did a good job. I’ll wait a few more days to give a final evaluation. Sure hope it worked.

By: Keef Date:03-Sep-16

Checked the field today. It looks like I got a great kill on the pigweed. What a relief. Alfalfa and oats were not bothered by it.

By: Tater Date:07-Sep-16

Pigweeds are resistant to glyphosate in large areas of the country. They have also developed resistance to PPO class of chemistry as well, this will include flexstar. Zidua + metribuzin at planting on soybeans works well as a residual for 3-4 weeks depending on weed pressure. Needs rainfall for activation. Grain drill or broadcast Liberty link soybeans, spray weeds less that 6″ tall with 32 oz of Liberty with a minimum of 15 gallon of water per acre for adequate spray coverage. Preferably spray between 9 and 2. Sunlight drives Liberty mode of actions late applications at dusk will less effective. Other option would be to plant roundup ready extend soybean. You can spray these with a tank is of roundup + Dicamba. Still need to spray small weeds. Take care to prevent off target drift with dicamba. It’s dangerous non roundup extend soybeans very sensitive to dicamba as well as many other broadleaf plants.

By: WeedDrJH Date:09-Sep-16

Good Info Tater. I will add a couple of thoughts. Obviously there is some PPO resistance in the waterhemp and Palmer (the two types of Gly Resistant Pigweed) populations but, currently they are isolated. Expect to see this becoming more widespread, along with HPPD resistance, over the next couple of years with lack of new options currently being developed from a preemergence herbicide standpoint. Currently the best options, even with Liberty Link beans from Bayer, are some type of PPO chemistry (Valor, Sonic, Authority, Fierce XLT) as a preemergence possibly in combination with metribuzin to help out with early flushes. Because the seeds are about the size of a speck of pepper and produce anywhere from 100-1,000,000 seeds per female plant, depending on the species, you are going to get multiple flushes if you get rain. Spraying liberty is great in liberty link beans as long as the plants are small as Tater said. Coverage is key because this is a contact herbicide and does not translocate in the plant like RR. Don’t skimp on the 15gpa or higher from taters recommendation. If you just have RR then you are limited. You can come back with Warrant (acetochlor)to help out with some residual for lateseason but, past that your only options really are PPO chemistries such as Flexstar(fomesafen) and Cobra (lactofen)or spot treatments of Butyrac (2,4-DB).The PPO chemistries for POST use are also contact herbicides and require a minimum of 15 GPA as well.

Tater also mentioned RR Extend Beans which are tolerant to Dicamba. There are several emerging seed technologies that will help with controlling this weed in the future (Extend from Monsanto, Enlist from Dow, Balance from Bayer). I currently would advise against using the Dicamba over the top of RR Extend Beans as there is no current Dicamba product on the market labeled for over the top use on these beans. Any application made in this manner is a violation of federal label and subject to fines and litigation if off target injury occurs . There are currently thousands upon thousands of acres, hundreds of millions of dollars, of beans with serious dicamba injury all across Missouri, Ark, TN, MS, etc from this blatant disregard for the law and horrible stewardship of the new technology. Its so bad the Ark Plant Board just banned dicamba applications in the state after April 15 for the foreseeable future. I don’t feel it is worth taking a risk to spray the dicamba for footplots until this is all settled and there is an actual label for it.

By: drycreek Date:09-Sep-16

I killed it one of my plots by planting RR beans two years in a row and spraying it when it was pretty small. In another plot, I still have a little, but I sprayed it a couple weeks ago and will do it again next year before spring planting.

By: Tater Date:10-Sep-16

WeedDrJH is right. I shouldn’t have left off that the extend system is not yet labeled. I was operationing on the assumption that it would receive a label prior to the next crop year. I am in Arkansas. It will not receive a state label until the UofA weed science dept have evaluated the new formulation for a minimum of 2 yrs. It has yet to be submitted. there were some real disasters in NE Ark and the Missouri boothill with off label application of generic dicamba formulations on extend soybeans. Lots of off target damage to susceptible crops. We have lost roundup and the PPO chemistry pretty much statewide here for pigweed control. Monsanto releasing that seed technology without a labeled product to use was a recipe for disaster.

By: WeedDrJH Date:10-Sep-16

You are correct Tater, Absolute Disaster!! I’m in Indiana but, know all the UofA Weed Science guys very well. Happy Hunting and good luck with the mess down there!

Controlling Prostrate Pigweed – Tips To Remove And Kill Prostrate Pigweed

Pigweed, in general, covers several different kinds of weeds. A common form of pigweed is prostrate pigweed (Amaranthus blitoides). It is also known as matweed or mat amaranth. This invasive weed has made itself at home in lawns and gardens. This leaves many homeowners wondering how to get rid of prostrate pigweed. Let’s take a look at prostrate pigweed identification and tips for prostrate pigweed control.

Prostrate Pigweed Identification

Prostrate pigweed grows in a circular form with low-growing stems coming from a central spot so it looks like a spider web. The radial stems are reddish-purple and can grow more than a foot long. The leaves on prostrate pigweed are about a half inch long and are oval shape.

The flowers on prostrate pigweed are reddish-green and are not significant. The flowers will produce seeds that look like small black sand grains. The prostrate pigweed spreads through these seeds.

Prostrate Pigweed Control

As with many weeds, the best way for controlling prostrate pigweed is to keep it from growing in your yard in the first place. This plant grows best in sandy soil and is commonly found in bare, sandy spots like riverbanks and near roads. If you find that you have problems with prostrate pigweed, this is an indication that you have sandy soil. Improving the sandy soil will help get rid of prostrate pigweed or keep them from growing to begin with.

This plant is an annual, but its seeds are very resilient and can live 20 years before they need to germinate. This means that total prostrate pigweed removal can be a long process. You need to remain persistent when controlling prostrate pigweed.

The nice thing about prostrate pigweed is that it grows in a shape that makes it very easy to hand pull the plants. Firmly grab the center of the prostrate pigweed plant and pull out the central stem with as much of the root as possible. The entire plant should come away. It is best to keep a sharp eye out for the plant in spring and pull it as soon as possible – before it develops seeds. When you get rid of prostrate pigweed before it goes to seed, you reduce its ability to come back in future years.

If you wish to kill prostrate pigweed with chemical controls, look for weed killers that contain the chemicals dicamba or glufosinate-ammonium or glyphosate. Glufosinate-ammonium or glyphosate are both non-selective weed killers and will kill any plant they come in contact with, so they should only be used in locations where you wish to clear out all weeds and plants. Weed killers that contain dicamba are selective to weeds that include prostrate pigweed and can be used among landscaping plants.

Controlling prostrate pigweed is not impossible and being persistent in your efforts to get rid of prostrate pigweed will be rewarded with a prostrate pigweed free yard.

Note: Chemical control should only be used as a last resort, as organic approaches are safer and much more environmentally friendly.

Controlling Redroot Pigweed

Redroot pigweed is a weed that invades many lawns, but can be kept under control through regular yard maintenance. It is a member of the amaranth family and blooms with white to pale yellow flowers during the summer season. Many homeowners consider this weed an unsightly nuisance when it grows and self-seeds in the lawn, in both dry and moist soil. While there are no biological control agents to keep this weed under control, there are several other means to keep the weed from growing in random spots in your yard.

Herbicides as a Control Agent

Some herbicides can keep redroot pigweed under control. Use a pre-emergent herbicides that will kill the small seedlings before they can grow to be adult plants. Apply per directions on the herbicide container, taking special care if you have children or outdoor pets.

Lawn Mowing as a Control Agent

Because one redroot pigweed plant carries up to 100,000 seeds—which can easily be dispersed into the soil and spread the following growing season—prevent seed production by regularly mowing the lawn once a week during the summertime. Once an adult plant reseeds, those seeds will remain in the soil up to 30 years and take over the lawn.


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Redroot pigweed is tough to control in later seeded crops.

Amaranthus retroflexus, as it is known to botanists, is an annual weed that has developed resistance to herbicides in Groups 2 and 5. More than 100,000 seeds per season gives the weed plenty of opportunity to select for genes that resist applications of everything but steel.

A post emergent application of herbicides can usually control pigweed in crops that develop good canopies early in spring. However, pigweed can be tough to kill and it will require a full rate application if it is allowed to grow for a month before application.


The weed thrives in hot conditions and is able to scatter a lot of seed. As a result, the ground will often be a thick carpet of seedlings where it has been allowed to reach maturity.

Redroot pigweed needs warm soil for seeds to germinate, so it often pops up after seeding before in-crop herbicide applications. Seeds remain viable for up to 40 years when buried in the soil.

The weed will sometimes germinate later in the growing season after early applications of post emergent products. This can be a serious problem in crops such as flax and lentils.

Products with some residual control are particularly useful when controlling the weed.

Redroot pigroot quickly develops a large, fleshy red root, which chases moisture and nutrients well, making it dangerous in dry conditions.

The weed sets seed in July and August as tall flower spikes with densely packed blossoms appear. Seeds are round, black and shiny.

Leaves are oval with a notch in the end early in the season but develop a diamond shape later in life.


Lower stalks are heavy and wide with a smooth surface, while upper areas and branches are rough with sparse, coarse hair.

The plant can sneak through the application season because of its rapid growth and season-long germination period, growing to a point where it is can be tough to control.

If allowed to reach maturity, it creates future problems while drastically reducing yields in most crops.

Redroot pigweed also acts a host plant for crop pests such as green peach aphid, tarnished plant bug, European corn borer, flea beetle, mosaic virus and strains of fusarium and rhizoctonia.

It is toxic to livestock, particularly hogs, accumulating oxalates to as much of 30 percent of its dry weight. As a result, larger infestations can’t be grazed or included in greenfeed or silage.

People can also suffer from this plant’s effects in the form of an allergic reactions to its pollen.


Resistance to Group 2 herbicides is limited to Manitoba, Ontario and North Dakota, while tolerance to Group 5 is found only in Ontario and some U.S. states.

Group 5 products include atrazine, which is likely where resistance formed. Group 2 products, such as the imazethapyr or thifensulfuron-methyl ALS inhibitors, are also known to have little effect on some populations. In vegetable production, the weed has also shown resistance to linuron.

A tank mix with other groups is recommended if Group 2 herbicides are used.

Delaying post-emergent applications of broadleaf products until soil temperatures are higher than 20 C can be an effective strategy to control new seedlings.

Vertical tillage or heavy harrows in the fall or early spring will hasten soil warming, which can help ensure earlier weed germination to coincide with crop development.

Ministry of Agriculture, Food and Rural Affairs

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Management strategies to control resistant pigweed in carrot production

The problem

Carrot growers in particular are struggling with resistant pigweed in Ontario fields, a problem that was studied extensively in 2011 and 2012. As far back as 1997, resistance to group 5 herbicides (prometryne) was noted. Then in 1998, resistance to group 2 (rimsulfuron) herbicides was noted. Resistance to group 7 (linuron) herbicides appeared in 1999. There are some weed populations with multiple resistance (i.e. resistance to both group 5 and group 7 herbicides or maybe even to three different herbicide groups).

Different pigweed species are showing resistance to herbicides, including:

Without effective herbicides, growers are using alternative methods to manage pigweed, including:

  1. Wick-weeding with glyphosate (Figure 1).
  2. Hand hoeing and removing pigweed from the field.

Figure 1. Wicking pigweed with glyphosate

At the recent Muck Crops Conference during the resistant weed workshop, we heard that 95% of producers have resistant weeds on their farm. The majority of resistance is Group 7 (linuron) resistant pigweed, with some cases having multiple resistance to Group 5 (prometryne).

Currently, the only other herbicides registered for control of pigweed in carrots are:

Herbicide Group Pigweed Control* Application Restrictions
(Treflan, Rival, Bonanza)
3 G Do not apply on soil with > 15% organic matter
(Dual II Magnum)
15 G
14 G Hooded sprayer between rows

*E = excellent; F = fair; G = good

The best strategy to manage this herbicide resistant pigweed is to use multiple approaches, also known as Integrated Weed Management (IWM):

1. Crop rotation

The more diverse the rotation the less selection pressure there will be on weeds to develop resistance because timing of tillage and other management practices will vary. Rotation to crops (e.g. onions, beets) where herbicides can be used to control pigweed can be beneficial. See table below for herbicides that can be used on common rotational crops of carrots. These are provided as a general outline only. Please refer to complete label before using these products.

Crop Herbicide Group
Onions Chateau, Goal, Aim 14
Prowl 3
Pardner 6
Frontier 15
Beets Nortron
– soil type restrictions
Upbeet 2

2. Minimizing the depth of tillage (when possible)

Deep tillage continually inverts the soil bringing weed seeds to the surface. If you shallowly till your fields (2-4 inches maximum) you will deplete the seed bank over time. This practice will result in a more even emergence of weeds, allowing better control from herbicide applications.

3. Removing weeds from the field – sanitation

It is important to remove suspected resistant weeds from the field before they go to seed. This will prevent seed return to the soil. Effective removal of plants by hand requires more than just cutting them off. Plants must be uprooted and removed from the field. Paying a crew of people to remove plants in mid-season should be considered a viable solution, even at a relatively high cost. The result of not doing so could be a substantial loss of income in future years. It is best to burn these weeds instead of feeding them to livestock or disposing by other means. It has been shown that fire will kill viable seeds left on the seed head. Whereas, many weed seeds can survive through the digestive track of livestock and could potentially become a problem for the producer taking the manure for fertilizer.

4. Cleaning equipment – sanitation

Resistant weed seeds can be easily spread by any and all types of farm equipment entering the field. Take special care to clean all equipment before you enter another field or drive significant distances along roads or highways.

5. Herbicides that are currently in the pesticide registration system

There are several projects currently in the Canadian Minor Use System for potential registration in the future (see Table below). Keep in mind that these products are not registered for these uses.

Herbicide Group Pigweed Control* Stage of Registration Potential Registration Date (Estimation)
Blazer Ultra 14 E Project initiated 2016
Nortron SC 16 F-G 2011 project, efficacy, residue and crop tolerance data required 2015
Prowl H2O 3 F – G Submitted 2012, residue analytical methodology required 2014
Sencor (potential resistance already) 5 E 008 project, residue data required 2014

*E = excellent; F = fair; G = good

Overall, remember once you have a resistant weed on your farm, it is there to stay. For example, pigweed can produce on average 100,000 seeds per plant and can remain in the soil for close to 40 years. It is best to use a combination of the above management techniques (integrated weed management) to help minimize the resistant seed return to the soil each year.

Figure 2. Size of redroot pigweed seed
Photo source: Steve Hurst, USDA-NRCS Plants Database

Figure 3. Pigweed seed in man’s hand
Photo source: http://talk.newagtalk.com/forums/thread-view.asp?tid=340200

Figure 4. Jar of 500,000 pigweed seeds
Photo source: http://ocj.com/2013/04/keep-close-watch-for-palmer-amaranth/

Figure 5. Weed seeds on axle of tractor

By: booner Date:21-Jul-16

Has anyone had any success at killing this in your food plots ? I have a plot that it’s just starting to show up, sprayed the plot with glypho (showdown was the brand) and seemed to have no effect on this stubborn weed. Any suggestions ?? Thanks scrub

By: booner Date:21-Jul-16

Also had a friend try a fire burn on some of his earlier and that didn’t work for him, tough stuff to get rid of I guess..

By: r-man Date:21-Jul-16


By: dm/wolfskin Date:21-Jul-16

Don’t let it go to seed head if you don’t kill it.

By: EmbryOklahoma Date:21-Jul-16

You need pigs. Come down and trap some on my place, for free. 🙂

By: t-roy Date:22-Jul-16

What is planted in the food plot? For soybeans, Flexstar or Phoenix will work. Flex star has a 10 month residual, so if you are going back with a brassica or other broadleaf plant, keep that in mind.

For corn, there is another herbicide that works pretty well. I can’t think of the name of it right now, but I will contact my farmer buddy (Mr. Greenjeans) & get the name of it. 2-4d works in corn as well, but it sometimes can cause the stalks to become brittle & more susceptible to wind damage & can cause the stalks to gooseneck as well.

Pigweed (waterhemp) is a real bitch here in Iowa. It’s by far, my biggest weed issue in my food plots.

By: ScrubBuck Date:22-Jul-16

There are beans in the plot right now…

By: ScrubBuck Date:22-Jul-16

i have the same prob. with the pigweed this year also. thanks

By: ScrubBuck Date:22-Jul-16

So your saying if i spray the flexstar or phoenix it will kill the beans also ?? and not getting the 10 month residual thing,,, this herbicide thing all new to me.. thanks for helping us..

By: ScrubBuck Date:22-Jul-16


By: ScrubBuck Date:22-Jul-16

lol..your helping both my dad and i here..

By: t-roy Date:22-Jul-16

No it won’t kill them if they are R Ready beans. It will kill the broadleaf weeds in your beans, not grasses. You need to mix glyphosate with it to kill the grasses. They can be mixed together.

The residual is also called carryover. It simply means that the agent in the chemical can still be present in the soil for up to 10 months, so that can possibly impact other broadleaf plants that you could possibly plant for a food plot the next year.

The herbicide that I used in my corn to kill pigweeds & other broadleaf is called Laudis.

Hopes this helps a little! I have to ask my farmer buddy too. He’s my go-to info guy.

By: drycreek Date:22-Jul-16

I have no trouble killing pigweed when it’s small with gly. Let it mature and it will take a flamethrower.

By: t-roy Date:22-Jul-16

Glyphosate won’t kill it here even when small here in Iowa anymore.

By: BOHUNTER09 Date:24-Jul-16

Same here in Southeastern Illinois for Pigweed. Glyphosate won’t touch it at any stage of growth. I’m trying pre emerge Dual next year.

By: Carnage2011 Date:24-Jul-16

Spray it with grazon. 24d will burn it down but won’t control it.

By: Candor Date:24-Jul-16

2-4 and glypho but it certainly has developed some resistance. It is about like declaring war to get rid of it. Some plots took 3 years to exterminate it.

By: Keef Date:24-Jul-16

I’ve been discing the pigweed under for a couple of months getting ready to plant alfalfa in August. If I spray any remaining weeds with gly and 2-4D is there any carryover to it? I know there are seeds still in the soil but I was hoping the alfalfa and oats might crowd it this fall and next spring I’ll move it regularly before the pigweed can come to seed. I know this will be a battle for a couple of years, what do you think?

By: Keef Date:25-Jul-16

Meant to say next spring I’ll MOW it regularly not move it.

By: lewis Date:25-Jul-16

Balsa gram kills it dead in my clovers not sure rr soybeans will work Lewis

By: Purdue Date:25-Jul-16

Different weeds go by the name “pigweed”, especially in different parts of the country. So you may not all be talking about the same thing.

By: shortstop Date:25-Jul-16

I doubt it’s pigweed, but rather waterhemp. Not that it makes a difference, it’s still undead, right? Waterhemp has developed resistence to roundup (glyco..)and looks almost identical to pigweed. The boys are right, 2,4,-D should smack it good!

By: Ollie Date:25-Jul-16

Paraquat is a restricted use pesticide meaning that it is unlawfull for anyone other than a licensed applicator to possess and use. Small exposures can be very dangerous. Don’t even think of using it unless you are licensed and properly trained to use it.

By: dm/wolfskin Date:25-Jul-16

Pigweeds Common broadleaves encompass a variety of weeds. One of the biggest offenders comes from the pigweed family, which includes Palmer amaranth and waterhemp, as well as spiny, smooth and redroot pigweed and several other species. Most pigweed plants are tall, with simple, alternate leaves that are oval to diamond-shaped. The plant structure is erect to bushy, with dense, profuse clusters of small, greenish flowers. Pigweeds thrive in hot, drought-like conditions, partially by using rapid stem elongation to avoid the shade. They also respond vigorously to high levels of readily available nutrients in the soil, such as from fast-release sources.

“The most common pigweed species – Palmer amaranth, waterhemp and redroot pigweed – compete aggressively with warm-season crops. They reproduce by abundant seed production. Pigweeds are easy to recognize, but because two or more pigweed species often occupy the same field, and significant variation can occur between them, correct identification of each species is often difficult. Furthermore, it’s impossible to tell at a glance if a pigweed is resistant or non-resistant to one or more herbicide modes-of-action. The only way to tell if a weed is truly resistant to an herbicide, and not just tolerant, is by laboratory testing.”

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