Fall Weed Management Tips

Many farmers have witnessed the value in applying herbicides in the fall to perennial weeds, especially perennial sow-thistle and dandelion (Figure 1). Often they will see a reduction in their population the next year as well as a delay in their shoot emergence. This allows the planted crop to have a competitive advantage over those perennial weeds. Unfortunately weather conditions around the time of application can be quite variable and can influence a herbicide’s effectiveness. Let’s go through three “top tips” to make the most of this application window.

  1. Choose the most effective products, rate and tank-mixes for the perennial weed that you are targeting. Table 1 outlines what public researchers in Ontario have found to be most effective at controlling perennial plants in the fall.
  2. Apply when air temperatures are above 8°C for a minimum of two hours after application. This is best accomplished by applying during late morning or mid-day so that the targeted plant is taking up glyphosate during the heat of the day.
  3. After a frost event, wait 2-3 days before evaluating weed growth and if the target plants look fine and air temperatures are above 8°C then resume applications. For example, milkweed is very sensitive to frost. Figure 2 shows a milkweed plant 3 days after an evening where the air temperature reached a low of -3°C. It would not make sense to apply glyphosate on a weed species in that state since its leaves are unlikely to absorb any herbicide. Alternatively, dandelion and wild carrot were not affected by the same frost event (Figure 3 and 4) and one could resume fall applications to those species based on the condition of their leaves.
  4. Wait a minimum of 72 hours after application to perennial weeds if you want to till the soil. The longer that you can wait after application before making a tillage pass, the more the herbicide will translocate within the plant and do a more effective job controlling the species.

Table 1. Best herbicide option for each targeted perennial plant based on research conducted by the University of Guelph, Department of Plant Agriculture.

Perennial Plant Product(s) Product Rate Average Control (Range in control)
Glyphosate (540 g/L)
1.34 L/ac 90% (84 – 100%)
Perennial Sow-thistle
Glyphosate (540 g/L)
1 L/ac 90% (85 – 100%)
Canada thistle
Glyphosate (540 g/L)
1.34 L/ac 90% (85 – 100%)
Glyphosate (540 g/L)+ 2,4-D Ester (564 g/L)
0.67 L/ac + 0.5 L/ac 95% (90 – 100%)
Wild carrot
Glyphosate (540 g/L)
1.34 L/ac 82% (49 – 100%)
Glyphosate (540 g/L)
1.34 L/ac 90% (85 – 100%)
Red clover
Glyphosate (540 g/L)+ Distinct
0.67 L/ac + 200 g/ac 99% (96 – 100%)

Figure 1: The spring following a fall application of glyphosate (left) compared to no application (right)

Figure 1: The spring following a fall application of glyphosate (left) compared to no application (right)

Figure 2: Milkweed plants in wheat stubble 3 days after a frost where the night time temperature was -3?C

Figure 2: Milkweed plants in wheat stubble 3 days after a frost where the night time temperature was -3°C

Figure 3: Dandelion unharmed 3 days after a frost event.

Figure 3: Dandelion unharmed 3 days after a frost event.

Figure 4: Wild carrot unharmed 3 days after a frost event.

Figure 4: Wild carrot unharmed 3 days after a frost event.

(Source – http://www.omafra.gov.on.ca/english/crops/field/news/croptalk/2016/ct-0916a1.htm)

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Till Tales: Weed-management in no-till farms

Periodically plowing your field is a great way to control your weeds.

Not plowing, on the other hand, is a great way to boost your soil profile and retain moisture.

So, say you decide to try the increasingly popular no-till farming method — how do you manage those pesky plants?

Kelly Kettner sprays residual herbicides early in the season and relies on a crop-rotation program.

“It’s not a big problem on my farm,” the Bailey County producer said.

But without caution, it easily could be.

Weed scientist Peter Dotray advises wasting no time in preventing weeds. For conventional farmers, that could mean turning up the soil during tillage, destroying weeds by their roots.

“A good principle for weed control in a season is to start clean,” he said. “For a grower that tills, one of the ways he can start clean is to till. A no-till grower is more challenged.”

Glimpse a freshly plowed field, and you’ll see his point. Tidy rows of soil are arranged in a repetetive pattern of tiny peaks and valleys, free of plants and rubbish. And no matter how weed-filled it had been earlier, the tillage gave it a fresh start.

Kettner’s no-till fields, in contrast, are filled with debris. You’ll find layers of old corn cobs and wheat stalks, all remnants from past growing seasons. He considers it organic matter, comparable to mulch in a garden.

The longtime Muleshoe-area farmer is a fan of pre-emergent herbicides. As opposed to post-emergents, which leave you with dead plants, pre-emergents prevent weeds from ever growing.

“I learned a long time ago to use residual herbicides to control the weeds, which meant I don’t have as many weeds come up,” he said.

The term residual refers to acting through the soil; those herbicides tend to provide extended control. Dotray, who works for Texas Tech and Texas A&M AgriLife, recommends that method on no-till fields.

“The key difference between the conventional guy and the no-till guy is what they’re doing to help them start cleaning,” he said. “They’ve likely gotta use more residual herbicides to help keep their fields clean.”

Dotray and Kettner both advise against procrastinating at herbicide-application time.

“Timeliness is also very important in no-till. When it’s time to spray, it’s time to spray — you can’t wait two or three weeks,” Kettner said.

Then there’s there commodity-mix. As evidenced by the variety of leftover crops on his fields, he tries not to plant the same thing more than twice in a row. One of his favorite rotation systems involves two seasons of corn, followed by a season of cotton and then one of barley. A rye cover crop grows between the corn and cotton seasons.

“A weed that’s easy to control in cotton can be hard to control in corn, and a weed that’s hard to control in corn can be easy to control in cotton,” he said.

Resistant pigweeds

A few years ago saw a weed-control heyday. Glyphosate — the active ingredient in Roundup — was cheap, easily available and quite effective. You could hardly blame farmers for overusing it.

But you couldn’t blame weeds for developing a resistance to it.

In 2011, researchers in Terry County confirmed the South Plains’ first glyphosate-resistant weeds. At the time, Dotray wondered “Where else is herbicide resistance?”

Five years later, a better question is “Where isn’t it?”

“It seems like every farm has some level of pigweed resistance,” he said.

Those nuisance plants are not likely to suddenly respond to glyphosate again, either; resistance grew embedded in their DNA.

“It’s not going anywhere — likely we’re gonna have some resistant weeds from now on,” Dotray said.

Kettner still sees a pigweed here and there, despite his residual treatments. With no comparably effective post-emergent herbicide on hand, he brings a hoe to the field to kill it old-school.


Why no-till?

You won’t meet many South Plains farmers who have been avoiding tillage for multiple generations. It’s been around too long to describe as a fad, but certainly gained popularity in the last few years.

“In general, we are seeing an increase in conservation tillage, including no-till, minimum-till and strip-till, largely due to better weed control through herbicides and innovations in these technologies,” David Gibson, executive director of Texas Corn Producers, said via email. “Also, many farmers are recognizing that these practices decrease soil moisture loss, and lessen wind erosion.”

Statewide, Texas has seen a 70-percent jump in reduced-tillage farming practices, said Quenna Terry, a public affairs specialist for the Natural Resources Conservation Service.

“I think over the years, there has been producers who have gained more interest in no-till,” she said.

Benefits can include better water retention, she added. For instance, a Dumas farmer boasted of cutting his irrigation about 15 percent after going no-till, but harvesting the same yields. The problem, though, is the time commitment to see those benefits.

“What we have found from some of the producers we work with is it takes time,” she said. “It’s a very challenging decision. A producer has to be really willing to make some changes. If they go full-blown conservation tillage, there’s a lot that goes into that.”

Kettner, who has been farming two decades, gave up tillage about 15 years ago. He started that method with a wheat cover crop to protect his cotton from blowing sand, then through some meetings discovered its other benefits.

“No-till is about a whole system revolving around not plowing and crop rotation,” he said. “I learned the goal of the whole no-till system is to increase the organic matter of the soil, which will increase the water-holding capacity of the soil. In a semi-arid environment like we live in, that’s very important.”

His fields’ layers of old wheat and corn break down gradually, eventually becoming organic matter in the soil. He estimates the process takes at least five years.

“By not disturbing the soil, we’re trying to slow down the breakdown of carbon so it will be incorporated into the soil rather than released into the atmosphere,” he said.

The “mulch” also works like a blanket, retaining moisture and protecting the soil from sunlight. A drawback is the soil’s slightly colder temperature; Kettner compensates by delaying cotton-planting three weeks longer than his plowing neighbors.

So, does he encourage all other farmers to give away their plows? He paused, suggesting it’s not that simple: “I would recommend it, but it takes a lot of trial and error.”

(Source -http://lubbockonline.com/local-news/2016-05-08/goodbye-plow-hello-pesky-plant-weed-management-no-till-farms#.VzgrBBV95jU)

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Meet the 4 Types of Weeds You Don’t Want in Your Fields

All weeds are created equal, right? Wrong. Some weeds are hardly troublesome while others cause huge problems for farmers, yield, machinery and more.

If you’re wondering which weeds are which, keep reading: The Weed Science Society of America has updated the definitions for the four—yes, four—different types of weeds.

Here they are:

Weed. “A plant that causes economic losses or ecological damages, creates health problems for humans or animals or is undesirable where is it growing.” Think crabgrass, giant foxtail or common lambsquarters, for example.

Noxious weed. “Any plant designated by federal, state or local government officials as injurious to public health, agriculture, recreate, wildlife or property. Once a weed is classified as noxious authorities can implement quarantines and take other actions to contain or destroy the weed and limit its spread.” For example, purple loosestrife, hydrilla and witchweed are all noxious weeds.There are over 100 weeds on the Federal Noxious Weed list.

Invasive weed. “Weeds that establish, persist and spread widely in natural ecosystems outside the plant’s native range. When in a foreign environment, these invaders often lack natural enemies to curtail their growth, which allows them to overrun native plants and ecosystems.” Examples of invasive weeds include tree-of-heaven, tamarisk and downy brome (cheatgrass). Many invasive weeds are also classified as noxious.

Superweed. “In addition to the science-based definitions above, many people use the slang term ‘superweed’ to describe weeds that have evolved characteristics that make them more difficult to manage as a result of repeated use of the same weed management tactic. The most common use of the slang refers to a weed that has become resistant to one or more herbicide mechanisms of action after their repeated use in the absence of more diverse weed control measures.” Click here for a comprehensive list of herbicide resistant superweeds.

As farmers know, weeds are bad news. Follow best management practices to make sure you beat these yield robbers, whether they a

(Source – http://www.agweb.com/article/meet-the-4-types-of-weeds-you-dont-want-in-your-fields-naa-sonja-begemann/)

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