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Herbicides for ‘volunteer’ weeds

At the outset of his talk, Donnie Miller tells those attending the Northeast Louisiana Research Station field day that his presentation will be “a little different.”

This particular tour stop, says the station’s research coordinator, is on weed control, “but I won’t be talking about controlling traditional weeds. The definition of ‘weed’ is simply a plant that’s growing out of place.

“We run into situations every year where crops are planted and there’s a stand failure — the population isn’t up to par due to inclement weather — but some of the plants do survive. With mild and sometimes dry winters, there are also times plants that survive” from the previous cropping season.

Such plants can actually compete with the crop. Studies done on the station located outside St. Joe, La., have shown that “at a density of a plant every 3 row of crop feet, soybeans can reduce cotton yield 14 percent; cotton can reduce soybean yield 6 percent; with corn as a volunteer weed at that density, expect a reduction in cotton lint yield of 5 to 8 percent.”

And those are just yield reductions. “We aren’t even talking about harvest efficiency and the problems you can have running a cotton plant through a combine or a soybean/corn plant through a cotton picker.”

Volunteer plants also have the potential to serve as hosts for disease and insects. “So, you need to take (such plants) out as soon as possible.”

Towards that end, every year Miller gets calls asking “‘what can I put on a particular crop to take care of a volunteer weed?’ We like to say we don’t have any Roundup-resistant weeds in this state that have been confirmed from a scientific standpoint. But some are highly suspect.

“However, all the crops I’m about to show you — corn, cotton and soybean — are Roundup Ready. So, they’re resistant to Roundup and that takes any (glyphosate-based product) out of the equation.”

Miller and colleagues “wanted to show you what (other) materials’ activity has.” All were applied on June 8, nine days before the field day. The rates — “and we didn’t have space or time to put all the rates and combinations out” — are all for single herbicides and the amounts used “are right in the middle of rate ranges or ones we think will work from our general weed control trials. And all had a maximum required surfactant.”

Miller, a mass of attendees in tow, begins walking the study and pointing out the various treatments.

First up: controlling corn with cotton and soybean herbicides.

• Harmony GT applied at one-third of an ounce per acre: “We use it a lot in burndown situations — it’s very good for broadleaf control. We see typical ALS symptoms: a lot of reddening, yellowing and purpling of the veins. ALS is represented by Harmony GT, Envoke, Staple or Classic. The plants haven’t been killed, but you can see the high (impact). That one thing to keep in mind: you don’t always need to kill the plants. You just need to reduce competition as much as possible. That’s especially true with the first application so another can finish them off.”

• Envoke at 0.1 ounce: “Both this and Staple LX are used in cotton for over-the-top weed control. I get a lot of calls on that — ‘Instead of using one of the grass herbicides, can I use these and get more bang for my buck? Control grasses, control volunteer corn and also broadleaves with residual?’ You’ll notice very similar symptomology to the Harmony GT.”

• Aim: “Every year, I get calls on Aim — it’s cheap, very effective and can be used in corn. I put it in here to show some of the speckling. That’s all you’ll get out of it. It looks much better in cotton.”

• Cotoran: “There’s a bit of interveinal chlorosis, but it doesn’t appear to be a very good option for taking out the corn at this point.”

• Linex: “I thought we’d see more activity out of Linex. All had a maximum, required surfactant. There’s a little burning and yellowing, but it isn’t as good as some other treatments now.”

• Sencor: “This is 4 ounces — a cheap shot to see what it would do. It’s caused some chlorosis in the veins but not stand-out control.”

• Select Max: “This is a grass herbicide at 10 ounces. It’s probably the product of choice in the broadleaf crops. It hasn’t killed the plants ‘graveyard’ dead but check out the yellowing and purpling. I can pull out the hearts of every one of the corn plants. They’re rotting and that’s exactly the mode of action. Another 14 to 21 days and these plants will probably go on down.”

• Gramoxone Inteon: “We went up to 40 ounces and it caused a lot of burning. But the corn isn’t dead at this point.”

• Valor SX at 2 ounces: “It has caused a little burning on the bottom and crinkling of leaves. But it didn’t provide a significant amount of control.”

• FirstRate at 0.3 ounces: “It’s used in soybeans for broadleaf control and has caused yellowing. The leaf curling and whitening it has caused in the terminal is often forms of symptomology we look for when we get called out on drift complaints on corn from an ALS herbicide.”

• Classic at 0.33 ounces: “Classic is getting a bit more activity than FirstRate at this point — but not at the level of Select, or a similar grass herbicide.”

• Ignite at 22 ounces: “There’s good weed control has been observed at that rate. Here, at this stage, it appears that the higher rate of 29 ounces may be needed for control.”

• Reflex at 16 ounces: “This is another herbicide used in soybeans. It’s burned the plants but will probably take something else for control.”

Herbicides and volunteer cotton:

• Accent at 0.67 ounce: “This is a popular herbicide used in corn. It’s showing a lot of yellowing in the terminals. Sometimes you’ll see some purpling on the back of the leaves. This product has pretty much shut the cotton down. Another application of (Accent) or something else will knock out its competitiveness.”

• Laudis at 3 ounces: “This is a newer corn herbicide. It is doing a good job.”

• Callisto at 2 ounces: “This is doing a good job of knocking the cotton back.”

• Permit at 0.75 ounce: “This herbicide is used not only in corn but in rice. It’s another SU (sulfonylurea) herbicide. It’s yellowing the plant and shutting the terminal down. The veins are purpling.”

• Atrazine at 32 ounces: “This is the old stand-by. Check out the interveinal chlorosis, the cupping and the burned plants.”

• Status at 4.5 ounces: “This is another new product and is pretty impressive. It contains dicamba — the active ingredient of Clarity. It is swelling stems and curling them down. This is first time I’ve looked at it and it’s doing really well on the cotton plants at this stage.”

• Harmony GT at 0.33 ounce: “We looked at this in burndown. Here’s what it does on broadleaves. ALS shuts the plant down, speckles it, and yellows the tops.”

• Aim at 2 ounces: “Two ounces of this does a fantastic job. I don’t think these plants are coming back. We use Aim for defoliation in cotton. This was sprayed nine days ago and destroyed these cotton plants. It’s one the best things we’ve got out here. Although not in this demonstration, a similar product, ET, has looked impressive in our broadleaf weed control research plots.”

• Cotoran at 24 ounces: “You can see the interveinal chlorosis although these plants are still sitting there.”

• Resolve at 1 ounce: “This is a new compound that DuPont is looking at for preplant burndown applications. It can be used in corn and it provides pretty good activity. It has knocked the cotton on back.”

• Linex at 16 ounces: “You can see some of the burning over the top, some of the leaf cupping. It hasn’t killed the plants but has knocked them back well.”

• Sencor at 4 ounces: “It’s doing a good job burning back the cotton, so far. I don’t know if it will kill the cotton. If a nice rain comes and the plants get going in this heat, they might recover.”

• Gramoxone Inteon at 40 ounces: “Remember what this did to corn, here’s what it does to cotton. This cotton is not coming back.”

• Valor SX at 2 ounces: “At 2 ounces per acre, it’s causing some burning. If you look at the symptoms, there’s kind of a whitish appearance around the necrotic spots. It is burned, but the terminals are doing fine. So, as with all herbicides, the smaller the plants are at application, the better.”

• FirstRate at 0.3 ounce: “This is another SU used in soybeans. It’s very similar to Classic. Again, we see the yellowing and waviness of the leaves. It’s stopped the plants although it may take another application to completely remove the competition. At this point, we’re actually seeing a bit more activity out of the Classic than the FirstRate. However, the FirstRate may catch up.”

• Ignite at 22 ounces: “This is another pretty good treatment at 22 ounces. This cotton is not coming back. So, there are three products that have done exactly what we wanted very quickly: Aim, Ignite and gramoxone.

• Flexstar at 16 ounces: “This is a soybean herbicide that is doing very well. It’s a PPO and does well on a number of broadleaves.”

Herbicides and volunteer soybeans

• Accent at 0.67 ounce: “This is used in corn but has activity on soybeans. It’s shutting them down.”

• Laudis at 3 ounces: “It’s a newer corn herbicide and burning the beans back.”

• Callisto at 2 ounces: “This has very similar activity to Laudis.”

• Permit at 0.75 ounce: “This is showing the purpling on the back of leaves and cupping of the terminals. These plants will probably go ahead and die. The stems are brown when cut and that’s a good sign.”

• Atrazine at 32 ounces: “This is showing a good burn with chlorosis on the leaves, shutting them down.”

• Status at 4.5 ounces: “This contains dicamba which, to beans, is like 2, 4-D on cotton. It’ll swell the stems, split them open and kill them.”

• Harmony GT at 0.33 ounce: “In a burndown situation, it’s showing typical ALS symptoms. I don’t know if it’ll kill the plants but it’s certainly limiting the ability of the beans to compete.”

• Envoke at 0.1 ounce/Staple at 2.6 ounces: “These are cotton herbicides we get a lot of questions about. Here they are side-by-side. Both do a good job knocking the plants down and may end up killing them. Envoke seems to have a bit quicker activity at this stage.”

• Cotoran: “Over-the-top it’s getting some leaf burn. The plants may come out of it, though.”

• Resolve: “This is an SU that DuPont is looking at for burndowns. It does a good job it does on soybeans. We’re looking at it as a preplant in soybeans for safety because it has good activity.”

• Linex: “Over-the-top it’s caused a little burn and yellowing.”

• Sencor: “It’s doing some burning but the terminals look okay. The plants may revive.”

• Gramoxone Inteon: “At 40 ounces it causes symptoms like what we saw on cotton. It does a good job of taking young beans down.”

• Valor SX: “It provides burning and necrosis and limits competition.”

• Ignite: “At 22 ounces, it looks good on soybeans. However, you might need to go with a 29-ounce rate to take the plants completely out.”


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