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Panel discussion at Pigposium discusses on-farm methods, costs, suggestions for control of glyphosate-resistant pigweeds.How deep into the fall should a farmer chop pigweeds?How to keep ditch banks clean?

David Bennett 1, Associate Editor

January 14, 2011

7 Min Read

Following a full day of speakers expounding on specific pigweed-related topics, the recent PigPosium wrapped up with a more free-wheeling panel discussion. Among those on stage to answer audience questions: Arkansas farmers David Wildy and Adam Chappell along with Bob Scott and Jason Norsworthy, weed scientists with the University of Arkansas Division of Agriculture.

Addressing how researchers approach programs that work for farmers, Scott said “it’s important to remember how we come up with recommendations. Adam (Chappell, Woodruff County farmer who spoke on measures taken to alleviate pigweed pressure on his farm) mentioned starting (a spray program) on cotyledon cotton, and risking some injury, in order to have the time to get across so many acres.”

When writing recommendations, “there are a lot of products we look at,” continued Scott. “And farmers point out more to me: Prefix early post and others. And some of those work and look pretty good.

“But one thing I try to keep in mind is putting (a product) in the mix that will buy growers time to get across 500 or 1,000 acres; or, get across a few acres while you’re planting some other crop at the same time.

“Just like the example of using residuals in LibertyLink soybeans. I think it buys you up to 21 days … as long as (the product) has some pigweed activity. It really frees up the post timing.

“I hear guys say, ‘I just want to make two shots of Ignite.’ We’ve talked today about why that’s a potential resistance issue. But I think, just from a practical management standpoint, it frees up a lot of time if you can get that first shot activated and have time to come back with a post. The same is true with using Prefix or something like that in Roundup Ready beans.”

How much did you spend per acre chopping in 2010?

“We were probably in the $20 per acre range,” said Wildy, who farms with his sons in Manila, Ark. “In years past, we were at $3 to $5.”

“I’d say $15 to $20 per acre,” said Chappell, who farms in Woodruff County. “We had two guys walking our farm. It would take a couple of weeks to get over it and they did it two or three times.”

How deep into the fall does a grower need to chop pigweeds?

“Basically pigweed flowers in response to day length,” said Norsworthy. “At the first of October, I’ve seen a pigweed emerge. Generally, you need two to three weeks of growth on that pigweed before it starts to produce seed…

“If you go four or five weeks without walking a field there can actually be resistant seed — or seed from a pigweed that’s emerged late — being produced.”

Clean ditch banks

How do producers keep ditch banks clean in zero-tolerance fields?

Wildy: “We’ve gone in and mowed some and then used Gramoxone around the edges to try and keep them clean. (Some) fields have a turn-row all the way around where we could disk and keep them really clean.

“As for other fields on our farm … we let a lot of pigweed go to seed on ditch banks and roadsides, this fall. We’re going to have to figure out a way to (deal with those pigweeds). Roundup used to clean up a lot of ditches and we didn’t have to mow them. Now, we’ll have to do something else, incorporate something else. It will present us with a real challenge…

“I heard (my son) tell the guys running the hippers this fall not to hip as close to the banks. We’re leaving a place where we can drive completely around the fields. We anticipate going around with a sprayer with Gramoxone, or something, to keep the borders cleaned up.”

Where large pigweeds “are being chopped and carried out … some are piling them on the turn-row” before pick-up,” said Norsworthy. “Pigweed seed readily float and if those plants have produced seed, they’ll shatter even though you’ve chopped them. … Let’s be mindful of that.

“Also, from a zero-tolerance standpoint, if chopped pigweed plants have seed and we leave them in the field, we haven’t accomplished much in reducing the soil seed bank.”

What about carryover of Flexstar into the following year?

“Biologically, milo is pretty sensitive,” said Scott. “I haven’t really seen a carryover to a lot of other crops.

“Having said that … it’s off-label to use more than the allotted amount each year and we can’t recommend it.

“But in terms of real carryover, if you’ve irrigated and gotten a normal amount of rainfall, I don’t anticipate a lot of carryover. I haven’t had a lot of calls on that yet.”

Moldboard plow

Has anyone tried a moldboard plow?

“Yes, we’ve had research for the past couple of years,” said Norsworthy. “The idea is to (deal) with a small patch of pigweed — half an acre, 1 acre — before it spreads across the farm. (To do that, maybe) we can deeply bury the seed.

“We tried it on a silt loam in Marianna, Ark., and it works a lot better in soybeans than in cotton. In cotton, we see a 50 to 60 percent reduction just by going out in the fall with a moldboard plow. This is something you want to use only once, not annually.

“The problem with a moldboard plow in cotton is when you run hippers back through to re-bed, we seem to be pulling back up a good amount of seed.

“In soybeans, (a moldboard plow) works better. Then, we come back in with a field cultivator, lightly run over the field to level it and drop back in the following spring with drill seeding.

“There, we were seeing upwards of 90 to 95 percent reduction in pigweed emergence. When I say ‘90 to 95 percent’ that’s actually a combination of treatments. We’re actually … working the moldboard plow, then we plant wheat — essentially double-cropping soybeans — or rye on top of the moldboard plow.

“Doing that appears to be very, very effective. But it isn’t foolproof. You’ll have to use some residual herbicides to carry it on out. But there are definitely some benefits.”

What about burning the residue?

“I’ve gotten that question two or three times already today,” said Scott. “If you can burn that seed, great. But when it falls to the ground and it’s moist or wet, we don’t always get enough heat” to destroy the seeds’ viability. “We’ve been burning fields and stubble for years and still have barnyardgrass and other weeds. By burning, you’ll get some of it — but not the seed on the wet ground. It just doesn’t get hot enough, in my opinion.”

Norsworthy agreed with Scott. “Several weeks ago, we initiated some plot research at Keiser, Ark. We are looking at fall management programs. One of those is burning the stubble. We’re in the process of quantifying what was actually removed.

“One thing we’ve done is to try and windrow soybean stubble. We took the straw-chopper off the combine … and successfully burned it. But, at this point, we’re not sure to what extent we reduced the seed going through the combine.

“This is something they’ve done in Australia. There, they try windrowing it and burning it. They’re also catching the chaff as it comes through the combine.

“I’ve told that to people in Arkansas and they say ‘that’s crazy. No way will I ever do that.’ But in some of these fields we’re confronted with, you’d be surprised at what you’d do to try and reduce the amount of pigweed going into the soil seed bank.”

I have wheat that I want to plant soybeans behind. Do I burn the straw or no-till into it?

If you burn that straw and … have ash on the soil surface, you’ve essentially taken yourself out of using a residual herbicide without tillage,” said Norsworthy. “Because the ash is there, if you place a residual on it, it will tie up the herbicide…

“The other option is to try and control those weeds extremely early with post-emergence herbicides. But the options are very limited.”

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About the Author(s)

David Bennett 1

Associate Editor, Delta Farm Press

David Bennett, associate editor for Delta Farm Press, is an Arkansan. He worked with a daily newspaper before joining Farm Press in 1994. Bennett writes about legislative and crop related issues in the Mid-South states.

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