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What Were Your Weeds, and Where Were They?

Saturday, December 1, 2001
filed under: Weeds

What Were Your Weeds, and Where Were They?

Knowing will go a long way to help control them next growing season

Every growing season seems to result in a different weed situation, depending on how the growing season and weather develops.

It was a drier growing season in many areas of North Dakota this year, and that bode well for kochia, which tends to thrive in drier conditions, says Brian Jenks, weed scientist at North Dakota State University, Minot. Wild buckwheat and biennial wormwood also seemed to be problematic this year. “We were fortunate, though, to have Section 18 label clearance for Spartan, which does an excellent job on kochia, wormwood, and other annual small-seeded broadleaf weeds,” says Jenks.

Canada thistle continues to be a major weed problem in many fields, best tackled before planting sunflower, in small grains, by applying mobile or systemic herbicides like 2,4-D, Banvel (dicamba – dma salt), Curtail (clopyralid + 2,4-D), and pre-harvest Roundup (glyphosate). Note that a number of products have residual carryover that requires a waiting interval between application and planting; follow label guidelines.

Leon Wrage, South Dakota State University extension weed specialist, says foxtail seemed to be a problem in South Dakota this year, as well as Canada thistle, kochia, wild buckwheat, and common lambsquarters. “We saw moisture stress mid season, and a small amount of foxtail can take its toll,” says Wrage. He stresses, just like Jenks, how crucial crop rotation is to weed control. Sunflower is an opportune time to control grassy weeds such as foxtail, yet it was a problem in some sunflower fields. “There are sunflower producers out there who really could have profited by a $5 to $11 per acre grass herbicide expenditure.”

A National Sunflower Association survey of sunflower fields late September indicated that in South Dakota, common lambsquarters was the most common weed evident in fields surveyed, followed by kochia, Canada thistle, pigweed, grassy weeds and wild buckwheat, cocklebur, nightshade and marshelder. In sunflower fields surveyed in North Dakota, grassy weeds were the most prevalent, followed by kochia, Canada thistle, marshelder and cocklebur.

“It’s evident from the survey that some farmers are not doing a good job of controlling the easy ones in sunflower; the volunteer small grains and grassy weeds, and there’s really no excuse for it, since there’s a good menu of pre-emergent (Prowl, Sonalan, Trifluralin) and post-applied (Poast, Select) herbicide products to choose from for grass control,” says Max Dietrich, the NSA’s production coordinator.

This was the first year for the crop survey, which also looked at other pest problems in sunflower, as well as yield. Sunflower fields in the Dakotas were surveyed this year, and plans are to expand the survey to the High Plains in 2002.

Weed control in some areas of the High Plains suffered this year because of a lack of timely rainfall needed to activate Spartan. “Some fields went 30 to 40 days without precipitation from the time it was applied last spring, and those fields saw increased weed pressure as a result,” says Roger Stockton, extension crops specialist, Kansas State University, Colby. “Maybe next year we need to apply Spartan further in advance of planting, to give a longer window of moisture for product activation.”

Stockton says moisture was variable, even within counties, resulting in uneven weed control and crop yields. “You’d have sunflowers on one side of a county zeroed out by the insurance adjuster, while flowers on the other side of the county were yielding 1,300 to 1,500 pounds per acre.”

Kochia has been a consistent weed problem in the High Plains, says Ron Meyer, Colorado State University extension agronomist, Burlington. He mentions pigweed and other broadleaf weeds as other problems that plague sunflower.

Meyer agrees that product activation was an issue for some sunflower producers this year. “It was dry around Interstate 70, and there was a little less success with Spartan and other herbicides. North of I-70, there was more rain and it was bit cooler, which extends the activity period.”

This fall at Burlington, Meyer began a research study to test the performance of fall-applied Spartan, and how sunflower might be affected by fall-applied Spartan when planted the next spring. He’s also testing the performance of fall-applied Valor on sunflower at rates of 2 and 3 oz/acre. Valor is a herbicide made by Valent that is labeled for some field crops, but currently not sunflower. The product is similar to Spartan in its activity, says Meyer. Both studies are no-till.

In a separate pre-plant herbicide plot trial this past summer, a tank mix of Spartan (2 ½ oz/acre) Prowl (3 pints/acre) and Roundup (1 quart/acre) received a half inch of rain shortly after the application, which resulted in excellent weed control in sunflower. “We included the Roundup to control volunteer wheat in wheat stubble. The rain stopped later in the season, so while yield in this test plot ended poorly, it had excellent weed control all season long,” says Meyer. “We have not had good luck with that tank mix in the past, and it didn’t work on other locations that didn’t get rain, but on this particular plot that received the timely rain, the weed control was outstanding.”

SDSU’s Wrage is evaluating herbicide treatments in plot trials as well, including the mix of Spartan and Roundup as a pre-plant burndown treatment. “We’re looking at the effect of timing, particularly with Spartan, and residual effectiveness. Glyphosate is a very effective product, but if some weeds such as buckwheat get large, control dissipates,” he says.

Map Weeds in Your Fields

Knowing what and where the weeds were on your fields this past growing season will go a long way to help control them next growing season.

Recall and record weed pockets and problems in each field, advises Denise McWilliams, formerly an extension crop production specialist at NDSU, now an extension agronomist at New Mexico State University. Evaluate early and late season weed pressure to determine how well your management program worked this year. Do comparisons across your fields and across neighbors' fields where tillage or herbicide programs are known to evaluate what went well this year and what could be improved next year.

Map out weed problems and any perceived trouble management areas, McWilliams advises. Specifically mark your maps with each weed culprit's name so that you have a list of weed species that you are gunning for next year. Site down the specifics on each weed in your notes in order to get a clear shot at the weed for next year: whether it is a perennial, biennial or annual; whether it is a broadleaf or grass; whether it was poorly controlled with the strategy used this year or well controlled but still lingering within the field in small numbers; whether it was a late germinator or came into the field early; if it was controlled early, minimizing some of the problem; or if it produced seeds.

You can simply use paper and pencil to plan your strategic maneuvers for next season, or go so far as to employ more sophisticated site-specific management. McWilliams says the utility of precision agriculture technology in integrated pest management is improvement in 1) Mapping and relocating pest populations; 2) Applying control tactics selectively to pest populations that are above your established thresholds, and 3) Keeping records over time to determine the impact of both the location and timing of pest resurgence.

“Like a well-planned deer hunt, weed walloping requires the dexterity of a hunter with a diligent dossier on each of the weed species wanted to trap, control and contain,” says McWilliams.

Mapping weed locations will allow you to observe any yield in the areas where weeds are prevalent in order to determine if yield loss occurs (a combine equipped with a yield monitor will give you an excellent idea). The maps will also provide you with a way to relocate the weed problem areas next year so that you can hone your tillage and/or herbicide skills in on the pest problem. By applying additional knowledge of location and timing of weed emergence to your pest problem, you can compare tillage techniques or herbicide efficacy to determine if targeting trouble can selectively narrow down weed populations.

“This will save you chemical costs and long-term weed control efforts. By maintaining a record of the weed problems over the years, you can further refine your control strategy to get the most for your efforts against major weed problems,” says McWilliams. “This will also, over time, give you a better idea (with harvests) of the economic impact of weed control on your fields and will allow you to know where best to utilize field scouting in future monitoring programs.” – Tracy Sayler


photo cutline: The plot in this photo is Clearfield sunflower. The specific treatment on this plot near Fargo, N.D. was Prowl + Spartan applied pre-emergence after planting, followed by Beyond (imazamox) + Arsenal post-emergence to the Clearfield sunflower hybrid in the 4 to 6 leaf stage on June 25, 2001. The Beyond + Arsenal combination simulates a Clearfield premix used in Europe and is being evaluated in North America for its fit into specific weed situations. Note the untreated comparison at right. Photo: Vince Ulstad, BASF.

Limited Clearfield Acreage Expected in 2002

Herbicide resistant technology— Clearfield and Express, with herbicide-resistant hybrids developed with conventional breeding, not biotechnology— may be the biggest hammer ever added to sunflower growers’ toolbox of weed control options.

“There are tools coming that will help control problem weeds that may in fact have been a factor in limiting sunflower acreage,” says Leon Wrage, extension weed specialist, South Dakota State University.

Non-biotech sunflower having tolerance to the sulfonylurea herbicide Express is being developed by Pioneer and DuPont. It is expected to be commercially released within a few years.

Conventionally bred sunflower resistant to imazamox will be commercialized sooner. BASF has developed the technology under the Clearfield name. Beyond is the product that will be labeled. “It has outstanding performance against a wide array of grassy and broadleaf weeds,” says Mark Dahmer, Clearfield crops project manager for BASF, Centennial, Colo.

A Section 18 label is being requested from the Environmental Protection Agency for the emergency use of Beyond on a limited amount of sunflower acreage in the Dakotas next year. “In all my years of applying for Section 18 labels, this is probably the strongest emergency condition. There is no post-emergent broadleaf herbicides available in sunflower, so the case for a Section 18 for this product in sunflower is pretty strong,” says Richard Zollinger, extension weed specialist at North Dakota State University.

Should a Section 18 label be approved, Mycogen has enough Clearfield sunflower seed available to grow about 15,000 acres next year, according to Scott Nelson, marketing specialist with Mycogen, who farms near Lakota, N.D.

“The main question I’m getting from guys is, ‘How much seed can I get and when?’ The demand is certainly there,” Nelson says. “This is going to be huge for the sunflower industry.” He says Mycogen will have a much larger supply of Clearfield sunflower seed ready for planting in 2003.

Other seed companies will have Clearfield sunflower ready in 2003 as well. “While Mycogen is the first of the major seed companies to come to market with Clearfield sunflower, we’re also seeing a lot of varietal progress from Interstate, Seeds 2000, and Nidera, and Argentine company. Those three companies have provided materials for us to screen, and next year we expect to see commercial hybrids available from them, and possibly a few others,” says Dahmer. “2003 will be a big opportunity for sunflower growers with Clearfield, provided the Section 18 is approved.” – Tracy Sayler

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