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Stretching Spartan

Tuesday, February 15, 2005
filed under: Weeds

It wasn¡¦t just too long ago when Spartan„µ (Sulfentrazone) wasn¡¦t even available as a pre-emergent weed control option in sunflower. ¡§Even in those first few years when Spartan was registered (it first received a ¡¥Section 18¡¦ label for use on sunflower in 1999) the adoption rate of growers was small at first, maybe 10 to 20% of growers were using it,¡¨ says Richard Zollinger, extension weed specialist at North Dakota State University.

But as familiarity and experience with the product increased ¡V along with no-till sunflower production ¡V Spartan caught on quickly. It offered excellent early-season control of annual small-seeded broadleaf weeds (including kochia, a particularly troublesome weed in sunflower) and the chemical only needed moisture for activation ¡V no incorporation was needed, ideal for a no-till system.

After five years of Section 18 use, Spartan finally received full label registration in the fall of 2003. The full label allowed Spartan to be applied in the fall, a beneficial option for minimum and no-till sunflower producers, permitting a wider window of application and a greater chance for moisture activation next spring.

But wheels fell off the Spartan wagon last fall.

FMC Corporation, which makes Spartan, announced that manufacturing constraints will prevent production of the dry flowable product (Spartan 75DF) in 2005. The shortfall affects the availability of sulfentrazone sold under different trade names (Authority, Blanket) for use on other crops as well. The company indicated that it expects the manufacturing snafu to be resolved in time for the 2006 growing season.

To help shore up the Spartan shortfall, FMC is funneling supply of Spartan 4F (FMC¡¦s liquid formulation, used mostly in the tobacco market) toward sunflower-producing areas. But Spartan 4F costs about 50% higher than Spartan 75DF on a per acre basis, and the supply is expected to meet only about 30% of the anticipated demand.

Hopefully, supply of Spartan 75DF will be back up to speed again in 2006, but sunflower growers will need to take a strategic approach to their early-season weed control options in the event they weren¡¦t able to find (or find enough) Spartan in 2005.

Obviously, weed control in the previous crop is an important consideration. Planting sunflower on the previous year¡¦s Roundup-Ready corn or soybean ground is an option to consider. Further, a number of broadleaf herbicides labeled for wheat and corn have excellent activity on kochia and other weeds that can be a problem in sunflower. But keep herbicide carryover in mind, as some broadleaf weed control products have residual activity that may not allow sunflower as a subsequent crop.

Some agronomists advise growers who solid seed to consider bumping up their planting rate, to thicken the plant canopy and give the sunflower crop a better chance to shade out weed competition.

Or, you might want to plant sunflower in rows. A row-planted crop often has better uniformity and seed size, and thus better marketability, particularly for dual purpose hybrids that can be sold into the hulling or crushing markets. Planting in rows also leaves the door open for cultivation or a between-the-rows application of glyphosate or Aim (carfentrazone) with a hooded sprayer.

Aim was recently labeled for use on sunflower. Sam Lockhart, technical support specialist with FMC, which makes the herbicide, says Aim is labeled for use both as a preplant burndown ahead of sunflower planting, and for use in a hooded-spray application. He notes several growers in South Dakota who are rigging their sprayers for hooded applications of the product in sunflower this summer.

¡§Glyphosate will get more weeds than Aim, but with glyphosate, any kind of drift at all and you risk killing sunflower,¡¨ says Lockhart. ¡§Glyphosate is translocated, Aim is more of a ¡¥contact burner.¡¦ Where as little as a drop of glyphosate would kill a sunflower plant, it would take more Aim to knock down a sunflower plant.¡¨

The 2005 NDSU Pest Control Guide indicates that Aim at1/2 oz 2EW (liquid formulation; EC is emulsifiable concentrate) controls kochia, lambsquarters, nightshade, pigweed, wild buckwheat, and waterhemp, with best results when applied to small weeds, less than two inches in height.

Preplant/pre-emerge options

There are also other preplant/pre-emerge herbicides available, such as Sonalan (ethalfluralin, from Dow) as well as Pendimax (Dow AgroSciences), and Prowl and Prowl H20 (BASF).

Both Sonalan and Prowl have been old standbys for early-season weed control in sunflower, but lost favor to Spartan in recent years as the preplant product of choice, since Spartan offers better kochia control and doesn¡¦t need to be incorporated. The 2005 NDSU Weed Control Guide rates the efficacy of Prowl and equivalents as fair on kochia, and Sonalan fair to good. Both products are rated as having excellent activity on foxtails, lambsquarters and pigweed when incorporated (good otherwise).

Prowl and Pendimax are both labeled for use on no-till sunflower as a preplant treatment, but without incorporation, moisture becomes the critical component to getting the chemical into the soil and into the root zone where weeds germinate. Allowing ample time for preplant/pre-emerge products to activate ¡V at least three weeks before planting ¡V is also extremely important. If the window between application and planting is too small, the herbicide simply doesn¡¦t have enough time to catch the moisture, get into the root zone, and activate against germinating weeds.

Both Dow¡¦s Brett Oemichen and Vince Ulstad of BASF say that granules will work better than a liquid formulation at sifting through residue to get to the soil. Liquid product is more likely to adhere to field residue, so a granular product is better in minimum/no-till situations.

Weed control will still be best when preplant products like Sonalan, Prowl, and Pendimax are worked into the top one to three inches of soil, into the root zone where early-season weeds like kochia germinate. ¡§There is equipment and practices out there where we can incorporate into a reduced tillage situation and still leave a good amount of residue on the surface,¡¨ says Oemichen.

Pendimax, Prowl and Prowl H20 all have the same active ingredient, pendimethalin. Introduced last year, Prowl H20 doesn¡¦t provide the same level of control against kochia as Spartan. However, according to Ulstad, this formulation of the soil-applied herbicide results in less odor, staining, and volatility compared to the conventional Prowl formulation. And observations indicate that it may be more effective in high-residue situations such as no-till at getting down to the soil line.

¡§With the Prowl formulation, you don¡¦t need foam markers, you can tell in the field pass where it¡¦s being applied. That¡¦s not the case with Prowl H20. This tells you that it¡¦s doing a better job of getting down into the soil,¡¨ says Ulstad.

Reduced rates of Spartan

No-till producers might want to consider Prowl H20 tankmixed with reduced rates of Spartan, either the granular or liquid formulation. Research and observations at both Colorado State University and Kansas State University indicate that Spartan will give good control of kochia and other small broadleaf weeds at reduced rates (1-2 oz/ac). The labeled rate of Spartan DF is 2-5.3 oz (lb ai/A) and 3-8 fl oz for the liquid formulation.

For example, research by CSU weed scientist Alan Helm and Brien Henry last year near Akron, Col. demonstrated excellent weed control (including kochia) with Spartan down to 1 oz (see list of treatment combinations and results).

Pre-plant applications of Spartan and Prowl/Prowl H20 were made on May 21, 47 days before planting. Dwarf Clearfield sunflower (TRX 3346CL) was planted on June 3. Glyphosate was applied as a burndown 14 days prior to the preplant applications, and Beyond was applied July 7 on sunflower at the V-6 stage.

Weed control evaluations were made on July 7, July 30, August 16 and September 14. On July 7, all treatments that included pre-plant applications of Prowl/Prowl H20 and Spartan provided at least 96% control of redroot pigweed, puncturevine, and kochia. Treatments including 1, 2, and 3 oz/ac of Spartan all provided 90% plus control of weed species in the study during the growing season when used in conjunction with Prowl H2O. Helm says kochia control with Spartan seemed to be slightly better with a non-ionic surfactant compared to crop oil as an adjuvant.

Helm says the plot trials received above average precipitation, which on one hand would encourage chemical activation and a greater likelihood of treatment success, but would also encourage weed growth and soil microbial activity that would be expected to pressure chemical residual activity, and that didn¡¦t seem to be the case.

The plots had a fair amount of kochia pressure, 40-50 plants per square meter. ¡§The control showed what Spartan is capable of doing. We had at least three different kochia emergence events this summer, and it emerged later than we would normally expect. But the results indicate we still obtained good control, even at 1 oz.¡¨ Helm stresses that his data is only one year; he plans to repeat the trials again next year.

¡§Many of us in the High Plains are convinced we can get good weed control with Spartan at less than the labeled rate,¡¨ says CSU extension agronomist Ron Meyer, who has observed good weed control with Spartan at 1.75 oz/ac. Bear in mind, however, the possibility that reducing the rate may in turn reduce the chemical¡¦s residual effectiveness, especially in lower moisture conditions. ¡§But if we can get that sunflower canopy going, we should be OK. Now, I would not want to encourage going with lower rates in a field that¡¦s known to have weed problems. But otherwise I wouldn¡¦t be afraid to go with a lower rate, especially if you have the soil pH to support it.¡¨

Phil Stahlman, weed specialist at Kansas State University, also has data which shows good results with Spartan at reduced rates ¡V weed control effectiveness down to 1 oz/ac was just as good as the 3 oz/ac rate. If using a reduced rate of Spartan, Stahlman advises tank-mixing it with Prowl (or Pendimax) or Prowl H20 at the full labeled rate. ¡§Spartan¡¦s strength is on the broadleaves, Prowl¡¦s strengths is on the grasses,¡¨ he says.

Using reduced rates of Spartan is not recommended in the Northern Plains. ¡§Soil pH, organic matter, and soil type are all part of the equation, and they have that in their favor in the High Plains,¡¨ says NDSU¡¦s Zollinger.

¡§Kochia is one of the more sensitive weeds there is to Spartan, that¡¦s in the grower¡¦s favor,¡¨ he continues. ¡§If you have high pH, light sandy soil with less than 1% organic matter, you may have good luck with lower rates of Spartan up here with good moisture for activation. Even if you have the soil pH to support it, we do have some pretty high organic matter out there, even as far west as Bismarck. And even in a medium-textured soil, the herbicide can get absorbed and tied up in the organic matter and clay particles. Then you can have marginal weed control.¡¨

Sunflower growers should consult with local farm input suppliers, retailers, and agronomists for more details on the availability of various forms of Sulfentrazone (Spartan), and recommended alternative weed control options. ¡V Tracy Sayler

Editors note: Efforts are underway to gain sunflower labels for Blanket and Authority in time for the 2005 season. Both are Sulfentrazone products. The NSA has encountered complicating legal issues between the various companies supplying Sulfentrazone products. Efforts are underway to get these legal issues resolved. Efforts are also underway in some sunflower-producing states to procure a possible Section 18 label for use of Valor (flumioxazin, made by Valent). Look for an update in our March/April issue.

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