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Spartan: The Workhorse Herbicide

Monday, February 1, 2010
filed under: Weeds

There was a great deal of celebration when the first Section 18 label for Spartan® (Sulfentrazone) was approved in 1999 in multiple states. This was the first multi-spectrum broadleaf herbicide to be labeled for sunflower.

The need was great. Growers had few alternatives other than dinitroaniline herbicides like Treflan, Sonalan and Prowl. Issues of weed resistance to this herbicide family were popping up. There was an increasing interest in no-till, and producing sunflower under that system was a real challenge prior to Spartan. With few alternatives in the market, it didn’t take long for Spartan to go to the top of the sunflower herbicide list.

The history of Spartan has not been the smoothest. Section 18 labels have always been a challenge to acquire, especially in multiple states. In 2005 the product’s manufacturer, FMC, encountered a production issue that shorted the market. There have been periodic crop damage and performance issues. But most of that has been worked out with research and field experience. Overall, the product has been a lifesaver for many sunflower producers. It is the most widely used sunflower herbicide today.

The key weed of interest has always been kochia. North Dakota State University weed scientist Rich Zollinger, who did much of the early work on the product, happily reported to the National Sunflower Association Board of Directors in 1998 that “Spartan literally ‘smokes’ kochia.” That scenario continues today, with excellent control of kochia along with other small-seeded broadleaves.

Spartan was first available as a 75 DF dry product. In 2005 it was changed to a liquid formulation, Spartan 4-F, for easier mixing. Today, Spartan is teamed up with other herbicides in a premix for further ease of handling. “Spartan Charge” is designed for the no-till producer. This formulation has added carfentrazone-ethyl (“Aim”) for faster preplant burndown of small susceptible broadleaf weeds such a ‘puffball’ kochia. “Spartan Advance” has glyphosate added to the formulation for broad-spectrum preplant burndown for no-till and conventional growers.

Use rates today are moderately lower than those during the early days of the product’s introduction, and mechanical incorporation is not recommended. Also, the use of Spartan on soils with less than 1% organic matter has been restricted.

Minimizing Crop Damage

Sam Lockhart, FMC technical support specialist, says FMC strongly advises growers to soil test to determine organic matter, soil type and soil pH. This is critical for determining an application rate. “One rate does not fit every soil type,” says Lockhart. Reducing rates is necessary on soils with a pH of 7.0 and greater, and on sandier and low-organic soils (often including hilltops).

Another area of concern is that growers who use Spartan after planting ensure that they apply the product well before seedlings begin to emerge and that seed furrows are closed. Lockhart also recommends that seeds be planted 1.0 inch or deeper when using Spartan postplant/preemerge. He advises growers and certified crop advisors to closely follow the label-recommended rates based on soil types and other soil factors described above. He also advises using variable rate technology when possible. “It is usually the eroded hilltops that result in some seedling injury without dropping the rates in those areas of the field,” Lockhart observes.

And if you do see seedling damage in parts of the field, like on hilltops? Bruce Due, Northern Plains district agronomist for Mycogen Seeds, says that in most cases the plants grow out of the injury and yield normally. “My experience is that the plants will be stunted, but not behind in growth stages. An uninjured eight-leaf plant may be six inches tall, while an injured plant will still be in the eight-leaf stage but perhaps only four inches tall,” Due states.

Rich Zollinger’s experience is that sunflower usually grows out of any damage — but it depends on the rate and the organic matter level. If the rate is too high and the soil is very light with little or no organic matter, injury can be permanent with a stand reduction.

FMC’s Lockhart agrees, saying that the injured plants usually grow out of the damage. The injured plant will be stunted and the leaves may be lighter in color — somewhat variegated and with dark lesions.

The bottom line is that everyone is doing a much better job of applying the proper Spartan rates in concert with soil types, and the damage issue has been greatly minimized since the introduction of the product.

Spartan has proven itself in weed control when timely rainfall occurs resulting in good incorporation. National Sunflower Association volunteers who participate in the annual sunflower crop survey seldom see a field with a kochia disaster. There may be a few plants here and there; but generally this weed has been put on the back burner as far as impacting yield. It is still the number one weed found in sunflower fields in most states, but the intensity of the weed population is greatly reduced when comparing it to the pre-Spartan days.

One of the major weeds in sunflower from southern Nebraska to Texas is Palmer amaranth. Spartan does a good job of controlling the various pigweeds, including Palmer amaranth. Lockhart says the key to controlling Palmer amaranth is moisture at planting for incorporation. A rain event (or irrigation) of at least 0.5 inch is critical for chemical activation. That is not always going to occur in that region, where the growing season is quite long and rain events can be greatly extended.

Is there a place for Spartan as more seed companies move their hybrids to either a Clearfield® or ExpressSun® trait system? Lockhart says Spartan is a great companion herbicide with Beyond- and Express-resistant hybrids. Both Express and Beyond are ALS herbicides, and ALS-resistant kochia is best controlled by Spartan in sunflower. “It is really the best way to control resistant kochia, and it is a great combined herbicide package — something that sunflower has really never had [before],” he concludes. — Larry Kleingartner

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