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 Spartan and The Crop Injury Issue March 2000 Editor’s Note: February’s issue of The Sunflower carried an article addressing the availability of Spartan® herbicide for control of broadleaf weeds in sunflower under a conservation tillage system. Most of that article focused on the weed control efficacy provided by Spartan, with some mention of crop safety issues. This month, we are expanding the discussion regarding possible crop injury and steps growers should consider to avoid it. Taking advantage of Section 18 labels available in several states last year, hundreds of producers applied Spartan for pre-emergence broadleaf weed treatment in conservation tillage sunflower fields. The consensus? Given sufficient moisture for activation, Spartan provided good to excellent control of such problem weeds as kochia, pigweed and Russian thistle. Intermingled among the satisfaction, however, were some reports of sunflower crop injury — e.g., stunting, chlorosis, a “rippling” effect on leaves — attributed to Spartan. While the sunflower plants usually recovered and went on to harvest without any apparent yield loss, there were certain instances where the crop never seemed to fully catch up following the early season injury. Spartan will be available in at least eight states once again this year under a Section 18 registration. The key to avoiding sunflower injury from Spartan, university weed science specialists emphasize, is to follow the label directions closely — particularly as they pertain to rates used on differing soil types. Label application rates range from 0.094 to 0.25 pound active ingredient per acre (i.e., 2.0 to 5.33 ounces of product). FMC Corporation, Spartan’s manufacturer, provides the following general rate recommendations: Coarse Soils — A 2.0- to 2.67-ounce rate if the organic matter is less than 1.5 percent; a 2.67- to 3.0-ounce rate if OM is between 1.5 and 3.0 percent; and a 3.0- to 4.0-ounce rate if OM is greater than 3.0 percent. FMC does not recommend using Spartan on coarse (“sand”) soils with less than 1.0 percent organic matter. Medium to Fine Soils — Rate of 2.67 to 3.0 ounces if organic matter is under 1.5 percent; 3.0 to 4.0 ounces if OM is between 1.5 and 3.0 percent; and a 4.0- to 5.33-ounce rate of Spartan if the organic matter is above 3.0 percent. Last year, Kansas State University researchers Curtis Thompson and Alan Schlegel established Spartan trials at two western Kansas locations. At one site (near Tribune in Greeley County), the tests took place on a silt loam soil with pH varying from 7.4 to 8.3 and organic matter from 1.2 to 1.7 percent. The second site (Stevens County) contained sandier soils with a 1.6-percent organic matter and a 7.7 pH level. Visual injury ratings were made at two and nine weeks after treatment. Thompson and Schlegel found that at the silt loam site, injury from Spartan increased in accordance with soil pH and calcium. The most injury occurred when soil pH was 8.0 or higher and when calcium levels were above 5,000 ppm. Crop injury did not translate into yield loss, however. On the sandier Stevens County site, sunflower crop injury actually occurred only with the 0.25-pound (5.33-ounce) high-end label rate of Spartan. While injury in that instance was significant, again it did not result in reduced sunflower yield. North Dakota State University weed scientist Richard Zollinger reported no sunflower injury problems in his 1999 trials with Spartan at the 1x rate. There was injury (ranging from 12 to 30 percent) at the 2x rate when Spartan was applied either preplant incorporated or as a pre-emergence treatment, Zollinger indicates. There also was herbicide-induced damage to seeds with the PPI treatment, he notes, with the higher percentage of PPI injury occurring with small seeds, as compared to their medium or large counterparts. Sunflower has exhibited good safety to Spartan on medium- to fine-textured soils with organic matter above three percent, Zollinger states in his North Dakota weed control guide for 2000. “Crop injury may occur on soils with low organic matter and soil pH greater than 8.0, especially on calcareous outcropping,” he observes. Like FMC, Zollinger does not advise using Spartan on coarse-textured soils with an organic matter of less than one percent. “Poor growing conditions at and following sunflower emergence; cold temperatures; soil compaction; or a rate too high based on soil type and organic matter may result in sunflower injury,” he points out. In his work with Spartan, Kansas State University weed scientist Phil Stahlman experienced sunflower stand reductions only when higher-than-recommended rates were used. “There is some risk of crop injury on high-pH, lower-organic soils,” he concurs, adding that he would like to see additional research to further refine Spartan use rates for these types of soils. Stahlman does not favor the use of Spartan as a PPI treatment. He feels there’s too great a risk of the herbicide coming into contact with the sunflower seeds, thereby harming seed germination rates and crop emergence. — Don Lilleboe  Back to Weeds Stories Back to Archive Categories
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