Article Archives
Spartan and The Crop Injury Issue
Wednesday, March 1, 2000
filed under: Weeds
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