In this Issue:
Sweet Corn Herbicide Advancements in 2008
Sweet Corn Herbicide Advancements in 2008
Roger Becker, University of Minnesota
Advancements in sweet corn herbicides continue with new products (Option, Laudis) or new uses of existing products (Harness, Surpass, others). Sweet corn herbicide labeling still lags behind that of field corn in part due to tolerance concerns for some sweet corn hybrids. Work by Joe Bollman, UW Extension, during his recent graduate school research with Chris Boerboom at the University of Wisconsin and with Vince Fritz and I here in Minnesota, defined the tolerance of sweet corn hybrids in the HPPD family (4-hydroxyphenyl-pyruvate-dioxygenase) which includes Impact, Laudis, and Callisto. Previous work by Jerald Pataky at the University of Illinois has shown tolerance of sweet corn is linked to the occurrence of the homozygous recessive nsf1 gene with additional tolerance gained with the heterozygous hybrids, and the best tolerance in hybrids with homozygous dominant Nsf1 gene. Chris Boerboom, UW Madison, led the effort to develop a fact sheet on sweet corn variety tolerance with the first for Accent and Callisto now available (See Fact Sheet). This reference can be used to assess the expected tolerance of various varieties to Accent or Callisto.
One of the first HPPD herbicides labeled for use on field corn was Balance (isoxaflutole). Isoxaflutole was tested on field and sweet corn in the mid to late 90s and received labeling for use on field corn in most states in the Midwest. Labeling was not granted in Wisconsin or Minnesota due to water quality issues however. The next HPPD herbicide to be registered was Callisto (mesotrione) and included sweet corn. Callisto was discussed at length at recent MFWPA Processing Crops and the MFVGA Conferences and has been the focus of considerable testing for sweet corn tolerance. Callisto offers the flexibility of preemergence soil application or postemergence use and was a welcomed new mode of herbicide action for the sweet corn market. Pre-packaged mixtures for soil applications are offered with metolachlor and mesotrione (Camix) and also with atrazine at different rates (Lumax and Lexar). Rotation restrictions limit rotating to peas, dry beans, snap beans, beets, etc. within an 18 month interval.
In 2006, the second HPPD herbicide was labeled for use on sweet corn, Impact (topramezone), including processing and fresh market sweet corn. Impact provides excellent broadleaf control with suppression or control of many annual grasses. Like Callisto, Impact has some carryover concerns. Its use where rotating to soybean or several vegetables requires a somewhat less efficacious reduced rate of 0.5 oz per acre in response to carryover seen at the 0.75oz per acre rate. Impact has shown excellent tolerance on sweet corn lines in our regional testing. Impact use is postemergence only.
The newest HPPD herbicide, labeled in 2008, is Laudis (tembotrione) and includes fresh market and processing sweet corn. Laudis comes prepackaged with a safener isoxadifen and as such, has excellent sweet corn tolerance. Use 3 oz of product per acre with 1 % methylated seed oil plus 8.5 lbs ammonium sulfate per 100 gallons of spray solution. Like Impact, broadleaf weed control is excellent with Laudis, and it also shows excellent control of many grass species. Apply POST up through the V7 stage in sweet corn (i.e., do not apply to sweet corn when the 8th leaf collar is visible). As with other HPPD herbicides, there are rotation concerns. With Laudis, peas and snap beans are allowed the following season, with an 18 month restriction required for dry beans and sunflowers.
With all of these HPPD herbicides, we recommend adding 0.5 to 0.75 lb ai atrazine per acre as it improves the consistency and spectrum of weed control. Which HPPD product should you use? Of the three HPPD herbicides labeled for use in the upper Midwest, all provide excellent efficacy particularly when tank mixed with reduced rates of atrazine. Callisto has the potential to show the yellow flash with post emergence applications on some hybrids but rarely results in yield loss, while Laudis and Impact have relatively good tolerance. Callisto provides the opportunity for soil applied or post emergence applications and thus offers more flexibility in use. Callisto is the weakest of the three on grasses providing crabgrass activity, but limited grass activity on other common annual grass weed species. Impact is limited to the lower 0.5 oz/a rate due to carryover concerns in many rotations yet offers good broadleaf and grass activity. Both Impact and Laudis can only be applied postemergence. Crop rotation limitations favor the use of Laudis whereas there are more concerns for rotations to various crops with Impact and Callisto. With the advent of Laudis and Impact, where do you use Callisto? Callisto still has a strong fit soil applied in the package mixtures of Camix, Lumax, and Lexar offering additional weed management options and excellent weed control. Callisto still has a strong fit to control volunteer potato when used post emergence with tests showing control better than that provided by Starane (fluroxypyr). The use of Accent may change in sweet corn with the advent of Impact and Laudis because of the additional broadleaf control provided by Impact and Laudis. Accent still may be the grass herbicide of choice providing better green foxtail and woolly cupgrass control than Laudis. However, Laudis would provide better crabgrass control than Accent. Long-term use of Laudis could shift grass weeds to dominance by green foxtail and fall panicum. Accent still may have a fit as use for a rescue treatment though sweet corn height restrictions must be observed. Additionally, the new Accent Q product includes the safener isoxadifen and should reduce tolerance concerns on intermediate tolerance varieties and reduce spray overlap concerns.
For the sulfonylurea herbicides, in addition to Accent, Option from Bayer Crop Science was labeled for sweet corn this spring. Option (foramsulfuron) contains a safener (isoxadifen), is applied at 1.5 to 1.75 oz product per acre postemergence and is similar to Accent in performance. Option is more active than Accent and requires the safener to gain acceptable crop tolerance. Sweet corn tolerance to Option was similar to, or less than that of Accent in Minnesota and Wisconsin trials. Option is somewhat better than Accent on crabgrass, though neither provides complete control. Accent provides better control of woolly cupgrass. Apply Option at the V1 through V6 stage. Option has a 45 day PHI for sweet corn which may be an issue. Accent does not have any PHI concerns.
Acetochlor products were also labeled for preemergence use on sweet corn in 2008. Acetochlor is available in encapsulated formulations and EC formulations and also is available in package mixtures with atrazine. Many manufacturers offer acetochlor products. The initial introduction into the field corn market was Harness and Surpass via Monsanto and Dow AgroSciences (Zeneca to Syngenta to Dow AgroSciences), respectively. Acetochlor cannot be used where light textured soils overlay water tables that are 30 feet or less below the soil surface. This will limit the use of acetochlor in some areas in Wisconsin and Minnesota. Rotational crops are one of the current areas of confusion when comparing various acetochlor products. We eventually expect most rotational crops to be allowed the year following acetochlor use, but at the time of this presentation, succulent peas and snap beans are not allowed as rotational crops the following year acetochlor. Whichever acetochlor product you may choose, be sure to follow the label on the product that you are using. Acetochlor offers grass control and small seeded broadleaf weed control similar to or better that that of other acetanilide products such as Lasso, Dual, and Outlook.
More sweet corn hybrids are becoming available with the Poast ProtectedTM gene which allows the use of sethoxydim (Poast or Poast Plus) for grass control. Apply sethoxydim only to Poast ProtectedTM hybrids or severe crop injury and crop failure will occur. These are not GMO hybrids as the resistance was evolved through tissue culture techniques at the University of Minnesota rather than through gene transformation. Sethoxydim offers excellent grass control and may be particularly useful for troublesome grasses such as wild proso millet and woolly cupgrass. Herbicide labeling is in flux for sweet corn and new technologies are coming online, providing welcomed management alternatives and weed control possibilities.
Always follow current labeling for the crop. A label must be in possession of the applicator. The product label always supersedes anything in this article.
Co-Editors: Bill Hutchison (email@example.com), Department of Entomology, University of Minnesota, Jeanne Ciborowski, Minnesota Department of Agriculture, Ag. Resources Management and Development Division, and Suzanne Wold-Burkness (firstname.lastname@example.org), Department of Entomology, University of Minnesota
The Newsletter is published weekly from May through August, cooperatively, by the Minnesota Department of Agriculture (MDA) and the University of Minnesota (U of MN). Reports are posted on the U of MN and MDA web sites on Fridays. If you have suggestions and/or comments, please send your contributions by 4 p.m., Wednesday to Jeanne Ciborowski, 651-201-6217, email@example.com , MDA, 625 Robert St. North, St. Paul, MN 55155. You can access the Newsletter at the U of MN web site in htm format at: www.vegedge.umn.edu/MNFruit&VegNews/mnindex.htm and at the MDA web site in pdf format at: www.mda.state.mn.us/plants/pestmanagement/ipm/ipmnews.htm
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Last Revised May, 2008 by firstname.lastname@example.org