Postemergence herbicides are very useful for weed management in sweet corn, but caution may be needed when certain herbicides are applied to sensitive hybrids. Over the past 3 years, we have conducted many sweet corn tolerance trials to postemergence herbicides.
Sweet Corn Tolerance to Accent, Callisto, Impact, and Laudis
Chris Boerboom, Extension Weed Scientist and Joe Bollman, Jefferson County Extension Agent
Postemergence herbicides are very useful for weed management in sweet corn, but caution may be needed when certain herbicides are applied to sensitive hybrids. Over the past 3 years, we have conducted many sweet corn tolerance trials to postemergence herbicides. These trials were coordinated by Joe Bollman during his graduate studies and we had several collaborators including M. VanGessel, University of Delaware, R. Becker, University of Minnesota, R. Bellinder, Cornell University, D. Morishita, Idaho State University, and E. Peachey, Oregon State University. This article summarizes the major findings of these trials.
Accent And Callisto Tolerance
Hybrid tolerance to postemergence-applied Accent and Callisto was evaluated in 18 field trials that were conducted at 11 sites from 2005 to 2007. The locations were in Delaware, Colorado, Idaho, Illinois, Minnesota, New, York, Oregon, and Wisconsin. Across all trials, Accent was tested on 185 hybrids and Callisto was tested on 179 hybrids. Both herbicides were applied at twice their labeled rates to determine which hybrids have good tolerance or might be sensitive. Accent was applied at 1.33 oz/a + 1% crop oil concentrate (COC) + 2 lb/a ammonium sulfate (AMS). Callisto was applied at 6 oz/a + 1% COC. Both herbicides were applied to sweet corn hybrids in the V3 growth stage. Injury was evaluated on a 0 to 100% scale at 7 and 14 days after treatment. Accent injury was based on stunting whereas Callisto injury was based on chlorosis or bleaching.
From these evaluations, we rated and summarized the tolerance of the tested sweet corn hybrids in a
Sweet Corn Hybrid Tolerance Rating (See link below) fact sheet, which can be found under the publications tab on this web site. Experimental hybrids that were evaluated were excluded from the fact sheet until they are released commercially. Consequently, the fact sheet lists 134 and 136 commercially available hybrids with tolerance ratings for Accent and Callisto and defines the potential risk and degree of injury. In addition to the ratings, the fact sheet describes guidelines to manage the risk of Accent or Callisto injury based on the hybrid’s rating. These recommendations are intended to supplement the guidelines that can be found on the Accent and Callisto labels.
PDF file >>>> SweetCorn-Hybrid-Tolerance2007.pdf
Impact And Laudis Tolerance
Impact and Laudis are all similar herbicides (HPPD-inhibiting or bleaching herbicides) to Callisto and are labeled for use in sweet corn. Previously, sweet corn hybrids have had limited evaluation to determine tolerance to Impact and Laudis. In 2007, two multi-state field studies were conducted to evaluate hybrid tolerance to Impact and Laudis applied postemergence.
Impact Tolerance Evaluation
The first study evaluated hybrid tolerance to several herbicides, including Impact, at sites in Oregon, Minnesota, Wisconsin, Illinois, New York, and Delaware. Impact was tested at twice the labeled rate to differentiate among tolerant and sensitive hybrids. Impact was applied at 1.5 fl oz/a + 1% COC + 8.5 lbs AMS / 100 gal water to sweet corn in the V3 growth stage. Chlorosis (or bleaching) ratings were taken at 7 and 14 days after treatment.
In this study, 58 of the 87 Impact-treated hybrids had 1% or less chlorosis at 7 DAT (data not shown). No hybrid exceeded 5% chlorosis when treated with the twice labeled rate of Impact. Of the 42 hybrids, which were tested for tolerance to both Impact and Callisto in this same trial, 60% of the hybrids had intermediate, sensitive, or highly sensitive responses to Callisto whereas none of the hybrids responded to Impact (Figure 1).
Figure 1. Classification of 42 sweet corn hybrids following treatment with a 2x rate of Impact or Callisto. Hybrid ratings are T = tolerant, I = intermediate, S = sensitive, and HS = highly sensitive.
Sweet corn hybrids exhibited excellent tolerance to Impact and many sweet corn hybrids had greater tolerance to Impact than Callisto. Based on this study, we do not intend to test additional hybrids for tolerance to Impact.
Although sweet corn has excellent tolerance to Impact, rotational restrictions should be considered when using Impact. At the 0.75 oz/a rate, soybeans and snap beans cannot be planted for 18 months after application. However, two supplemental labels allow soybeans and snap beans to be planted after 9 months if 0.5 oz/a of Impact is applied. The supplemental label for snap beans is new for 2008 and is for Wisconsin, Minnesota, and Illinois.
Laudis Tolerance Evaluation
This study was designed as a preliminary study to determine the potential need for future hybrid tolerance testing of Laudis. This 2007 study was conducted in Minnesota, Wisconsin, New York, and Delaware. Twenty-eight hybrids (Table 1) were selected for testing because they range in tolerance to Callisto. Laudis was applied at twice the labeled rate to differentiate among tolerant and sensitive hybrids and was applied at 6 fl oz/a + 1% COC + 8.5 lbs AMS / 100 gal water. Chlorosis (or bleaching) ratings were taken at 7 and 14 days after treatment. Green husk yields were taken at crop maturity.
In this study, Merit was the only hybrid of the 28 hybrids that had significant injury from Laudis and was killed. Merit was the only hybrid to have a yield reduction compared to the nontreated control when treated with Laudis (data not shown). J. Pataky, University of Illinois also screened 249 hybrids for Laudis tolerance and found excellent tolerance except for 7 hybrids that were highly sensitive.
Table 1. Sweet corn hybrids used to evaluate crop response to 2x rate of Laudis.
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Argent
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Basin R
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Cahill
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Celestial
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CSUWP1-7
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Delectable
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DMC 21-84
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Dynamo
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Early Gold
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GH 2042
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GH2547
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GH4927
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GH 9597
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GSS 1477
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GSS 2008
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GSS 2914
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Hollywood
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How Sweet It Is
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Legacy
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Merit
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Mystique
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Overland
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Passion
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Rocker
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SS Jubilee Plus
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Suregold
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Temptation
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Trinity
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Sweet corn hybrid tolerance to Laudis was excellent to a twice labeled rate for all hybrids tested except for the known highly sensitive hybrid Merit. A few highly sensitive hybrids (Merit, DM 20-38, HMX 6386 S, and Shogun) should not be treated with Laudis. Based on this study and the results of other testing, we do not intend to test additional hybrids for tolerance to Laudis.