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 Dicamba has been on the market since the 1960s, but the
herbicide is only used on about 17% of corn acres in the U.S. It
still appears to be effective on waterhemp and its troublesome
weedy relatives, but dicamba isn’t currently labeled for use in
sweet corn because of known sensitivity issues in the crop.
“Twenty years ago, herbicide sensitivity was the number one pest
management concern in the sweet corn industry. There were a lot
of important hybrids that had adverse responses,” says Marty
Williams, a USDA-ARS ecologist and adjunct professor in the
Department of Crop Sciences at the University of Illinois.
Williams co-authored the new study in Weed Science.
But scientists know a lot more now about the genes that help
corn safely metabolize dicamba and other herbicides. So it was
time for Williams and his research team to take another look at
the risk of sweet corn injury from dicamba. And their
recommendations offer practical guidance beyond sweet corn.
“The gene that confers tolerance to dicamba and other herbicides
in sweet corn is the same as in field corn, so our study system
is representative of other types of corn,” Williams says.
The gene in question – Nsf1 – is a cytochrome P450 involved in
detoxification of multiple herbicide families in plants. With
two functional copies of the gene, corn fights off dicamba’s
cellular attacks before they can cause injury. But mutant
versions of the gene also exist in some corn lines. Plants with
two mutant copies of the gene are highly sensitive to dicamba,
while mutant-functional gene pairings offer intermediate
protection.
Chris Landau, a postdoctoral researcher working with Williams,
confirmed these patterns in sweet corn by applying dicamba to
three hybrids representing functional, mutant, and intermediate
genotypes. He applied the herbicide at three growth stages, V3,
V6, and V9, and mixed the herbicide with the safener
cyprosulfamide in half the treatments.
“Ours is the first study in corn to
simultaneously evaluate the combination of genotype, application
timing, and safener on dicamba injury,” Landau says.
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As expected, sweet corn with mutant and intermediate Nsf1 genes
showed more dicamba injury than corn with two copies of the
functional Nsf1 gene. The study also showed dicamba application
at the latest timing, V9, caused injury regardless of genotype,
suggesting earlier applications are safer for all sweet corn
lines. The safener eased symptoms somewhat, but didn’t erase
injury altogether.
“For almost every injury metric we looked at,
including ear breakage, ear length, total ear mass, kernel mass, and
others, the safener helped,” Landau says. “It also consistently
lowered injury at the earlier timings, V3 and V6, but that effect
wasn't as profound as the V9 application.”
The results indicate dicamba could be used safely in sweet corn,
given a few caveats (and approved labeling by the U.S. Environmental
Protection Agency): Apply with safeners before V9, and avoid
applying in sweet corn with mutant Nsf1 genes, if possible.
“This work really establishes what’s needed for more utility of
dicamba in sweet corn,” says co-author Aaron Hager, associate
professor and Extension specialist in crop sciences. “That includes
working with breeders in their continued efforts to get rid of the
sensitive alleles. Also, we know application timing is going to be
important, as it is in field corn. We know now that safeners can
bring some margin of increased selectivity in sweet corn. The work
lays the foundation for the industry to use a tool that has not been
widely used in this particular cropping sequence.”
The article, “Significance of application timing, formulation, and
cytochrome P450 genotypic class on sweet corn response to dicamba,”
is published in Weed Science [DOI: 10.1017/wsc.2022.5]. Co-authors
include Chris Landau, Mark Bernards, Aaron Hager, and Marty
Williams.
The Department of Crop Sciences is in the College of Agricultural,
Consumer and Environmental Sciences at the University of Illinois
Urbana-Champaign.
[Sources: Marty Williams, Chris
Landau,
Aaron Hager
News writer: Lauren Quinn]
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