<p>Control of weeds that have survived a postemergence (POST)
herbicide often need to be controlled in order to prevent seed production and
interference with crops. The most efficacious herbicides and timings used for
respray applications has not been determined in many problematic weed species.
Previous research has demonstrated that weeds clipped to simulate a failed
herbicide application responded differently to herbicide applications to
regrowth based on herbicide used and weed species. Other research is
conflicting as to the optimum timing of an herbicide respray application with
various herbicides. Gaining a better understanding of how to maximize respray
herbicide performance will help growers and land managers to preserve crop
yield and prevent weed seed production in the event of POST contact herbicide
failure. The objectives of this research were to determine the optimum respray
herbicide and timing combinations for control of four problematic weed species
in the midwestern United States that have survived an application of either
glufosinate or fomesafen: waterhemp<i> </i>[<i>Amaranthus tuberculatus</i> (Moq.) J. D. Sauer], Palmer amaranth (<i>Amaranthus palmeri</i> S. Watts), giant
ragweed (<i>Ambrosia trifida</i> L.), and
horseweed (<i>Erigeron canadensis</i> L). Through
a series of field and greenhouse experiments we determined that respray
herbicide, respray application timing, initial herbicide, and level of injury
from the initial application influence efficacy of the respray herbicide in a
species-specific manner. Waterhemp regrowth following a failed
glufosinate application was controlled most effectively by applying glufosinate
or fomesafen 7 to 11 days after initial treatment. When following fomesafen,
applications of 2,4-D 3-7 days after initial treatment or glufosinate 7 to11
days after initial treatment were most effective. Control of Palmer amaranth
regrowth following either initial herbicide is best achieved with respray
applications of glufosinate, fomesafen, or 2,4-D applied no later than 7 days
after initial treatment. The best strategy to control giant ragweed regrowth
following a failed fomesafen applications is to apply 2,4-D, dicamba, fomesafen, or glufosinate at any timing between 3 and 11
days after initial treatment. Efficacy of the respray glufosinate application was
maximized when applied 11 days after the initial application rather than 3 days
after initial application. Horseweed regrowth was best controlled by 2,4-D,
dicamba, or glufosinate applied at any timing between 3 and 11 days after the
initial application. Where injury from the initial herbicide application is
high, there were fewer differences among herbicide treatments and treatment
timings. A greenhouse bioassay revealed that as waterhemp injury from an
initial glufosinate application increases, control with a respray herbicide
also increases. Therefore, complete control of weed regrowth is achieved more
easily with increasing injury from the initial application. This research
suggests that timing of herbicide respray applications is more urgent than
previously thought, so scouting must be done within days of a contact herbicide
application to ensure adequate control. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/8028878 |
| Date | 14 May 2019 |
| Creators | Jesse A Haarmann (6623615) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/The_Effect_of_Herbicide_Respray_Treatments_and_Timings_on_Regrowth_of_Four_Weed_Species/8028878 |
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