Banca de QUALIFICAÇÃO: LUMA LORENA LOUREIRO DA SILVA RODRIGUES

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
DISCENTE : LUMA LORENA LOUREIRO DA SILVA RODRIGUES
DATA : 06/03/2026
HORA: 10:00
LOCAL: Zoom
TÍTULO:

CHAPTER I: Changing Landscape of Waterhemp Herbicide Resistance in Wisconsin: A Comparative Analysis Over Time

CHAPTER II : Characterization of Postemergence and Preemergence Herbicide Resistance in Wisconsin Waterhemp (Amaranthus tuberculatus) Accessions

PALAVRAS-CHAVES:

herbicide resistance evolution, herbicide site of action, postemergence herbicide, preemergence herbicide

PÁGINAS: 63
RESUMO:

CHAPTER I:

Waterhemp [Amaranthus tuberculatus (Moq.) Sauer]is a highly adaptive weed that has developed resistance to multiple herbicide sites of action, threatening sustainable weed management in corn and soybean systems. This study evaluated the response of waterhemp accessions collected across Wisconsin in 2023 to commonly used postemergence (POST) and preemergence (PRE) herbicides, and compared resistance patterns with accessions collected in 2018 to assess resistance evolution. Greenhouse experiments applied herbicides at 0.5×, 1×, and 3× labeled rates, classifying resistance based on survival (≥50%) and density reduction (<90%) thresholds. In 2023, 100%, 88%, 83%, 41%, and 24% of accessions exhibited ≥50% survival following POST application of atrazine, 2,4-D, dicamba, fomesafen, and mesotrione at the 1× rate, respectively. Glufosinate provided complete control across all accessions. PRE applications of mesotrione, metribuzin, and S-metolachlor resulted in greater than 95% density reduction, while atrazine and fomesafen were less effective, with less than 90% density reduction in 50% and 82% of accessions, respectively. Compared to 2018, 2023 accessions showed significantly higher survival to several POST herbicides, including 2,4-D (11% to 52%), dicamba (8% to 49%), atrazine (11% to 81%), fomesafen (3% to 21%), and mesotrione (2% to 11%). Changes in density reduction for PRE herbicides were also observed between 2018 and 2023, including atrazine (from 84% to 91%), fomesafen (from 97% to 81%), and S-metolachlor (from 98% to 95%). No changes were detected in density reduction for mesotrione and metribuzin at the 1× and 3× rates. These findings demonstrate rapid evolution of herbicide resistance in Wisconsin waterhemp populations over five years and highlight the urgent need for diversified herbicide programs and integrated weed management strategies to maintain herbicide efficacy and limit further resistance development.

 

CHAPTER II: 

Waterhemp [Amaranthus tuberculatus (Moq.) Sauer] is a major weed species in Midwestern U.S. cropping systems due to its high genetic diversity and extensive herbicide resistance. While resistance to postemergence (POST) herbicides is well documented, less is known about resistance expression under preemergence (PRE) applications and how responses differ between application timings. This study investigated resistance to multiple herbicide sites of action in seven Wisconsin waterhemp accessions under both POST and PRE applications using greenhouse dose-response experiments. POST experiments assessed resistance to 2,4-D, atrazine, fomesafen, and mesotrione, while PRE experiments evaluated atrazine, fomesafen, mesotrione, and S-metolachlor. Resistance was defined by ED90 values exceeding labeled field rates and resistance indices at least twofold higher than susceptible reference accessions. Widespread resistance to 2,4-D, atrazine, and fomesafen was detected, with most accessions requiring rates above labeled recommendations for effective control. Mesotrione resistance was confirmed under POST but not PRE applications, indicating reduced expression of resistance during early developmental stages. For fomesafen, resistance levels were consistent across application timings, with a strong positive correlation observed between POST and PRE ED90 values (r = 0.90, p = 0.0057), suggesting similar resistance mechanisms throughout growth stages. Resistance to S-metolachlor was identified in accession A133, representing the first documented case of Group 15 resistance in Wisconsin waterhemp. These findings revealed widespread multiple resistance among Wisconsin waterhemp populations and highlight differences in resistance expression between POST and PRE applications. Understanding these patterns is critical for optimizing herbicide programs and developing integrated management strategies to mitigate the evolution of resistance.

MEMBROS DA BANCA:
Externo à Instituição - VICTOR HUGO VIDAL RIBEIRO
Externo à Instituição - RODRIGO WERLE
Externa à Instituição - TATIANE SEVERO SILVA
Externo à Instituição - VICTOR HUGO VIDAL RIBEIRO