Evaluating Evapotranspiration and Management of Glyphosate-Resistant Palmer amaranth (Amaranthus palmeri S. Watson)

Authors

Jasmine Mausbach, University of Nebraska-LincolnFollow

First Advisor

Amit J. Jhala

Second Advisor

Suat Irmak

Date of this Version

8-2021

Citation

Mausbach JM (2021) Evaluating evapotranspiration and management of glyphosate-resistant Palmer amaranth (Amaranthus palmeri S. Watson). University of Nebraska-Lincoln Digital Commons.

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Agronomy, Under the Supervision of Professors Amit J. Jhala and Suat Irmak. Lincoln, Nebraska: August, 2021

Copyright © 2021 Jasmine M. Mausbach

Abstract

Palmer amaranth (PA) is the most problematic weed in agronomic cropping systems in the United States. Acetolactate synthase (ALS) inhibitor-/glyphosate-resistant (GR) PA has been confirmed in Nebraska and is widespread in several counties. Soybean resistant to isoxaflutole/glufosinate/glyphosate has been developed to provide additional herbicide sites of action for control of herbicide-resistant weeds. The objectives of this study were to evaluate herbicide programs for control of ALS inhibitor/GR PA and their effect on PA density and biomass, as well as soybean injury and yield in isoxaflutole/glufosinate/glyphosate-resistant soybean. A PRE herbicide fb glufosinate controlled PA 80%–99% 21 d after late-POST in 2018 and reduced density 89%–100% in 2018 and 58%–100% in 2019 at 14 d after early-POST. Weed-crop competition models offer a significant tool for understanding and predicting crop yield losses due to crop-weed interference. Within current empirical models, weed biological characteristics are unknown, which limits understanding of weed growth in competition with crops and how that competition affects crop growth parameters. The objective of this study was to determine the effect of center-pivot and subsurface drip irrigation on the average evapotranspiration (ETa) of PA grown in corn, soybean, and fallow in south central Nebraska. Results suggest irrigation affects subplot ETa differences early in the growing season, but crop system and progression of plant growth with available water have a greater effect on ETa differences than irrigation type later in the growing season. Thus, crop management will likely have greater effects on PA ETa values than irrigation practices alone. This study provides base data on weed evapotranspiration and its relation to weed morphological features for future use in mechanistic weed-crop competition models.Velvetleaf is another troublesome broadleaf weed that competes with agronomic crops for resources such as soil moisture. The objective of this study was to determine the effect of degree of water stress on the growth and fecundity of velvetleaf using soil moisture sensors under greenhouse conditions. The results of this study demonstrate that velvetleaf can survive ≥ 50% field capacity (FC) continuous water stress conditions, although with reduced leaf number, plant height, and growth index compared to 75% and 100% FC.

Advisors: Amit J. Jhala, Suat Irmak