Preemergence activity of chloroacetamide herbicides on a multiple herbicide-resistant population of waterhemp (amaranthus tuberculatus)

Chloroacetamide herbicides have been an integral part of preemergence (PRE) weed management programs in corn and soybean since their discovery in the 1950’s. Today they are applied either alone, or with other active ingredients in herbicide premixes. Known as ‘Old Chemistries’, their importance is due to the excellent control of annual grasses and small-seeded broadleaf weeds when applied PRE, and relatively high crop safety. Waterhemp [Amaranthus tuberculatus (Moq.) Sauer] is a small-seeded, summer annual weed species native to the Midwest. Waterhemp is dioecious with an ability to evolve resistance to herbicides from various sites-of-action. This, paired with high reproductive output, prolonged emergence, genetic diversity, and seed dormancy, has allowed waterhemp to become one of the most problematic weeds in Midwestern agronomic cropping systems. Waterhemp has displayed resistance to herbicides from six different site-of-action groups including: acetolactate synthase (ALS) inhibitors, 5-enolpyruvyl-shikimate-3-phosphate (EPSPS) inhibitors, protoporphyrinogen oxidase (PPO) inhibitors, synthetic auxins, Photosystem II inhibitors (PSII), and 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors. Chloroacetamide herbicides, however, have remained effective. During research on the first HPPD-resistant population of waterhemp from Mclean County, IL (MCR), significantly less-than-anticipated PRE control was reported with the chloroacetamide herbicide S-metolachlor. Similar observations were made on a separate waterhemp population from Champaign County, IL (CHR) with resistance to HPPD-, ALS-, PSII-, and PPO-inhibitors and 2,4-D. In both cases, another active ingredient from the same class, acetochlor, remained effective. With such similar observations on geographically separated waterhemp populations, field research began at the CHR location in 2016 to investigate this reoccurring anomaly. Chapter 1 of this thesis includes a literature review of chloroacetamide herbicides including their development, mode of action, selectivity, and the environmental interactions of a specific active ingredient, S-metolachlor. Additionally, a section reviewing waterhemp biology is included. Chapter 2 highlights field experiments conducted at the Champaign Co. site and greenhouse dose-response experiments with acetochlor and S-metolachlor. Results from field experiments demonstrated very poor control with each Group 15 herbicide except non-encapsulated acetochlor, alachlor, and pyroxasulfone, which provided 75, 67, and 56% control, respectively, 28 days after treatment (DAT). Greenhouse dose-response experiments with S-metolachlor revealed a large difference in herbicide effective dose values between populations with multiple herbicide-resistance, including resistance to HPPD-inhibitors and atrazine, and sensitive populations. A 17.9 fold difference was documented between progeny of CHR (M6) and a known sensitive population (WUS) in response to S-metolachlor 21 DAT. The difference was calculated based on the herbicide dose required to reduce the number of surviving seedlings by 50% (LD50), and S-metolachlor was not effective in controlling M6 at a field-use rate. Acetochlor, however, was effective at controlling all populations at, or below, a field-use rate. Chapter 3 describes growth chamber experiments to examine edaphic interactions as possible causes of the decreased effectiveness of Group 15 herbicides in the field, although results were inconclusive. Also included in Chapter 3 is a synopsis of experiments and their implications for future research.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Crop Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2018

Author dc:creator

• Strom, Seth Arthur

Contributors dc:contributor

• Hager, Aaron G.
• Riechers, Dean E.
• Davis, Adam S.

• waterhemp
• herbicide resistance
• chloroacetamide
• soil-applied
• preemergence

Statement dc:rights

• Copyright 2018 Seth Strom

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/101048

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/101048