Murray State Theses and Dissertations

Abstract

Herbicide use is central to weed management in Illinois corn production; however, long-term changes in the balance between systemic and contact herbicides have not been well quantified at the statewide scale. This study analyzes herbicide trends in Illinois corn from 1982 to 2016 using secondary data from the USDA Agricultural Chemical Use Survey, paired with climate, regulatory, and herbicide resistance information. Herbicide active ingredients were classified into systemic and contact functional categories and grouped according to Weed Science Society of America (WSSA) mode-of-action (MOA) codes. For each survey year, total herbicide load (lb a.i./acre), functional proportions, MOA-specific contributions, and a qualitative index of herbicide program complexity were calculated. Descriptive statistics and trend analyses were used to evaluate temporal changes, with interpretation guided by major regulatory and resistance developments.

Results indicate that total herbicide load in Illinois corn increased over the study period, with systemic herbicides consistently accounting for the majority of total load. The systemic proportion increased from approximately 79% in the early 1980s to a peak in 2010, followed by a decline by 2016 as contact herbicide load increased and herbicide programs diversified. MOA profiles shifted from atrazine- and ALS-dominated systems to glyphosate-dominant programs, followed by increased contributions from PPO and HPPD inhibitors in response to widespread herbicide resistance. Herbicide program complexity also increased over time, reflected by greater MOA diversity and increased use of mixtures and layered applications. Thesis findings reject the null hypothesis of no change in the systemic-to-contact proportion and highlight the importance of functional and MOA diversification for sustainable weed management in Illinois corn production systems.

Year manuscript completed

2026

Year degree awarded

2026

Author's Keywords

Active Ingredient, Contact Herbicide, Systemic Herbicide, Mode of Action (MOA), Multiple Resistance, Program Complexity

Degree Awarded

Master of Science

Department

Agriculture

College/School

Hutson School of Agriculture

Thesis Advisor

Alyx Shultz

Committee Member

Katelynn Mollett

Committee Member

Nick Lancaster

Committee Member

Chadwick Gaylord

Document Type

Thesis

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