Weed control efficacy and biodegradation characteristics of imazethapyr
Cantwell, John Robert
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Permalink
https://hdl.handle.net/2142/21435
Description
Title
Weed control efficacy and biodegradation characteristics of imazethapyr
Author(s)
Cantwell, John Robert
Issue Date
1989
Doctoral Committee Chair(s)
Liebl, Rex A.
Department of Study
Crop Sciences
Discipline
Crop Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Agronomy
Language
eng
Abstract
The soybean herbicide imazethapyr (2-(4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl) -5-ethyl-3-pyridinecarboxylic acid) was evaluated in the field for weed control in soybean (Glycine max) during 1985 and 1986. Imazethapyr at 0.05, 0.07, 0.10, and 0.14 kg ai/ha was applied preplant incorporated (PPI), preemergence (PRE), or postemergence (POST). Imazethapyr controlled 90% or more smooth pigweed (Amaranthus hybridus) regardless of application method or herbicide rate. Imazethapyr control of jimsonweed (Datura stramonium) at 0.5 kg/ha was 30% better POST compared to soil applications. Imazethapyr at 0.10 kg ai/ha controlled 90% or more velvetleaf (Abutilon theophrasti) regardless of application method.
Biodegradation of $\sp{14}$C-imazethapyr and $\sp{14}$C-imazaquin (2- (4,5-dihydro-4-methyl-4-(1methylethyl)-5-oxo-1H-imidazol-2-yl) -3-quinolinecarboxylic acid) in soil was measured in an invitro system which allowed 90% recovery of applied herbicide. Triallate, (S-(2,3,3,-trichloroallyl) diisopropylthiocarbamate was used as a standard. Herbicide degradation was compared on two soils, a Cisne silt loam with 14% sand, 74% silt, 12% clay, 1.3% organic matter, and cation exchange capacicity (CEC) of 12 meq/100g, and a Drummer silty clay loam with 9% sand, 57% silt, 34% clay, 5.8% organic matter, and a CEC of 40 meq/100g. Herbicide degradation in gamma radiation sterilized soil was compared to fresh soil. $\sp{14}$CO$\sb2$ evolution, extractable parent, metabolites, and inextractable residue were measured. After 12 weeks of incubation, 95% of the radioactivity could be extracted as parent from sterilized soil. Imazaquin and imazethapyr degraded at a similar rate in unsterilized soil which was dependent upon soil type. All herbicides degraded slower in the Drummer soil, however triallate degraded 2-3 times faster than the imidazolinones on either soil. Evolution of $\sp{14}$CO$\sb2$ from an imazethapyr treated Cisne soil, containing a serial dilution of activated charcoal, demonstrated that adsorption of herbicide was negatively correlated with degradation. Therefore the amount of herbicide in soil solution as determined by soil characteristics will regulate imidazolinone microbial degradation.
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