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EFFECTS OF WEED DENSITY, HERBICIDE ANTIDOTES, AND SOIL ADSORPTION ON HERBICIDE BIOACTIVITY
Abstract
Herbicide bioactivity was decreased with increased weed densities, with herbicide antidotes, and from herbicide adsorption to soil organic matter and clay. Effects of differential weed densities on herbicide bioactivity and uptake by plants were examined in greenhouse, laboratory, and field research. Increasing densities of white mustard (Brassica hirta Moench) and foxtail millet {Setaria italica (L.) Moench} resulted in increased atrazine {2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine} and alachlor {2-chloro-2', 6'-diethyl-N-(methoxymethyl)acetanilide} concentrations required to produce equivalent fresh weight reductions in greenhouse bioassays. Less ('14)C-labeled alachlor and atrazine were absorbed per plant in the greenhouse as seeding rates of foxtail millet and white mustard, respectively, increased. Herbicide uptake expressed on fresh weight basis, ug absorbed/g fresh weight, also decreased as seeding rate increased for both herbicides except for the lowest atrazine concentration. In the laboratory, less ('14)C-labeled alachlor was absorbed per seedling as foxtail millet densities increased from 5 to 50 seeds/petri dish. Field experiments indicated that as 'Rox Orange' {Sorghum bicolor (L.) Moench} forage sorghum density increased, more alachlor was required for equivalent weed control. EPTC (S-ethyl dipropylthiocarbamate) plus R-25788 (N-N-diallyl-2,2-dichloroacetamide) was more effective than alachlor or metolachlor {2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxyl-1-methyl-ethyl)acetamide} in controlling Rox Orange densities up to 100,000 seeds/57 m('2) plot. Several antidotes were used to decrease plant injury as a result of herbicide bioactivity in corn (Zea mays L.) and sorghum {Sorghum bicolor (L.) Moench.} Tank mixes (8:1 herbicide:antidote) of R-25788 and H-31866 {N,-allyl-N-(3,3-dichlorallyl)dichloroacetamide} with alachlor and metolachlor on a Sharpsburg silty clay loan (sic1) and Tripp sandy loan (sl) provided good crop protection for corn in a greenhouse bioassay. In a sorghum bioassay on a Sharpsburg sicl, Tripp sl and Rosebud loam (1), CGA-43089 {(alpha)-(cyanomethoximino)-benzacetonitrile} seed treatment (1.25 g/kg) applied to sorghum seed before planting was found to be more effective than the R-25788 tank mix in countering the phytotoxic effects of alachlor and metolachlor. In a field experiment, CGA-43089 seed treatment provided excellent protection against alachlor and metolachlor injury, whereas a tank mix of R-25788 provided only minimum protection. At a Rox Orange seeding rate of 10,000 seeds/57 m('2), sorghum yields were increased by alachlor and metolachlor with CGA-43089 seed treatment. In laboratory experiments, CGA-43089 did not affect the uptake, distribution, or metabolism of ('14)C-labeled metolachlor in sorghum. Atrazine and alachlor bioactivity, as measured by GR(,50) (concentration required to reduce growth of test species 50%) decreased with increased adsorption to nine Nebraska soils. Positive correlation coefficients resulted between GR(,50) and adsorption coefficient (K(,D)), herbicide mobility, percent organic matter (OM), cation exchange capacity (CEC), and percent clay. Organic matter and clay content were found to be most important factors governing soil adsorption and subsequently herbicide bioactivity. Adsorption coefficient (K(,D-OM)) values to OM and percent adsorption due to soil OM were greater than 40 and 50, respectively, when averaged over nine Nebraska soils. Equilibrium between herbicide adsorbed to soil and in solution was attained after 12 h for Sharpsburg sicl and Tripp sl and 24 h for Rosebud 1. The equilibrium did not change for 2880 h. In a column leaching and desorption study, where soil and herbicide were allowed to equilibrate from 6 to 1296 h, no significant differences in alachlor or atrazine leached resulted after the 6 h equilibration time. Herbicide leached increased significantly from Sharpsburg sicl to Tripp sl.
Subject Area
Agronomy
Recommended Citation
WINKLE, MARK EDWARD, "EFFECTS OF WEED DENSITY, HERBICIDE ANTIDOTES, AND SOIL ADSORPTION ON HERBICIDE BIOACTIVITY" (1980). ETD collection for University of Nebraska-Lincoln. AAI8017629.
https://digitalcommons.unl.edu/dissertations/AAI8017629