Comparative Studies With Several Selective Postemergence Grass Herbicides for Soybeans
Gealy, David Robert
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Permalink
https://hdl.handle.net/2142/68472
Description
Title
Comparative Studies With Several Selective Postemergence Grass Herbicides for Soybeans
Author(s)
Gealy, David Robert
Issue Date
1981
Department of Study
Agronomy
Discipline
Agronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Plant Physiology
Language
eng
Abstract
Several selective postemergence grass herbicides were studied in field, greenhouse, and laboratory experiments. When applied postemergence over soybeans, giant foxtail (Setaria faberii) was controlled adequately at young growth stages with very low crop toxicity by 0.125 kg/ha BAS 9052 (2-{1-(ethoxyimino)-butyl)-5-(2-(ethylthio)-propyl)-3-hydroxy-2-cyclohexene-1-one), or 0.5 kg/ha KK80 (4-{4-{4-(trifluoromethyl)phenoxy}phenoxy}-2-pentenoate), and diclofop-methyl (methyl 2-{4-(2,4-dichlorophenoxy)phenoxy}propanoate). Larger grass stages required more of each chemical for adequate control, but proportionately more of diclofop-methyl. Surfactant greatly enhanced control by KK80 and diclofop-methyl but not that by BAS 9052. Tank mixing KK80 with 1 kg/ha bentazon increased soybean burn and decreased grass control.
Greenhouse studies were undertaken to determine site of maximum herbicide toxicity to volunteer corn plants. Plants were susceptible via foliage application or in nutrient culture, in the order BAS 9052 > diclofop-methyl (DBLTURN) KK80. The latter two were apparently less mobile, since spot application to leaf tips did not kill plants even at high concentrations, whereas BAS 9052 gave good control over a wide concentration range when applied to any plant part.
Toxicity symptoms from all three compounds are similar and include sharp reduction of grass growth within one day followed closely by necrosing of young, non-green leaf tissue near the stem base. Increased membrane permeability in this tissue could be detected as early as 6-8 hours after herbicide application to older corn leaves.
Photosynthesis (Ps) of singly treated leaves was initially greatly inhibited in soybean but not in corn by field rates of these herbicides. Transpiration decline always closely followed that for Ps, but lagged behind 1 or 2 hours with slightly less inhibition. Within several days, recovery to nearly untreated levels occurred in soybean leaves and plants continued normal growth. Corn leaf growth was inhibited greatly in a matter of hours by spot treated BAS 9052 while 1 to 2 days passed before a rapid decline in Ps occurred. Plants eventually died. The length of time between treatment and rapid Ps decline increased as distance of herbicide placement away from the sensitive stem base tissue increased. KK80 and diclofop were ineffective at inhibiting growth or Ps when applied in this manner, presumably due to their comparatively poor translocation. Apparently Ps inhibition in treated corn leaves was not a primary mode of action for any of these herbicides and was likely a secondary effect resulting from cell disruption in the stem base.
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