Glyphosate-based weed control products are among the most widely used broad-spectrum herbicides in the world. The herbicidal properties of glyphosate were discovered in 1970, and commercial formulations for nonselective weed control were first introduced in 1974 (Franz et al. 1997). Formulations of glyphosate, including Roundup® Herbicide (RU)1 (Monsanto Company, St. Louis, MO), have been extensively investigated for their potential to produce adverse effects in nontarget organisms. Governmental regulatory agencies, international organizations, and others have reviewed and assessed the available scientific data for glyphosate formulations and independently judged their safety. Conclusions from three major organizations are publicly available and indicate RU can be used with minimal risk to the environment (Agriculture Canada 1991; USEPA 1993a; WHO 1994). Several review publications are available on the fate and effects of RU or glyphosate in the environment (Carlisle and Trevors 1988;Smith and Oehme 1992 ; Malik et al. 1989;Rueppel et al. 1977; Sullivan and Sullivan 1997;Forestry Canada, 1989). In addition, several books have been published about the environmental and human health considerations of glyphosate and its formulations (Grossbard and Atkinson 1985; Franz et al. 1997). In addition, RU and other glyphosate formulations have been selected for use in a number of weed control programs for state and local jurisdictions in the United States. Many of these uses require that ecological risk assessments be conducted in the form of Environmental Impact Statements or Environmental Assessments. These documents are comprehensive and specific to local use situations. Documents are available for risk assessments in Texas, Washington, Oregon, Pennsylvania, New York, Virginia, and other states (USDA 1989;USDA 1992;USDA 1996;USDA 1997;USDI 1989; Washington State DOT 1993).

Ecotoxicological Risk Assessment for Roundup ® Herbicide

The very wide use of glyphosate to control weeds in agricultural, silvicultural and urban areas throughout the world requires that special attention be paid to its possible transport from terrestrial to aquatic environments. The aim of this review is to present and discuss the state of knowledge on sorption, degradation and leachability of glyphosate in soils. Difficulties of drawing clear and unambiguous conclusions because of strong soil dependency and limited conclusive investigations are pointed out. Nevertheless, the risk of ground and surface water pollution by glyphosate seems limited because of sorption onto variable-charge soil minerals, e.g. aluminium and iron oxides, and because of microbial degradation. Although sorption and degradation are affected by many factors that might be expected to affect glyphosate mobility in soils, glyphosate leaching seems mainly determined by soil structure and rainfall. Limited leaching has been observed in non-structured sandy soils, while subsurface leaching to drainage systems was observed in a structured soil with preferential flow in macropores, but only when high rainfall followed glyphosate application. Glyphosate in drainage water runs into surface waters but not necessarily to groundwater because it may be sorbed and degraded in deeper soil layers before reaching the groundwater. Although the transport of glyphosate from land to water environments seems very limited, knowledge about subsurface leaching and surface runoff of glyphosate as well as the importance of this transport as related to ground and surface water quality is scarce.

Fate of glyphosate in soil and the possibility of leaching to ground and surface waters: a review.

Challenges and opportunities in implementing allelopathy for natural weed management

N-(phosphonomethyl)glycerine (glyphosate) is an extremely effective broad spectrum herbicide. This manuscript reviews glyphosate metabolism in plants and yeasts, its uses in agricultural applications, interactions with soil and water, glyphosate biodegradation, and effects on microbial activities and populations in soil.

Glyphosate in the environment

Greenhouse and laboratory experiments were conducted to investigate mechanisms of glyphosate resistance in horseweed populations from Mississippi, Arkansas, Delaware, and Tennessee. A nondestructive leaf-dip bioassay was developed to confirm resistance and susceptibility in individual test plants. A single leaf was excised from each plant, and the petiole and bottom one-fourth of leaf was dipped in a 600 mg ae L−1 glyphosate solution for 2 d followed by visually estimating the injury on a scale of 0 to 10. Plants were classified as resistant (R) if the score was 2 to 3 and susceptible (S) if the score was 5 to 6. 14C-glyphosate solution was applied on the adaxial surface of a fully expanded leaf of the second whorl of four-whorl rosette plants. Plants were harvested 48 h after treatment and radioactivity was determined in treated leaf, other leaves, crown, and roots. Absorption of 14C-glyphosate was similar (47 to 54%) between R and S plants from within and among the four states, suggesting absor...

https://bioone.org/journals/Weed-Science/volume-53/issue-1/WS-04-102R/Role-of-absorption-and-translocation-in-the-mechanism-of-glyphosate/10.1614/WS-04-102R.pdf

Role of absorption and translocation in the mechanism of glyphosate resistance in horseweed (Conyza canadensis)

Absorption, Translocation, and Activity of CGA-136872, DPX-V9360, and Glyphosate in Rhizome Johnsongrass (Sorghum halepense)

In the greenhouse, soil applications of primisulfuron (40 g ai ha–1) reduced growth of emerged rhizome johnsongrass plants more than nicosulfuron (40 g ai ha–1). Both herbicides reduced growth more when applied to foliage only; a further decrease in growth did not occur for applications to both soil and foliage. Primisulfuron did not completely prevent regrowth of johnsongrass with any application method. Nicosulfuron prevented regrowth when applied to the foliage and to both soil and foliage. In single-year field studies in corn at four dryland sites and two irrigated sites, 50:50 split applications of primisulfuron (40 g ai ha–1) and nicosulfuron (35 g ai ha–1) approximately 2 wk apart provided the most consistent rhizome johnsongrass control compared with early or late single applications when visually rated 8 wk after the first application. Nicosulfuron treatments were more effective than primisulfuron treatments at both dryland sites the first year and at one of two dryland sites the second year. Primisulfuron and nicosulfuron at the irrigated site the first year were equivalent in efficacy. Nicosulfuron was more effective than primisulfuron at the irrigated site the second year. Primisulfuron or nicosulfuron treatments more than doubled corn yields at the dryland sites both years regardless of application timing. Split applications of primisulfuron or nicosulfuron provided the highest yields (approximately 80% increase over untreated plots) at the irrigated site the first year. All treatments provided equivalent yield increases (approximately 50%) the second year.

Rhizome johnsongrass (Sorghum halepense) control in corn (Zea mays) with primisulfuron and nicosulfuron.

Factors Influencing Microbial Degradation of 14C-Glyphosate to 14Co2 in Soil

An in-row competition study was conducted in 1991 and 1992 near Silver Lake, KS to determine the relationship of noncultivated common sunflower density to soybean yield, PAR at the soybean canopy, and common sunflower dry matter production. Because of environmental differences, year main effect interactions occurred, so results are presented by year. For example, 0.3 common sunflower plant/m 2 produced 4030 kg/ha of aboveground dry matter in 1991 and 1300 kg/ha in 1992. Soybean yield reduction ranged from 19 and 17% with 0.3 common sunflower plant/m 2 to 97 and 95% with 4.6 plant/m 2 , in 1991 and 1992, respectively. Assuming a treatment cost of $35/ha and a soybean market price of $0.21/kg, economic threshold levels were 0.1 common sunflower plant/m 2 in 1991, and 0.07 in 1992. Common sunflower at 0.3 plant/m 2 reduced PAR at the soybean canopy by 390 and 300 μE/m 2 /s, or 24 and 18% in 1991 and 1992, respectively. We conclude that the ability of common sunflower to intercept PAR above the soybean canopy is an important component in its interference with soybean.

Loren J. Moshier

Papers

Absorption, Translocation, and Activity of CGA-136872, DPX-V9360, and Glyphosate in Rhizome Johnsongrass (Sorghum halepense)

Rhizome johnsongrass (Sorghum halepense) control in corn (Zea mays) with primisulfuron and nicosulfuron.

Factors Influencing Microbial Degradation of 14C-Glyphosate to 14Co2 in Soil

Common sunflower (Helianthus annuus) interference in soybean (Glycine max)

Influence of Environment on Corn (Zea mays) Tolerance to Sethoxydim