Glyphosate: environmental fate and impact

Glyphosate is the most used herbicide worldwide, which has contributed to concerns about its environmental impact. Compared with most other herbicides, glyphosate has a half-life in soil and water that is relatively short (averaging about 30 d in temperate climates), mostly due to microbial degradation. Its primary microbial product, aminomethylphosphonic acid, is slightly more persistent than glyphosate. In soil, glyphosate is virtually biologically inactive due to its strong binding to soil components. Glyphosate does not bioaccumulate in organisms, largely due to its high water solubility. Glyphosate-resistant crops have greatly facilitated reduced-tillage agriculture, thereby reducing soil loss, soil compaction, carbon dioxide emissions, and fossil fuel use. Agricultural economists have projected that loss of glyphosate would result in increased cropping area, some gained by deforestation, and an increase in environmental impact quotient of weed management. Some drift doses of glyphosate to non-target plants can cause increased plant growth (hormesis) and/or increased susceptibility to plant pathogens, although these non-target effects are not well documented. The preponderance of evidence confirms that glyphosate does not harm plants by interfering with mineral nutrition and that it has no agriculturally significant effects on soil microbiota. Glyphosate has a lower environmental impact quotient than most synthetic herbicide alternatives.

Use of Glyphosate and Herbicide Alternatives for Weed Control in Florida Landscape Planting Beds

This new 10-page article is written for landscape professionals and those maintaining landscape areas to guide them in selecting alternatives to glyphosate (the active ingredient in RoundUp®) for postemergence weed control in Florida. Information is also included on preemergence herbicides and integrated weed management (use of chemical and non-chemical controls), which should be the basis of a weed management program. Written by Chris Marble, Joe Neal, and Andy Senesac, and published by the UF/IFAS Environmental Horticulture Department. https://edis.ifas.ufl.edu/ep580

CHEMICAL WEED MANAGEMENT IN GRAIN SORGHUM AND SELECTIVITY OF ATRAZINE + S-METOLACHLOR TO DIFFERENT HYBRIDS

ABSTRACT - Grain sorghum (Sorghum bicolor) is one cereal crop that faces huge problems with weed interference mostly because the lack of selective herbicides. This study aimed to assess the efficacy and safety of herbicide alternatives for weed control in grain sorghum as well as the selectivity of atrazine + s-metolachlor to different hybrids. Three field trials were designed as a randomized complete block with four replications. All experiments were conducted in Jardinópolis-SP and Mogi Mirim-SP during the 2015/16 growing season. Two trials included acetochlor, flumioxazin, fluroxypyr, mesotrione and s-metolachlor, applied in pre or post-emergence, in association or not with atrazine. A third trial was carried out with rates of the premix containing atrazine + s-metolachlor applied to the following hybrids: 1G100, 1G220, 1G230, 1G244, 1G282, 50A10, 50A40, 50A50 and 50A70. The pre‑emergence herbicides that exhibited satisfactory efficacy of weed control and selectivity to sorghum crop were flumioxazin, atrazine + mesotrione and atrazine + s-metolachlor. For post‑emergence, atrazine, atrazine + acetochlor, atrazine + s-metolachlor and atrazine + fluroxypyr were the best treatments for both efficacy and selectivity. The application of atrazine + s-metolachlor at the evaluated rates was considered selective to the nine hybrids assessed.Keywords: acetochlor, fluroxypyr, mesotrione, herbicide tolerance, weed control. MANEJO QUÍMICO DE PLANTAS DANINHAS EM SORGO GRANÍFERO E SELETIVIDADE DE ATRAZINE + S-METOLACHLOR PARA DIFERENTES HÍBRIDOS RESUMO – O sorgo granífero (Sorghum bicolor) é um dos cereais de verão que mais enfrenta problemas com plantas daninhas em razão da interferência destas espécies e carência de herbicidas para controlá-las. O objetivo deste estudo foi avaliar a eficácia e segurança de herbicidas alternativos no controle de plantas daninhas em sorgo granífero, assim como a seletividade de atrazine + s-metolachlor para diferentes híbridos. Três experimentos foram realizados em campo com delineamento de blocos ao acaso e quatro repetições, sendo conduzidos em Jardinópolis-SP e/ou Mogi Mirim-SP, ao longo da safra 2015/16. Em dois experimentos, acetochlor, flumioxazin, fluroxypyr, mesotrione e s-metolachlor foram avaliados em pré e/ou pós-emergência da cultura, em associação ou não (isolados) com atrazine. O terceiro experimento foi realizado com doses crescentes de atrazine + s-metolachlor e os híbridos de sorgo granífero 1G100, 1G220, 1G230, 1G244, 1G282, 50A10, 50A40, 50A50 e 50A70. Os tratamentos com controle satisfatório de plantas daninhas e seletividade à cultura, em pré-emergência, foram flumioxazin, atrazine + mesotrione e atrazine + s-metolachlor. Em pós-emergência, eles foram atrazine, atrazine + acetochlor, atrazine + s-metolachlor e atrazine + fluroxipyr. A aplicação de atrazine + s-metolachlor nas doses testadas foi seletiva para os nove híbridos avaliados.Palavras-chave: acetochlor, fluroxypyr, mesotrione, tolerância a herbicidas, controle de plantas daninhas. metolachlor at the evaluated rates was selective to the nine hybrids assessed.

Tomato Root Uptake of Carfentrazone

Fresh market tomato is an important and valuable crop in Florida, accounting for 630 million dollars farm-gate value, which was 45% of the total value of the U.S. crop in 2010. In order to maintain or increase its productivity, labeled herbicide alternatives to methyl bromide are important to limiting seed production of weeds emerging between the raised plasticulture beds. A study was conducted inside a greenhouse where carfentrazone was applied as a drench at 0.03125×, 0.0625×, 0.125×, 0.25×, 0.5×, 1×, 2×, 4×, and 8× and as a subsurface irrigation at 0.0625×, 0.125×, 0.25×, 0.5×, 1×, 2×, 4×, 8×, and 16× rates. The 1× rate equaled the maximum labeled rate of carfentrazone (35.1 g ai ha−1) that would be applied to an area of 0.360 m2. Both the drench and subsurface trials showed an increase in plant injury and reduced growth as the rate of carfentrazone increased. The drench trial, however, was observed to have higher visible injury and greater growth reduction (based on plant measurement) than the subsurface trial, when comparing similar rates. For the 1× rate of carfentrazone in the drench trial vs. the subsurface trial, injury was 66 and 24.5%, respectively. For the 1× rate the tomato plants had estimated growth, based on the curves fit for the data, of 4.8% vs. 39.9% for the drench and subsurface trials, respectively. The subsurface trial better represents what happens in the field when carfentrazone root uptake injury is observed since it is normally observed to be around 10% or less. This still leaves a level of concern; once a 10% injury level in the subsurface trial was estimated to have reduced tomato growth, fruit weight, and total shoot dry weight by 33, 15, and 9.5%, respectively.

Response of Immature Trembling Aspen to Season and Height of Cut

Forest managers in Ontario have identified trembling aspen (Populus tremuloides Michx.) as the most significant competitor of our commercially important spruce and pine crop. Although herbicides can be used to effectively control aspen, the public of Ontario would prefer to have herbicide alternatives, such as motor-manual cutting, used on public lands. Cutting of aspen has not been very successful, and research is required to improve its effectiveness. Effects of season and height of cutting to control the regrowth of young trembling aspen were studied on four sites in Ontario,Canada, with each location providing a replicate for the trial. Aspen stems, averaging 1.5 to 3.2 m in height, were cut in fall (October 1993), winter (February/March 1994), and summer (June/July 1994) at 10, 25, 50, 75, or 100 cm above ground level. Density and height of new root suckers;number, point of origin, and growth of stem sprouts; and tissue mortality in cut stems were evaluated by analyses of variance with linear contrasts to determine the effects of cutting height, season of cutting, and their interactions. Two years of post-treatment data indicate that aspen regeneration may be reduced if manual cutting occurs in June/July, at a cutting height of 50 to 75 cm. This timing and cutting height provides maximum stem mortality with minimum number of sprouts per stem and minimum sucker regeneration. If aspen regeneration is the goal, cut in the fall at 25 cm for maximum regrowth. North. J. Appl. For. 16(2):108-114.

Selection of Herbicide Alternatives Based on Probable Leaching to Groundwater

Extension workers are sensing pressure to use soils information and chemical characteristics data to guide farmers in selecting pesticides least prone to leach into groundwater. Our objective was to estimate differences in herbicide migration to groundwater under conditions typical for the Southeast Coastal Plain, and to consider how a farmer might be advised to use such knowledge in selecting herbicides. We used a simple computer code for microcomputers to predict persistence and migration of 17 herbicides through a hypothetical, coarse-textured soil typical of the Southeast Coastal Plain. Appropriate herbicides were selected for several common crop-weed problems, such as sicklepod in soybean and Palmer amaranth in corn. Groundwater was assumed to be 3.15 m below the soil surface. Herbicides selected covered a broad range of half-lives and organic carbon partition coefficients. Only after the first-order degradation rate constant was reduced by a factor of five did predicted soil water concentrations of several herbicides at the groundwater interface reach normal detection limits. Still, predicted concentrations were below the level established for health effects advisory purposes. Due to the large number of uncertainties and the inability to estimate practical benefits, we conclude that data relating to soil and herbicide characteristics cannot be used at this time to override cost effectiveness, efficacy, and other factors normally considered by farmers and Extension professionals in herbicides for weed control.