Emergence of common lambsquarters (Chenopodium album L.) is influenced by the landscape position in which seeds developed

In a 2-yr field study, we evaluated the emergence and early growth of Chenopodium album L. (common lambsquarters) seedlings as affected by the landscape position in which the seeds (i) developed, (ii) overwintered, and (iii) were planted. Results indicated that a higher proportion of seeds originating from lower slope positions emerged compared with seeds originating from the backslope or upper slope. The timing of emergence was the same for all seed source locations. There was no influence of overwintering location on weed emergence. Regardless of the seed source, we observed faster emergence and growth of C. album planted in the lower slope, where soil conditions were more conducive to growth. These experiments will support the development of new strategies and decision aids to improve weed management

Transformation Kinetics and Mechanism of the Sulfonylurea Herbicides Pyrazosulfuron Ethyl and Halosulfuron Methyl in Aqueous Solutions

Little is known about how popular herbicides react and degrade in soil or aquatic environments. Two of these herbicides include Pyrazosulfuron Ethyl (PE) and Halosulfuron Methyl (HM), which are part of the sulfonylurea herbicide category. Both are post-emergence herbicides and are so highly effective that they need to be applied only at rates of grams per hector. Because these herbicides inhibit the key enzyme that participates in protein synthesis in plants, they can have a major effect on sensitive agricultural areas such as legumes or pastures for grazing. Typically these types of herbicides only degrade because of microbial influences or chemical hydrolysis. To understand the pathway and conditions for chemical hydrolysis degradation, ISTC’s Wei Zheng collaborated with researchers at the U.S. Department of Agriculture to conduct several laboratory experiments. Full results reported in Zheng, Wei et al (2008). "Transformation Kinetics and Mechanism of the Sulfonylurea Herbicides Pyrazosulfuron Ethyl and Halosulfuron Methyl in Aqueous Solutions." Journal of Agricultural and Food Chemistry 56(16), 7367-7372. https://doi.org/10.1021/jf800899eOpe

Maize, Switchgrass, and Ponderosa Pine Biochar Added to Soil Increased Herbicide Sorption and Decreased Herbicide Efficacy

Biochar, a by-product of pyrolysis made from a wide array of plant biomass when producing biofuels, is a proposed soil amendment to improve soil health. This study measured herbicide sorption and efficacy when soils were treated with low (1% w/w) or high (10% w/w) amounts of biochar manufactured from different feedstocks [maize (Zea mays) stover, switchgrass (Panicum vigatum), and ponderosa pine (Pinus ponderosa)], and treated with different post-processing techniques. Twenty-four hour batch equilibration measured sorption of 14C-labelled atrazine or 2,4-D to two soil types with and without biochar amendments. Herbicide efficacy was measured with and without biochar using speed of seed germination tests of sensitive species. Biochar amended soils sorbed more herbicide than untreated soils, with major differences due to biochar application rate but minor differences due to biochar type or post-process handling technique. Biochar presence increased the speed of seed germination compared with herbicide alone addition. These data indicate that biochar addition to soil can increase herbicide sorption and reduce efficacy. Evaluation for site-specific biochar applications may be warranted to obtain maximal benefits without compromising other agronomic practices

Quantification of Persistence of Escherichia coli O157:H7 in Contrasting Soils

Persistence of Escherichia coli (E. coli) O157:H7 in the environment is a major concern to vegetable and fruit growers where farms and livestock production are in close proximity. The objectives were to determine the effects of preplant fumigation treatment on the survival of E. coli O157:H7 in two soils and the effects of indigenous bacterial populations on the survival of this pathogen. Real-time PCR and plate counts were used to quantify the survival of E. coli O157:H7 in two contrasting soils after fumigation with methyl bromide (MeBr) and methyl iodide (MeI). Ten days after fumigation, E. coli O157:H7 counts were significantly lower (P = .0001) in fumigated soils than in the non-fumigated. Direct comparison between MeBr and MeI within each soil indicated that these two fumigants showed similar impacts on E. coli O157:H7 survival. Microbial species diversity as determined by DGGE was significantly higher in clay soil than sandy soil and this resulted in higher initial decline in population in clay soil than in sandy soil. This study shows that if soil is contaminated with E. coli O157:H7, fumigation alone may not eliminate the pathogen, but may cause decrease in microbial diversity which may enhance the survival of the pathogen

Quantification of Persistence of Escherichia coli O157:H7 in Contrasting Soils

Persistence of Escherichia coli (E. coli) O157:H7 in the environment is a major concern to vegetable and fruit growers where farms and livestock production are in close proximity. The objectives were to determine the effects of preplant fumigation treatment on the survival of E. coli O157:H7 in two soils and the effects of indigenous bacterial populations on the survival of this pathogen. Real-time PCR and plate counts were used to quantify the survival of E. coli O157:H7 in two contrasting soils after fumigation with methyl bromide (MeBr) and methyl iodide (MeI). Ten days after fumigation, E. coli O157:H7 counts were significantly lower (P = .0001) in fumigated soils than in the non-fumigated. Direct comparison between MeBr and MeI within each soil indicated that these two fumigants showed similar impacts on E. coli O157:H7 survival. Microbial species diversity as determined by DGGE was significantly higher in clay soil than sandy soil and this resulted in higher initial decline in population in clay soil than in sandy soil. This study shows that if soil is contaminated with E. coli O157:H7, fumigation alone may not eliminate the pathogen, but may cause decrease in microbial diversity which may enhance the survival of the pathogen