Response of Barnyardgrass (<i>Echinochloa crus-galli</i>), Green Foxtail (<i>Setaria virdis</i>), Longspine Sandbur (<i>Cenchrus longispinus</i>), and Large Crabgrass (<i>Digitaria sanguinalis</i>) to Nicosulfuron and Rimsulfuron

Experiments were conducted to determine the efficacy, absorption, and translocation of nicosulfuron, rimsulfuron, and nicosulfuron + rimsulfuron on barnyardgrass, green foxtail, longspine sandbur, and large crabgrass. In the greenhouse, nicosulfuron, rimsulfuron, and nicosulfuron + rimsulfuron were applied at 0.0625, 0.125, 0.25, 0.5, 0.75, 1, and 2 times their label rates of 35, 13, and 26 + 13 g ai ha−1, respectively, on 5- to 10-cm plants. Three weeks after treatment (WAT), barnyardgrass was the most susceptible species to all three herbicides, and large crabgrass was the least susceptible. The nicosulfuron, rimsulfuron, or nicosulfuron + rimsulfuron rates causing 50% visible injury (GR50) for barnyardgrass were 10.9, 4.8, and 6 + 3 g ai ha−1, respectively. Similarly, the GR50for large crabgrass were 25.6, 9.9, and 14.3 + 7.2 g ai ha−1, respectively, 3 WAT. Absorption of nicosulfuron, rimsulfuron, and nicosulfuron + rimsulfuron was greater in barnyardgrass than in large crabgrass. Absorption of nicosulfuron + rimsulfuron in barnyardgrass and large crabgrass was 74% and 57%, respectively, 7 d after treatment (DAT). In addition, translocation of nicosulfuron, rimsulfuron, and nicosulfuron + rimsulfuron out of the treated leaf was 14, 12, and 14% higher, respectively, in barnyardgrass than in large crabgrass. The differential response of these weed species to nicosulfuron, rimsulfuron, and nicosulfuron + rimsulfuron might be due to differences in herbicide absorption and translocation.</jats:p

Response of Acetolactate Synthase–Resistant Grain Sorghum to Nicosulfuron Plus Rimsulfuron

The lack of POST herbicides to control grasses in grain sorghum prompted researchers to develop acetolactate synthase (ALS)–resistant grain sorghum. Field experiments were conducted to evaluate the differential response of ALS-resistant grain sorghum to POST application of nicosulfuron + rimsulfuron applied at three growth stages. ALS-resistant grain sorghum was treated with 0, 13 + 7, 26 + 13, 39 + 20, 52 + 26, 65 + 33, 78 + 39, and 91 + 46 g ai ha−1of nicosulfuron + rimsulfuron when plants were at the three- to five-leaf, seven- to nine-leaf, or 11- to 13-leaf stage. In general, as nicosulfuron + rimsulfuron rates increased, visible injury increased at the three- to five-leaf and seven- to nine-leaf stages. Injury was greatest 1 wk after treatment for the three- to five-leaf and seven- to nine-leaf stages across all ratings, and plants then began to recover. No injury was observed at any rating time for the 11- to 13-leaf stage. Plant height and sorghum grain yield were reduced as nicosulfuron + rimsulfuron rates increased when applied at the three- to five-leaf stage. However, nicosulfuron + rimsulfuron applied at the seven- to nine-leaf and 11- to 13-leaf stages did not decrease sorghum yield. This research indicated that nicosulfuron + rimsulfuron application at the three- to five-leaf stage injured ALS-resistant grain sorghum; however, application at the seven- to nine-leaf or 11- to 13-leaf stages did not result in grain yield reduction.</jats:p

The indigenous origin of Witwatersrand "carbon"

In the Witwatersrand approximately 40% of the gold is intimately associated with so-called "carbon" in "carbon seam reefs, which occur in over a dozen paleoplacers, many of them concentrated at two stratigraphic levels in the 7000-m-thick succession of Archean siliciclastic sedimentary rocks. This is reduced carbon, present as kerogen admixed in various proportions with derivative (now solid) bitumen(s). Oil generation and migration were active geological processes during Early Earth history. Numerous possible source rocks for oil generation, including the carbon seams themselves, occur within the Witwatersrand basin. In the Witwatersrand ore, oil-bearing fluid inclusions are also present, derived like the bitumen, by thermal maturation of the kerogen. The presence of kerogen and bitumen in the Witwatersrand sedimentary rocks, together with a wealth of observations on the spatial distribution of the carbon seams confirm that the carbon originated in situ from living organisms in microbial mat cover, as opposed to flowing in from elsewhere as liquid hydrocarbons as some researchers have suggested. Paleochannels, which truncated auriferous carbon seams early in the depositional history, are of widespread occurrence, and micro-synsedimentary faults offset carbon seams. The carbon seams are thus indigenous biogenic markers that grew contemporaneously with placer development. The various features highlighting the nature and spatial distribution of Witwatersrand carbon seams provide a classic case where field evidence trumps laboratory data in the reconstruction of geological processes.14 page(s

Sulfur Isotope Evidence for Penetration of MVT Fluids into Igneous Basement Rocks, Southeast Missouri, USA

Previous studies of galena and sphalerite from Paleozoic MVT deposits in the Viburnum Trend, southeast Missouri documented large variations in δ34S values throughout the ore-forming event. The present study of Cu-Fe-sulfides reveals a similar δ34S variation that reflects two end-member sulfur reservoirs whose relative importance varied both temporally and spatially. More 34S-enriched sulfides (δ34S approaching 25‰) indicate introduction of sulfur from basinal sedimentary sources, whereas more 32S-enriched sulfides (δ34S \u3c 5‰) may reflect fluids moving through underlying granitic basement. Two areas containing Precambrian, igneous-hosted FeCu mineralization in southeast Missouri (West and Central Domes of Boss-Bixby) were investigated to elucidate their relationship to Cu-rich MVT orebodies hosted nearby within the overlying Cambrian Bonneterre Dolomite. Mineralization at Boss-Bixby is composed of an early phase of iron oxide deposition followed by Cu-Fe-sulfides. The Central Dome is faulted and its mineralization is more fracture-controlled than the typically podiform ores of the West Dome. The δ34S values of West Dome sulfides are 0.9 to 6.5‰ and pyrite-chalcopyrite indicate a temperature of 525° ± 50°C. These data indicate an igneous source of sulfur during Precambrian ore deposition. In contrast, δ34S values of Central Dome sulfides are 9.4 to 20.0‰ and pyrite-chalcopyrite indicate temperatures of 275° ± 50°C. Similar δ34S values are obtained for chalcopyrite from the overlying MVT deposits. We speculate that deeply circulating, basin-derived MVT fluids mobilized sulfur and copper from the underlying igneous basement and redeposited them in overlying Curich MVT orebodies, as well as overprinting earlier Precambrian sulfides of the Central Dome with a later, Paleozoic MVT sulfur isotope signature. Many models for MVT fluid circulation in the Midcontinent region of North America assume that igneous basement rocks are an impermeable boundary, but in southeast Missouri, evidence exists for structurally controlled MVT fluid movement \u3e 600 m vertically through underlying Precambrian igneous rocks. Such basement involvement has been suggested for other carbonate-hosted base-metal districts (e.g. Irish base metal deposits) and should be considered an integral part of the ore-forming process in southeast Missouri