Field studies were conducted from 1990 through 1997 to evaluate the long-term effect of 2- and 3-yr rotations on the control of downy brome, jointed goatgrass, and feral rye in winter wheat. At the completion of the study, jointed goatgrass and feral rye densities averaged 8 plants/m2 and < 0.1 plant/m2 for the 2- and 3-yr rotations, respectively. Downy brome densities averaged < 0.5 plant/m2 for both the 2- and 3-yr rotations, with no treatment differences observed. Winter annual grasses were not eradicated after two cycles of the 3-yr rotations, but weed densities were reduced 10-fold compared to densities after one cycle and more than 100-fold compared with the 2-yr rotations. Wheat grain contamination with dockage and foreign material followed a similar trend. The 3-yr rotations were economically competitive with 2-yr rotations and provided superior control of the winter annual grass weeds.

Based on bermudagrass ground cover 2 wk prior to sugarcane planting, tillage plus glyphosate applied postemergence sequentially at 3.4 followed by 2.2 kg ai/ha or a single application at 3.4 kg/ha during the summer fallow period was more effective than tillage alone. Effectiveness of tillage was enhanced when less rainfall was received during the summer fallow period the first year. Rainfall of less than 1 cm 20 d after preemergence application of sulfometuron at 0.2 kg ai/ha in June resulted in 100% bermudagrass ground cover the first year compared with 37% the second year with 15 cm of rainfall during the same period. Terbacil applied after sugarcane planting and metribuzin applied in February resulted in bermudagrass ground cover in May or June of 62% (experiment 1) and 2% (experiment 2) when sulfometuron was used during the fallow period, but no more than 5% when terbacil and metribuzin followed glyphosate plus tillage or tillage alone. In most cases, bermudagrass ground cover at that time was greater when the same glyphosate/tillage treatments were followed by atrazine after planting and pendimethalin plus atrazine in February compared with terbacil after planting and metribuzin in February. When after-planting and February herbicide treatments were applied, sugarcane stalk population, height, and yield each was equivalent regardless of the previous fallow treatment.

Growth-regulating characteristics of trinexapac-ethyl, paclobutrazol, and flurprimidol were investigated on ‘Tifway’ bermudagrass and four turfgrass weeds (large crabgrass, goosegrass, bahiagrass, and purple nutsedge). All treatments reduced the height of Tifway bermudagrass (25 to 37%) and large crabgrass (14 to 34%), but the height of purple nutsedge, goosegrass, and bahiagrass was not consistently changed. In 1995, all rates of trinexapac-ethyl reduced clipping weights of Tifway bermudagrass (70 to 87%) and bahiagrass (53 to 59%) more than large crabgrass, goosegrass, or purple nutsedge (< 39%). Trinexapac-ethyl (0.4 kg ai/ha) and paclobutrazol (1.1 kg ai/ha) applications increased both large crabgrass clipping weight and canopy visible density. Increased large crabgrass density was attributed to greater tiller numbers with trinexapac-ethyl (60 tillers/pot) and paclobutrazol (63 tillers/pot) compared to untreated large crabgrass plants (53 tillers/pot). Weed growth was not suppressed as much as Tifway bermudagrass growth; therefore, turfgrass stands may be adversely affected by plant growth regulator use under weedy conditions.

A 3-yr field study was conducted in peanut in which weed control systems with varying levels of herbicides, cultivation inputs, or both were supplemented with mowing to remove weeds extending above the crop canopy. Highest yield and net returns were consistently obtained with the highest level of herbicide/cultivation inputs, and mowing was of no value. However, mowing was consistently beneficial to yield and net return when the only other weed control inputs were paraquat and 2,4-DB applied at 4 wk after planting (WAP) and cultivation at 10 WAP. In the absence of any other weed control inputs, mowing was detrimental in a drought stress year, but beneficial in years with near-normal growing conditions. Although disease incidence was aggravated by the lack of weed control inputs, it was generally independent of mowing.

Field studies evaluated wild radish control in oat with thifensulfuron plus tribenuron in 1995 and 1997. Thifensulfuron plus tribenuron at 16 or 21 g ai/ha controlled wild radish completely in both years. In tolerance studies conducted in 1995 and 1996, thifensulfuron plus tribenuron reduced vigor of ‘Bay,’ ‘Belle,’ ‘Dane,’ ‘Ensiler,’ ‘Gem,’ ‘Horicon,’ ‘Ogle,’ ‘Porter,’ and ‘Prairie’ oat varieties and Wisconsin test selection oat ‘X6396-1’ up to 25% 7 d after treatment (DAT), but all chlorotic symptoms had disappeared 28 DAT. Thifensulfuron plus tribenuron reduced oat height 13 to 19% in 1995 and 21 to 24% in 1996 7 DAT. Bay, Belle, Dane, Ensiler, Horicon, Prairie, and X6396-1 recovered from height reductions by 28 DAT in 1995; however, in 1996 only Horicon and Porter recovered. Thifensulfuron plus tribenuron did not reduce 1995 grain yields, but 1996 Bay and Porter grain yields were reduced 29 and 15%, respectively. Dane and Prairie seed weights were reduced 7 and 14%, respectively, in 1995, whereas no seed weight reduction occurred in 1996.

Absorption, translocation, and metabolism of rimsulfuron were studied in three solanaceous weeds. Eastern black nightshade is sensitive (> 95% injury), hairy nightshade is moderately sensitive (50 to 99% injury), and black nightshade is tolerant to rimsulfuron postemergence (POST). Seedlings at the four- to six-leaf stage were treated with foliar-applied 14C-labeled rimsulfuron for 3, 6, 24, and 48 h after treatment. Absorption of rimsulfuron by all weeds increased with time. Black and eastern black nightshade absorbed comparable amounts of radioactivity at each exposure time. Hairy nightshade absorbed less radiolabeled herbicide than the other two nightshades at any treatment time. Hairy nightshade absorbed 54% of the applied radioactivity at 48 h, compared to 74% absorbed by the other weeds. Translocation of rimsulfuron out of the treated leaf was rapid in all species. Black and eastern black nightshade translocated 50 to 70% of the absorbed radioactivity out of the treated leaf with 40 to 50% moving to the upper foliage. In hairy nightshade, about 40% of the absorbed radioactivity translocated out of the treated leaf with equal amounts moving to the upper and lower foliage. Metabolism of 14C-rimsulfuron was rapid in the three nightshades with approximately 54% remaining as rimsulfuron at 3 h after treatment. The levels of the detected metabolites of rimsulfuron were similar in the three nightshade weeds. Differential early uptake and translocation may account for the differential sensitivity of these nightshade species to rimsulfuron.

The ability of grassed waterways to remediate herbicide loads in runoff water was evaluated using simulated and on-site nursery research. Isoxaben plus oryzalin and isoxaben plus trifluralin were applied to model grassed (zoysiagrass or ‘Tifway 10’ hybrid bermudagrass) and nongrassed, metal and clay loam waterways, and runoff samples were collected. Grassed waterways reduced runoff volume an average of 47% and herbicide residues an average of 56% compared to nongrassed waterways. The smallest herbicide residues were from the clay/grass waterways. In a nursery study, isoxaben and trifluralin were applied to containerized landscape plant production beds. Overhead irrigation was applied and runoff water was channeled into either a clay/gravel waterway or a hybrid bermudagrass waterway. Samples were collected for 22 d following application. Isoxaben persisted through 15 d after application. Trifluralin was detected through 2 d after application. Total isoxaben recovered from the clay/gravel waterway was 32% of applied, and total trifluralin recovered was 0.9% of applied. The grass waterway reduced residues of isoxaben and trifluralin by 22 and 66%, respectively, compared to the clay/gravel waterway.

Field studies were conducted in South Carolina to evaluate the herbicides acifluorfen, chlorimuron, and imazaquin for control of Palmer amaranth and smooth pigweed in soybean, when applied 3 wk after weed emergence. Palmer amaranth was more difficult to control than smooth pigweed. Compared to untreated controls, acifluorfen, chlorimuron, and imazaquin reduced Palmer amaranth and smooth pigweed biomass 78 and 96%, 80 and 98%, and 82 and 99% at 30 d after treatment (DAT), 60 DAT, and at soybean harvest, respectively. The high rate (140 g/ha) of imazaquin provided greater control of Palmer amaranth than other herbicide treatments at soybean harvest. Except for the 140 g/ha rate of imazaquin, inadequate control of Palmer amaranth resulted in lower soybean seed yields for all herbicide treatments than the weed-free control. However, all herbicides controlled smooth pigweed to provide soybean seed yields similar to the weed-free control.

Field studies were conducted to determine if metribuzin–diclofop combinations could provide selective control of mature goosegrass in common bermudagrass turf. In two field trials, diclofop at 1.7 kg ai/ha provided 19% control of mature goosegrass at 7 wk after treatment (WAT), whereas metribuzin at 0.28 or 0.56 kg ai/ha controlled 30 and 53%, respectively. When diclofop at 1.7 kg/ha was combined with metribuzin at 0.28 or 0.56 kg/ha, goosegrass control increased to 68 and 90%, respectively. That degree of mature goosegrass control with a single application of metribuzin at 0.56 kg/ha plus diclofop at 1.7 kg/ha was equivalent to metribuzin at 0.56 kg/ha plus MSMA at 2.2 kg ae/ha followed by MSMA at 2.2 kg/ha 1 wk later. The metribuzin–diclofop combination injured common bermudagrass turf less than or equivalent to the metribuzin–MSMA combination. The injury was transitory; at 3 WAT, none of the treatments injured common bermudagrass.

Field studies were conducted in 1993–1994 and 1994–1995 to evaluate the effects of preherbicide mowing and herbicide rate on tropical soda apple (TSA) control. Mature TSA plants were mowed one, two, or three times to a 7.5-cm stubble with a 60-d interval between mowings. Triclopyr was applied at 0, 0.6, and 1.1 kg ai/ha at 375 L/ha at 207 kPa 60 d after each mowing treatment. Mowing TSA plants twice before an application of 0.6 kg ai/ha triclopyr resulted in 100% control. Tropical soda apple control (2-yr average) for the triclopyr treatment increased between one (28% control) and two (82% control) preherbicide mowings, with no additional control benefits from three mowings (84% control). In a second study, TSA control increased from 10% 60 d after a single mowing to 92% after three consecutive mowings at 60-d intervals with no herbicide. Total nonstructural carbohydrates in TSA crowns decreased from 19.1% for unclipped plants to 4.3% 60 d after three preherbicide mowings.

Mugwort is a noxious perennial weed that interferes with the growth and establishment of crop species. The present study was designed to understand the role of allelopathy as a potential mechanism of interference by mugwort. Soils amended with mugwort plant material and leachates were analyzed for their chemical characteristics. The effect of amended soils on seedling growth of red clover was studied. The influence of NP fertilization and charcoal on modification of allelopathic potential of amended soils, in terms of their effect on soil characteristics and red clover seedling growth, was also investigated. In addition, red clover seedling growth was compared in sterilized and nonsterilized soils amended with mugwort leachate and NP fertilization. In general, addition of mugwort leachates and plant matter (amended soil) resulted in chemical changes in soil, including changes in available phenolics. Red clover seedling growth was reduced in amended soils, when compared to that in nonamended soils. Although the different amounts of NP fertilization in nonsterilized soil amended with mugwort leachate could not counteract its interference to red clover growth (root reduction, 67–79%; shoot reduction, 34–44%), the addition of charcoal did eliminate leachate effects on red clover growth. This indicates the probable allelopathic interference of mugwort to red clover growth. Addition of NP fertilization might have resulted in higher microbial activity, which is likely to influence qualitative and/or quantitative availability of phenolic compounds. Data on phenolic levels and red clover growth in sterilized and nonsterilized soil amended with mugwort leachate and NP fertilization indirectly indicate the significance of soil microbes in mugwort interference to red clover.

A 1984–1985 and 1988–1989 field study near Pullman, WA, evaluated the effect of two winter wheat planting geometries on the growth of wheat and competition against jointed goatgrass. Treatments included paired and constant row planting geometries of wheat and locations of jointed goatgrass within each geometry. No planting geometry by weed location interactions occurred at any harvest date for plant height, shoot number, leaf area, plant dry weight, or N uptake for either wheat or jointed goatgrass. During the 1984–1985 growing season, N uptake data indicated that by heading, jointed goatgrass had taken up N that had been deep-banded between wheat rows located 25 cm from the weed. Winter wheat yields were not different in the paired-row and the constant row spacing geometry in a weed-free environment. Within years, for both planting geometries, winter wheat yield reduction from weed competition was similar for the jointed goatgrass locations. In contrast, based on jointed goatgrass spikelets produced, wheat grown in paired-rows was more competitive against jointed goatgrass compared to constant row spacing.

The fire-weed glows in the centre of the drive ways.

Time (weekly ed.) Rudyard Kipling, 1892

Fireweed is in the evening primrose family, Onagraceae, which includes 17 genera (Brummitt (1992). The genus Epilobium encompasses 200 especially western North America species of annuals, biennials, and herbaceous and semievergreen subshrubs. Epilobium is widely distributed in the temperate regions on waste and disturbed ground, stony slopes, river gravels, and subalpine screes and meadows. While some species are cultivated for their showy flowers, windborne seeds and spreading rhizomes make many others invasive (Brickhill and Zuh 1997).