Rice cutgrass is encroaching into rice fields from ditch banks and canals, especially into continuous rice fields where tillage is limited in the Mississippi Delta region of Arkansas. Experiments were conducted to evaluate the effectiveness of various herbicides applied alone on rice cutgrass and to determine if the effectiveness of bispyribac on rice cutgrass is influenced by number of applications, adjuvant type, and adjuvant rate. Glyphosate, glufosinate, and clethodim were the most effective herbicides when applied alone; however, none of these are labeled for over-the-top application in rice. Of those herbicides that can be applied over the top of rice, imazethapyr and bispyribac were the most effective, providing 52 to 62% rice cutgrass control, albeit imazethapyr can be used only in imidazolinone-resistant rice. The addition of an adjuvant to bispyribac improved rice cutgrass control, and sequential bispyribac applications were generally superior to a single application. Methylated seed oil/organosilicone/urea ammonium nitrate adjuvant increased rice cutgrass control with bispyribac, especially when bispyribac was applied as a single application. A single application of imazethapyr, bispyribac, halosulfuron, penoxsulam, clomazone, thiobencarb, cyhalofop, propanil, quinclorac, and fenoxaprop provided less-than-acceptable control, which partially explains the difficulty that growers are experiencing in controlling rice cutgrass, especially in continuous rice production.

Research was conducted in North Carolina to compare weed control by various rates of imazapic POST alone or following diclosulam PRE. In a second experiment, weed control by imazapic applied POST alone or with acifluoren, diclosulam, or 2,4-DB was compared. In a final experiment, yellow nutsedge control by imazapic alone and with the fungicides azoxystrobin, chlorothalonil, pyraclostrobin, and tebuconazole was compared. Large crabgrass was controlled more effectively by imazapic POST than diclosulam PRE. Common lambsquarters, common ragweed, and eclipta were controlled more effectively by diclosulam PRE than imazapic POST. Nodding spurge was controlled similarly by both herbicides. Few differences in control were noted when comparing imazapic rates after diclosulam PRE. Applying either diclosulam PRE or imazapic POST alone or in combination increased peanut yield over nontreated peanut in five of six experiments. Few differences in pod yield were noted when comparing imazapic rates. Acifluorfen, diclosulam, and 2,4-DB did not affect entireleaf morningglory, large crabgrass, nodding spurge, pitted morningglory, and yellow nutsedge control by imazapic. Eclipta control by coapplication of imazapic and diclosulam exceeded control by imazapic alone. The fungicides azoxystrobin, chlorothalonil, pyraclostrobin, and tebuconazole did not affect yellow nutsedge control by imazapic.

Thirteen field experiments were conducted in Illinois, Indiana, Ohio, and Ontario from 2005 to 2007 to determine the effects of simulated glyphosate drift followed by in-crop applications of nicosulfuron/rimsulfuron plus dicamba/diflufenzopyr or foramsulfuron plus bromoxynil plus atrazine on nontransgenic corn injury, height, stand count, shoot dry weight, and yield. Simulated glyphosate drift at 100 and 200 g/ha, resulted in 11 to 61% visual crop injury and a 19 to 45% decrease in corn height. Simulated glyphosate drift at 200 g/ha caused a reduction in shoot dry weight by 46%, stand count by 28% and yield by 49 to 56%. Generally, simulated glyphosate drift followed by the in-crop herbicides resulted in an additive response with respect to visual crop injury, height, stand count, shoot dry weight, and yield.

Studies were conducted in 2005 and 2006 at three Iowa locations to determine the effect of soybean seeding rate and glyphosate application timing on weed management and grain yields in glyphosate-resistant soybean. End-of-season weed populations were affected by soybean seeding rate at only one location, with higher weed densities present in the lowest seeding rate when glyphosate was applied at the V2 soybean growth stage. Although weed populations were not consistently affected by soybean population, weed biomass present at soybean harvest was inversely related to soybean population. At the location with the highest weed populations, no single glyphosate application provided yields equivalent to the weed-free control. At the other locations, glyphosate application timing did not affect soybean yield. Lower soybean yields occurred with 240,000 seed/ha compared with 420,000 seed/ha at all locations and with 300,000 seed/ha at two locations.

In the northern Great Plains, fields are land rolled after the planting of annual pulse and forage crops to push rocks back into the soil to prevent damage to harvest equipment. Field trials were conducted in 2004 and 2005 to determine if land rolling influenced weed density or biomass associated with field pea, forage barley, and summer fallow. The experiment included two planting dates, conventional and delayed, for both barley and pea. Separate fallow plots were included with each planting date. Preplant tillage was conducted with a field cultivator for all treatments. Across years, crops, and planting dates, land rolling approximately doubled densities of tumble mustard, Russian thistle, kochia, and redroot pigweed shortly after crop emergence and at harvest compared with nonrolled. Land rolling increased density of early-emerging green foxtail but density at harvest was not affected. Wild oat densities were not influenced by rolling. Weed biomass at harvest was greater after land rolling than nonrolled. Land rolling after planting decreased subsequent pea yield by 330 kg/ha, but did not influence water use or water use efficiency. Land rolling is advantageous by hastening depletion of soil broadleaf weed seed banks in forage barley, but may increase problematic broadleaf weeds in pea.

The selection of herbicide-resistant weeds in grain sorghum production has prompted researchers to explore alternative herbicides to prevent, delay, and manage herbicide-resistant weed biotypes. Greenhouse and field experiments were conducted to evaluate the differential response of sorghum hybrids to POST application of mesotrione. In a greenhouse experiment, 85 sorghum hybrids were treated with 0, 52, 105, 210, and 315 g ai/ha mesotrione when plants were at the three- to four-leaf collar stage. Sorghum response ranged from susceptible to tolerant sorghum hybrids. ‘Pioneer 84G62’, ‘Pioneer 85G01’, and ‘Triumph TR 438’ were the three most susceptible, whereas ‘Dekalb DKS35-70’, ‘Frontier F222E’, and ‘Asgrow Seneca’ were the three most tolerant hybrids. One week after treatment (WAT), the mesotrione rate causing 50% visible injury ranged from 121 to 184 and 64 to 91 g/ha in the most tolerant and susceptible hybrids, respectively. Mesotrione dose–response studies were conducted under field conditions on four sorghum hybrids. One WAT, injury symptoms were greater (up to 23%) in Pioneer 85G01 than in Asgrow Seneca (< 14%). However, all plants appeared normal by the end of the growing season. In addition, sorghum yields were not reduced by mesotrione treatments as verified by correlation coefficient analysis.

Field experiments were conducted in Nebraska with the experimental herbicide KIH-485 on soils with three different levels of organic matter (OM) to ascertain a dose response for weed control and corn tolerance. Dose–response curves based on the log-logistic model were used to determine the effective dose that provides 90% weed control (ED90 values) for three grasses (green foxtail, field sandbur, large crabgrass) and two broadleaf weeds (velvetleaf, tall waterhemp). The ED90 values for green foxtail control were 143, 165, and 202 g ai/ha for soils with 1, 2, and 3% OM, respectively at 28 d after treatment (DAT). The highest dose of 371 g ai/ha was needed for field sandbur control at 28 DAT, compared with 141 g ai/ha for large crabgrass, 152 g ai/ha for tall waterhemp, and 199 g ai/ha for velvetleaf. There was no significant corn injury observed. Grain yield increased with increasing doses of KIH-485; optimum yield was achieved at about 195 g ai/ha. From the dose–response curves it is clear that the proposed label rate of KIH-485 of 200 to 300 g ai/ha will provide excellent control of most grasses and certain broadleaf weeds in corn for at least the first 4 wk of the growing season on soils up to 3% OM in the state of Nebraska.

Western Australian growers are adopting no-tillage farming systems, which have a greater reliance on integrated weed management systems that include competitive cultivars, high seeding rates, strategic fertilizer placement, and narrow row spacing. At the same time, they are sowing more of their barley area to cultivars with a semidwarf habit. This study compared six two-row, spring malting barley cultivars with different morphological traits at two dates of planting and three crop densities, with nil-added and added rigid ryegrass at five sites. Four cultivars, ‘Buloke’, ‘Flagship’, ‘Hamelin’, and ‘Vlamingh’, had an erect early growth habit; the other two, ‘Baudin’ and ‘Gairdner’, had a prostrate, semidwarf early growth habit. Increasing the density of rigid ryegrass plants from 16 to 125 plants/m2 decreased barley grain yield by reducing crop biomass production, tiller number, grain number, and harvest index. Average grain weight was also reduced at most sites. The impact of competition on grain yield varied across sites and cultivars, but did not interact with date of planting. Baudin, Flagship, and Hamelin were more competitive with rigid ryegrass than Buloke, Gairdner, and Vlamingh. Differences in competitiveness between cultivars did not appear to be strongly related to morphological traits that affect light interception such as canopy closure, plant height, and tiller number. Differences in cultivar competitiveness were cultivar-specific and not generic. Rigid ryegrass productivity (dry matter and tiller number) tended to be lower under the more competitive cultivars. Increasing barley plant density increased grain yield, and reduced both rigid ryegrass dry matter and tiller number. Barley density had a larger impact on rigid ryegrass productivity than crop cultivar. The impact of barley density on reducing rigid ryegrass tiller number was larger with the first planting date than the second, and higher in the added rigid ryegrass plots than the nil-added plots. This study highlights the importance of high barley seeding rate for the integrated management of rigid ryegrass.

Infestations of glyphosate-resistant (GR) horseweed have become widespread in the eastern United States. This biotype is problematic in no-tillage production that relies extensively on glyphosate for weed control. Because horseweed is treated at various stages of growth, a greenhouse study explored rate response of glyphosate-resistant and -susceptible horseweed at three growth stages. GR horseweed was more responsive to glyphosate at the seedling stage than at the large rosette or bolting stages. A field study evaluated GR horseweed response when treated with glyphosate at soybean planting time, POST in-crop (about 45 d after planting), or both at planting and POST in-crop. There was a cumulative effect of the at-planting followed by POST in-crop glyphosate applications. When evaluating single glyphosate applications, the at-planting application was more effective at suppressing GR horseweed than a POST in-crop application. Because glyphosate cannot control GR horseweed, this biotype should be controlled with an herbicide with an alternate mode of action and applied at the most effective timing.

Field experiments were conducted in Platte County, Missouri, during 2006 and 2007 to evaluate PRE, POST, and PRE followed by (fb) POST herbicide programs for the control of glyphosate-resistant waterhemp in soybean. All PRE fb POST treatments resulted in at least 66 and 70% control of glyphosate-resistant waterhemp in 2006 and 2007, respectively. Control of glyphosate-resistant waterhemp was less than 23% with lactofen and acifluorfen in 2006, but at least 64% in 2007. Variability in control likely resulted from differences in trial locations and a population of protoporphyrinogen oxidase (PPO)–resistant waterhemp at the Platte County site in 2006 compared with 2007. In both years, glyphosate resulted in less than 23% control of glyphosate-resistant waterhemp and provided the least control of all herbicide programs. Programs containing PRE herbicides resulted in waterhemp densities of less than 5 plants/m2, whereas the POST glyphosate treatment resulted in 38 to 70 plants/m2. Waterhemp seed production was reduced at least 78% in all PRE fb POST programs, from 55 to 71% in POST programs containing lactofen and acifluorfen and by only 21% in the POST glyphosate treatment. Soybean yields corresponded to the level of waterhemp control achieved in both years, with the lowest yields resulting from programs that provided poorest waterhemp control. PRE applications of S-metolachlor plus metribuzin provided one of the highest net incomes in both years and resulted in $271 to $340/ha greater net income than the glyphosate-only treatment. Collectively, the results from these experiments illustrate the effectiveness of PRE herbicides for the control of glyphosate-resistant waterhemp in glyphosate-resistant soybean and the inconsistency of PPO-inhibiting herbicides or PPO-inhibiting herbicide combinations for the control of waterhemp populations with multiple resistance to glyphosate and PPO-inhibiting herbicides.

Mesotrione, a carotenoid biosynthesis inhibitor, is being evaluated for use in turfgrass systems. It was hypothesized that root absorption of soil-applied mesotrione is necessary for effective weed control. Greenhouse studies were conducted to compare the effects of foliar-, soil-, and soil-plus-foliar–applied mesotrione at 0.14 and 0.28 kg ai/ha on yellow nutsedge and large crabgrass. In general, greatest control of yellow nutsedge and large crabgrass was by treatments that included soil application. In addition, mesotrione applied at 0.28 kg/ha generally controlled both yellow nutsedge and large crabgrass more effectively than mesotrione applied at 0.14 kg/ha. Soil- and soil-plus-foliar–applied mesotrione at 0.28 kg/ha controlled yellow nutsedge more than foliar-applied mesotrione 56 d after treatment. Soil-plus-foliar–applied mesotrione at 0.28 kg/ha controlled large crabgrass more than any other treatment 28 d after treatment. Soil- and soil-plus-foliar–applied mesotrione at both rates reduced large crabgrass foliar dry weight more effectively than did foliar-applied mesotrione. Results indicate that root absorption of mesotrione from soil is beneficial for the effective control of both yellow nutsedge and large crabgrass. For this reason, methods such as granular or high-volume applications, which enhance delivery of mesotrione to soil, would be potentially beneficial for turfgrass weed control.

Centipedegrass is tolerant of both atrazine and mesotrione when applied separately to established turf. However, no information is available regarding the use of mesotrione or the synergistic mixture of atrazine plus mesotrione applied to centipedegrass during seeded establishment. Research was conducted to evaluate centipedegrass tolerance to various rates and combinations of atrazine plus mesotrione when applied 14 d after emergence (DAE). Experiment 1 evaluated centipedegrass tolerance to atrazine and mesotrione in a broad rate-range screen in a greenhouse environment. Variations were observed between greenhouse trial runs with respect to injury and biomass with less injury and decrease in biomass observed in run 2. Overall, atrazine alone and atrazine plus mesotrione were more injurious for a greater time period and decreased biomass more than mesotrione alone. In fact, although mesotrione alone initially reduced centipedegrass photosystem II efficiency, an overall increase in efficiency was observed 28 d after treatment (DAT). Based on experiment 1, atrazine at 0.28 kg ai/ha was the maximum rate that could be applied to seedling centipedegrass when tank mixed with mesotrione. Experiment 2 evaluated atrazine at 0.28 kg/ha plus mesotrione at 0.03 to 0.28 kg/ha on centipedegrass field establishment. Although all atrazine plus mesotrione treatments reduced centipedegrass ground cover 28 DAT; no treatment reduced centipedegrass ground cover 49 DAT.

Dry edible bean class and cultivar response to dimethenamid and metolachlor was investigated in the greenhouse and field. Kidney and cranberry cultivars, as well as a small red cultivar, were not injured by dimethenamid applied PRE at 2,100 g ai/ha in the greenhouse, whereas pinto bean tolerance varied and navy and black bean cultivars were injured by this rate. Injury to navy bean was greater in the greenhouse when dimethenamid and metolachlor were placed in the zone above and including the seed, compared with placement in the seed, root, or root plus seed zone. In an application timing field study, dimethenamid at 1,300 g/ha applied at the crook or unifoliate growth stage caused injury to navy bean, delayed maturity, and reduced seed yield. Metolachlor at 1,400 g ai/ha delayed maturity when applied at the unifoliate growth stage but did not reduce seed yield. Dimethenamid or metolachlor PRE, at 1,300 or 2,800 g ai/ha, respectively, injured navy and black bean cultivars, but seed yield was not reduced in a cultivar tolerance field study. In a planting date study, dimethenamid PRE at 2,300 g/ha reduced leaf area and delayed maturity compared with the nontreated control when pooled over five planting dates and cultivars in each of 2 yr. Metolachlor PRE at 2,800 g/ha reduced leaf area in 1 yr and delayed maturity in both years when pooled over planting dates and cultivars. If weed control and herbicide costs are comparable, metolachlor at a standard use rate is a safer choice than dimethenamid for use in navy and black bean production.

Organic vegetable producers have limited options for managing weeds. They cite weed management as their number one research priority. Studies were conducted in 2004 and 2005 at the Black Sea Agricultural Research Institute, Samsun, Turkey, to determine the weed suppressive effects of summer cover crops in organic kale production. Treatments consisted of grain sorghum, sudangrass, hairy vetch, grain amaranth, pea, and fallow. Weed density and total weed dry biomass were assessed before and at 14, 28, and 56 d after incorporation (DAI) of the cover crops. Kale was transplanted 14 DAI and hand weeded once after last weed evaluation (56 DAI). All cover crops produced at least 1 ton/ha (t/ha) biomass; grain sorghum produced more dry matter than all other cover crops in both years. After incorporation of the cover crops, hairy vetch and sorghum treatments showed fewer species, lower weed density, and total weed dry biomass compared with other treatments. Cover crops suppressed emergence of common purslane, common lambsquarters, redroot pigweed, European heliotrope, field pennycress, annual sowthistle, black nightshade, shepherd's-purse, wild mustard, sun spurge, Persian speedwell, annual mercury, and jimsonweed up to 56 DAI. Total kale yield in hairy vetch treatments was more than double that of the no cover crop, and was significantly higher than yield from the other cover crop treatments. These results indicate that hairy vetch, grain sorghum, and sudangrass have ability to suppress early-season weeds in organic kale production.

The effects of flumioxazin in irrigation water were evaluated on four row crop species (corn, cotton, soybean, and wheat) and three ornamental species (begonia, impatiens, and snapdragon). Plants were overhead irrigated one time with flumioxazin at concentrations of 0, 10, 25, 50, 100, 200, 400, 800, 1,600, and 3,200 µg ai/L in water equivalent to 1.27 cm. Ornamental plant tolerances on the basis of a 10% reduction in dry weight (effective concentration 10 [EC10]) were as follows: impatiens (40) < begonia (103) < snapdragon (7,024). The EC10 values of flumioxazin on the basis of dry weight values for row crop species were wheat (35) < corn experiment 1 (53) < cotton (106) < corn experiment 2 (181) < soybean (193). EC10 values for plant height were similar to values for plant dry weight for ornamental and crop species. Snapdragon was the only plant evaluated that was mature at the time of treatment; consequently, all other species were moderately to highly sensitive to irrigation water containing flumioxazin. These data show that flumioxazin can injure and kill immature ornamental and crop species within the potential maximum concentration of 400 µg/L; however, the very short half-life of this herbicide in water with pH 7.0 to 9.0 (ca. 16 h to 17 min) could result in less injury than suggested in this study.

When solid stands of foxtail millet are cut for swath grazing, the grazing season for cattle is extended and winter feeding costs reduced. The economic success of this practice depends on inexpensive weed control. Eight single- and double-rate herbicide combinations (g ai/ha) were evaluated and compared to a weed-free check: MCPA + bromoxynil (280 + 280 or 560 + 560); MCPA + clopyralid (560 + 100 or 1120 + 200); MCPA + fluroxypyr (562 + 108 or 1124 + 216); and MCPA + clopyralid + fluroxypyr (560 + 100 + 144 or 1120 + 200 + 288). This study was conducted at Indian Head, Saskatchewan (SK) in 2004, 2005, 2006, and 2007 and at Scott, SK, in 2006 and 2007. Crop injury and dry matter yield were measured. Results of the study indicate that crop injury exceeded 20% at only one out of six sites at 7 to 14 d after herbicide treatment. Double-rate MCPA + bromoxynil treatments had higher injury ratings than the weed-free check 7 to 14 d after treatment in all site years. As the growing season progressed, injury ratings tended to decline except at Scott in 2007, where injury ratings at the 21 to 35 d period were numerically greater than the other two rating periods. There were no differences among treatments for crop biomass production. We conclude that all four herbicide combinations at the labeled rate are safe to use on foxtail millet in Saskatchewan, and probably in other areas with similar environmental growing conditions.

Geospatial technologies are increasingly important tools used to assess the spatial distributions and predict the spread of invasive species. The objective of our research was to quantify and map four dominant invasive plant species, including saltcedar, Russian olive, Canada thistle, and musk thistle, along the flood plain of the North Platte River corridor within a 1-mile (1.6-km) buffer. Using the Airborne Imaging Spectroradiometer for Applications (AISA) hyperspectral imager (from visible to near infrared), we evaluated an image processing technique known as spectral angle mapping for mapping the invasive species distribution. A minimum noise fraction algorithm was used to remove the inherent noise and redundancy within the dataset during the classification. The classification algorithm applied on the AISA image revealed five categories of invasive species distribution including (1) saltcedar; (2) Russian olive; and a mix of (3) Canada and musk thistle, (4) Canada/musk thistle and reed canary grass, or (5) Canada/musk thistle, saltcedar, and reed canary grass. Validation procedures confirmed an overall map accuracy of 74%. Saltcedar and Russian olive classes showed producer and user accuracies of greater than 90%, whereas the mixed categories revealed accuracy values of between 35 and 74%. The immediate benefit of this research has been to provide information on the spatial distribution of invasive species to land managers for implementation of management programs. In addition, these data can be used to establish a baseline of the species distributions for future monitoring and control efforts.

Reflectance data were subjected to a variety of analysis methods to determine the utility of hyperspectral reflectance for differentiating soybean, soil, and six weed species commonly found in Mississippi agricultural fields. Weed species evaluated were hemp sesbania, palmleaf morningglory, pitted morningglory, prickly sida, sicklepod, and smallflower morningglory. Hyperspectral reflectance data were collected from mature plant leaves three times in 2002 and two times in 2003. Vegetation indices were calculated and subjected to principal component analysis (PCA) and linear discriminant analysis (LDA). The PCA, using vegetation indices, produced the poorest classification accuracies for the plant species studied, generally less than 50%, whereas LDA resulted in classification accuracies greater than those from PCA. Best spectral band combination (BSBC) provided the greatest classification accuracies, with all better than 80% for all data sets. The BSBC indicated three wavelength bands of interest for species discrimination in the short wavelength infrared portion of the electromagnetic spectrum, which are not commonly used in current vegetation indices for species differentiation. These areas of interest were located from 1,445 to 1,475 nm, 2,030 to 2,090 nm, and 2,115 to 2,135 nm. The top 10 wavelengths determined by BSBC were then added to the vegetation indices and reanalyzed using PCA and LDA. Classification accuracies increased for all species when these wavelengths were added rather than using vegetation indices alone, suggesting greater crop and weed species differentiation can be obtained when using sensors that include these wavelength regions of the short wavelength infrared portion of the electromagnetic spectrum.

Natural products might provide an organic means of weed control. Our objective was to evaluate the potential use of vinegar and a clove-oil product with regard to how volume, concentration, and application timing affect weed control and crop response. Treatments included broadcast applications of 200- and 300-grain vinegar at 318 liters per hectare (L/ha), 150- and 200-grain vinegar at 636 L/ha, a 3.4% v/v clove oil mixture in water (318 L/ha), and a 1.7% clove oil mixture in 200-grain vinegar (318 L/ha). Field trials were conducted in sweet corn, onion, and potato. Weed control, weed biomass, crop injury, and yield data were collected. Corn treated at 15 and at 30 to 45 cm was initially burned and stunted by these products. By 4 wk after application much of the initial injury was outgrown. Late applications significantly reduced yields of early-maturing sweet corn ‘Trinity’. With the exception of the 200-grain vinegar (318 L/ha) treatment, early applications to sweet corn ‘Avalon’ did not reduce marketable yield. Two hundred-grain vinegar (636 L/ha) applied to pre-emergence–flag stage onion reduced the duration of the first handweeding by 59 to 67%. All treatments reduced onion yields when treated at the 2-leaf stage. Potato treated early (2 to 10 cm) and late (30 cm) were injured by all vinegar treatments 59 to 83%, 1 d after treatment (DAT). Potato yield losses were insignificant with applications of 3.4% clove oil and with some low-volume (318 L/ha) vinegar treatments. Product efficacy was dependent on the weed species and their size at the time of application. Weed control was greatest (83%, 1 DAT) with 200-grain vinegar (636 L/ha). Broadcast applications of vinegar and clove oil have potential for use on young, actively growing sweet corn, onion, and potato.

Field studies were conducted in 2001 and 2002 to determine the effect of tillage on the emergence of common waterhemp from the soil seedbank. Emergence of common waterhemp was three times greater in no-till than chisel-till cultivation. Tillage did not affect the initial time of emergence; however, the time to 50% emergence was longer in no-till than chisel till. Duration of emergence did not differ among tillage systems. Common waterhemp seed was concentrated near the soil surface in no-till plots, whereas seed in the chisel-till plots were primarily found between 9 and 15 cm. The delayed and increased emergence in no-till cultivation may contribute to the greater problems in managing common waterhemp in no-till plots compared with plots where tillage is used.