Field experiments were conducted near Beaumont, TX, to evaluate red rice control in imidazolinone-tolerant rice. Imazethapyr was applied preplant incorporated (PPI) and preemergence (PRE) at 70 and 105 g ai/ha and postemergence (POST) at 36, 52, and 70 g/ha. Single imazethapyr applications were made at each rate and timing and in sequential PPI or PRE followed by POST treatments. Red rice control ranged from 92 to 98% with sequential imazethapyr applications. Red rice control was higher when imazethapyr was applied PPI alone than PRE alone. But when these treatments were followed by a POST application of imazethapyr, there were no differences in red rice control between PPI and PRE application. Red rice control with sequential treatments was not improved with increased rates of imazethapyr POST. Visual injury to the 93AS3510 imidazolinone-tolerant variety was 5% or less 20 d after treatment (DAT), and there was no injury by 45 DAT. But POST applications of 70 g/ha imazethapyr may produce minor yield reductions to this experimental variety without improving red rice control. Results indicate that an imidazolinone-tolerant rice production system can be effective for controlling red rice and that PRE applications must be followed by a POST application to achieve maximum red rice control. PPI applications of imazethapyr at 70 g/ha should also be followed by a POST application to maximize red rice control.

Field studies were conducted to compare venturi-type nozzles to a fan nozzle with respect to the efficacy of postemergence herbicides applied to common cocklebur and broadleaf signalgrass. Spray solutions of glufosinate, glyphosate, and paraquat were applied through all combinations of three nozzles and two application volumes. Venturi nozzles were a Delavan Raindrop Ultra (RU) and a Spraying Systems AI Teejet (AI). A Spraying Systems XR Teejet (XR) fan nozzle was included as a standard. Previous work indicated droplet size spectra differed among these nozzles. There was a difference in common cocklebur control among nozzles (AI = XR > RU), although control was at least 90% for all nozzles. Herbicide choice had a greater effect on broadleaf signalgrass control than nozzle type. Broadleaf signalgrass control differed among herbicides (glufosinate = paraquat > glyphosate) and among nozzles (AI = XR > RU). Herbicide performance varied between nozzles (AI > RU), but the AI nozzle was as effective as the XR fan nozzle.

Combinations of grass and legume mulches were planted in growing corn during the fall in 1985 and 1986, and the following spring no-till corn was planted into these living mulches. Mulch treatments consisted of a single species or grass plus legume mixtures. Fluazifop-P, 2,4-D, and atrazine were broadcast applied in late April to suppress the mulches and reduce their competition with corn. Chewings fescue and ladino clover competed least with dryland corn. Weed growth associated with chewings fescue and the ladino clover mulches was similar to that in the conventional disk-plant treatment, but corn yields were lower. Hairy vetch mulch was killed by 2,4-D. The winter rye mulch competed with corn and reduced yield.

Deciding on the most efficacious PRE and POST herbicide options and their ideal application timing can be challenging for soybean producers. Climatic events during the 14 d before and after herbicide application can further complicate decisions because of their influence on herbicide effectiveness. Nine field trials were conducted at three locations in southwestern Ontario from 2003 to 2006, to determine the most effective PRE and POST soybean herbicides for control of common lambsquarters, common ragweed, green foxtail, and redroot pigweed. When precipitation was low at least 7 d before and after herbicide application weed control was reduced in treatments that included imazethapyr (PRE or POST) or flumetsulam/S-metolachlor (a premix formulation) (PRE). Cumulative precipitation during the 12 d after PRE application that exceeded the monthly average by at least 60% reduced common lambsquarters control when metribuzin was applied and green foxtail control when imazethapyr was applied. Delaying application of imazethapyr + bentazon to a later soybean growth stage decreased control of common lambsquarters and green foxtail; however, environmental conditions appeared to influence these results. Precipitation on the day of application decreased control of common ragweed and redroot pigweed more with quizalofop-p-ethyl + thifensulfuron-methyl + bentazon compared with imazethapyr + bentazon. Soybean yield varied among POST herbicide treatments because of reduced weed control. This research confirms that environmental conditions pre- and postapplication, as well as application timing, influence herbicide efficacy and should be considered by growers when selecting an herbicide program.

Field experiments were conducted on six loam and sandy loam soils to study the influence of various soil parameters on atrazine, cyanazine, alachlor, metolachlor, and pendimethalin efficacy. Herbicidal activity was highly correlated to the soil organic content. Humic matter content was equally or better correlated (r = 0.70 to 0.91) with herbicide bioactivity than was organic matter content (r = 0.66 to 0.84). Regression equations were determined which allow herbicide rate recommendations for 80% weed control to be calculated based on soil humic matter or organic matter levels.

A replacement series study was conducted in a greenhouse in 1998 and 1999 to evaluate the interference interactions among two rice cultivars and two red rice ecotypes. Plants were established in proportions of 3:0, 2:1, 1:2, and 0:3 (rice–red rice) plants/pot. Relative yield of Kaybonnet based on the shoot dry weight was lower than that of KatyRR or LA3, whereas PI 312777 was comparable to that of KatyRR and LA3. These results indicate that Kaybonnet was less competitive than PI 312777 when contrasted with KatyRR and LA3 red rice ecotypes. Kaybonnet (commercial rice cultivar) was dominated by both KatyRR (suspected rice × red rice cross) and LA3 (tall red rice ecotype) in tiller production, whereas PI 312777 (weed-suppressive cultivar) was comparable to either KatyRR or LA3. Both KatyRR and LA3 considerably reduced the leaf area of Kaybonnet. In contrast, PI 312777 reduced the growth of KatyRR, and its leaf area was comparable to that of LA3. The data suggest that high tillering capacity, as demonstrated by PI 312777, should be considered when breeding for rice cultivars that are competitive against weeds. This agronomic characteristic of rice may improve the success of reduced herbicide rate application programs.

Three methods of predicting the impact of weed interference on crop yield and expected economic return were compared to evaluate the economic importance of weed spatial heterogeneity. Density of three weed species was obtained using a grid sampling scheme in 11 corn and 11 soybean fields. Crop yield loss was predicted assuming densities were homogeneous, aggregated following a negative binomial with known population mean and k, or aggregated with weed densities spatially mapped. Predicted crop loss was lowest and expected returns highest when spatial location of weed density was utilized to decide whether control was justified. Location-specific weed management resulted in economic gain as well as a reduction in the quantity of herbicide applied.

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.

There is an urgent need to accelerate the development and implementation of effective organic-compliant herbicides that are environmentally safe and that help the producer meet increasing consumer demand for organic products. Therefore, greenhouse experiments were conducted to evaluate the effectiveness of acetic acid (5%), acetic acid (30%), citric acid (10%), citric acid (5%) + garlic (0.2%), citric acid (10%) + garlic (0.2%), clove oil (45.6%), and corn gluten meal (CGM) compounds as natural-product herbicides for weed control. The herbicides were applied to the broadleaf weeds stranglervine, wild mustard, black nightshade, sicklepod, velvetleaf, and redroot pigweed and to narrowleaf weeds crowfootgrass, Johnsongrass, annual ryegrass, goosegrass, green foxtail, and yellow nutsedge. The herbicides were applied POST at two weed growth stages, namely, two to four and four to six true-leaf stages. CGM was applied PPI in two soil types. Citric acid (5%) + garlic (0.2%) had the greatest control (98%) of younger broadleaf weeds, followed by acetic acid (30%) > CGM > citric acid (10%) > acetic acid (5%) > citric acid (10%) + garlic (0.2%), and clove oil. Wild mustard was most sensitive to these herbicides, whereas redroot pigweed was the least sensitive. Herbicides did not control narrowleaf weeds except for acetic acid (30%) when applied early POST (EPOST) and CGM. Acetic acid (30%) was phytotoxic to all broadleaf weeds and most narrowleaf weeds when applied EPOST. Delayed application until the four- to six-leaf stage significantly reduced efficacy; acetic acid was less sensitive to growth stage than other herbicides. These results will help to determine effective natural herbicides for controlling weeds in organic farming.

Glyphosate-resistant giant ragweed in Arkansas was reported in 2005. A study was conducted to (1) confirm and characterize the glyphosate resistance in giant ragweed, (2) determine if reduced absorption or translocation is the mechanism of glyphosate resistance in giant ragweed, and (3) evaluate the efficacy of nine POST-applied soybean herbicides to control glyphosate-resistant and -susceptible giant ragweed. Based on the rate required to kill 50% of plants (LD50 values), resistant giant ragweed biotypes from Greene and Jefferson counties were 2.3- to 7.2-fold less sensitive to glyphosate compared to susceptible biotypes. Glyphosate absorption and translocation for glyphosate-resistant and -susceptible biotypes was similar at 24 and 72 h after treatment. Thus, differential absorption or translocation is not a mechanism of glyphosate resistance in this resistant giant ragweed biotype. Control of resistant giant ragweed biotypes with glyphosate at a labeled field application rate of 840 g ha−1 was only 60% or less compared to complete control of a susceptible giant ragweed biotype. However, bentazon, carfentrazone, cloransulam, and fomesafen controlled both biotypes more than 95%.

Living mulches are cover crops grown simultaneously with and in close proximity to cash crops. Advantages of living mulches over dead cover crops may include increased weed suppression, reduced erosion and leaching, better soil health, and greater resource-use efficiency. Advantages of living mulches over synthetic mulches may include enhanced agroecosystem biodiversity and suitability for a wider range of cropping systems. A major disadvantage of this practice is the potential for competition between living mulches and cash crops. The intensity and outcome of mulch-crop competition depend on agroecosystem management as well as climate and other factors. In this review, we consider the management of living mulches for weed control in field and vegetable cropping systems of temperate environments. More than 50 yr of research have demonstrated that mechanical or chemical suppression of a living mulch can limit mulch-crop competition without killing the mulch and thereby losing its benefits. Such tactics can also contribute to weed suppression. Mechanical and chemical regulation should be combined with cultural practices that give the main crop a competitive advantage over the living mulch, which, in turn, outcompetes the weeds. Promising approaches include crop and mulch cultivar selection; changes to planting time, density, and planting pattern; and changes to fertilization or irrigation regimes. A systems approach to living mulch management, including an increased emphasis on the interactions between management methods, may increase the benefits and lower the risks associated with this practice.

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.

An experiment was conducted at four locations in North Carolina during 1994 and 1995 to evaluate weed control, cotton yield, fiber quality, and net returns in no-tillage bromoxynil-tolerant cotton. The experiment focused on using bromoxynil or pyrithiobac sodium applied early POST over-the-top as alternatives to fluometuron plus MSMA applied early POST directed. Fluometuron plus MSMA was more effective than bromoxynil or pyrithiobac sodium on tall morningglory, large crabgrass, goosegrass, and broadleaf signalgrass. Bromoxynil and fluometuron plus MSMA were similarly effective on common lambsquarters, common ragweed, and eclipta and more effective than pyrithiobac sodium. Pyrithiobac sodium and fluometuron plus MSMA were similarly effective on smooth pigweed and Palmer amaranth and more effective than bromoxynil. Prickly sida control by bromoxynil and pyrithiobac sodium was equal to or greater than control by fluometuron plus MSMA. All early POST herbicides controlled pitted morningglory similarly. Regardless of the early POST herbicides used, fluometuron applied PRE and cyanazine plus MSMA applied late POST directed increased control of most weeds and increased cotton yield and net returns. Bromoxynil and pyrithiobac sodium effectively substituted for fluometuron plus MSMA only in systems that included fluometuron applied PRE and cyanazine plus MSMA applied late POST directed. Effects of herbicide systems on cotton fiber quality were minor.

The dissipation of four commonly used soil-applied herbicides was examined in a standardized field experiment in three southern states (Kentucky, Mississippi, and Tennessee). Averaged over the three soils and 2 yr, the relative order of increasing half-life defined as time for 50% disappearance in days (DT50) was acetochlor (6.3 d) = alachlor (6.3 d) = SAN 582 (7.3 d) < metolachlor (13.7 d). Metolachlor was the most persistent in the soil surface, and this could potentially translate into greater duration of weed control into the growing season. All examined herbicides had a DT50 that averaged less than 14 d in all states in both years, so full-season weed control of susceptible species would not be expected. Rapid herbicide degradation was encouraged in these field sites by adequate to excessive soil moisture and warm temperatures throughout the sampling interval. The soils also were light textured, and the lower adsorption of the herbicide allowed for degradation ease and perhaps leaching below the sampling depth.

Soybean seed yield losses due to interference from common cocklebur, velvetleaf, and jimsonweed, with and without a PPI application of 0.42 kg ai ha-1 metribuzin, were determined in 1986, 1987, and 1988. Damage functions were calculated based on weed density, weed leaf density, and relative weed leaf area index, respectively. Functions relating crop yield losses to weed density varied significantly among treatments and years for each species. Weeds which escaped soil-applied metribuzin were shorter with fewer leaves at 3 wk after planting, and caused lower crop yield losses than control plants at equal densities. Yield loss estimates based upon relative weed leaf area at 3 wk after planting showed least variation between years and treatments.

The discipline of weed science is entering a critical period in its development. Decisions made in the next few years will determine if weed science will remain weed control technology oriented or develop into a broad-based scientific discipline. Over the last 30 yr the evolution of weed science has been based on the development of weed control methods. Currently, most crop production systems rely very heavily on one weed control technology, herbicides. Agriculture is now in a debate with society over how food and fiber should be produced. Society is asking weed science, because of food safety and water quality concerns, to develop new methods to control weeds. To do this, weed science must put more emphasis on principles-based research that can provide the basic knowledge required to develop new weed control technology. Weed scientists must join forces with private citizens and organizations concerned with the effect of current agricultural practices on the environment, to obtain, through the political process, new resources for weed science research. These resources are needed to develop the basic principles that will support the development of new weed control technologies with reduced environmental impact. Weed scientists must decide if they are going to lead the direction of weed science research or be led reluctantly by others.

Seven postemergence (POST) herbicides were evaluated alone and in various mixtures for Palmer amaranth control in peanut from 1992 through 1994. AC 263,222 at rates as low as 0.04 kg/ha controlled ≥ 95% Palmer amaranth. Imazethapyr at rates of 0.05 to 0.07 kg/ha controlled ≥ 90% Palmer amaranth in 2 of 3 yr. Acifluorfen alone or in combination with bentazon or 2,4-DB and lactofen alone controlled > 90% Palmer amaranth in 2 of 3 yr. Bentazon or pyridate failed to provide adequate control (≤ 60%), while 2,4-DB provided good control (80%) in only 1 of 3 yr.

The introduction of soybean and cotton traits with resistance to synthetic auxin herbicides has led to an increase in concern over the off-target movement of dicamba and 2,4-D. A direct-mail survey was sent to Missouri pesticide applicators in January of 2016 to understand current herbicide application practices and applicator knowledge and awareness of the new synthetic auxin technologies. Completed surveys were returned by 2,335 applicators, representing approximately 11% of the state’s registered pesticide applicators. Survey data reported herein provides information regarding current pesticide applicator knowledge and practices and highlights areas that need more emphasis during applicator training. Overall, survey respondents were familiar with physical drift and methods to minimize that risk. However respondents were less familiar with volatility and temperature inversions, which can each influence off-target herbicide movement. Of the 427 commercial applicators and 1,535 noncommercial applicators who answered questions regarding volatility, 81% and 74% respectively, recognized that high temperatures can contribute to a herbicide’s ability to volatilize. However, only 48% and 39% understood that a herbicide’s vapor pressure influences volatility. Answers from the survey indicate further education is needed on the synthetic auxin technologies, such as what herbicides can be used with each technology, proper methods for inspecting and cleaning spray equipment, and the importance of reading herbicide labels. When asked whether applicators were aware of the new 2,4-D-resistant and dicamba-resistant traits, 76% of 443 commercial applicators and only 40% of 1,713 noncommercial applicators selected “yes.” Additionally, survey results suggests that current methods aimed to facilitate communication among producers and applicators, such as FieldWatch and Flag the Technology, may not be successfully adopted, at least in Missouri. Findings from this survey can be utilized to enhance training of pesticide applicators in preparation for the synthetic auxin herbicide technologies.

Chlorsulfuron, thifensulfuron, bromoxynil, 2,4-D, glyphosate, and a combination of 2,4-D plus glyphosate were applied on newly planted and established ‘Lemberger’ wine grape at 1/3, 1/10, 1/33, and 1/100 of the maximum labelled rate in wheat or fallow to simulate exposure to drifted herbicides. All herbicides produced symptoms on grape but the most severe symptoms were with 2,4-D and the least severe with bromoxynil. Newly planted grape was more sensitive to herbicides than established grape. Although established grape recovered from injury caused by all treatments except 2,4-D and the highest rate of chlorsulfuron and glyphosate, newly planted grape recovered only from lower rates of bromoxynil. All herbicides resulted in diagnostic symptoms, but other symptoms were very similar to those caused by other stresses.

The manufacturer's recommended rate for fomesafen in snap beans, dry beans, and soybeans may cause carryover injury in sweet corn. A field experiment, a survey, and multiple greenhouse experiments were conducted to (1) estimate the fomesafen residue concentrations in the soil that might result from use of lower than registered rates, (2) estimate fomesafen residue concentrations in growers' fields and evaluate grower practices for their effects on carryover potential, and (3) investigate the effects of soil type and sweet corn variety on the potential for fomesafen to cause injury to sweet corn. Results of the dissipation study predicted average soil concentrations to be approximately 0.019 mg fomesafen/kg soil at the start of the sweet corn planting season. Half-life values ranged between 28 and 66 d, with an average of 50 d. Residues in grower fields were slightly less than those found in the dissipation study. Injury from fomesafen varied significantly by sweet corn variety and by soil type. Sweet corn grown in soils with high organic matter and low pH were most susceptible to injury from fomesafen. At high rates of fomesafen (0.12 mg/kg), reductions in dry weight of sweet corn varieties ranged from 5 to 60%. At rates of fomesafen slightly higher than those detected in field soils at the time of sweet corn planting (0.03 mg/kg), dry weight either increased slightly (variety trial) or decreased by 6 to 12% (soil-effect trial) depending on soil type. The risk of sweet corn yield losses because of fomesafen carryover appear relatively low. Growers can reduce the risk of carryover injury by planting tolerant varieties in fields where fomesafen was applied the preceding year.