Southern wax myrtle is a pernicious weed in south Florida pastures and this plant can eliminate all forage production under high densities. Previous work has shown that triclopyr at 1.12 kg/ha is the most effective herbicide on this species. The introduction of the Burch Wet Blade (BWB) mowing system provides an alternative application method to traditional broadcast herbicide applications. The objective of this experiment was to compare the efficacy of triclopyr and other herbicides using both broadcast and the BWB application systems. In general, broadcast applications of at least 1.1 kg/ha triclopyr provided better control than the same treatments applied with the BWB system in 1998. In 1999, control was lower overall compared to 1998, but the same trend was observed. Broadcast applications of triclopyr reduced wax myrtle densities better than when herbicides were applied with the BWB system in 1998. However, in 1999, dicamba + triclopyr, and at least 1.1 kg/ha triclopyr reduced wax myrtle densities compared to the mow-only treatment, regardless of application method. Although the BWB system provided an initial overall reduction in plant height, recovery of plants was sufficient and often outgrew those receiving broadcast applications of herbicides. Regardless of application method, retreatment of wax myrtle plants 1 yr after the initial application will likely be needed to obtain adequate control.

Site-specific herbigation using a linear-move irrigation system equipped with an automated irrigation control system was evaluated in a series of field trials conducted at the University of Idaho Aberdeen Research and Extension Center near Aberdeen, ID. In the first study, the experimental area was divided into site-specific management zones that were randomly assigned herbigation treatments of metolachlor at 0, 1.8, 2.7, or 3.6 kg ai/ha. In a second study, site-specific herbigation treatments of metribuzin at 0, 0.28, 0.42, or 0.56 kg ai/ha were applied. The tests covered a range in system flow rate from 29 to 90% of maximum design flow. Average metolachlor rates applied were within 1, 2, and 4% of the target 1.8, 2.7, and 3.6 kg/ha rates, respectively, and average metribuzin rates were on target at the 0.28 kg/ha rate and within 5 and 2% of the 0.42 and 0.56 kg/ha target rates, respectively. In a third study, potato (Solanum tuberosum) fields were divided into management zones, and low, medium, or high populations of Indian mustard (Brassica juncea) and foxtail millet (Setaria italica) were seeded in each zone. Different rates of a metolachlor plus metribuzin mixture were herbigated in each zone—higher rates in zones with high populations and lower rates in zones with low populations. Weed control was excellent in all zones. Results suggest good potential for site-specific herbigation when linear-move or center-pivot irrigation systems are equipped with the automated irrigation control system.

Experiments were conducted in pots and in the field to determine the influence of seed depth on seedling emergence pattern and control of Mexican sunflower with or without imazethapyr plus pendimethalin. Mexican sunflower seeds were placed at 0-, 2.5-, 5-, 7.5-, and 10-cm soil depths, and imazethapyr–pendimethalin mixture was applied PRE at 0, 0.05 + 0.65, 0.09 + 1.31, and 0.18 + 2.62 kg ae (+ ai)/ha. Mexican sunflower emergence was 57, 30, 14, 3, and 2% from 0-, 2.5-, 5-, 7.5-, and 10-cm seed depths, respectively. Seedling emergence started 2 to 3 d after planting and continued for 4 to 5 d. At 0- to 5-cm seed depths, 84 to 100% of total seedling emergence occurred within 3 d after the first seedling emerged, but emergence rate was less from 7.5- and 10-cm seed depths. Imazethapyr plus pendimethalin at 0.05 + 0.65 and 0.09 + 1.31 kg/ha had no effect on seedling emergence in Mexican sunflower, but subsequent growth was severely inhibited regardless of seed depth. The herbicide treatments were more injurious to Mexican sunflower seedlings that emerged from 5- to 10-cm depths than to those that emerged from 0 and 2.5 cm. Burying seeds 7.5 cm deep or more is a potential control measure for Mexican sunflower, and the deeper the emergence depth, the more susceptible the seedling is to imazethapyr plus pendimethalin.

Experiments were conducted to determine the energy requirements and the most effective rotary tiller configuration for incorporating cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile} on an 18-cm band centered on top of the previous year's corn (Zea mays L.) ridge. When the rotary tiller was operated full width at a 10-cm depth, the least cyanazine concentration was found in the center of the ridge, and the greatest concentration was found between ridges. The treatment having the greatest cyanazine concentrations in the center of the ridge and the least in the inter-row between ridges consisted of a ridge cleaner, a cyanazine application, and the rotary tiller configured to till a. 30-cm strip on the center of the ridge with a rotor enclosure. Energy requirements for operating the rotary tiller increased as the depth of operation increased, and the 10-cm depth of operation required less energy than two passes with a tandem disk.

This research was designed to determine if sethoxydim-resistant corn hybrids exhibited levels of cross-resistance to other acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicides. Three sethoxydim-resistant hybrids were tested in 1995 and four in 1996. The hybrids were treated with the 1 × (labeled use rate for annual grass control) and 4 × rate of clethodim, fenoxaprop-P plus fluazifop-P, fluazifop-P, quizalofop-P, and sethoxydim. At the 1 × rate, similar levels of corn safety were observed in both years with sethoxydim, quizalofop-P (except Asgrow RX620SR in 1995), and in 1996, fenoxaprop-P plus fluazifop-P. Corn treated with the 4 × rate of sethoxydim did not exhibit injury, while all other ACCase-inhibiting herbicides cause > 50% corn injury. Sethoxydim-resistant com hybrids used in this study did not consistently exhibit acceptable levels of cross-resistance to other ACCase-inhibiting herbicides. The use of clethodim will control volunteer sethoxydim-resistant corn in rotational crops.

Increasing the air temperature from 20 to 32 C, the water temperature from 21 to 30 C, and the wind velocity from 0 to 8 km/h increased the loss of EPTC (S-ethyl dipropyl carbamothioate) from water applied through a sprinkler by 24 to 138%. Decreasing the water temperature from 21 to 10 C decreased the loss of EPTC by 35 to 50%. Decreasing the water pressure or nozzle size by 33% or doubling the herbicide concentration did not affect the percentage of EPTC lost.

The name Polygonum is a very ancient derivative, composed of the two Greek words, polys, many, and gony, knee or joint, alluding to the numerous and conspicuous nodes in the stems of many species. The Greek physician Heraclides Tarentina (third and second centuries BC) prescribed prostrate knotweed, P. aviculare L., as a remedy against bleeding from the ear. Dioscorides, a Greek botanist, was the first to characterize Polygonum as having “numerous slender branches, creeping on the ground like grass, with fruit at each leaf.” Subsequently, other Greek physicians, poets, and botanists applied the name to the knotweed/smartweed group, and in 1753, Linneaus adopted it for the genus. The species name for pale smartweed, lapathifolium, is from lapathi, meaning sorrel-like or dock-like (Gledhill 1985; Hyam and Pankhurst 1995; Small 1895).

The movement and degradation of agricultural chemicals in soil and groundwater is a complex process, influenced by climatic conditions, site characteristics, chemical properties, and agricultural practices. Because of this complexity, mechanistic models are useful tools in evaluating environmental fate. Although currently available unsaturated zone models often do not provide accurate concentration profiles when compared with field measurements, they can be used to estimate the depth and extent of movement. Another application of modeling is to compare predicted movement under different simulation conditions to determine the significance of the various factors affecting the behavior of agricultural chemicals. When properly designed and interpreted, modeling studies can contribute to the understanding of the environmental fate of agricultural chemicals. When necessary, modeling can also be useful in developing management practices included on the label or in state regulations. Modeling has been a frequently used tool in developing restrictions for minimizing the movement of aldicarb residues into groundwater and preventing residues in drinking water. Examples of model use include optimizing application timing, estimating well setback distances, and identifying vulnerable soils.

Johnsongrass control systems that included commercially available corn herbicides applied to crop sequences of continuous corn or corn–cotton–corn rotation were evaluated over a 3-yr period at the Texas Agricultural Experiment Station in Burleson County. Herbicide treatments evaluated were EPTC + R-25788 applied preplant incorporated (PPI); metolachlor applied preemergence (PRE); nicosulfuron applied postemergence (POST); and the combination of metolachlor PRE and glyphosate POST applied after corn harvest. Weed control practices applied to plots planted to cotton in the second growing season provided excellent johnsongrass control (≈ 95%). Visual control ratings indicated that nicosulfuron provided the best johnsongrass control (> 80%) among the herbicides evaluated all three years. Metolachlor and glyphosate combinations provided acceptable johnsongrass control the third year of the experiment in both cropping sequences. Corn grain yield and johnsongrass control were best in cotton-rotated plots. The highest returns observed in continuous corn were from either nicosulfuron or the combination of metolachlor and glyphosate. Net returns for all control systems in corn–cotton–corn rotated plots were greater than the weedy check and were equivalent to the lead systems in continuous corn.

Carpetgrass is a warm season grass used in the south as low maintenance turf, especially in wet areas where other turf species do not persist. The response of carpetgrass to postemergence (POST) herbicides currently available for turf producers has not been thoroughly investigated and was the objective of four experiments conducted over a 2-yr period. Slight reduction in turf quality followed application of atrazine (2.2 kg ai ha-1), bentazon (2.2 kg ai ha-1), imazaquin (0.4 and 0.6 kg ai ha-1), mecoprop (1.1 kg ai ha-1), triclopyr (0.6 kg ai ha-1), metsulfuron (0.2 kg ai ha-1), 2,4-D (1.1 kg ai ha-1), 2,4-D plus dicamba (0.8 + 0.3 kg ai ha-1), and 2,4-D plus dicamba plus mecoprop (0.9 + 0.1 + 0.5 kg ai ha-1). Marginally acceptable turf quality followed sulfometuron (0.2 kg ai ha-1), sethoxydim (0.3 and 0.6 kg ai ha-1), and diclofop (2.2 kg ai ha-1) treatments. Unacceptable turf quality resulted from asulam (2.2 kg ai ha-1) and MSMA (1.1 and 2.2 kg ai ha-1) treatments. Carpetgrass tolerated most POST broadleaf and sedge herbicides but was sensitive to most POST grass herbicides used in other turf species, with the exception of sethoxydim.

POST control of cowpea in cotton was evaluated in 1990 and 1991. Early POST-directed (EPD) application of fluometuron + MSMA provided 89% cowpea control 2 wk after treatment. Cowpea control 4 wk after the early treatments was similar with fluometuron + MSMA EPD and sequential directed applications of MSMA followed by (fb) MSMA, methazole + MSMA fb cyanazine + MSMA, and fluometuron + MSMA fb cyanazine + MSMA. The average reduction in cowpea biomass 12 wk after planting with these treatments was 93%. MSMA fb MSMA POST-directed was the only treatment with a lint cotton yield similar to that of weed-free cotton. Lint cotton yields with fluometuron + MSMA, methazole + MSMA fb cyanazine + MSMA, and fluometuron + MSMA fb cyanazine + MSMA were similar to those obtained with MSMA fb MSMA.

Seasonal variations in tolerance of jack pine and white spruce to glyphosate and triclopyr were investigated in field and growthroom studies. Foliar injury was higher in both species following field applications of herbicides in July during periods of active growth than in September and October when the plants were not growing actively. Herbicides applied to trees in the growthroom 3 weeks after bud break caused greater injury than applications either before or 14 weeks after bud break. White spruce tolerated both glyphosate and triclopyr better than jack pine. Triclopyr injured both species more than glyphosate. Chemical analysis and electron micrographs showed that the cuticular wax deposition on both species was greater in field-grown trees than in growthroom-grown trees and was greater at 14 weeks after bud break than at 3 weeks. Increased wax deposition with time after bud break may reduce herbicide uptake and may account partially for the increased tolerance of both species to glyphosate and triclopyr.

2,4-dimethylamine salt (2,4-D) is a synthetic auxin herbicide used extensively in turfgrass for selective broadleaf weed control. Previous research has shown that 2,4-D can dislodge from treated turf, notably in the presence of canopy moisture. Practitioners commonly apply 2,4-D in combination with various commercially available surfactants to increase efficacy. Field research was completed to evaluate the effect of surfactant inclusion and sample collection time within a day on dislodgeable 2,4-D residue from perennial ryegrass. Research was initiated May 24, 2016 in Raleigh, NC and repeated in time to quantify dislodgeable 2,4-D following application (2.1 kg ae ha–1) either alone or with a nonionic surfactant (0.5% vol/vol). Sample collection occurred 1, 2, 3, 6, 12 or 24 d after treatment (DAT) at AM [7:00 AM Eastern Standard Time (EST)] and PM (2:00 PM EST) sample timings within a day. 2,4-D applied with surfactant (0.4% to 25.4% of applied) reduced dislodgeable foliar residue compared to 2,4-D applied alone (0.5% to 31.2%) from 1 through 6 DAT, whereas dislodgeable 2,4-D was not detected at 12 and 24 DAT. Regardless of surfactant inclusion or absence, samples collected in the AM resulted in a 5- to 10-fold increase in dislodgeable 2,4-D compared to samples collected in the PM from 1 through 6 DAT, suggesting that 2,4-D dislodgeability may be influenced by conditions favoring canopy moisture development. This research will improve turfgrass management practices and research designed to minimize human 2,4-D exposure.

Enhanced dissipation of atrazine has been documented in many parts of the world where the herbicide has been extensively used. Atrazine is widely used in corn in Illinois, but enhanced dissipation in the field has not been documented. In this study, the dissipation of atrazine was measured in three fields. Two of the fields (URB-1 and URB-2) had not been treated with atrazine for 3 and 4 yr, respectively, whereas the third field (ORR-1) had received annual applications of atrazine for 9 yr. A laboratory assay conducted on soil collected from these fields prior to atrazine application indicated that soil from ORR-1 had enhanced atrazine dissipation (half life [DT50] 1.7 d). Soil from fields URB-1 and URB-2 dissipated atrazine much slower (DT50 was 13 and 11d, respectively). In the field, the rates of atrazine dissipation were similar to those measured in the laboratory. The DT50s were 2.4, 8.4, and 12.6 d for ORR-1, URB-2, and URB-1, respectively. Testing the soils collected from the fields at the last sampling time for atrazine dissipation showed that all of them had enhanced atrazine dissipation, suggesting that the soil microbial populations had adapted to the presence of atrazine in the field.

Field experiments were conducted in Louisiana and Mississippi from 2011 through 2013 to evaluate crop injury, weed control, and yield in field corn following pyroxasulfone applied PRE and POST. Pyroxasulfone PRE or POST did not injure corn at any evaluation. Barnyardgrass control was not improved with the addition of any POST treatment to pyroxasulfone alone or atrazine plus pyroxasulfone PRE; however, all POST treatments increased barnyardgrass control to at least 95% at all evaluations following atrazine PRE. All treatments that contained a PRE followed by POST application controlled browntop millet ≥90% at all evaluations. All POST treatments increased ivyleaf morningglory control to ≥92% following atrazine or pyroxasulfone alone PRE. However, control with atrazine plus pyroxasulfone PRE was similar or greater 28 d after POST than all treatments that received a POST application. In the absence of a POST treatment, pyroxasulfone or atrazine plus pyroxasulfone PRE controlled Palmer amaranth 93 to 96% at all evaluations, but atrazine alone PRE provided 84, 82, and 66% control 7, 14, and 28 d after POST, respectively. All programs that contained a PRE followed by POST herbicide treatment controlled Palmer amaranth >90% at all evaluations. Corn yield following all treatments except atrazine alone PRE and the nontreated were similar and ranged from 10990 to 12330 kg ha−1. This research demonstrated that pyroxasulfone can be a valuable tool for weed management in a corn weed management program.

Devil's-claw and smellmelon are summer annual broadleaf weed problems in the southwest cotton production region. Field studies conducted in 1993 and 1994 evaluated the efficacy of pyrithiobac for postemergence (POST) control of devil's-claw and smellmelon compared with soil-applied fluometuron or prometryn. Pyrithiobac at 0.07 and 0.14 kg ai/ha early POST and 0.14 kg ai/ha mid-POST controlled devil's-claw more than 84% at the late rating. Devil's-claw control with mid-POST applications of pyrithiobac at 0.07 kg ai/ha was reduced when compared with other rates and application timings. Smellmelon control with pyrithiobac ranged from 57 to 84% and, except when applied at 0.07 kg ai/ha early POST, was equivalent to or greater than either fluometuron or prometryn. Crop injury with pyrithiobac treatments 16 d after treatment was 5 to 13%, but 33 d later, was no more than 3%.

Field studies were conducted for four consecutive years to determine if repeated applications of trifluralin (preplant incorporated), metolachlor (preemergence), and fluazifop (postemergence) herbicides alone or combined could be utilized in soybean to effectively control grass weed populations and maintain optimum yield in an irrigated environment where metribuzin plus dinoseb (preemergence) and 2,4-DB plus linuron (postemergence) were used as a standard weed control system. After repeated applications each year, all treatments maintained similar yields that were no different from yields obtained from the standard system. Grass weed infestation did not increase significantly in the treatment that received only the standard weed control herbicides over the duration of the study.

Weeds often limit productivity of organic cropping systems. Radish is a fast-growing, potentially allelopathic cover crop that has the potential to improve weed management in organic systems. To evaluate the effect of radish on density, cover, and biomass of weeds in organically managed corn, 2-yr field experiments were conducted over 4 site years. Four cover-crop planting treatments (fall-only, spring-only, fall + spring, and no cover) were tested in factorial with three cultivation treatments (standard [three to four passes], false seedbed [standard with a false seedbed], and reduced [two passes]). All plots were tilled before planting. Shoot biomass averaged 3,057 kg ha−1 for fall-seeded radish and 385 kg ha−1 for spring-seeded radish. Radish cover crops generally did not improve management of weeds during the corn growing season. However, in the absence of a false seedbed, fall-seeded radish reduced field pennycress density from 9 to < 1 plant m−2 and horseweed density from 6 to 2 plants m−2 in spring in site years where these weeds were present. Fall-seeded radish also reduced cover of summer annual weeds during the fall cover-crop growing season from 4 to 0% in 1 site year, preventing these weeds from setting seed. Radish cover crops did not affect corn grain yield.

Reforestation in the Inland Northwest, including northeastern Oregon, USA, is often limited by a dry climate and soil moisture availability during the summer months. Reduction of competing vegetative cover in forest plantations is a common method for retaining available soil moisture. Several spring and summer site preparation (applied prior to planting) herbicide treatments were evaluated to determine their efficacy in reducing competing cover, thus retaining soil moisture, on three sites in northeastern Oregon. Results varied by site, year, and season of application. In general, sulfometuron (0.14 kg ai ha–1 alone and in various mixtures), imazapyr (0.42 ae kg ha–1), and hexazinone (1.68 kg ai ha–1) resulted in 3 to 17% cover of forbs and grasses in the first-year when applied in spring. Sulfometuron+glyphosate (2.2 kg ha–1) consistently reduced grasses and forbs for the first year when applied in summer, but forbs recovered in the second year on two of three sites. Aminopyralid (0.12 kg ae ha–1)+sulfometuron applied in summer also led to comparable control of forb cover. In the second year after treatment, forb cover in treated plots was similar to levels in nontreated plots, and some species of forbs had increased relative to nontreated plots. Imazapyr (0.21 and 0.42 kg ha–1) at either rate, spring or summer 2007, or at lower rate (0.14 kg ha–1) with glyphosate in summer, provided the best control of shrubs, of which snowberry was the dominant species. Total vegetative cover was similar across all treatments seven and eight years after application, and differences in vegetation were related to site rather than treatment. In the first year after treatment, rates of soil moisture depletion in the 0- to 23-cm depth were correlated with vegetative cover, particularly late season soil moisture, suggesting increased water availability for tree seedling growth.

Provisia™ rice was developed recently by the BASF Corporation for control of grass weeds and is complementary to existing Clearfield® technology. Our previous research showed that resistance of Provisia™ rice to the acetyl coenzyme-A carboxylase herbicide quizalofop-p-ethyl (QPE) in laboratory and greenhouse environments is governed by a single dominant Mendelian gene. However, these results may not be consistent in different populations or field environments. Therefore, the first objective of the current research is to determine the inheritance of resistance to QPE in rice using different segregating populations evaluated under U.S. field environments. The second objective is to evaluate the response of QPE-resistant breeding lines to various herbicide concentrations at two U.S. locations. Chi-square tests of 12 F2 populations evaluated in Louisiana during 2014 and 2015 indicated that QPE seedling resistance at 240 g ai ha−1 was governed by a single dominant Mendelian gene with no observable maternal effects. Similar results were obtained in five F3 populations derived from the aforementioned F2 populations. Allele-specific SNP markers for QPE resistance also followed Mendelian segregation in the five F2 populations. For the second objective, six QPE-resistant inbred lines showed transient leaf injury at 1× (120 g ai ha−1) or 2× (240 g ai ha−1) field rates 7 and 21 d after treatment (DAT). However, a trend of reduced injury (recovery) from 7 through 33 DAT was observed for all breeding material. No differences in grain yield were found between untreated QPE-resistant lines and those treated with 1× or 2× QPE field rate. Single gene inheritance and good levels of QPE herbicide field resistance in different genetic populations suggest feasibility for rapid and effective development of new QPE-resistant varieties and effective stewardship of the Provisia™ technology.