Sicklepod seed production and germination were evaluated in density and weed-free period studies without herbicide treatment and after imazaquin or metribuzin plus chlorimuron were applied PRE in soybean. Neither herbicide nor sicklepod density affected sicklepod seed germination, but delaying emergence of sicklepod from 0 wk to 8 wk after soybean emergence reduced subsequent sicklepod seed germination from 92% to 48%. Increasing sicklepod density from two to eight plants per row m reduced sicklepod seeds per plant, but increased sicklepod seeds per m2, regardless of herbicide. Extending the weed-free period from 0 to 8 wk reduced sicklepod seeds per plant and seeds per m2. Imazaquin and chlorimuron plus metribuzin reduced sicklepod seeds per m2 more than 50% at 0 or 2 wk weed-free intervals, compared with nontreated plants at these same intervals.

Several sulfonylurea herbicides are labeled for use on established bermudagrass or seashore paspalum, but label recommendations for many of these chemicals vary for sprigged turf. The objective of this study was to determine the safety of various sulfonylurea herbicides on newly planted, ‘Tifway’ bermudagrass and ‘Aloha’ seashore paspalum sprigs in Arkansas and Louisiana. Treatments were arranged as a five by two by two factorial with five herbicides (foramsulfuron at 29 and 59 g ai ha−1, halosulfuron at 35 and 70 g ai ha−1, metsulfuron at 21 and 42 g ai ha−1, sulfosulfuron at 66 and 131 g ai ha−1, and trifloxysulfuron at 28 and 56 g ai ha−1), two herbicide rates (low and high), and two application timings at 2 or 4 wk after sprigging (WAS). There was no discernable herbicide injury to, or reduction in, Tifway bermudagrass coverage in Arkansas, regardless of herbicide, application timing, or application rate. Trifloxysulfuron and metsulfuron were more injurious than other herbicides in Louisiana when applied at 2 WAS to Tifway bermudagrass, but injury levels were acceptable (< 15%), and there was no long-term reduction in establishment. Metsulfuron or halosulfuron applied at 2 or 4 WAS and sulfosulfuron applied at 4 WAS allowed > 90% establishment of Aloha seashore paspalum at both locations. Both trifloxysulfuron and foramsulfuron were injurious to seashore paspalum and reduced its establishment. These results suggest that sulfonylurea herbicides can be safely applied shortly after sprigging to Tifway bermudagrass and that metsulfuron, halosulfuron, and sulfosulfuron could be useful herbicides for establishing Aloha seashore paspalum from sprigs.

Field and pot experiments were conducted in Greece to study the occurrence of resistance in silky windgrass to acetolactate synthase (ALS)- and acetyl-CoA synthase (ACCase)-inhibiting herbicides. Twenty-four populations of silky windgrass were examined in whole-plant response experiments. High levels of field-evolved resistance to chlorsulfuron (0% to 28% control in terms of fresh weight reduction) with the recommended field rates were confirmed in most silky windgrass populations. However, other ALS inhibitors, such as pyroxsulam and a premix of mesosulfuron-methyl and iodosulfuron, provided adequate control (76% to 100% in terms of fresh weight reduction) of most populations, except eight silky windgrass populations that were found to be cross-resistant to all ALS-inhibiting herbicides tested (i.e., chlorsulfuron, commercial mixture of mesosulfuron-methyl plus iodosulfuron, and pyroxsulam). Conversely, most silky windgrass populations were controlled effectively (90% to 100% in terms of fresh weight reduction) with the recommended field rates of ACCase inhibitors cycloxydim, clethodim, and pinoxaden, but five populations were also found to be resistant to clodinafop-propargyl (10% to 68% control in terms of fresh weight reduction). The ALS gene sequencing of the eight silky windgrass populations, with cross-resistance to ALS inhibitors, revealed a point mutation at the Pro-197 position, causing amino acid substitution by Ser or Thr in the ALS enzyme. Overall, chlorsulfuron and clodinafop-propargyl were selecting agents of field-evolved multiple resistance to ALS- and ACCase-inhibiting herbicides in five silky windgrass populations. As the available postemergence-applied chemistries/modes of action registered for grass weed control in cereals are rather limited, adopting integrated management practices and implementing proactive and reactive measures to delay the evolution of resistant populations is essential.

Methyl bromide (MBr) has been an industry standard for soil fumigation in a multitude of crops for decades. However, it has been banned by the United Nations Environment Programme, and alternatives to MBr must be implemented to sustain productivity in many vegetable crops that depend on soil fumigation. One alternative that has been implemented in some areas is methyl iodide (MeI). Efficacy of MeI has been demonstrated on many pest species and has been generally similar to MBr. Methyl iodide is a costly material, which has likely limited its adoption. Virtually impermeable film (VIF) and totally impermeable film (TIF) provide greater fumigant retention than low-density and high-density polyethylene film, which can allow for reduced fumigant application rates while maintaining fumigant efficacy. The objectives of this research were to evaluate TIF with reduced rates of shank-applied MeI : chloropicrin (Pic) (50 : 50 w/w) for the control of yellow nutsedge in tomato. Treatments included a standard rate of MeI : Pic (93.3 L ha−1 [178 kg ha−1 broadcast]) under VIF and TIF, three reduced rates (37.3, 56, 74.6 L ha−1 [71.2, 106.8, 142.5 kg ha−1 broadcast, respectively]) under TIF, and a nontreated control under TIF. Results indicate fumigant use rates may be reduced from a standard 93.3 L ha−1 under VIF to 37.3 L ha−1 (60% reduction) under TIF while providing yellow nutsedge control and maintaining tomato yields.

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.

Field studies were conducted near College Station, TX, in 2006 and 2007 to evaluate the economic impact of common sunflower interference in field corn. A density of one common sunflower per 6 m of crop row caused a yield loss of 293 kg ha−1. Estimated losses at a net corn price of $0.08 kg−1 was $92 ha−1 for infestation levels of four common sunflower plants per 6 m of row. Corn yield was increased by 32 kg ha−1 by each 1,000 plant ha−1 increase in corn planting density. Corn planting densities of 49,400 and 59,300 plants ha−1 provided the greatest net returns with or without the presence of common sunflower competition. Corn yields were reduced by extended duration of sunflower competition, with losses exceeding 1,500 kg ha−1 per week and increasing in magnitude at a decreasing rate throughout the growing season. Herbicide treatments provided net returns of $600 to $1,300 ha−1 above no weed control in both 2006 and 2007. Net returns of $609 and $653 ha−1 were obtained without the use of any herbicide for sunflower control. Determining the economic impact of common sunflower interference in field corn allows producers to estimate the overall net return on the basis of duration of common sunflower interference and density, while considering varying net corn prices, crop planting density, and herbicide application costs.

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.

Smooth pigweed is one of the most troublesome weeds in Argentina. The objective of this study was to evaluate the sensitivity of 50 smooth pigweed accessions to fomesafen, topramezone, glyphosate, 2,4-D, and dicamba. Accessions were collected from soybean fields in various cropping areas in Argentina. The herbicide treatments included 2,4-D (1,140 g ae ha−1), dicamba (560 g ae ha−1), fomesafen (250 g ai ha−1), topramezone (34 g ai ha−1), and glyphosate (1,080 g ae ha−1). Plant survival was evaluated 30 d after each treatment application. Of the smooth pigweed accessions tested, 84% and 76% were susceptible (0% survival) to 2,4-D and dicamba, respectively. More than 90% of the accessions showed high (>60%) survival to glyphosate. While none of the accessions showed total sensitivity (0% survival) to the other herbicides evaluated, 43% and 72% of the accessions showed greater than 60% survival to fomesafen and topramezone, respectively. The differences in survival among accessions confirm the existence of genetic variability in Argentinian smooth pigweed and suggest that weed management practices should be prioritized to preserve the efficacy of these commonly used herbicides.

The benefits of no-till fallow, which include reduced soil erosion, improved soil health, and increased stored soil water, are in jeopardy because of the widespread development of glyphosate resistance in Russian thistle. The objective of this research was to evaluate the efficacy of soil-active, residual herbicides for Russian thistle control in no-till fallow. The combinations of sulfentrazone + carfentrazone and flumioxazin + pyroxasulfone, and metribuzin alone were each applied in late fall, late winter, and split-applied in late fall and late winter at three sites: Adams, OR, in 2017–2018; Lind, WA, in 2018–2019; and Ralston, WA, in 2019–2020. All treatments provided good to excellent control of the initial flush of Russian thistle when assessed in mid-May, except the late-fall application of metribuzin at all three sites, and the late-fall application of sulfentrazone + carfentrazone at Adams. Cumulative Russian thistle densities, evaluated monthly throughout the fallow season, were lowest for the sulfentrazone + carfentrazone treatments, except for the late-fall application at Adams. However, flumioxazin + pyroxasulfone and metribuzin provided greater control of tumble mustard and prickly lettuce than did sulfentrazone + carfentazone. Sulfentrazone + carfentrazone, flumioxazin + pyroxasulfone, and metribuzin can all be used for Russian thistle control in fallow. To reduce the risk for crop injury to subsequently planted winter wheat, a late-fall application of sulfentrazone + carfentrazone may be the preferred treatment in low-rainfall regions where winter wheat–fallow is commonly practiced. A late-winter application may be preferred in higher rainfall regions where a 3-year rotation (e.g., winter wheat–spring wheat–fallow) is common. Flumioxazin + pyroxasulfone should be considered if other broadleaf weeds, such as tumble mustard or prickly lettuce, are of concern. The use of these soil-applied herbicides will reduce the need for the frequent application of glyphosate for Russian thistle control in no-till fallow.

Common bean and azuki bean are poor competitors with weeds and demonstrate sensitivity to herbicides used for weed control in soybean. S-metolachlor, flufenacet, and acetochlor are categorized as Group 15 herbicides and provide control of multiple annual grass and select small-seeded broadleaf weeds. By way of field trials near Exeter and Ridgetown, Ontario, in 2019, 2020, and 2021, four dry bean market classes (azuki, kidney, small red, and white bean) were evaluated for their tolerance to 1× established label rates and 2× rates of S-metolachlor (1,600 and 3,200 g ai ha−1), flufenacet (750 and 1,500 g ai ha−1) and acetochlor (1,700 and 3,400 g ai ha−1) applied preplant incorporated (PPI). Injury was evaluated by assessing visible injury symptoms, density, shoot biomass, height, seed moisture content, and seed yield. Azuki bean was more sensitive to the Group 15 herbicides than other dry bean market classes; the Group 15 herbicides caused a 12% reduction in azuki bean growth at 2 wk after emergence; growth reduction was ≤2% in the other bean classes. Flufenacet (2× rate) was the most injurious treatment, causing a 27% reduction in azuki bean yield. This study concludes that kidney, small red, and white bean have a sufficient margin of crop safety to flufenacet, acetochlor, and S-metolachlor applied PPI. Azuki bean was sensitive to flufenacet; additional research is needed to investigate azuki bean tolerance to acetochlor and S-metolachlor applied PPI.

The extensive and intensive use of herbicides has resulted in the spread of herbicide-resistant weeds in many crop production systems; therefore, it is imperative to devise new organic weed control methods. Recently, the application of spent coffee grounds (SCG) in agricultural fields has been found to inhibit plant growth and germination and is thus considered a potentially effective weed control measure. This study aimed to evaluate the effects of different amounts and methods of SCG application on weed growth through field experiments. The field experiments were conducted in an upland field converted from a paddy in western Japan. The results show that the plow-in application of over 10 kg m−2 of SCG and mulching application of 20 kg m−2 decreased the weed dry weight compared with the control. In addition, the growth of weed species of families other than Gramineae, such as wingleaf primrose-willow and horseweed, was not significantly affected by SCG application. Weed species of families other than Gramineae are dominant in some upland fields. Hence, the inhibitory effect of SCG on weeds may be lower in original upland fields than in the upland field converted from paddy field that was investigated in the present study. Overall, this study demonstrated that the plow-in application of 10 kg m−2 of SCG every 4 mo was effective for weed control in an upland field converted from a paddy field. Because SCG worked against grass weeds under the specific conditions in this study, it would be valuable to explore other potential applications of this novel means of weed control.

Management of volunteer horseradish is a challenge when it is grown in rotation with other crops, such as corn and soybean. Although volunteer horseradish may not cause yield loss, these plants serve as hosts for various soilborne pathogens that damage subsequent horseradish crops. In addition to volunteer horseradish, glyphosate-resistant Palmer amaranth is becoming difficult to control in southwestern Illinois, as a consequence of the plant’s ability to withstand glyphosate and drought, produce many seeds, and grow rapidly. Field studies were conducted to evaluate the effect of glyphosate and dicamba on volunteer horseradish and Palmer amaranth control in 2014 and 2015. Glyphosate alone (1,265 and 1,893 g ae ha−1) and glyphosate plus dicamba at the high rate (1,680 g ae ha−1) provided the greatest volunteer horseradish control, ranging from 81% to 89% and 90% to 93%, respectively. Measures of root biomass reduction followed similar trends. Glyphosate alone provided the greatest reduction in volunteer horseradish root viability (79% to 100%) but was similar in efficacy to applications of glyphosate plus dicamba in most comparisons. Efficacy of PRE-only applications on Palmer amaranth control ranged from 92% to 99% control in 2014 and 68% to 99% in 2015. However, PRE-only applications were often similar in efficacy to PRE followed by (fb) glyphosate plus dicamba applied POST. Treatments containing flumioxazin did not control Palmer amaranth as well as other treatments. POST applications alone were not effective in managing Palmer amaranth. Many of the PRE fb POST treatment options tested will improve resistance management over PRE-only treatments, provide control of Palmer amaranth, and allow horseradish to be planted the following spring.

Branched broomrape, an obligate root parasitic weed, has recently re-emerged in tomato fields in several California counties. California produces more tomato than any other state, and the outbreak of this noxious weed could potentially wreak havoc on the industry’s economy. Preventive measures must be taken to stop or reduce the spread of branched broomrape seeds to other areas. Branched broomrape can produce thousands of tiny seeds, which can easily spread with farm machinery over short and long distances. To prevent branched broomrape seed dispersal, sanitation and disinfection of farm equipment are necessary before entering a new farm. We tested the effectiveness of various ammonium compounds, including didecyl dimethyl ammonium chloride (DDAC), alkyl dimethyl benzyl ammonium chloride (ADBC), didecyl dimethyl ammonium bromide (DDAB), ammonium bromide (AB), and ammonium chloride (AC) on prevention of branched broomrape seed germination. Dose-response analysis showed that three chemical products, ADBC, DDAB, and DDAC, could completely inhibit branched broomrape seeds (potentially making them nonviable) at 1%, 1%, and 10% wt/vol concentrations, respectively. These three compounds were further tested in an exposure duration experiment that additionally included Egyptian broomrape. Only 10 min of exposure to these compounds was needed to prevent germination of both branched and Egyptian broomrape seeds at 1% (ADBC, DDAB) and 10% wt/vol (DDAC). Lower concentrations can provide similar inhibition effects when combined with longer exposure times. Egyptian broomrape seeds were more sensitive than branched broomrape seeds. Findings suggest that quaternary ammonium compounds could be used as potential sanitation agents to disinfect agriculture machinery from branched and Egyptian broomrape seeds.

Delaying cover crop termination until cash crop planting (i.e., planting green) is an emerging no-till practice. Improved management recommendations are needed for optimizing weed suppression benefits while minimizing other pest, fertility, and crop management risks when planting green in corn production systems. In a 2-yr field experiment, we evaluated the interaction between cereal rye residue management tactics (standing residue, roll-crimping, roll-crimping with row cleaners) and herbicide programs (1-pass preemergence [PRE], 2-pass postemergence [POST]) when planting green on weed recruitment spatial patterns and corn performance compared to standard termination (14 d preplant [DPP]) and ryelage harvest (14 DPP) practices. In a 2-yr on-farm experiment, we evaluated corn performance in response to the same residue management tactics. Cereal rye biomass production varied significantly across years in on-station experiments, with average (4.9 Mg ha−1) and anomalous (9.9 Mg ha−1) levels observed in 2020 and 2021, respectively. In 2020, planting green with an integrated roll-crimper/row cleaner system resulted in greater intrarow weed density compared with planting green into standing cereal rye. Interrow weed density was lower when roll-crimping was employed compared to early termination (14 DPP). Planting green into standing cereal rye resulted in greater mean corn height (V5 stage) compared to other treatments, but corn population and yield did not differ. In 2021, few differences in weed recruitment patterns were observed, but corn population and yield were significantly lower in planting green treatments compared to early termination. In both years, late-season weed biomass was lower in two-pass POST programs compared to one-pass PRE programs. On-farm trials showed that planting green into standing residue increases corn height and can reduce corn populations, which may lead to reduce yields. Our results suggest that management recommendations for optimizing herbicide application timing should consider intrarow and interrow weed recruitment dynamics associated with residue management tactics needed to optimize corn performance.

Weed management is one of the major challenges responsible for growers’ reluctance to switch from conventional to organic vegetable production. Competition from uncontrolled weeds can significantly reduce the yield and water use efficiency (WUE) of vegetable crops. A field study was conducted during the summers of 2019 and 2020 at the Quaker Research Farm of Texas Tech University, in Lubbock, TX, to determine physiology, plant growth, yield, soil water depletion pattern, and WUE of pumpkin as affected by five weed control treatments: 1) ammonium nonanoate 5% ai, 2) ammonium nonanoate 6% ai, 3) clove oil + cinnamon oil 4.5% ai, 4) clove oil + cinnamon oil 9% ai, and 5) an untreated control. Each plot received the same herbicide treatment at 20 and 30 d after planting (DAP). The experiment was conducted in a randomized complete block design with four replications of each treatment. Both herbicides resulted in significant weed suppression compared to the untreated control and weed control was 88% to 98% with ammonium nonanoate and 39% to 69% with clove oil + cinnamon oil. Photosynthesis rate, stomatal conductance, shoot dry biomass, average fruit weight, total fruit yield, and WUE of pumpkin were significantly higher in plants that were treated with ammonium nonanoate compared to the untreated control. All the aforementioned parameters were not significantly different between clove oil + cinnamon oil and the untreated control. Use of higher active ingredient concentration did not improve the performance of either herbicide. Soil water depletion and evapotranspiration were comparable among all the treatments. Based on the results, ammonium nonanoate at its lower concentration could be an option for effective weed control, and for improving fruit yield and WUE of pumpkin.

Herbicide resistance coupled with a dearth of selective herbicide options has increased the complexity of annual bluegrass control in hybrid bermudagrass putting greens. Cumyluron, endothall, and methiozolin are herbicides that control annual bluegrass by inhibiting novel sites of action compared with the herbicides currently used for turfgrass management in the United States. However, peer-reviewed literature contains no information on hybrid bermudagrass putting green tolerance to these herbicides. Sixteen field studies were established on eight golf greens in Midlothian, VA, in 2021 and 2022 to evaluate effects of cumyluron, endothall, methiozolin, pronamide, and trifloxysulfuron on bermudagrass spring transition. The 16 studies were split equally between initiation during full dormancy versus mid-spring transition. Methiozolin applied at 500 and 1,000 g ai ha−1 typically increased the heat units (growing degree days with a base temperature of 15 C) required for hybrid bermudagrass to visibly achieve 90% green coverage (T90) when applied to fully dormant hybrid bermudagrass. This delay in green coverage was more pronounced at sites where hybrid bermudagrass vigor was seemingly reduced via abiotic stressors. Endothall was generally more injurious than all other treatments when applied to hybrid bermudagrass during mid-transition. Endothall applied at 840 g ai ha−1 injured hybrid bermudagrass for 0 to 9 d over a threshold of 30% (DOT30), depending on location. In two site-years characterized by increased abiotic stress, methiozolin applied at 1,000 g ai ha−1 caused 44 DOT30. Cumyluron never injured hybrid bermudagrass by more than 30% or delayed T90 regardless of application timing. These results indicate that methiozolin should be applied only within labeled rates to actively growing hybrid bermudagrass putting greens, cumyluron can be safely applied at 6,450 g ai ha−1 to dormant or actively growing bermudagrass greens, and endothall applications should be limited to dormant bermudagrass greens unless transient phytotoxicity is acceptable.

In 1998, 1,260 soil samples were collected from 63 of 99 Iowa counties to characterize the weed seedbanks in fields under the conservation reserve program (CRP) and adjacent fields under continuous cultivation. Five annual grass and 13 broadleaf weed species were identified in both the CRP and adjacent cultivated fields. Seedbank differences between CRP and adjacent cultivated fields were evident only for foxtails, common lambsquarters, pigweeds, and sweetclover, with the average of 3,288, 10,681, 38, and 1,709 seeds/m2, respectively; the corresponding seed population in adjacent CRP fields was 59, 57, 1,924, and 74%, respectively. However, weed species diversity was not significantly different between fields in CRP and continuous cultivation. Only CRP fields in the northwest Iowa crop-reporting district had a higher foxtail species seed population (4,915 seeds/m2) than the adjacent cultivated fields (1,782 seeds/m2). Land under CRP in northern (N), eastern, and southern (S) districts had 58% (4,158 seeds/m2), 6% (312 seeds/m2), and 18% (594 seeds/m2) of the continuously cultivated foxtail species seedbank. Common lambsquarters seed populations were 4,128 and 3,801 seeds/m2 in the cultivated fields of the N and central (C) districts, compared with 772 and 252 seeds/m2 in adjacent CRP fields, respectively. Pigweed species seeds were more numerous in the cultivated fields than in adjacent CRP fields in the northeast, C, and S Iowa districts. Sweetclover seed population was consistently higher in CRP land because it was included as part of the CRP covers seeding. Overall, broadleaf weed seeds comprised 90% of the seedbanks in both CRP and adjacent cultivated land. A competitive cover crop canopy in CRP probably reduced weed seedbanks by suppression of weeds and seed production. Also, annual seed production, differences in weed biology, and differential herbicide performance in cultivated fields may have contributed to higher seed populations.

Air-assist nozzles that use pneumatic energy to help atomize the spray liquid were reviewed. These nozzles use larger orifices than conventional hydraulic nozzles for low-volume applications. By changing the air pressure, various droplet sizes can be produced without changing nozzle tips. Several systems use air to transport the atomized spray to specific target sites. Various air volumes and velocities have been evaluated in these systems. Preliminary research indicated that air can improve canopy penetration and can cover the entire plant more uniformly. Undersides of leaves can be treated easier with air-assist systems compared to conventional applications with hydraulic nozzles.

The effect of glyphosate applied as a desiccant to field bindweed-infested alfalfa in the final year of seed production was examined in field experiments near Lovelock, NV. Glyphosate at 2.5 and 5.0 kg ae/ha flat fan applied was equal to and/or superior to dinoseb for desiccation of foliage, respectively. Alfalfa seed yield and quality following glyphosate treatment were similar to that of dinoseb-treated alfalfa. Glyphosate treatment reduced some alfalfa and field bindweed stands. A beneficial interaction between low-volume control droplet application (CDA) and glyphosate was not evident.

Field experiments were conducted in 1998, 1999, and 2000 at two locations (Harrow and Ridgetown) in southwestern Ontario to determine the biologically effective rates (I90) of a commercial formulation of flufenacet plus metribuzin for weed control and processing tomato tolerance. At the proposed label use rate, flufenacet plus metribuzin provided excellent (≥90%) early-season (22 to 29 d after planting) control of velvetleaf, good (80 to 89%) control of barnyardgrass and redroot pigweed, and fair (60 to 79%) control of common lambsquarters. Flufenacet plus metribuzin provided fair late-season (59 to 97 d after planting) control of redroot pigweed and common lambsquarters and poor (≤59%) control of barnyardgrass and velvetleaf. At Harrow and Ridgetown, I90 values for early-season weed control ranged from 70 to 1,300 g ai/ha and 50 to 1,900 g ai/ha, respectively. Flufenacet plus metribuzin provided poor weed control at Ridgetown. This result was not attributable to higher weed density or particular weed species but may have been caused by lack of rainfall and too low application rates for the medium-textured soil type. It is estimated that flufenacet plus metribuzin at 1,400 g/ha can control green foxtail season-long, whereas barnyardgrass and common lambsquarters would require 1,900 g/ha. Season-long control of velvetleaf and redroot pigweed would require application rates of 3,200 and 7,100 g/ha, respectively. Only slight early-season crop injury was observed, which was not reflected in yields. Optimum yields of tomatoes were obtained at Harrow at rates lower or slightly higher than the registered rates for corn and soybean. Tomato yields were higher at Harrow than at Ridgetown, which may have been due to differences in soil texture. Tomatoes grown in a medium-textured (Ridgetown) soil appeared to be less competitive against weeds than those grown in a coarse-textured soil (Harrow).