The colloidal state (stable, coagulated, or gel-like) and the rheological properties of Na-rich montmorillonite (Wyoming) dispersions are strongly influenced by organic cations. This effect is shown for homologous organic cations: alkyl trimethylammonium ions, paraquat, diquat, alkyl bispyridinium ions, and the triphenylmethane dyes crystal violet, methyl green, and tris (tri-methylammonium phenyl) methane chloride. The critical coagulation concentrations, cK, are small (often < 1 mmol/L) because the cations are enriched in the Stern layer and influence the solvent structure near the surface. The strong adsorption of the counterions at the clay-mineral surface causes cK values to increase with the solid content. Charge reversal (recharging) of the particles was observed with the longer chain alkyl trimethyl-ammonium ions, dodecyl bispyridinium ions, and crystal violet. Other cations reduced the electrophoretic mobility to zero but positive particle charges were not observed.

The plastic viscosity increased sharply at the critical coagulation concentration and showed a minimum slightly below cK, which was caused by the electroviscous effect. Yield values were developed at concentrations above cK. In most cases, yield values reached a plateau where the amount of organic cations was ∼0.5 mmol/g, i.e., about half of the cation-exchange capacity. The cK values decreased with increasing hydrophobicity of homologous compounds, but the yield value showed maxima at intermediate chain lengths. The yield value of several 0.5% dispersions was high, e.g., dodecyl trimethylammonium ions, 71 Pa; paraquat, 100 Pa; diquat, 42 Pa; hexyl bispyridinium ions, 53 Pa (vs. Ca2+, 0.2 Pa; Al3+, 0.7 Pa). The storage modulus as a function of the number of organic cations changed in a similar way as the yield value, and high values were observed (e.g., dodecyl trimethylammonium ions, hexyl bispyridinium ions: 1000 Pa, paraquat: >4000 Pa). Thus, dispersions with high viscosity, yield value, and pronounced viscoelasticity are obtained by coagulating Na-rich montmorillonite dispersions with organic cations.

Postemergence herbicides used to control weeds in the space between raised, plastic-covered beds in plasticulture production systems are typically banded, and herbicides are applied to weeds and to where weeds do not occur. To reduce the incidence of off-targeted applications, the University of Florida developed a smart-spray technology for row middles in plasticulture systems. The technology detects weed according to categories and applies herbicides only where the weeds occur. Field experiments were conducted at the Gulf Coast Research and Education Center in Balm, FL, in fall 2021 and spring 2022. The objective was to evaluate the efficacy of postemergence applications of diquat and glyphosate in row middles in jalapeno pepper fields when banded or applied with smart-spray technology. The overall precision of the weed detection model was 0.92 and 0.89 for fall and spring, respectively. The actuation precision achieved was 0.86 and 1 for fall and spring, respectively. No significant differences were observed between banded and targeted applications either with glyphosate or diquat in terms of broadleaf, grass, and nutsedge weed density. No significant pepper damage was observed with either herbicide or application technique. The smart-spray technology reduced herbicide application volume by 26% and 42% in fall and spring, respectively, with no reduction in weed control or pepper yield compared to a banded application. Overall, the smart-spray technology reduced the herbicide volume applied with no reductions in weed control and no significant effects on crop yield.

Winter annual weeds begin to germinate as zoysiagrass enters winter dormancy in autumn. These weeds can suppress zoysiagrass shoot development the following spring through competition for sunlight, moisture, and nutrients. Previous research involving winter annual weed control in dormant turfgrass has been conducted primarily on bermudagrass, but less is known about how various herbicides used for this purpose will influence zoysiagrass after dormancy transition. Two field studies were conducted over 7 site-years between 2016 and 2020 to evaluate 17 herbicide treatments that are typically marketed for broadleaf weed control in spring and 18 herbicide treatments that are typically marketed for annual bluegrass control during winter for their effects on a variety of weeds and semidormant ‘Meyer’ and dormant ‘Zeon’ zoysiagrass, respectively. Glufosinate, glyphosate + simazine, and indaziflam + simazine controlled Persian speedwell by more than 90% and control was significantly greater with auxin-type and other herbicide combinations. Dandelion and Persian speedwell were better controlled with a combination of simazine and glyphosate than when glyphosate was applied alone. Glufosinate controlled dandelion, hairy bittercress, and Persian speedwell more effectively than glyphosate. In Meyer zoysiagrass, glyphosate and glufosinate controlled annual bluegrass equivalently, whereas in Zeon zoysiagrass, glyphosate controlled annual bluegrass better than glufosinate did. Foramsulfuron or treatments that contained simazine resulted in >90% control of annual bluegrass. A flumioxazin admixture with diquat, glufosinate, or glyphosate improved annual bluegrass control. Herbicide treatments that contain diquat, glufosinate, glyphosate, and metsulfuron alone or in a tank-mix should not be applied to Meyer zoysiagrass with 5% visual green turf cover due to high injury potential. In both studies, glufosinate was more injurious to Meyer and Zeon zoysiagrass than glyphosate. Overall, several herbicides that control annual bluegrass or broadleaf weeds can be safely applied to Zeon zoysiagrass during dormancy or Meyer zoysiagrass during post-dormancy transition.

Water is the primary carrier for herbicide applications. Spray water qualities such as pH, hardness, temperature, or turbidity can influence herbicide performance and may need to be amended for optimum weed control. Water quality factors can affect herbicide activity by reducing solubility, enhancing degradation in the spray tank, or forming herbicide-salt complexes with mineral cations, thereby reducing the absorption, translocation, and subsequent weed control. The available literature suggests that the effect of water quality varies with herbicide chemistry and weed species. The efficacy of weak-acid herbicides such as glyphosate, glufosinate, clethodim, sethoxydim, bentazon, and 2,4-D is improved with acidic water pH; however, the efficacy of sulfonylurea herbicides is negatively impacted. Hard-water antagonism is more prevalent with weak-acid herbicides, and trivalent cations are the most problematic. Spray solution temperature between 18 C and 44 C is optimum for some weak-acid herbicides; however, their efficacy can be reduced at relatively low (5 C) or high (56 C) water temperature. The effect of water turbidity is severe on cationic herbicides such as paraquat and diquat, and herbicides with low soil mobility such as glyphosate. Although adjuvants are recommended to overcome the negative effect of spray water hardness or pH, the response has been inconsistent with the herbicide chemistry and weed species. Moreover, information on the effect of spray water quality on various herbicide chemistries, weed species, and adjuvants is limited; therefore, it is difficult to develop guidelines for improving weed control efficacy. Further research is needed to determine the effect of spray water factors and develop specific recommendations for improving herbicide efficacy on problematic weed species.

Herbicide-resistant weed management is one of the greatest agricultural challenges in crop production. Thus, the quick identification of herbicide-resistant weeds is extremely important for management. This study aimed to evaluate resistance to PSI-inhibiting herbicides (diquat) and physiological response to paraquat application in Sumatran fleabane [Conyza sumatrensis (Retz.) E. Walker; syn.: Erigeron sumatrensis Retz.]. The research was conducted with two C. sumatrensis biotypes, one susceptible and the other with multiple resistance to herbicides from five different modes of action (glyphosate, paraquat, diuron, saflufenacil, and 2,4-D). A dose–response assay was carried out to evaluate herbicide resistance to diquat in the paraquat-resistant C. sumatrensis biotype. The enzymatic activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), hydrogen peroxide (H2O2) content, and chlorophyll a (Chl a) fluorescence were measured in both biotypes after paraquat (400 g ai ha−1) application. The dose–response assay confirmed resistance of C. sumatrensis to diquat with resistance factor levels of 26-fold and 6-fold for LD50 and GR50 values, respectively, compared with the susceptible biotype. Accumulation of H2O2 occurred more rapidly in the paraquat-susceptible biotype than in the resistant one. Paraquat treatment caused an increase in SOD and APX activity in the susceptible biotype, but antioxidant enzyme activities were unaffected by paraquat in the resistant one at 5 h after application (HAA). Chl a fluorescence increased across the first 4 HAA in both resistant and susceptible biotypes. However, at 24 HAA, the resistant biotype showed a decline in fluorescence close to untreated plants, while the susceptible biotype died, confirming resistance to diquat in the paraquat-resistant C. sumatrensis biotype. The paraquat-resistant biotype does not induce antioxidative enzymes, as a possible mechanism of resistance to paraquat, but shows rapid recovery of photosynthesis and continuous growth when subjected to paraquat, while the paraquat-susceptible biotype does not survive.

Hairy fleabane and horseweed are pervasive weed species in agriculture. Glyphosate-resistant (GR) and glyphosate/paraquat–resistant (GPR) biotypes challenge current management strategies. These GR and GPR biotypes have non–target site resistance, which can confer resistance to herbicides with different sites of action (SOAs). This study’s objective was to characterize the response of GR, GPR, and glyphosate/paraquat–susceptible (GPS) biotypes of both weed species to herbicides with a different SOA. Whole-plant dose–response bioassays indicated a similar response among tested biotypes of both weed species to rimsulfuron, dicamba, hexazinone, glufosinate, flumioxazin, saflufenacil, or mesotrione. The hairy fleabane GR and GPR biotypes were 2.7- and 2.9-fold resistant to 2,4-D relative to the GPS biotype (GR50 766.7 g ai ha–1), confirming 2,4-D resistance in hairy fleabane for the first time in California. The GR and GPR biotypes were not cross-resistant to dicamba. No differences in response to 2,4-D were observed among horseweed biotypes with a GR50 ranging from 150.2 to 277.4 g ai ha–1. The GPR biotypes of both species were cross-resistant to diquat, with a 44.0-fold resistance in hairy fleabane (GR50 863.7 g ai ha–1) and 15.6-fold resistance in horseweed (GR50 563.1 g ai ha–1). The confirmation of multiple resistances to glyphosate, paraquat, and 2,4-D in hairy fleabane curtails herbicide SOA alternatives and jeopardizes resistance management strategies based on herbicide rotation and tank mixtures, underscoring the critical need for nonchemical weed control alternatives.

Cowpea bean (Vigna unguiculata) is usually submitted to pre-harvest burndown with herbicides aiming to an early harvest. We aimed to quantify the residues of paraquat, diquat, glufosinate-ammonium and glyphosate in cowpea grains subjected to two timings of pre-harvest burndown. Three identical experiments were installed in Dourados (Lat. 22° S), Sinop (Lat. 11° S) and Teresina (Lat. 05° S), Brazil, comprising the pre-harvest burndown of cowpea bean with these herbicides, applied either with 50 or 75% of the pods dry and ready for harvest. As hotter and drier the location as slower the herbicide dissipation. Glyphosate should not be used for pre-harvest burndown of cowpea. Herbicide residues were above the maximum levels stated by the Brazilian legislation when applied with 50% dry pods. Burndown herbicides aiming to speed harvest should be applied with at least 75% dry pods in cowpea to ensure safe herbicide residue levels in grains.

Field trials were conducted in North Carolina in 2017 and Louisiana and Mississippi in 2018 to determine the effect of pretransplanting applications of diquat on sweetpotato crop tolerance, yield, and storage root quality. In North Carolina treatments consisted of two rates of diquat (560 or 1,120 g ai ha−1) alone or mixed with 107 g ai ha−1 flumioxazin and applied 1 d before transplanting (DBP), sequential applications of diquat (560 or 1,120 g ha−1) 1 and 17 DBP, 107 g ha−1 flumioxazin alone, and a nontreated check. In Louisiana and Mississippi treatments consisted of diquat (560 or 1,120 g ha−1) applied 1 DBP either alone or followed by (fb) rehipping rows or 107 g ha−1 flumioxazin immediately prior to transplanting. Additional treatments included 546 g ha−1 paraquat applied 1 DBP and a nontreated check. In North Carolina injury was ≤3% for all treatments through 23 d after transplanting (DAP), and no injury was observed after 23 DAP. Visual sweetpotato stunting pooled across the Mississippi and Louisiana trials ranged from 1% to 14%, 0% to 6%, and 0% to 3% at 2, 4, and 6 wk after planting (WAP), respectively, and no crop injury was observed after 6 WAP. Diquat applied 1 DBP and not fb rehipping resulted in greater crop injury (12%) than comparable treatments that were rehipped (2%). In North Carolina single and sequential diquat applications resulted in reduced No. 1 sweetpotato yield (24,230 and 24,280 kg ha−1, respectively) compared with the nontreated check, but No. 1 yield when diquat plus flumioxazin (26,330 kg ha−1) was used was similar to that of the nontreated check. No. 1 yield did not differ by treatment in Louisiana and Mississippi.

Florida strawberry growers apply the nonselective herbicide paraquat for crop termination. Alternative herbicides are desirable because of recent label restrictions on paraquat use and the occurrence of three paraquat-resistant weed species found in strawberry fields. Field experiments were conducted at the Gulf Coast Research and Education Center at Balm, FL, to compare the efficacy of diquat, paraquat, and glufosinate and determine the optimal rate for strawberry termination. Peak control occurred at 14 d after treatment and strawberry foliage desiccation increased as herbicide rate increased. The highest rate of diquat (2,240 g ai ha−1) and paraquat (2240 g ai ha−1) provided 59% and 79% strawberry control, respectively, and 39% and 77% strawberry foliage desiccation, respectively. The highest rate of glufosinate (2,624 g ai ha−1) provided 82% and 84% strawberry control and desiccation, respectively. Regression analysis determined the rates required to provide 50% strawberry control measured 1,100, 650, and 550 g ha−1 for diquat, paraquat, and glufosinate, respectively, whereas the rates required to provide 80% strawberry control were greater than 2,240 g ha−1 for the first two herbicides and 2,020 g ha−1 for glufosinate. Herbicide rates required to provide 50% strawberry foliage desiccation measured 480, 550, and 330 g ha−1 for diquat, paraquat, and glufosinate, respectively, whereas the rates required to provide 80% strawberry foliage desiccation were greater than 2,240 g ha−1 for the first two herbicides and 1150 g ha−1 for glufosinate. Overall, these results indicate glufosinate is the most effective herbicide for strawberry termination, whereas diquat is the least effective herbicide.

Carolina redroot is a common weed of New Jersey cranberry beds that competes with crops for nutritional resources but also serves as a food source for waterfowl. Greenhouse studies were conducted in 2017 in Chatsworth, NJ, to determine control of Carolina redroot aboveground vegetation and rhizome production with 10 herbicide active ingredients. Herbicides were applied as a single application on 10- to 15-cm-tall plants. Diquat at 560 g ai ha−1 and mesotrione at 280 or 560 g ai ha−1 controlled more than 90% of emerged shoots at 63 d after treatment (DAT). Aboveground vegetation control at 63 DAT reached 87% with 2,4-D and flumioxazin but was limited with glyphosate, not exceeding 40%. Mesotrione at 560 g ai ha−1 provided 98% control of roots and rhizomes (root/rhizome) at 63 DAT, a 10% increase compared with 280 g ai ha−1; and 2,4-D (90%), glyphosate (87%), diquat (86%), and flumioxazin (85%) also showed excellent root/rhizome control. The greatest reduction of plant biomass compared with the nontreated check (UNT) was noted with 2,4-D, mesotrione at 280 g ai ha−1 and 560 g ai ha−1, and diquat, with decreases from 73% to 80% for shoots and from 82% to 88% for roots/rhizomes. Glyphosate had less impact on shoot biomass reduction (−56%) but similar effect on root/rhizome dry weight (−79%) compared with 2,4-D, mesotrione, and diquat. Flumioxazin and fomesafen significantly reduced root/rhizome biomass by 78% and 72%, respectively. Concurrently, 2,4-D, flumioxazin, fomesafen, and diquat reduced the number of secondary shoots 70% to 90% compared with the UNT, whereas glyphosate and mesotrione completely inhibited emergence of new shoots. These data suggest that mesotrione applied POST provides excellent control of Carolina redroot. Future research should evaluate field applications of mesotrione in early summer when Carolina redroot regrowth occurs following the dissipation of PRE herbicide activity.

Economically solvent fresh-market potato production is predominantly dependent on the ability to efficiently produce consistent tuber quality and high yield, and the ability to meet first-to-market demand with early-season potatoes. Unfortunately, these two qualifiers often work against each other in terms of production management. In response, we studied integrated potato vine management programs that support timely early-season potato harvest. Vine management with a flail chopper, roller, and flame burner used alone or followed by diquat was evaluated when initiated 21 or 14 d prior to harvest in 2015 and 2016. Potato varieties included ‘Yukon Gold’ and ‘Dark Red Norland’. Potato leaf and stem management, as well as tuber skinning, stolon separation, grade, and yield were quantified. Among mechanical methods, potato leaf and stem management were poor when vines were rolled or mowed but better when flail chopped. In general, vine management and tuber skin set was better when treatments were initiated 21 d prior to harvest as opposed to 14 d. Vine management, tuber skin set, and yield were comparable when potato vines were flail chopped followed by flame burning and where diquat was applied twice, offering a viable program for smaller scale or organic production.

Interactions of water-soluble soil organic matter (WSSOM) with the herbicides bromacil, metribuzin, alachlor, diquat, and paraquat were examined to determine if these interactions can improve predictions of herbicide leaching potential. A high-performance liquid chromatography gel filtration column was used to separate WSSOM extracts from four mineral agricultural soils into fractions with approximate log molecular weights of 4.96 to 6.82. WSSOM fractions were predominantly anionic in nature with some hydrophobic character. The amount of paraquat bound by WSSOM ranged from 1.1 to 2.1 mmol g−1DOC−1 with KDOC (partition coefficient for dissolved organic carbon) values from 0.050 to 0.187 L kg−1. Diquat was bound at 0.9 to 1.5 mmol g−1DOC−1 by the extracts with KDOC values from 0.044 to 0.143 L kg−1. Bromacil, metribuzin, and alachlor did not bind to the extracts tested. WSSOM did not increase paraquat solubility in the presence of soil. Binding of these herbicides to WSSOM in the soils used in this study would not be a significant mechanism for increased mobility and groundwater contamination potential.

Results from the “Potato Ecosystem Project,” a cropping systems study in northern Maine, were used to test the hypothesis that greater reliance on organic nutrient sources and less reliance on synthetic fertilizer sources can benefit weed management efforts. ‘Atlantic’ potato was grown in a 2-yr rotation within a factorial arrangement of three pest management systems, two soil management systems, and both rotation entry points. Weed control in the conventional (CONV) pest management system relied on full rates of herbicides, whereas the biointensive (BIO) system relied exclusively on cultivation. The reduced input (RI) pest management system relied on cultivation in 1991 and 1992 and on 50% of standard herbicide rates plus cultivation from 1993 to 1995. The two soil management systems, unamended (barley/red clover rotation crop; 1× synthetic fertilizer for potato) and amended (pea/oat/hairy vetch green manure rotation crop; manure, compost, and 0.5× synthetic fertilizer for potato) contrasted practices typical for the region to those designed to achieve rapid improvements in soil quality. Midseason weed biomass in potato was dominated by common lambsquarters. In 1991 and 1992, weed biomass in potato was least in the CONV system and did not differ between the RI and BIO systems. In 1993, weeds in both RI and CONV potatoes were effectively suppressed below the level measured in the BIO system. Soil management had no effect on weed biomass from 1991 to 1993 but became an important factor affecting weeds in the BIO system in 1994 and 1995. Weed biomass was 77% lower in 1994 and 72% lower in 1995 in the amended soil management system than in the unamended system. No significant yield loss due to weeds was detected in the 1994 BIO system, but in 1995 yield loss due to weeds was 37% in the unamended system compared to 12% in the amended system. Soil management effects on weeds in the 1994 BIO pest management system carried through to the following season's germinable seed bank. Density of germinable common lambsquarters seed (0 to 10 cm soil depth) in the 1995 BIO system was 4,082 m−2 in the unamended soil management system compared to 1,280 m−2 in the amended soil management system. We suggest that organic amendments and green manure promote a potato crop better able to compete with weeds and that these inputs be considered as potentially important components of integrated weed management systems that have minimal reliance on herbicides.

Cross-resistance of the paraquat-resistant (R) hairy fleabane to other compounds that accept electrons from photosystem I (PSI) or produce toxic oxygen species was determined by chlorophyll loss, electron microscopy, and chlorophyll fluorescence suppression. Although the R bioype is approximately 100 x more resistant to paraquat than the susceptible (S) biotype based upon the assays for tissue damage, little or no cross-resistance was observed to a number of other PSI electron acceptors, including the bipyridilium herbicide morfamquat. A low level of resistance (approximately 10-fold) was noted to diquat and the singlet oxygen generator rose bengal. As measured by chlorophyll fluorescence suppression, the R biotype was about 100-fold resistant to paraquat, but only 10-fold resistant to diquat, and exhibited no resistance to morfamquat. Because differences observed with this protocol are direct measures of the ability of the herbicide to reach the active site and the results correlate with the level of resistance observed by chlorophyll bleaching or electron microscopy, these data suggest that compartmentalization is the major factor in paraquat resistance in hairy fleabane.

Selected biological and physiological parameters of hydrilla [Hydrilla verticillata (L.f.) Royle # HYLLI] biotypes were compared in growth chambers, glasshouse, or outside aquaria. Salinity tolerance was similar for both biotypes with an injury threshold of approximately 13 parts per thousand (ppt). The registered aquatic herbicides diquat (6,7-dihydrodipyrido [1,2-α:2′,1′-c] pyrazinediium ion) and dipotassium and monoamine salts of endothall (7-oxabicyclo [2.2.1] heptane-2,3-dicarboxylic acid)4 produced similar injury to both biotypes. Biomass of the monoecious plants, growing in controlled environments, declined under short days. Tuber production in monoecious plants was greatest under short days and was significantly higher than in dioecious plants under the same conditions. Growth response to temperature was similar among all plants and was retarded at 15 C. Tuber germination occurred at lower temperatures in the monoecious plants, which was indicative of a lower temperature tolerance. Vegetative propagules were the only perennating structures observed in the monoecious biotype, and regrowth was entirely from tubers and turions. The annual growth habit, in conjunction with rapid and abundant propagule production, adapts the monoecious biotype to northern areas with short growing seasons.

Paraquat and diquat were used from 1963 until 1986 to control capeweed and other annual weeds on an alfalfa field at Elmhurst, Victoria, Australia. From 1983, control of capeweed with these bipyridyl herbicides was no longer satisfactory. In experiments conducted on this field in 1986 and 1987, 800 g ai/ha of diquat was required to equal the control of capeweed obtained by 100 g/ha diquat in an adjacent pasture field with no history of herbicide use. There were substantial numbers of a diquat-resistant biotype within the population in the alfalfa field. It is concluded that the diquat-resistant biotype of capeweed became dominant due to the strong selection pressure provided by over 20 yr of use of the bipyridyl herbicides.

Greenhouse and field experiments were conducted to identify alternative herbicide treatments for the control of a biotype of American black nightshade which has been shown to tolerate paraquat. In greenhouse experiments the combination of paraquat and the metal chelator diethyldithiocarbamate at either 1% w/v or 3% w/v, and diquat alone significantly lowered I50 values, based on dry weight, when compared with paraquat alone. None of these treatments provided acceptable control (>90%) in field experiments. Treatments that controlled American black nightshade under field conditions were: monocarbamide dihydrogensulfate at 9 kg ai ha-1, monocarbamide dihydrogensulfate at 9 kg ha-1 + paraquat at 0.6 kg ha-1, lactofen at 0.6 kg ha-1, oxyfluorfen at 0.6 kg ha-1, and acifluorfen at 0.6 kg ha-1. Addition of tridiphane at 1.7 kg ha-1 to paraquat at 0.6 kg ha-1 did not improve control of American black nightshade under field conditions.

Enzymatically isolated American pondweed (Potamogeton nodosus Poir.) epidermal tissues were exposed to 14C-labeled dichlobenil (2,6-dichlorobenzonitrile), diquat (6,7-dihydrodipyrido[1,2-α: 2′, 1′-c] pyrazinediium ion), silvex [2-(2,4,5-trichlorophenoxy) propionic acid] or 2,4-D [(2,4-dichlorophenoxy)acetic acid] at concentrations of 5 × 10−4, 5 × 10−5, and 5 × 10−610M, and the amount of herbicide crossing the tissue layer was measured. Rates of herbicide movement were compared to those found when copper sulfate pentahydrate was added as a potential synergist at concentrations of 5 × 10−5 M (12.5 ppm), 5 × 10−6 M (1.25 ppm), and 5 × 10−7 M (0.125 ppm). Copper sulfate at 5 × 10−6 M increased the rate of movement of all herbicides. However, diquat and dichlobenil exhibited the most enhanced movement in the presence of copper sulfate. Without copper sulfate, 0.1 nmoles of 5 × 10−6 M 14C diquat penetrated the tissue within 24 h, compared to 1.3 nmoles following the addition of 5 × 10−7 M of copper sulfate.

The sharp decline in the area of lupin grown in Australia is partly attributed to the failure to control herbicide-resistant weeds in narrow-leaf lupin crops grown with the conventional 25-cm-wide row spacing. Growing lupin with wider row spacing allows for interrow weed control by nonselective herbicides using a sprayshield or physical methods. During 2003 to 2006, two experiments conducted at five sites evaluated the efficacy of interrow weed control techniques in narrow-leaf lupin crops grown in 55- to 65-cm-wide rows within the Western Australia wheatbelt. Interrow herbicides were applied POST using sprayshields, intrarow herbicides were banded on lupin rows at seeding, and interrow weeds were mowed using a garden mower. The main weed species at each site was rigid ryegrass, blue lupin, or wild radish. Paraquat plus diquat applied on the interrow of the lupin crop with sprayshields controlled up to 100% of weeds between rows, leading to increases in lupin grain yield in most of the sites. Glyphosate alone, a mixture of glyphosate plus metribuzin, and glyphosate followed by paraquat plus diquat also controlled interrow weeds, but did not increase lupin grain yield at any site. Thus, paraquat plus diquat is a better choice for interrow weed control in wide row lupin than glyphosate. Mowing did not improve weed control, but mowing followed by paraquat plus diquat increased lupin grain yield at one site. Regression models predicted that there was a strong relationship between weed biomass and lupin grain yield.