Studies were conducted to develop a model from field and laboratory studies to predict the emergence phenology of Chenopodium album. A mechanistic model to predict the phenology of weed seedling emergence across locations, years, and tillage systems is presented. This was accomplished by the integration of hydrothermal time to describe germination and thermal time to describe shoot elongation. The interaction of soil moisture and temperature in the model was accounted for by the integration of hydrothermal time in algorithms predicting seed germination. Soil temperatures within the weed seed germination zone were predicted by temperature ranges at different depths in the soil. Emergence phenology of C. album seedlings was predicted with greater accuracy under no-till and moldboard plow systems than under a chisel plow system. We attributed this lower accuracy in the chisel plow system to increased heterogeneity in the soil matrix and vertical distribution of the seedbank caused by the chisel plow. The presence or absence of Zea mays did not affect model performance. The use of soil temperature to calculate thermal time was a better predictor of C. album seedling emergence than air temperature. The ability to predict weed seedling emergence phenology is an important component of an integrated weed management strategy.

Experiments were conducted in controlled environments and in the field on winter-hardy Triticum aestivum and three weed species commonly found in cereal fields in the United Kingdom to examine whether overwinter shoot growth of individual plants could be described by accumulated thermal time calculated using base temperatures derived from growth cabinets. Individuals of each species were grown in a controlled environment at constant temperatures ranging from 5 to 20 C and harvested sequentially. Base temperatures for the increase of dry weight and green area were estimated by fitting a simple linear model describing growth in response to the thermal sum. The estimated base temperatures for shoot dry matter accumulation of Alopecurus myosuroides, Stellaria media, Galium aparine, and T. aestivum were −0.8, −3.3, −1.4, and 0.2 C, respectively, and estimated base temperatures for increase in green area were 0.4, −1.7, 1.9, and 2.2 C, respectively. Each species also was grown in monoculture in the field over 2 yr at a range of sites to examine whether the base temperatures estimated from the controlled environment studies could be used to model weed and crop growth in response to thermal time in the field. The field data were described well when an expolinear function was fitted to accumulated thermal time calculated using the base temperatures derived from the controlled environment studies.

Weed seed rain was monitored in field plots under three fallow types and four land-use intensities in Ibadan, Nigeria, in 1994 and 1995. The fallow types were natural bush, planted Leucaena leucocephala, and Pueraria phaseoloides. The land-use intensities consisted of continuous cropping, involving Zea mays/Manihot esculenta and fallowing for 1, 2, and 3 yr, with each fallow period followed by 1 yr of Z. mays/M. esculenta cultivation. In 1994, seed rain in plots cropped after P. phaseoloides fallow was significantly lower than in plots cropped after bush or L. leucocephala fallow. Pueraria phaseoloides plots had similar seed rain as bush fallow plots in 1995, and the seed rain in these plots was significantly lower than in L. leucocephala plots. Weed seed rain was significantly higher in continuously cultivated plots across all fallow types than in plots that were cultivated after one or more years of fallow. The lowest seed rain was in plots that were cropped once after a 3-yr fallow. The largest quantity of weed seed input in the plots occurred in either August or September, reflecting the life cycle of the annual weeds that dominated the vegetation. Individual species differed in pattern and duration of shedding seeds within the fallow systems and land-use intensities. Annual weeds dominated the seed rain in continuously cropped plots, and seeds of perennial weeds were dominant in plots fallowed for more than 1 yr before cultivation. Weeds flowered earlier in continuously cropped plots than in plots that were cropped after 2 or 3 yr of fallow. Increased land-use intensity caused an increase in seed rain and consequently increased the soil seed bank. Pueraria phaseoloides fallow was more effective in shading weeds and probably reducing the quantity of light reaching them than the natural bush and planted L. leucocephala fallow systems, and this may have been the basis of the significantly lower seed rain in P. phaseoloides plots.

Two Glycine max near-isolines, GL2415 (glyphosate sensitive) and GL2600RR (glyphosate resistant), were compared for susceptibility to Sclerotinia sclerotiorum, the fungus that causes white mold disease (also known as Sclerotinia stem rot). A formulated isopropylamine salt of glyphosate (RU) at 840, 1,680, and 2,520 g ae ha−1; the RU formulation blank containing only adjuvants (RUFB) at 0.4% (v/v); organosilicone at 0.3% (v/v); a crop oil concentrate at 1.0% (v/v); and a nonionic surfactant at 0.5% (v/v) were evaluated for their influence on V5 G. max susceptibility to S. sclerotiorum in the field. The same treatments plus a formulated isopropylamine salt of glyphosate lacking adjuvants at 2,520 g ae ha−1 and a formulated trimethylsulfonium salt of glyphosate at 2,520 g ae ha−1 were applied to GL2600RR G. max in the greenhouse. Results from these studies indicated no differences in fungal growth, disease development, or G. max yield for any of these treatments. To determine if any interaction occurred between the chemicals, plants, and S. sclerotiorum, leaflets from both cultivars were dipped into and immediately removed from solutions of the RU at 4, 7, and 10% (v/v) and the RUFB and adjuvants at the rates described. The resulting lesion developments were similar across both cultivars but not across chemical treatments. Lesion developments were smaller on leaflets treated with RUFB and RU, but larger on leaflets treated with the other three adjuvants. Sclerotinia sclerotiorum mycelia growing on potato dextrose agar were inhibited by high concentrations of RU and of RUFB at 100 mM ae glyphosate and by the three adjuvants at 1% (v/v). Formulated glyphosate lacking adjuvants did not inhibit mycelial growth on potato dextrose agar. The glyphosate resistance trait did not appear to be associated with the susceptibility of G. max to S. sclerotiorum. Neither the glyphosate resistance trait nor the applications of glyphosate and adjuvants influenced G. max susceptibility to S. sclerotiorum.

Greenhouse, field, and laboratory experiments were conducted in northern Greece during 1996, 1997, and 1998 to study possible metribuzin resistance in Amaranthus retroflexus (redroot pigweed) and Chenopodium album (common lambsquarters) biotypes found in potato fields. The greenhouse experiments indicated that the suspected resistant biotypes (R) of both species were not controlled by metribuzin applied either pre- or postemergence at rates of 245, 490, 980, and 1,960 g ai ha−1 (the higher rate is eight times greater than the rate recommended for weed control in Solanum tuberosum [potato]). However, susceptible biotypes (S) were completely controlled by 245 g ai ha−1. Also, both R- and S-biotypes of either species were effectively controlled by prometryn applied either pre- or postemergence at 1.5 kg ai ha−1. The field trials confirmed that metribuzin applied either pre- or postemergence at rates of 490, 980, and 1,960 g ai ha−1 gave fair or partial control of the R-biotype of C. album, whereas prometryn applied preemergence at 1.5 kg ai ha−1 gave excellent control of this weed. Chlorophyll fluorescence measurements performed in laboratory experiments indicated that photosynthetic electron transport in metribuzin-incubated leaves detached from plants of the R-biotypes was not affected, but it was inhibited in leaves detached from plants of the S-biotypes. Electron transport was inhibited by prometryn in leaves detached from both S- and R-biotypes of either species. These results show clearly that the biotypes of both species developed resistance to metribuzin, but they were not cross-resistant to prometryn.

If decision-aid software models of weed emergence and growth are ever to help producers better time weed management, these models must be able to predict perennial weed shoot emergence from vegetative propagules. In this research, Cirsium arvense shoot emergence from adventitious root buds in spring was modeled using degree-day heat sums. Fractional C. arvense shoot emergence was best modeled as a logistic dose–response function of degree-day heat sum as follows: Y = 1.108/(1+[X/488.344]−5.161) where Y = fractional C. arvense shoot emergence (0 to 1) and X = heat sum in degree-days above 0 C after day 91 of the year (April 1) with an upper limit of 800 degree (C) days (r2 = 0.83). This empirical model was validated by graphing observed vs. model-predicted C. arvense shoot emergence using two independently gathered data sets, one of C. arvense emergence in autumn chisel-plowed Triticum aestivum (r2 = 0.82) and the other in no-till fallow (r2 = 0.63). The model slightly overestimated emergence at low fractional emergence (< ∼7% at 0.1 fractional emergence) and underestimated emergence at high fractional emergence (10 to 20% at 0.8 to 1.0 fractional emergence). Below an emergence fraction of 0.8, the model adequately estimated observed emergence to within about 10% of the predicted regression line. Using the model, about 1% and 80% of C. arvense shoots should emerge from adventitious root buds after a heat sum accumulates of about 197 and 587 C d, respectively, starting from day 91 of the year. Consequently, farmers should begin monitoring C. arvense patches for emergence and height growth after about 197 C d accumulate and expect to control C. arvense before about 587 C d accumulate, which is when about 80% of shoots have emerged.

Amaranthus retroflexus L. is a common annual weed worldwide. It can be found in a wide range of habitats and causes substantial yield reduction in many crops mainly through competition. Alternaria spp. are airborne molds that are considered to have potential for the biological control of weeds. The aim of this study was to assess the effect of spore concentration, host-plant growth stage, dew period, and temperature on the pathogenicity of three Alternaria alternata isolates against A. retroflexus. The pathogenicity of A. alternata increased with increasing spore concentration and length of dew period. A spore concentration of 107 spores ml−1 in a rapeseed oil emulsion and given a 24 h dew period caused 100% mortality of A. retroflexus plants at the four-leaf stage. Infection and mortality in older plants (>four-leaf stage) was lower. The highest levels of plant mortality were obtained at post-inoculum temperatures between 20 and 30 C. These experiments confirm the potential of A. alternata as a mycoherbicide under specific environmental conditions.

Experiments were conducted in 1998 and 1999 at the Central Crops Research Station near Clayton, NC, to evaluate density-dependent effects of Datura stramonium on weed growth and seed rain and Gossypium hirsutum growth and yield. Datura stramonium height was not affected by density in either year. Crop height never exceeded weed height during the growing season, indicating that competition for light occurred between the two species. Eight weeks after planting or later, G. hirsutum height decreased as D. stramonium density increased. An increase in D. stramonium density from 1 to 32 plants (9.1 m of row)−1 resulted in a decrease in capsule production per plant of 92 and 60 in 1998 and 1999, respectively. Total D. stramonium dry weight per 9.1 m of row increased via a quadratic relationship as weed density increased. Gossypium hirsutum lint yields decreased as D. stramonium biomass and density increased in both years. Estimated yield losses of 10 and 25% were caused by D. stramonium at 0.5 and 1.5 plants (9.1 m of row)−1 (572 and 1,716 plants ha−1), respectively, in 1998 and 0.6 and 1.8 plants (9.1 m of row)−1 (690 and 2,060 plants ha−1), respectively, in 1999.

Echinochloa oryzoides and E. phyllopogon have become the most serious weeds in California Oryza sativa since continuous flooding was used to suppress E. crus-galli. Continuous use of a limited number of available graminicides and an increasing number of control failures led to the investigation of herbicide resistance in E. oryzoides and E. phyllopogon. Greenhouse dose-response studies with postemergence (POST) applications of molinate, thiobencarb, fenoxaprop-ethyl, and bispyribac-sodium estimating GR50 (herbicide dose to inhibit growth by 50%) values suggested resistance to all herbicides in two E. phyllopogon accessions and to molinate and thiobencarb in one E. oryzoides accession when compared with susceptible E. phyllopogon and E. oryzoides controls, respectively. No resistance was detected in dose-response studies with propanil. Minimum and maximum ratios (R/S) of the GR50 values of resistant to susceptible E. phyllopogon plants (in two experiments involving two resistant accessions) were 7.8 and >13.3 for thiobencarb, 2.2 and 4.3 for molinate, 16.5 and 428.7 for fenoxaprop-ethyl, and 2.0 and 12.0 for bispyribac-sodium. Minimum and maximum E. oryzoides R/S ratios (average of two experiments) were 21.9 and 4.6 for thiobencarb and molinate, respectively. A resistant E. phyllopogon (one accession tested) and the susceptible control were killed by POST applications of glyphosate, glufosinate, and clomazone, and by a preemergence application of pendimethalin. Thus, the repeated use of the few available grass herbicides in the predominantly monocultured O. sativa of California has selected for herbicide resistance in E. oryzoides and E. phyllopogon. The introduction of herbicides with new mechanisms of action will be useful to manage herbicide-resistant E. oryzoides and E. phyllopogon. However, cross- and multiple resistance emphasize the need to integrate herbicide use with nonchemical means of weed management.

Parasitic plants, including the root holoparasites Orobanche spp., cause devastating damage to crops worldwide. Arabidopsis thaliana is widely used as an amenable model plant system to study host–pathogen interactions. Understanding the molecular basis involved in host–parasite interactions will provide practical tools for the detection of genes responsible for incompatibility and resistance responses. In preliminary petri dish experiments, A. thaliana induced seed germination of O. aegyptiaca, O. minor, and O. ramosa at the rate of 87, 72, and 67% of maximum seed germination, respectively. Arabidopsis thaliana induction of O. crenata and O. cumana seeds was negligible (less than 2% of maximum germination). In additional polyethylene bag studies, A. thaliana was parasitized by O. aegyptiaca, O. ramosa, and O. minor resulting in 12, 5, and 2 parasites per host plant, respectively. The results facilitate the use of A. thaliana in host-parasitic plant interaction research.

Herbicide soil/solution distribution coefficients (Kd) are used in mathematical models to predict the movement of herbicides in soil and groundwater. Herbicides bind to various soil constituents to differing degrees. The universal soil colloid that binds most herbicides is organic matter (OM), however clay minerals (CM) and metallic hydrous oxides are more retentive for cationic, phosphoric, and arsenic acid compounds. Weakly basic herbicides bind to both organic and inorganic soil colloids. The soil organic carbon (OC) affinity coefficient (Koc) has become a common parameter for comparing herbicide binding in soil; however, because OM and OC determinations vary greatly between methods and laboratories, Koc values may vary greatly. This proposal discusses this issue and offers suggestions for obtaining the most accurate Kd, Freundlich constant (Kf), and Koc values for herbicides listed in the WSSA Herbicide Handbook and Supplement.

Field studies were conducted in three site-years to measure no-till Glycine max yield loss in relation to Apocynum cannabinum vegetative shoot density. Apocynum cannabinum densities of 28 to 40 shoots m−2 reduced predicted G. max yield 58 to 75% and 62 to 94% with the rectangular hyperbolic and linear regression models, respectively. Differences between locations were attributed to rainfall and temperatures, with delayed G. max canopy closure and higher yield loss where soil moisture remained high and temperatures were relatively cool. Application of these predictive G. max yield loss equations to field populations of A. cannabinum showed that between 19 and 36% and 20 and 29% G. max yield loss could be expected from within A. cannabinum patches for the rectangular hyperbolic and linear regression models, respectively. The rectangular hyperbolic regression model appeared to describe the relation between G. max yield loss and A. cannabinum density accurately; however, the model appeared to be dominated by the initial linear phase. This may indicate a lack of high levels of intraspecific competition among A. cannabinum shoots. The results of this study indicate that there is a strong linear relation between G. max yield loss and A. cannabinum shoot density. We conclude that the biological basis for the use of the rectangular hyperbolic model for creeping perennial weeds is questionable.

Secale cereale is a serious weed problem in winter Triticum aestivum–producing regions. The interference relationships and economic thresholds of S. cereale in winter T. aestivum in Colorado, Kansas, Nebraska, and Wyoming were determined over 4 yr. Winter T. aestivum density was held constant at recommended planting densities for each site. Target S. cereale densities were 0, 5, 10, 25, 50, or 100 plants m−2. Secale cereale–winter T. aestivum interference relationships across locations and years were determined using a negative hyperbolic yield loss function. Two parameters—I, which represents the percent yield loss as S. cereale density approaches zero, and A, the maximum percent yield loss as S. cereale density increases—were estimated for each data set using nonlinear regression. Parameter I was more stable among years within locations than among locations within years, whereas maximum percentage yield loss was more stable across locations and years. Environmental conditions appeared to have a role in the stability of these relationships. Parameter estimates for I and A were incorporated into a second model to determine economic thresholds. On average, threshold values were between 4 and 5 S. cereale plants m−2; however, the large variation in these threshold values signifies considerable risk in making economic weed management decisions based upon these values.

Few studies report animal grazing effects on weed populations. A study was conducted to assess weed populations in annual and perennial forage grasses grazed at various intensities by cattle over a 4-yr period. The perennial forages were Bromus inermis and Bromus riparius, and the annual forages were winter Triticosecale and a mixture of Hordeum vulgare and winter Triticosecale. With few exceptions, results from the two annual pastures could be adequately described as a group, as could the results from the two perennial pastures. The two most prevalent weed species were Capsella bursa-pastoris and Taraxacum officinale; other species encountered over the course of the study were analyzed as a group. Tillage (seedbed preparation) in the annual system supported a proliferation of annual weeds in the spring. In the perennial pasture system, a lack of tillage and spring MCPA allowed T. officinale to increase as the study progressed, especially at the highest grazing intensity. In the perennial pastures, each unit increase in grazing intensity led to 51 more C. bursa-pastoris m−2 and 4 more T. officinale m−2. At lower levels of grazing intensity, C. bursa-pastoris and other species were most abundant in the annual pastures. Weed population shifts in response to grazing pressure in the annual pasture systems were restricted because of annual tillage and MCPA. Therefore, pasture managers may subject annual pastures to heavy grazing pressure with less negative weed population consequences than perennial pastures where herbicides are not applied.

Field studies were conducted in 1998 and 1999 to evaluate crop response, weed control, Glycine max yield, and economic returns of labeled (1×) and one-half labeled (½×) rates of early preplant (EPP) sulfentrazone plus chlorimuron and postemergence glyphosate, compared to glyphosate-alone systems in no-till, narrow-row, glyphosate-resistant G. max. Treatments containing a 1× or ½× rate of EPP sulfentrazone plus chlorimuron with glyphosate followed by (fb) a postemergence treatment of glyphosate provided 80 to 100% control of Xanthium strumarium, Ambrosia artemisiifolia, and Polygonum pensylvanicum and 82 to 100% control of Setaria faberi and Amaranthus rudis if glyphosate was applied mid-postemergence (MPOST) or late postemergence (LPOST). Glyphosate alone EPP fb glyphosate postemergence or sequential postemergence treatments of glyphosate provided 77 to 100% control of S. faberi, A. artemisiifolia, and P. pensylvanicum. Glycine max yield did not significantly differ between treatments that contained 1× or ½× rates of sulfentrazone plus chlorimuron EPP with postemergence glyphosate or sequential glyphosate. Residual herbicides fb glyphosate reduced overall weed control variability but did not reduce the overall yield variability compared to glyphosate alone. Greater weed control, G. max yield, net incomes, and lower coefficient of variation (CV) of net incomes were generally associated with treatments that included both EPP and postemergence treatments vs. single herbicide applications. A greenhouse study was conducted to determine the optimal spray additive to maximize the foliar activity of sulfentrazone on three annual weeds. Sulfentrazone alone and in combination with a nonionic surfactant (NIS), methylated seed oil (MSO), crop oil concentrate (COC), and a silicone-based surfactant (SBS), with and without ammonium sulfate (AMS), were applied on two sizes of Abutilon theophrasti, P. pensylvanicum, and S. faberi. AMS provided little additional efficacy of sulfentrazone on S. faberi, but improved efficacy on A. theophrasti and P. pensylvanicum. SBS or MSO plus AMS with sulfentrazone generally provided the greatest efficacy on all species.

Seed production and seedling emergence of three broadleaf weed species were evaluated following glyphosate application at initial seed set, mid seed fill, and physiological maturity. In greenhouse experiments averaged across glyphosate rates of 0.42, 0.63, and 0.84 kg ae ha−1, Xanthium strumarium 100-bur weight and burs per plant were reduced at least 69 and 70%, respectively, for application at initial fruit set compared with later applications, and seedling emergence was 3% of the nontreated check. Glyphosate application at initial seed set reduced Sesbania exaltata 100-seed weight 73%, seed per plant 86%, and seedling emergence 94%. Senna obtusifolia 100-seed weight, seed per plant, and seedling emergence were reduced 46, 83, and 66%, respectively, when glyphosate was applied at initial seed set. In field experiments, X. strumarium and S. exaltata seed production were reduced only when glyphosate was applied at initial seed set. Compared with the nontreated check, seedling emergence following initial seed set application was reduced 82% for X. strumarium and 94% for S. exaltata. S. obtusifolia response in the field was inconsistent with no reductions in seed per plant or seedling emergence observed the first year. The second year, initial seed set application reduced seed per plant 88% and seedling emergence 72%.

Herbicides applied to soils potentially affect soil microbial activity. Quantity and frequency of glyphosate application have escalated with the advent of glyphosate-tolerant crops. The objective of this study was to determine the effect of increasing glyphosate application rate on soil microbial biomass and activity. The soil used was Weswood silt loam. The isopropylamine salt of glyphosate was added at rates of 47, 94, 140, and 234 µg ai g−1 soil based on an assumed 2-mm glyphosate–soil interaction depth. Glyphosate significantly stimulated soil microbial activity as measured by C and N mineralization but did not affect soil microbial biomass. Cumulative C mineralization, as well as mineralization rate, increased with increasing glyphosate rate. Strong linear relationships between mineralized C and N and the amount of C and N added as glyphosate (r 2 = 0.995, 0.996) and slopes approximating one indicated that glyphosate was the direct cause of the enhanced microbial activity. An increase in C mineralization rate occurred the first day following glyphosate addition and continued for 14 d. Glyphosate appeared to be directly and rapidly degraded by microbes, even at high application rates, without adversely affecting microbial activity.

A 2-yr field study was conducted to compare the growth of Amaranthus palmeri, A. rudis, A. retroflexus, and A. albus planted in June and July. Rates of height increase (centimeters per growing degree day) were 0.21 and 0.18 for A. palmeri, 0.16 and 0.11 for A. rudis, 0.12 and 0.09 for A. retroflexus, and 0.08 and 0.09 for A. albus in 1994 and 1995, respectively, when planted in June. A. palmeri had among the highest values for plant volume, dry weight, and leaf area, while A. albus had the lowest. Specific leaf area values (cm2 g−1) ranged from 149 to 261 for A. palmeri, 160 to 205 for A. rudis, 150 to 208 for A. retroflexus, and 127 to 190 for A. albus. Maximum relative growth rates (g g−1 day−1) for any measured period were 0.32 for A. palmeri, 0.31 for A. rudis, 0.30 for A. retroflexus, and 0.26 for A. albus. Recent increases in species range and observed changes in weed community structure may be partially explained by the growth characteristics of A. palmeri and A. rudis. Herbicide rate and timing recommendations for mixed populations of these weeds should be based on A. palmeri because of its high growth rates.

Sulfentrazone persistence in soil requires many crop rotational restrictions. The sorption and mobility of sulfentrazone play an important role in its soil persistence. Thus, a series of laboratory experiments were conducted to mimic the soil properties of cation and anion exchange with different intermediates. The molecular characterization and ionization shift of sulfentrazone from a neutral molecule to an anion were determined using a three-dimensional graphing technique and titration curve, respectively. Sorption and mobility of 2.6 × 10−5 M 14C-sulfentrazone were evaluated using a soil solution technique with ion exchange resins and polyacrylamide gel electrophoresis, respectively. Solution pH ranged from 4.0 to 7.4. As pH increased, sulfentrazone sorption to an anion resin increased and its sorption to a cation resin decreased. Percent sulfentrazone in solution was pH-dependent and ranged between 0 to 18% and 54 to 88% for the anion and cation resins, respectively. Mobility of sulfentrazone on a 20% polyacryalmide gel resulted in Rf values of +0.02 and +0.39 for pH of 4.0 and 7.4, respectively. A double peak for sulfentrazone was detected in the polyacrylamide gel when the pH (6.0 and 6.8) was near the reported pKa of 6.56. There was no clear interaction for the sorption of sulfentrazone at 1.0 mg kg−1 to Congaree loamy sand or Decatur silty clay loam saturated with either calcium or potassium. Sulfentrazone behavior with the polyacrylamide electrophoresis gels and ion resins indicate the potential for this herbicide to occur as a polar or Zwitter ion. Sulfentrazone was adsorbed by potassium, calcium, and sodium saturated resins and subsequently desorbed using variable pH solutions. The level of sulfentrazone adsorption will vary among soil types and the amount of desorption into solution may be soil cation-dependent.

Most farmers now rely on herbicides and, to a lesser extent, cultivation to control weeds in Glycine max in the Midwest. However, the general public is concerned that widely used herbicides will contaminate surface and groundwater. Alternative ways to control weeds in field crops are needed to reduce or prevent herbicide contamination of surface and groundwater. A new between-row-mowing weed management system that consists of band-applied herbicides over crop rows + two or more between-row mowings was tested in G. max over 6 yr in Missouri. Mowing weeds close to the soil surface two or more times between crop rows killed or suppressed annual grass and broadleaf weeds, chiefly Setaria faberi, Ambrosia artemisiifolia, and Amaranthus spp., if properly timed. Shading by crop canopy closure contributed to weed suppression in this weed management system. G. max yield also could not be distinguished from weed-free check plots and was greater than the weedy check plots. Herbicide use was reduced 50% by banding because only 50% of the field area was sprayed. The between-row-mowing weed management system may have use in environmentally sensitive areas to help reduce soil erosion or water contamination by herbicides.