Weed management is complicated by the presence of soil seed banks. The complexity of soil–seed interactions means that seed persistence in the field is often difficult to measure, let alone predict. Field trials, although accurate in their context, are time-consuming and expensive to conduct for individual species. Some ex situ techniques for estimating seed life expectancy have been proposed, but these fail to simulate the environmental complexity of the field. Also, it has been questioned whether techniques such as the controlled aging test (CAT) are useful indicators of field persistence. This study aimed to test the validity of the standard CAT (seed aging at 45 C and 60% relative humidity) in use at the Royal Botanic Gardens, Kew, U.K., for predicting field seed-persistence. Comparison of seed persistence and CAT data for 27 northwest European species suggested a significant positive correlation of 0.31. Subsequently, 13 species of emerging and common weeds of Queensland were assessed for their seed longevity using the CAT. The seed longevity data of these species in the CAT were linked with field seed-persistence data according to three broad seed-persistence categories: < 1 yr, 1 to 3 yr, and > 3 yr. We discuss the scope for using the CAT as a tool for rapid assignment of species to these categories. There is a need for further studies that compare predictions of seed persistence based on the CAT with seed persistence in the field for a larger range of species and environments.

The molecular basis for acetolactate synthase (ALS)–inhibitor resistance was determined for 6 susceptible (HS) and 24 resistant (HR) kochia populations from western Canada. The latter included 3 HR populations from Alberta (AB), 3 from Manitoba (MB), and 18 from Saskatchewan (SK). HR plants survived application of the ALS-inhibitor herbicide thifensulfuron–tribenuron mixture in the greenhouse. Most of the HR populations were heterogeneous and contained both HR and HS individuals. The molecular basis for resistance was determined in 273 HR individuals by sequencing the ALS gene (2,270 base pair [bp]) or by conducting a TaqMan genotyping assay developed in this study using real-time polymerase chain reaction (PCR) for single nucleotide polymorphism (SNP) 1709, where a G to T substitution resulted in a Leu for Trp substitution at amino acid position 574 (Trp574Leu mutation). A total of 16 SNPs were identified in the ALS gene sequences (0.7% polymorphism), 5 of which resulted in amino acid changes that confer resistance to ALS-inhibiting herbicides. The SNPs correspond to three target-site mutations: Pro197 (SNPs 565 and 566), Asp376 (SNP 1116), and Trp574 (SNPs 1708 and 1709). The Trp574Leu mutation was predominant (189 HR plants). The next most common mutation was the highly variable residue Pro197 (44 HR plants) with substitution by one of nine amino acids. The least-frequent were Asp376Glu (9 plants) and Trp574Arg (3 plants) substitutions. The presence of two ALS target-site mutations was found in 30 individual kochia plants, the first report from field-selected weed populations. These include combinations Pro197 + Trp574 (23 plants) and Pro197 + Asp376 (7 plants). The detection of Pro197, Asp376, and Trp574 mutations, as well as both combinations, from geographically separate regions suggests multiple origins of these mutations.

The effects of diluent volume and calcium concentration on glyphosate [N-(phosphonomethyl] glycine] phytotoxicity were evaluated by adding 0.0, 0.0025, 0.005, 0.01, 0.02, and 0.04 M CaCl2 to 1.68 kg/ha glyphosate and applying at 130, 190, 375, and 750 L/ha to tall morningglory [Ipomoea purpurea (L.) Roth] plants that were 10 to 12 cm tall. Thirty days after treatment, glyphosate phytotoxicity was reduced by calcium at diluent volumes of 375 and 750 L/ha. Addition of a sulfonine red dye to the spray solution showed that at 130 L/ha, runoff from tall morningglory leaves was negligible. At 375 and 750 L/ha different volumes, ½ to ¾ of the spray solution, as measured by dye retention, ran off the leaf surface. At 750 L/ha, the water and dye collected at the leaf margins and the spray pattern on the leaf surface was not uniform.

Weed suppression by cover crops grown during the winter fallow period in continuous corn may lead to a reduction in herbicide use. Rye, crimson clover, and subterranean clover cover crops were compared with corn stubble under a conventional management system (CS) that included plowing and use of preemergence residual herbicides and a low-input management system (LIS) that included no-tillage and use of a presowing nonresidual herbicide for three consecutive years (1994–1996). Cover crop and above-ground weed biomass prior to desiccation were not influenced by management system. Cover crop biomass ranged from 1,420 to 5,657 kg ha−1 for rye, from 563 to 4,217 kg ha−1 for crimson clover, and from 563 to 4,248 kg ha−1 for subterranean clover. At crop planting, rye reduced weed biomass from 54 to 99%, crimson clover from 22 to 46% (with a negative value in 1995), and subterranean clover from 21 to 67%. Weed growth suppression was usually higher in years when cover crop biomass was higher. There were no differences in weed suppression by cover crops later in the season (corn in the fourth leaf stage), while total weed density was higher in LIS than CS in 2 of 3 yr. Total weed cover at corn's ‘full dent’ stage ranged from 1 to 7% in CS and from 24 to 47% in LIS. Cover crops influenced weed composition only in years when cover crop growth was high; otherwise their effect was masked by that of the management system. Weed communities showed higher diversity under LIS than under CS. Consistency of associations between weed species and treatments over sampling dates and years was found especially for some of the species associated with LIS. After 3 yr, redroot pigweed, common lambsquarters, and black nightshade were regularly associated with rye-LIS at an early corn growth stage; this may indicate a species shift toward a more troublesome composition.

A diclofop-methyl-resistant biotype of Italian ryegrass was characterized to determine the expression and inheritance of herbicide resistance and whether this trait was due to the presence of a diclofop-insensitive form of acetyl-coenzyme A carboxylase (ACCase). At the whole plant level, the resistant biotype was > 93-fold more resistant to diclofop-methyl than the susceptible biotype. Crosses of diclofop-resistant and –susceptible plants were performed to produce F1 plants. No maternal effects were evident in responses of reciprocal F1 plants to diclofop. GR50 diclofop rates determined for resistant, F1, and susceptible plants were 15, 6.3, and 0.16 kg ha−1, respectively. F2 populations treated with a 7.5 kg ha−1 rate of diclofop exhibited three injury response phenotypes 3 wk after treatment: a susceptible (S) phenotype which was killed, an intermediate resistance (I) phenotype with severe injury, and a resistant (R) phenotype with little or no injury. Testcross progeny exhibited only I and S phenotypes. Observed segregation of phenotypes in F2 and testcross populations conformed to segregation ratios predicted for a trait with inheritance controlled by a single partially dominant nuclear gene. ACCase activity determined in crude cell-free extracts of resistant, F1, and susceptible biotypes exhibited I50 values of 50, 20, and 0.7 μM diclofop, respectively. A positive relationship between the injury response phenotype and site of action (ACCase) response to diclofop was evident in both F1 and F2 populations. In extracts from R, I, and S phenotype F2 plants, 20 μM diclofop acid inhibited ACCase-mediated incorporation of 14C by 27.1, 45.1, and 78.9%, respectively. The ACCase data are consistent with the hypothesis that diclofop resistance in Italian ryegrass is conferred by a diclofop-insensitive form of ACCase.

The presence of wheat straw mulch in no-tillage systems can increase corn yields in the central Great Plains, but information is needed on the optimal mulch level and the toxicity of metolachlor on corn growth. Research was conducted to determine the effect of winter wheat straw mulch levels of 0, 1.7, 3.4, 5.1, and 6.8 t ha–1 and metolachlor rates of 0, 0.5, 1.0, and 1.5X-rates on corn growth and yield in a winter wheat-ecofallow-corn-fallow rotation at three locations across Nebraska. Response of corn to different mulch levels and metolachlor rates varied with climate and location. In general, early corn growth was retarded by increasing amounts of mulch due to reduced soil temperatures, but after tasseling corn grew taller under increasing mulch levels because of increased soil moisture. Soil water content, kernel moisture at harvest, stover dry matter, total dry matter, ears per plant, and kernel weight increased with increasing mulch level. Corn grain yield reached a maximum at a mulch level of 5.1 t ha–1. Kernel weight, kernel number, and grain yield increased with higher mulch levels and 0.5 and 1.0X metolachlor rates as weed competition was reduced, but decreased at the 1.5X-rate of metolachlor due to corn injury. Lack of sufficient growing degree-days to compensate for lower soil temperatures or corn injury reduced corn yields at the higher mulch levels and 1.5X-rate of metolachlor in west-central and western Nebraska. From a practical standpoint, a mulch level of 3.4 to 5.1 t ha–1 and a metolachlor rate near the X-rate should increase corn yield (14 to 15%) over unmulched corn in the central Great Plains.

Most well-drained Mississippi Delta soils have been used for cotton production, but corn has recently become a desirable alternative crop, and subsequently, atrazine use has increased. Between 2000 and 2001, 21 surface soils (0 to 5 cm depth) with known management histories were collected from various sites in Leflore, Sunflower, and Washington counties of Mississippi. Atrazine degradation was assessed in 30-d laboratory studies using 14C-ring–labeled herbicide. Mineralization was extensive in all soils with a history of one to three atrazine applications with cumulative mineralization over 30 d ranging from 45 to 72%. In contrast, cumulative mineralization of atrazine from three soils with no atrazine history was only 5 to 10%. However, one soil with no history of atrazine application mineralized 54 and 29% of the atrazine in soils collected in 2000 and 2001, respectively. Methanol extracted 15 to 23% of the 14C-atrazine 7 d after treatment in soils having two applications within the past 6 yr, whereas 65 to 70% was extracted from no-history soils. First-order kinetic models indicated soil with 2 yr of atrazine exposure exhibited a half-life of less than 6 d. Most probable number (MPN) estimates of atrazine-ring mineralizing-microorganisms ranged from 450 to 7,200 propagules g−1 in atrazine-exposed soils, and none were detected in soils with no history of atrazine use. Although most soils exhibited rapid atrazine mineralization, analysis of DNA isolated from these soils by direct or nested polymerase chain reaction (PCR) failed to amplify DNA sequences with primers for the atzA atrazine chlorohydrolase gene. These results indicate that microbial populations capable of accelerated atrazine degradation have developed in Mississippi Delta soils. This may reduce the weed control efficacy of atrazine but also reduce the potential for off-site movement. Studies are continuing to identify the genetic basis of atrazine degradation in these soils.

Germination of African mustard seeds collected from southern Australia was not influenced by light conditions at the optimum temperature of 20/12 C. However, seed germination was inhibited by light at the lower temperature (15/9 C). Presence of light increased the sensitivity of seeds to low temperature, as well as salt and osmotic stress. In dark conditions, seed germination was relatively unaffected at a low level of salinity (80 mM NaCl) but decreased even at 10 mM NaCl in light/dark conditions. In the dark, seed germination was unaffected up to an osmotic potential of −0.6 MPa but declined thereafter. Seeds of African mustard germinated over a broad range of pH from 4 to 10. Seed germination was stimulated by potassium nitrate (from 0.005 to 0.04 M) and gibberellic acid (0.001 M). Seedling emergence of African mustard was the greatest (51%) for seeds buried at 1 cm but no seedlings emerged from seeds placed at a depth of 5 cm. At the end of the growing season, seed decay (77 to 87%) and dormant (12 to 18%) components were similar among different seed burial depths. Information gained in this study will be important in developing a better understanding of the requirements for African mustard germination and emergence.

Herbicides are very effective tools to control weeds but there has been an overreliance on their use at the expense of other useful methods of weed management. Farmers are interested in alternative methods of weed management but are concerned about the risk of adopting such practices with current small profit margins. Research on the Canadian Prairies has found that cropping systems that utilize zero tillage, diverse crop rotations, competitive cultivars, higher crop seed rates, specific fertilizer management, and cover crops can effectively manage weed populations, especially when used in conjunction with targeted but limited use of herbicides. Farmers are gaining confidence in the merits of such agronomic practices in terms of sustainable weed management and are gradually adopting these integrated cropping systems on their farms. Further research and extension efforts are required to ensure that these integrated weed management systems are biologically and economically robust to facilitate greater adoption at the farm level.

Glyphosate treatments to glyphosate-resistant (GR) cotton have been associated with poor pollination and increased boll abortion. Anatomical studies were conducted to characterize the effect of glyphosate treatments on the development of male and female reproductive organs of cotton flowers at anthesis. In comparison with nontreated plants, glyphosate applied at both the four-leaf stage postemergence (POST) and at the eight-leaf stage POST directed inhibited the elongation of the staminal column and filament, which increased the distance from the anthers to the receptive stigma tip by 4.9 to 5.7 mm during the first week of flowering. The increased distance from the anthers to the stigma resulted in 42% less pollen deposited on stigmas of glyphosate-treated plants than in nontreated plants. Moreover, pollen from glyphosate-treated plants showed numerous morphological abnormalities. Transmission electron microscopy showed the presence of large vacuoles, numerous starch grains, and less organized pockets of the endoplasmic reticulum containing fewer ribosomes in pollen from glyphosate-treated plants than from nontreated plants. Pollen development in glyphosate-treated plants is likely inhibited or aborted at the vacuolate microspore and vacuolate microgamete stages of microgametogenesis, resulting in immature pollen at anthesis. Although stigmas from glyphosate-treated plants were 1.2 to 1.4 mm longer than those from nontreated plants, no other anatomical differences in stigmas were visibly evident. The presence of the GR 5-enolpyruvylshikimate-3-phosphate synthase (CP4-EPSPS) enzyme from Agrobacterium sp. strain CP4 was quantified in reproductive and vegetative tissues using enzyme-linked immunosorbent assay. The content of CP4-EPSPS in the stigma, anther, preanthesis floral bud (square), and flower petals was significantly less than that in the vegetative leaf tissue. Glyphosate effects on the male reproductive development resulting in poor pollen deposition on the stigma, as well as production of aborted pollen with reduced viability, provide a likely explanation for reports of increased boll abortion and pollination problems in glyphosate-treated GR cotton.

Ethyl N,N-dipropylthiolcarbamate [EPTC] inhibited the deposition of external foliage wax of cabbage (Brassica oleracea L. var. capitata, L.). Wax inhibition was correlated directly with the rate of application of EPTC. Differential inhibition of wax deposition showed that foliage waxes were important in inhibiting the penetration and absorption of the alkanolamine salts of 4,6-dinitro-o-sec-butylphenol [DNBP]. Several other thiolcarbamates also altered the susceptibility of treated plants to subsequently applied herbicides. When EPTC was applied as a spray, only leaves then in the bud were affected. Leaf primordia developed later were not affected. Granular applications of EPTC extended the period during which the formation of foliage wax was inhibited. The reduction of foliage wax resulted in increased spray retention and decreased contact angle of spray droplets. EPTC increased the transpiration rate proportionally to its rate of application.

Formulation and preparation of herbicidal chemicals for the selective control of weeds in mechanized crop production have become increasingly more difficult with the introduction of a wide variety of organic and inorganic herbicides during recent years. Commercial herbicides and experimental chemicals are usually applied in systems which contain not only the active ingredients but also various solvents, cosolvents, surfactants (surface-active agents), carriers, and other adjuvants. Formulations of herbicides are usually evaluated for their maximum effects on weeds and minimum effects on crop plants. The manner in which the inactive constituents of formulations influence the ultimate herbicidal activity of the active ingredients is not well understood and extensive research will be required to obtain the fundamental information needed.

Herbicides 3-(p-chlorophenyl)-1,1-dimethylurea (monuron); 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine); 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine); 2-methoxy-4,6-bis(isopropylamino-s-triazine (prometone); 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine); and 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne) were studied in four soils. The behavior of monuron, propazine, atrazine, and simazine was similar in each soil, while prometryne and prometone exhibited greater interactions with the soils. Phytotoxicity and movement of the herbicides in soil were inversely related to extent of adsorption.

Using competitive crops and cultivars can be an important integrated weed management (IWM) tool, useful in both conventional and low-external-input (LEI) farming systems. Barley is considered a competitive crop, but cultivar competitiveness varies. There are two aspects of cultivar competitive ability; the ability to compete (AC) and the ability to withstand competition (AWC). However, the relationship between these aspects has not been addressed in barley. A study was conducted to explore aspects of barley cultivar competitive ability with oats, and to examine the feasibility of ranking cultivars based on either, or both, AWC and AC. Field trials were undertaken in 2001 and 2002 to determine cultivar competitive ability for 29 barley cultivars commonly grown on the Canadian prairies. Cultivars were selected from semidwarf and full height, hulled and hull-less, 2- and 6-row, and feed and malt classes. Yield loss ranged from 6 to 79% while weed seed return ranged from 10 to 83% of gross yield. As a class, semidwarf and hull-less cultivars were less competitive than full height and hulled cultivars, respectively. However, considerable variation existed within these classes, and an absolute relationship between class membership and competitive ability did not exist. Ability to withstand competition was significantly correlated with ability to compete, but correlation coefficients were not strong enough to attempt reliable co-selection within a breeding program. Ability to compete was a more consistent measure of competitive ability than AWC. Ranking barley cultivar competitive ability would make it a valuable IWM tool for farmers and extension personnel.

Saflufenacil (Kixor™) is a new protoporphyrinogen IX oxidase (PPO) inhibiting herbicide for preplant burndown and selective PRE dicot weed control in multiple crops, including corn. The biokinetic properties and the mechanism of selectivity of saflufenacil in corn, black nightshade, and tall morningglory were investigated. After root treatment of plants at the third-leaf stage, the difference in the phytotoxic selectivity of saflufenacil in corn and the weed species has been quantified as approximately 10-fold. The plant species showed similar selectivity after foliar applications; the plant response to saflufenacil was approximately 100-fold more sensitive compared with a root application. PPO enzyme activity in vitro was inhibited by saflufenacil, a 50% inhibition lay in a concentration range from 0.2 to 2.0 nM, with no clear differences between corn and the weed species. Treatments of light-grown plants and dark-grown seedlings with [14C]saflufenacil revealed that the herbicide is rapidly absorbed by root and shoot tissue. The [14C]saflufenacil was distributed within the plant systemically by acropetal and basipetal movement. Systemic [14C]saflufenacil distribution can be explained by the weak acid character of saflufenacil and its metabolic stability in black nightshade and tall morningglory. Metabolism of [14C]saflufenacil in corn was more rapid than in the weeds. In addition, low translocation of root-absorbed [14C]saflufenacil in the corn shoot was observed. It is concluded that rapid metabolism, combined with a low root translocation, support PRE selectivity of saflufenacil in corn.

In 1987, two applications of the methyl ester of diclofop failed to effectively control Italian ryegrass in some growers' fields. As a result of these observations, studies were initiated to determine if the surviving ryegrass is more tolerant to diclofop than previously untreated ryegrass. Growth chamber studies on five accessions of ryegrass demonstrated that collections from two growers' fields were highly tolerant of diclofop. Diclofop GR50 (rate required to reduce shoot weight by 50%) values of accessions A and B and commercial ryegrass, when diclofop was applied to seedlings at the two-leaf stage, were 2.9, 3.4, and 0.0056 kg ai/ha, respectively. Diclofop-tolerant biotypes were not more tolerant to postemergence barban or preemergence-incorporated triallate plus postemergence diuron or metribuzin. These herbicides are possible alternative treatments in fields where diclofop is no longer effective.

Glyphosate is a broad-spectrum herbicide that has been used extensively for more than 20 yr. The first glyphosate-resistant weed biotype appeared in 1996; it involved a rigid ryegrass population from Australia that exhibited an LD50 value approximately 10-fold higher than that of sensitive biotypes. We have characterized gene expression levels and glyphosate sensitivity of 5-enolpyruvylshikimate 3-phosphate synthase (EPSPS), the target enzyme for glyphosate inhibition, in sensitive and resistant lines derived from this population. Restriction fragment length polymorphism analyses were also performed to examine the distribution of EPSPS gene variants and the gene copy number. A two- to threefold increase in basal EPSPS messenger RNA (mRNA) and enzyme activity levels was observed in the most resistant lines analyzed; however, differences among lines in the sensitivity of EPSPS to glyphosate were not apparent. Induction of EPSPS was observed within 48 h after application of 1.5 kg ae ha−1 of glyphosate. This was reflected in elevated levels of both EPSPS mRNA and enzyme activity. Similarly, 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase mRNA levels increased after glyphosate treatment; however, basal and induced transcript levels were comparable for sensitive and resistant lines in this case. The restriction fragment length polymorphism analyses showed no evidence for gene amplification or cosegregation of a specific EPSPS gene variant with glyphosate resistance. EPSPS expression in lines exhibiting an intermediate level of resistance was indistinguishable from that in glyphosate-sensitive lines, suggesting that the mechanism could, at least in part, be non–target-based.

Application of nitrogen (N) fertilizer to sorghum at planting is a common practice that could confound competitive relationships of the crop with weeds. We studied the competitiveness of grain sorghum (Pioneer Brand 8333) relative to that of the annual weed shattercane and the perennial weed johnsongrass. The taxa are closely related, so survival requirements should be similar thus increasing the likelihood of finding differences associated with traits of the crop vs. weediness. Objectives of this research were to establish a competitive hierarchy for this crop–weed complex and to determine if relative competitiveness was affected by added N. A replacement design experiment was used in which plants were grown for 31 d in soil-filled pots placed outdoors. Taxa were planted in monocultures and 50:50 mixtures, representing all possible combinations of taxa, at a total density of 16 plants pot−1. Soil moisture was maintained at field capacity by daily additions of water or 30 μg ml−1 N in the form of an inorganic salt solution (KNO3). There was no response to the solution containing exogenous N likely because the amount of N in soil was greater than demand. Actual shoot and root dry weights in mixtures were compared with the expected dry weights, which were calculated as 50% of the root and shoot dry weights in monoculture. For grain sorghum, actual dry weights in mixture were often better than expected. Replacement series indices calculated from dry weight data described grain sorghum as competitively superior to its weedy relatives. These results indicate that further research on N management for cultivated sorghum, as a means of increasing crop competitiveness relative to that of weeds, may be unwarranted. However, a better understanding of other competition mechanisms inherent in grain sorghum might suggest management alternatives to enhance crop competitiveness with weeds.

Leaf tissue and leaf-tissue extracts from annual wormwood and pure artemisinin were evaluated for their effects on plant growth when incorporated into sandy loam soil. Dried leaf tissue was successively extracted with methylene chloride (MeCl2), ethanol (EtOH), and water, and the extracts and residue were reduced to dryness and stored at −20 C. Leaf tissue was incorporated in soil at rates equivalent to 0, 0.37, 0.73, or 1.1% (w/w) based on soil dry weight. Peat moss treated with extracts or artemisinin was incorporated into soil at a rate equivalent to the 0.73% (w/w) treatment. Inhibition of growth was species-specific; estimated reduction of dry weight by 0.73% (w/w) leaf tissue was 82, 49, 25, and 9% for redroot pigweed, common lambsquarters, soybean, and corn, respectively. The effects of the MeCl2 extract, which contained all of the extractable artemisinin, on germination and growth of redroot pigweed were similar to that of leaf tissue. Annual wormwood leaf tissue and MeCl2-extract treatments were the only treatments that resulted in a reduction in seedling survival. Artemisinin at levels equivalent to that contained in the MeCl2 extract and leaf-tissue treatments had significantly less effect on seedling survival, germination, and growth of redroot pigweed than the MeCl2 extract. Furthermore, the aqueous extract, which did not contain artemisinin, and the extract residue had activities similar to that of the artemisinin treatment. Thus, the allelopathic effects of annual wormwood can not be attributed to artemisinin alone.

Field experiments were conducted at Ashland Bottoms in northeastern Kansas and at Hays in western Kansas in 2001, 2002, and 2003 to determine the response of soil microbial and nematode communities to different herbicides and tillage practices under a glyphosate-resistant cropping system. Conventional herbicide treatments were a tank mixture of cloransulam plus S-metolachlor plus sulfentrazone for soybean and a commercially available mixture of acetochlor and atrazine for corn. Glyphosate was applied at 1.12 kg ai ha−1 when weeds were 10 or 20 cm tall in both corn and soybean. Soil samples were collected monthly at Ashland Bottoms during the growing period for soil microbial biomass (SMB) carbon determination. In addition, substrate-induced respiration (SIR) and BIOLOG substrate utilization were determined at the end of the growing season each year at Ashland Bottoms, and nematode populations were determined at the beginning and the end of the growing season at both sites. Direct effects of glyphosate rates on soil microbial and nematode communities were also studied in a controlled environment. Values for SMB carbon, SIR, and BIOLOG substrate utilization were not altered by glyphosate. Nematode community response to the glyphosate treatment was similar under both conventional tillage and no-till environments. Total nematode densities were similar with the glyphosate and conventional herbicide treatments. SMB carbon and BIOLOG substrate utilization did not differ between tillage treatments. Nematode densities were greater under conventional tillage than in the no-till system. This study showed that soil health when glyphosate was applied in a glyphosate-resistant cropping system was similar to that of cropping systems that used conventional herbicides.