The combined influence of two agricultural contaminants on natural communities of phytoplankton and zooplankton.

Concentrations of glyphosate observed in the environment are generally lower than those found to exert toxicity on aquatic organisms in the laboratory. Toxicity is often tested in the absence of other expected co-occurring contaminants. By examining changes in the phytoplankton and zooplankton communities of shallow, partitioned wetlands over a 5 month period, we assessed the potential for direct and indirect effects of the glyphosate-based herbicide, Roundup WeatherMax(©) applied at the maximum label rate, both in isolation and in a mixture with nutrients (from fertilizers). The co-application of herbicide and nutrients resulted in an immediate but transient decline in dietary quality of phytoplankton (8.3 % decline in edible carbon content/L) and zooplankton community similarity (27 % decline in similarity and loss of three taxa), whereas these effects were not evident in wetlands treated only with the herbicide. Thus, even at a worst-case exposure, this herbicide in isolation, did not produce the acutely toxic effects on plankton communities suggested by laboratory or mesocosm studies. Indirect effects of the herbicide-nutrient mixture were evident in mid-summer, when glyphosate residues were no longer detectable in surface water. Zooplankton abundance tripled, and zooplankton taxa richness increased by an average of four taxa in the herbicide and nutrient treated wetlands. The lack of significant toxicity of Roundup WeatherMax alone, as well as the observation of delayed interactive or indirect effects of the mixture of herbicide and nutrients attest to the value of manipulative field experiments as part of a comprehensive, tiered approach to risk assessments in ecotoxicology.

Exposure of juvenile green frogs (Lithobates clamitans) in littoral enclosures to a glyphosate-based herbicide.

The majority of studies on the toxicity of glyphosate-based herbicides to amphibians have focused on larval life stages exposed in aqueous media. However, adult and juvenile amphibians may also be exposed directly or indirectly to herbicides. The potential for such exposures is of particular interest in the littoral zone surrounding wetlands as this is preferred habitat for many amphibian species. Moreover, it may be argued that potential herbicide effects on juvenile or adult amphibians could have comparatively greater influence on overall recruitment, reproductive potential and thus stability of local populations than effects on larvae. In this experiment, juvenile green frogs (Lithobates clamitans) were exposed to two concentrations (2.16 and 4.27 kg a.e./ha) of a glyphosate-based herbicide formulation (VisionMax®), which were based on typical application scenarios in Canadian forestry. The experimental design employed frogs inhabiting in situ enclosures established at the edge of small naturalized wetlands that were split in half using an impermeable plastic barrier. When analyzed using nominal target application rates, exposure to the glyphosate-based herbicide had no significant effect on survival, body condition, liver somatic index or the observed rate of Batrachochytrium dendrobatidis infection. However, there were marginal trends in both ANOVA analysis and post-hoc regressions regarding B. dendrobatidis infection rates and liver somatic index in relation to measured exposure estimates. Results from this study highlight the importance of field research and the need to include multiple endpoints when examining potential effects of a contaminant on non-target organisms.

Compensatory indirect effects of an herbicide on wetland communities.

The direct effects of large-scale disturbances are readily studied because their effects are often apparent and result in large changes to ecosystems. Direct effects can cascade through the ecosystem, leading to indirect effects that are often subtle and difficult to detect. Managing anthropogenic disturbances, such as chemical contamination, requires an understanding of both direct and indirect effects to predict, measure, and characterize the impact. Using a replicated whole-ecosystem experiment and path analyses (assesses the effects of a set of variables on a specified outcome, similar to multiple regression), we examined the direct and indirect effects of a glyphosate-based herbicide and nutrient enrichment on wetland communities. The latter did not impact any measured endpoints. The strongest drivers of macrophyte, benthic invertebrate, and amphibian assemblages were the ephemerality and the size of wetlands, factors which were not altered by herbicide applications. The herbicide had a direct negative effect on macrophyte cover, amphibian larval abundance, and the proportion of predatory benthic invertebrates. However, both amphibians and invertebrates were positively affected by the reduction in the macrophyte cover caused by the herbicide applications. The opposing directions of the direct and indirect effects lead to no net change in either group. The compensatory dynamics observed herein highlight the need for a better understanding of indirect effects pathways to determine whether common anthropogenic disturbances alter the ecological communities in small wetland ecosystems.

Imidacloprid in leaves from systemically treated trees may inhibit litter breakdown by non-target invertebrates.

Imidacloprid is a systemic insecticide that is used in trees to control several invasive, wood-boring insect pests in North America. Applications to deciduous trees result in foliar concentrations of imidacloprid that could pose a risk of harm to non-target decomposer invertebrates when autumn-shed leaves fall to forest floors or adjacent water bodies. Selection experiments were conducted in aquatic and terrestrial microcosms to test the hypothesis that non-target, leaf-shredding invertebrates can detect and avoid leaves from imidacloprid-treated trees thereby circumventing effects on leaf litter decomposition. There was no significant preferential feeding on non-contaminated leaves in selection microcosms indicating that the invertebrates could not detect and avoid imidacloprid-containing leaves. Mass loss and area consumed of both imidacloprid-containing and natural leaves in selection microcosms were significantly less than in control microcosms, indicating a sub-lethal feeding inhibition effect from consumption of leaf material at realistic field concentrations of 18-30microg/g fresh weight. Our results indicate that imidacloprid at realistic concentrations in leaves can inhibit leaf litter breakdown through adverse sub-lethal effects on decomposer invertebrates.

Are leaves that fall from imidacloprid-treated maple trees to control Asian longhorned beetles toxic to non-target decomposer organisms?

The systemic insecticide imidacloprid may be applied to deciduous trees for control of the Asian longhorned beetle, an invasive wood-boring insect. Senescent leaves falling from systemically treated trees contain imidacloprid concentrations that could pose a risk to natural decomposer organisms. We examined the effects of foliar imidacloprid concentrations on decomposer organisms by adding leaves from imidacloprid-treated sugar maple trees to aquatic and terrestrial microcosms under controlled laboratory conditions. Imidacloprid in maple leaves at realistic field concentrations (3-11 mg kg(-1)) did not affect survival of aquatic leaf-shredding insects or litter-dwelling earthworms. However, adverse sublethal effects at these concentrations were detected. Feeding rates by aquatic insects and earthworms were reduced, leaf decomposition (mass loss) was decreased, measurable weight losses occurred among earthworms, and aquatic and terrestrial microbial decomposition activity was significantly inhibited. Results of this study suggest that sugar maple trees systemically treated with imidacloprid to control Asian longhorned beetles may yield senescent leaves with residue levels sufficient to reduce natural decomposition processes in aquatic and terrestrial environments through adverse effects on non-target decomposer organisms.

Effects on litter-dwelling earthworms and microbial decomposition of soil-applied imidacloprid for control of wood-boring insects.

BACKGROUND: Imidacloprid is an effective, systemic insecticide for the control of wood-boring insect pests in trees. Systemic applications to trees are often made by soil injections or drenches, and the resulting imidacloprid concentrations in soil or litter may pose a risk of harm to natural decomposer organisms. The authors tested effects of imidacloprid on survival and weight gain or loss of the earthworms Eisenia fetida (Savigny) and Dendrobaena octaedra (Savigny), on leaf consumption rates and cocoon production by D. octaedra and on microbial decomposition activity in laboratory microcosms containing natural forest litter. RESULTS: Dendrobaena octaedra was the most sensitive of the two earthworm species, with an LC(50) of 5.7 mg kg(-1), an LC(10) of about 2 mg kg(-1) and significant weight losses among survivors at 3 mg kg(-1). Weight losses resulted from a physiological effect rather than from feeding inhibition. There were no effects on cocoon production among survivors at 3 mg kg(-1). The LC(50) for E. fetida was 25 mg kg(-1), with significant weight losses at 14 mg kg(-1). There were no significant effects on microbial decomposition of leaf material at the maximum test concentration of 1400 mg kg(-1). CONCLUSION: The results indicate that, when imidacloprid is applied as a systemic insecticide to the soil around trees, it is likely to cause adverse effects on litter-dwelling earthworms if concentrations in the litter reach or exceed about 3 mg kg(-1).

Inhibition of larval growth and adult fecundity in Asian long-horned beetle (Anoplophora glabripennis) exposed to azadirachtins under quarantine laboratory conditions.

BACKGROUND: The Asian long-horned beetle [ALB; Anoplophora glabripennis (Motschulsky)] is an invasive, wood-boring insect posing significant economic and ecological threats to the deciduous forests of North America. An efficacious and environmentally acceptable chemical control technique is a requirement of a comprehensive, integrated response strategy. RESULTS: Results of this study demonstrate statistically significant, concentration-dependent effects of azadirachtins, a family of natural compounds derived from the neem tree, on both ALB larval and adult life stages. Growth inhibitory effects on ALB larvae were greatest on early life stages. Significant effects on adults included inhibition of female feeding, oviposition effort and fecundity for adults exposed to azadirachtins via maturation feeding on systemically loaded twigs. CONCLUSION: These quarantine laboratory experiments verify multi-mechanistic, deleterious effects on both larval and adult life stages of ALB, an exotic, invasive insect pest of critical importance in North America. Field efficacy studies are required to further understand dose acquisition by larval and adult ALB life stages following systemic injections to host trees under semi-operational use scenarios. Such studies could also be used to test postulates regarding optimal deployment strategies to meet objectives such as slowing the spread of this pest and protection of high-value deciduous forest resources. © 2017 Her Majesty the Queen in Right of Canada Pest Management Science © 2017 Society of Chemical Industry.

Author Correction: DNA metabarcoding and morphological macroinvertebrate metrics reveal the same changes in boreal watersheds across an environmental gradient.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

DNA metabarcoding and morphological macroinvertebrate metrics reveal the same changes in boreal watersheds across an environmental gradient.

Cost-effective, ecologically relevant, sensitive, and standardized indicators are requisites of biomonitoring. DNA metabarcoding of macroinvertebrate communities is a potentially transformative biomonitoring technique that can reduce cost and time constraints while providing information-rich, high resolution taxonomic data for the assessment of watershed condition. Here, we assess the utility of DNA metabarcoding to provide aquatic indicator data for evaluation of forested watershed condition across Canadian eastern boreal watersheds, subject to natural variation and low-intensity harvest management. We do this by comparing the similarity of DNA metabarcoding and morphologically derived macroinvertebrate metrics (i.e. richness, % Ephemeroptera, Plecoptera and Trichoptera, % chironomid), and the ability of DNA metabarcoding and morphological metrics to detect key gradients in stream condition linked to forested watershed features. Our results show consistency between methods, where common DNA metabarcoding and morphological macroinvertebrate metrics are positively correlated and indicate the same key gradients in stream condition (i.e. dissolved oxygen, and dissolved organic carbon, total nitrogen and conductivity) linked to watershed size and shifts in forest composition across watersheds. Our study demonstrates the potential usefulness of macroinvertebrate DNA metabarcoding to future application in broad-scale biomonitoring of watershed condition across environmental gradients.

Effect of release herbicide on mortality, avoidance response, and growth of amphibian larvae in two forest wetlands.

Effects of Release herbicide (triclopyr butoxyethyl ester, [TBEE]) on mortality, avoidance response, and growth of larval amphibians (Rana clamitans, Rana pipiens) were investigated using in situ enclosures deployed in two forest wetlands in northern Ontario, Canada. Release was applied at nominal concentrations ranging from 0.26 to 7.68 mg TBEE acid equivalents (AE)/L. No significant deleterious effects of this herbicide on larval growth were detected. However, concentration-dependent mortality and abnormal avoidance response were observed. Most mortality occurred within 96 h following treatment. Median lethal concentration (LC50) values for each species and experimental site ranged from 2.79 to 3.29 mg AE/L, while median effective concentration (EC50) values (abnormal avoidance response) ranged from 1.67 to 3.84 mg AE/L. The LC10 and EC10 endpoints approximated aqueous concentrations (0.59 mg AE/L) expected under direct aerial overspray scenarios, indicating a potential risk of impacts for a small proportion of native amphibian larvae. However, given the low frequency and limited use of this herbicide formulation in Canadian forestry, these risks are considered negligible. Changes in usage patterns would require concurrent chemical and biological monitoring of operational spray programs to accurately quantify the probability and magnitude of real-world exposures and to relate these exposure levels to concentration-response relationships including those described in this study.

Fate of spinosad in litter and soils of a mixed conifer stand in the Acadian forest region of New Brunswick.

Spinosad is a natural insecticide, produced via fermentation culture of the actinomycete Saccharopolyspora spinosa, with potential use against a number of forest pests including spruce budworm (Choristoneura fumiferana [Clem]). Persistence of spinosad was determined in terrestrial fate experiments conducted within a semimature stand of black spruce (Picea mariana [Mill.]) and balsam fir (Abies balsamea [L]) in the Acadian forest region of New Brunswick, Canada. Results of experiments established under full coniferous canopy and in a canopy opening indicated that spinosad dissipated rapidly following hyperbolic kinetics in both litter and soils and was not susceptible to leaching. Time to 50% dissipation estimates for spinosyn A ranged from 2.0 to 12.4 days depending upon matrix and experimental conditions. Spinosyn D dissipated to levels below quantitation limits (0.02 microg/g of dry mass) within 7 days in all cases. Sporadic low-level detection of the demethylated metabolites suggested that parent compounds were degraded in situ.

Some ecological implications of a neem (azadirachtin) insecticide disturbance to zooplankton communities in forest pond enclosures.

A neem-based insecticide, Neemix 4.5, was applied to forest pond enclosures at concentrations of 10, 17, and 28 microg l(-1) azadirachtin (the active ingredient). At these test concentrations, significant, concentration-dependent reductions in numbers of adult copepods were observed, but immature copepod and cladoceran populations were unaffected. There was no evidence of recovery of adult copepods within the sampling season (May to October). The ecological significance of this disturbance to the zooplankton community was examined by determining biomass as a measure of food availability for higher predators, plankton community respiration, dissolved oxygen (DO) concentrations, and conductivity as functional indicators of ecosystem stress, and zooplankton food web stability as a measure of effects on trophic structure. The selective removal or reduction of adult copepods was sufficient to measurably reduce total zooplankton biomass for several weeks mid-season. During the period of maximal impact (about 4-9 weeks after the applications), total plankton community respiration was significantly reduced, and this appeared to contribute to significant, concentration-dependent increases in dissolved oxygen and decreases in conductivity among treated enclosures. The reductions in adult copepods resulted in negative effects on zooplankton food web stability through eliminations of a trophic link and reduced interactions and connectance. Comparing the results here to those from a previous study with tebufenozide, which was selectively toxic to cladocerans and had little effect on food web stability, indicates that differential sensitivity among taxa can influence the ecological significance of pesticide effects on zooplankton communities.

Community-level disruptions among zooplankton of pond mesocosms treated with a neem (azadirachtin) insecticide.

A natural, plant-derived insecticide, neem, is being evaluated as an alternative insect pest control product for forestry in Canada. As part of the process to investigate the environmental safety of neem-based insecticides, a mesocosm experiment was conducted to assess the effects of neem on natural zooplankton communities. Replicate (n=5), shallow (<1 m) forest pond enclosures were treated with Neemix 4.5, at concentrations of 0.035 (the expected environmental concentration), 0.18, 0.70, and 1.75 mg/l active ingredient, azadirachtin. Zooplankton communities were quantitatively sampled over a 4-month experimental period in treated and control enclosures, and water samples were collected to track azadirachtin concentrations. Concentrations in water declined linearly with estimated DT(50) values of 25-29 days. Trends in abundance over time among populations of cladocerans, copepods, and rotifers were found to differ significantly among treatments. At the two highest test concentrations, adverse effects were obvious with significant reductions in several cladoceran species, and near elimination of the three major copepod species present. More subtle effects at the two lowest test concentrations were determined by comparing the community structure of enclosures across treatment levels and over time through an analytical process based on the multivariate statistical software, PRIMER. Significant effects on community structure were detected at both of these lower concentrations, including the expected environmental concentration of 0.035 mg/l azadirachtin. Differential responses among species (some increases, some decreases) caused detectable disruptions in community structure among zooplankton of treated enclosures. Perturbations to zooplankton communities were sufficient to cause measurable differences in system-level metabolism (midday dissolved oxygen concentrations) at all but the lowest test concentration.

Comparative effects of pH and Vision herbicide on two life stages of four anuran amphibian species.

Vision, a glyphosate-based herbicide containing a 15% (weight:weight) polyethoxylated tallow amine surfactant blend, and the concurrent factor of pH were tested to determine their interactive effects on early life-stage anurans. Ninety-six-hour laboratory static renewal studies, using the embryonic and larval life stages (Gosner 25) of Rana clamitans, R. pipiens, Bufo americanus, and Xenopus laevis, were performed under a central composite rotatable design. Mortality and the prevalence of malformations were modeled using generalized linear models with a profile deviance approach for obtaining confidence intervals. There was a significant (p < 0.05) interaction of pH with Vision concentration in all eight models, such that the toxicity of Vision was amplified by elevated pH. The surfactant is the major toxic component of Vision and is hypothesized, in this study, to be the source of the pH interaction. Larvae of B. americanus and R. clamitans were 1.5 to 3.8 times more sensitive than their corresponding embryos, whereas X. laevis and R. pipiens larvae were 6.8 to 8.9 times more sensitive. At pH values above 7.5, the Vision concentrations expected to kill 50% of the test larvae in 96-h (96-h lethal concentration [LC50]) were predicted to be below the expected environmental concentration (EEC) as calculated by Canadian regulatory authorities. The EEC value represents a worst-case scenario for aerial Vision application and is calculated assuming an application of the maximum label rate (2.1 kg acid equivalents [a.e.]/ha) into a pond 15 cm in depth. The EEC of 1.4 mg a.e./L (4.5 mg/L Vision) was not exceeded by 96-h LC50 values for the embryo test. The larvae of the four species were comparable in sensitivity. Field studies should be completed using the more sensitive larval life stage to test for Vision toxicity at actual environmental concentrations.

Effects of Vision herbicide on mortality, avoidance response, and growth of amphibian larvae in two forest wetlands.

The effects of Vision (glyphosate, 356 mg acid equivalents (a.e.)/L) on mortality, avoidance response, and growth of larval amphibians (Rana clamitans and Rana pipiens) were investigated using in situ enclosures deployed in two forest wetlands of northern Ontario, Canada. In addition to untreated controls, Vision was applied to yield initial concentrations ranging from 0.29 to 14.3 mg a.e./L (0.94-46.1 mg/L of Vision). Resultant 96-h median lethal concentration (LC50) values ranged from 2.70 to 11.5 mg a.e./L (8.71-37.1 mg/L of Vision) depending on the species or site involved. Substantial mortality and incidences of abnormal avoidance response occurred only at concentrations exceeding the expected environmental concentrations (EEC) (1.43 mg a.e./L, or 4.61 mg/L of Vision) as calculated by Canadian regulatory authorities. The concentration dependence of larval growth rate and maximum size varied depending on site and species. Mean growth rates and maximum sizes exposed to 1.43 mg a.e./L (EEC) treatments were the same or greater than controls. Experimental site and biotic/abiotic factors therein, such as pH and suspended sediments, substantially affected the expression of Vision herbicide toxicity in the amphibian larvae tested. Overall, results suggest that the silvicultural use of Vision herbicide in accordance with the product label and standard Canadian environmental regulations should have negligible adverse effects on sensitive larval life stages of native amphibians.

Chemical and biomonitoring to assess potential acute effects of Vision herbicide on native amphibian larvae in forest wetlands.

In conjunction with operational forest herbicide spray programs in Ontario, Canada, chemical and biological monitoring studies were conducted in 51 different wetlands to quantify the probability and magnitude of contamination by a glyphosate herbicide formulation (Vision). Wetlands were classified as oversprayed, adjacent, or buffered in relation to the operational target spray blocks. Results show that vegetated buffers significantly mitigated against exposure and thus potential for acute effects. Aqueous concentrations of glyphosate in buffered wetlands were below analytical limits of quantitation (0.02 mg acid equivalent [a.e.]/L) in 14 of 16 cases, with mean concentration (0.03 +/- 0.02 mg a.e./L) significantly (p < 0.05) less than that of either adjacent (0.18 +/- 0.06 mg a.e./L) or oversprayed wetlands (0.33 +/- 0.11 mg a.e./L). Biomonitoring with caged amphibian larvae showed no significant differences among mean mortality (48 h) of either Rana pipiens (p = 0.194) or Rana clamitans larvae (p = 0.129) exposed in situ to Vision under these various wetland conditions. Percent mortality was not significantly (p = 0.05) correlated with exposure concentrations for either amphibian species tested. Results suggest that exposures typically occurring in forest wetlands are insufficient to induce significant acute mortality in native amphibian larvae.

Effect of pH and Release on two life stages of four anuran amphibians.

Using three native Canadian and one exotic anuran species, the interactive toxicity of pH and the forestry used-herbicide Release (triclopyr [3,5,6-trichloro-2-pyridl-oxyacetic acid]) was assessed. Embryonic and larval (Gosner 25) stages of Rana pipiens, Rana clamitans, Bufo americanus, and Xenopus laevis were exposed to treatments for at least 96 h in a static-renewal system using a central composite rotatable design. Mortality and the prevalence of malformations were modeled using generalized linear models with a profile deviance approach to obtain confidence intervals. Consistent trends of greater toxicity with lower pH were observed, with the majority of models (five of seven models) showing significant (p < 0.05) inverse relations. Larval lethal concentration estimates were eight to twenty-three times less than those observed for embryos, indicating that the larval stages were more sensitive to treatments. Further, the median lethal concentration (LC50) values for the larvae were below the expected environmental concentration (EEC) as calculated by Canadian regulatory authorities for Release. Species sensitivity was similar, with an average larval 96-h LC50 of 0.89 mg acid equivalents (AE)/L at pH 5.5 and 1.6 mg AE/L at pH 7, suggesting that X. laevis is a reasonable surrogate for native amphibians in laboratory toxicity testing. For the embryo tests, R. pipiens were slightly less sensitive in comparison with the other three species. Based on a hazard quotient analysis (EEC/LC50 > 1) for the most sensitive larval life stages, higher tier ecotoxicological testing under more realistic environmental conditions is strongly recommended.

Fate of spinosad in litter and soils of a white spruce plantation in central Ontario.

Spinosad is a natural insecticide with potential as a novel biorational control agent for spruce budworm (Choristoneura fumiferana [Clem]), the most destructive insect defoliator of spruce and balsam fir in Canada. Concurrent terrestrial fate experiments were conducted under full coniferous canopy and in a natural opening of a mature white spruce (Piecea glauca [Moench]) plantation of central Ontario to examine the fate and persistence of spinosad in the forest floor and underlying soils. Mean initial residues of spinosyn A and D were approximately 0.2 and 0.02 microgram g-1, respectively, in thatch and exposed soils, but were substantially higher, 2.72 and 0.36 micrograms g-1, in litter under coniferous canopy. Results demonstrated that spinosad residues in spruce litter, graminaceous thatch and exposed sandy loam soils dissipated rapidly, following hyperbolic or exponential decline models. Dissipation time (DT50) values ranged from 2.0 to 7.8 days, depending on matrix and experimental conditions. Transient increases in demethylated metabolite residues confirmed that the parent product was degraded in situ. No evidence of vertical mobility of any of the analytes was observed.

The direct and indirect effects of a glyphosate-based herbicide and nutrients on Chironomidae (Diptera) emerging from small wetlands.

Laboratory and mesocosm experiments have demonstrated that some glyphosate-based herbicides can have negative effects on benthic invertebrate species. Although these herbicides are among the most widely used in agriculture, there have been few multiple-stressor, natural system-based investigations of the impacts of glyphosate-based herbicides in combination with fertilizers on the emergence patterns of chironomids from wetlands. Using a replicated, split-wetland experiment, the authors examined the effects of 2 nominal concentrations (2.88 mg acid equivalents/L and 0.21 mg acid equivalents/L) of the glyphosate herbicide Roundup WeatherMax, alone or in combination with nutrient additions, on the emergence of Chironomidae (Diptera) before and after herbicide-induced damage to macrophytes. There were no direct effects of treatment on the structure of the Chironomidae community or on the overall emergence rates. However, after macrophyte cover declined as a result of herbicide application, there were statistically significant increases in emergence in all but the highest herbicide treatment, which had also received no nutrients. There was a negative relationship between chironomid abundance and macrophyte cover on the treated sides of wetlands. Fertilizer application did not appear to compound the effects of the herbicide treatments. Although direct toxicity of Roundup WeatherMax was not apparent, the authors observed longer-term impacts, suggesting that the indirect effects of this herbicide deserve more consideration when assessing the ecological risk of using herbicides in proximity to wetlands.

Laboratory and field exposure of two species of juvenile amphibians to a glyphosate-based herbicide and Batrachochytrium dendrobatidis.

Herbicides are commonly used in agriculture and silviculture to reduce interspecific competition among plants and thereby enhance crop growth, quality, and volume. Internationally, formulations of glyphosate-based herbicides are the most widely used herbicides in both these sectors. A large amount of work has focused on the effects of these herbicides on amphibians. Several laboratory and mesocosm studies have demonstrated that various formulations of glyphosate herbicides can be acutely toxic to larval and juvenile amphibians at concentrations at the upper end of environmental realism. However, to date there has been little work done investigating such effects in natural systems, limited work on juvenile amphibians, and only a few studies have investigated interactions with other stressors. We conducted a 16 day field experiment in which juveniles of two amphibian species (Lithobates clamitans and Lithobates pipiens) were exposed to the herbicide Roundup WeatherMax™ at four application rates (0, 2.16, 4.32 and 8.64 kg a.e./ha) to investigate effects on survival, liver somatic index (LSI), body condition, and incidence of disease caused by Batrachochytrium dendrobatidis (Bd). In a separate 16 day laboratory experiment, we exposed juvenile L. clamitans to both the herbicide and Bd. Results of our studies showed that this particular herbicide formulation had no effect on juvenile survival, LSI, body condition, or disease incidence, nor was there an interaction between exposure to herbicide and exposure to the disease in tests which closely mimic real world exposure scenarios. These experiments suggest that Roundup WeatherMax as typically used in agriculture is unlikely to cause significant deleterious effects on juvenile amphibians under real world exposure conditions.