An evaluation of methods for assessing the impacts of Bt‐maize MON810 cultivation and pyrethroid insecticide use on Auchenorrhyncha (planthoppers and leafhoppers)

1 Auchenorrhyncha (Planthoppers and Leafhoppers) are not only pests of many crops, but they are also nontarget organisms with respect to Bt‐protein expressing genetically modified plants. As herbivorous arthropods, planthoppers and leafhoppers ingest Cry proteins depending on their feeding behaviour. Consequently, they are directly exposed to these entomotoxic proteins and can also serve as a source of Cry protein exposure to predatory arthropods. Therefore, it is reasonable to use Auchenorrhyncha in the risk assessment of genetically modified crops. 2 During a 2‐year field study, we evaluated four different methods in terms of their feasibility to assess the impacts of plant‐incorporated protectants from Bt‐maize and of insecticide use on this group of arthropods. Visual assessment of plants, sweep netting, yellow traps and custom made sticky traps were utilized in field plots of Bt‐maize MON810, untreated near‐isogenic maize and insecticide‐treated near‐isogenic maize and were compared with respect to their capability to reflect the diversity and abundance of Auchenorrhyncha species. 3 Zyginidia scutellaris (Herrich‐Schäffer) (Cicadomorpha: Cicadellidae) represented more than 94% of all captured individuals in both years. The analysis of Z. scutellaris data showed no consistent differences between Bt‐maize MON810 and the untreated near isogenic hybrid, demonstrating no negative impact of MON810 on this species. Insecticide treatment, on the other hand, was not equivalent to the isogenic maize in terms of Z. scutellaris densities. Based on the collected data and on practical considerations, we recommend the combined use of transect‐wise sweep netting and sticky traps for the sampling of Auchenorrhyncha in maize.     

Efficient monitoring of maize orange leafhopper, <Emphasis Type="Italic">Cicadulina bipunctata</Emphasis> (Hemiptera: Cicadellidae), and small brown planthopper, <Emphasis Type="Italic">Laodelphax striatellus</Emphasis> (Hemiptera: Delphacidae), in forage maize fields using yellow sticky traps

The monitoring of insect pests in fields of forage maize is difficult because plants are tall and grow at a high density. We investigated the effectiveness of colored sticky traps and appropriate conditions for monitoring insect pests in forage maize fields. Large numbers of the maize orange leafhopper, Cicadulina bipunctata Melichar (Hemiptera: Cicadellidae), and the small brown planthopper, Laodelphax striatellus Fallen (Hemiptera: Delphacidae), were collected during the experimental period with yellow and blue sticky traps placed in summer crop forage maize fields. A greater number of insects were trapped in yellow traps relative to blue traps. Traps located at a lower height (40 cm above the ground) attracted larger numbers of C. bipunctata, whereas L. striatellus did not demonstrate a height-dependent preference. These results indicated that yellow-colored sticky traps located at low height are effective for collecting C. bipunctata and L. striatellus simultaneously. Seasonal occurrence data obtained by the yellow sticky traps showed clearer seasonal occurrences than that obtained by two previously developed methods, suction and light traps, indicating that sticky traps are effective for monitoring the seasonal occurrence of these two insects in forage maize fields.     

Responses of invertebrates to herbicide in Salix cinerea invaded wetlands: Restoration implications

The use of herbicides to control weeds, particularly large invasions, has now become an essential management tool in many ecological restoration projects. The herbicide glyphosate is routinely used to control the invasive weed, Grey Willow (Salix cinerea), within New Zealand wetlands. However, little is known about the effects of glyphosate on invertebrates. We determine the short‐term effects of glyphosate on the abundance and composition of the nontarget canopy invertebrate community in wetlands invaded by Grey Willow in New Zealand. Initially, the application of glyphosate and a surfactant showed no detectable effect on the canopy invertebrates examined in this study. However, 27 days after herbicide application, significant Grey Willow canopy loss caused dramatic decreases in the abundance of invertebrates in the glyphosate‐treated plots compared with the unsprayed plots. Invertebrates appeared to be sensitive to changes in vegetation structure, such as canopy loss. These results agree with previous studies that have shown that the negative impacts of glyphosate on invertebrate communities are related to indirect effects via habitat modification as the herbicide‐treated vegetation dies. From a terrestrial invertebrate perspective, this study suggests that the use of glyphosate herbicide is suitable for the control of invasive weeds within wetland restoration projects as it appears to have negligible impact on the canopy invertebrate assemblage.     

Two heteropteran predators in relation to weed management in herbicide-tolerant corn

Deployment of genetically modified (GM), herbicide-tolerant corn may alter weed flora abundance and composition and may affect pests and their natural enemies. Among on-plant predators, Orius spp. are the prevalent group in Spain and were selected to study the impact of glyphosate use on predators. We also studied Nabis sp. which is commonly recorded on corn in the study area. For this, a 4-year study was conducted in NE Spain. Three different herbicide regimes were compared: two glyphosate (a broad-spectrum herbicide) treatments per season, no herbicide treatment, and one pre-emergence conventional treatment with selective herbicides against broadleaf and grassy weeds. Density of main arthropod herbivores and the above two predatory groups was recorded on plants. Differences between herbicide regimes were observed in the two functional groups studied, herbivores and heteropteran predators. The comparison of glyphosate-treated and untreated plots showed significant differences for both functional groups, but the differences between glyphosate-treated and conventionally treated plots for the two functional groups were lower. For Orius spp., annual density per plot was significantly correlated with annual density of leafhoppers and to a lesser extent, with aphids. Nabis sp. densities were never different between glyphosate-treated and conventionally treated plots, and Nabis sp. density showed no relation to any of the herbivores tested. We concluded that no significant changes in heteropteran predator densities may be expected from moderate alterations in weeds arising from the deployment of herbicide-tolerant corn varieties and that leafhoppers are probably the herbivore prey that most influences Orius spp. densities in corn in our study area.     

Farm‐scale evaluation of the impact of Cry1Ab Bt maize on canopy nontarget arthropods: a 3‐year study

The cultivation of Cry1Ab‐expressing genetically modified MON810 (Bt maize) has led to public concern in Europe, regarding its impact on nontarget arthropods (NTAs). We have assessed the potential effects of DKC 6451 YG (MON810) maize on canopy NTAs in a farm‐scale study performed in Central Spain during 3 years. The study focused on hemipteran herbivores (leafhoppers and planthoppers) and hymenopteran parasitic wasps (mymarids) collected by yellow sticky traps, which accounted for 72% of the total number of insects studied. The dynamics and abundance of these groups varied among years, but no significant differences were found between Bt and non‐Bt maize, indicating that Bt maize had no negative effect on these taxa. Nonetheless, the Cry1Ab toxin was detected in 2 different arthropods collected from Bt maize foliage, the cicadellids Zyginidia scutellaris and Empoasca spp. A retrospective power analysis on the arthropod abundance data for our field trials has determined that Z. scutellaris and the family Mymaridae have high capacity to detect differences between the Bt maize and its isogenic counterpart. The use of these canopy NTAs as surrogates for assessing environmental impacts of Bt maize is discussed.     

Effects of genetically modified maize events expressing Cry34Ab1, Cry35Ab1, Cry1F,and CP4 EPSPS proteins on arthropod complex food webs

Four genetically modified (GM) maize (Zea mays L.) hybrids (coleopteran resistant, coleopteran and lepidopteran resistant, lepidopteran resistant and herbicide tolerant, coleopteran and herbicide tolerant) and its non‐GM control maize stands were tested to compare the functional diversity of arthropods and to determine whether genetic modifications alter the structure of arthropods food webs. A total number of 399,239 arthropod individuals were used for analyses. The trophic groups’ number and the links between them indicated that neither the higher magnitude of Bt toxins (included resistance against insect, and against both insects and glyphosate) nor the extra glyphosate treatment changed the structure of food webs. However, differences in the average trophic links/trophic groups were detected between GM and non‐GM food webs for herbivore groups and plants. Also, differences in characteristic path lengths between GM and non‐GM food webs for herbivores were observed. Food webs parameterized based on 2‐year in‐field assessments, and their properties can be considered a useful and simple tool to evaluate the effects of Bt toxins on non‐target organisms.     

Influence of herbicide tolerant soybean production systems on insect pest populations and pest-induced crop damage

Conventional soybean weed management and transgenic herbicide-tolerant management were examined to assess their effects on soybean insect pest populations in south Georgia in 1997 and 1998. Soybean variety had very little impact on the insect species observed, except that maturity group effects were observed for stink bug, primarily Nezara viridula (L.), population densities on some sampling dates. Stink bugs were more abundant on the early maturing varieties in mid-season. Velvetbean caterpillar, Anticarsia gemmatalis Hübner, potato leafhopper, Empoasca fabae (Harris), and grasshoppers Melanoplus spp. were more numerous on either conventional or herbicide-tolerant varieties on certain dates, although these differences were not consistent throughout the season. Soybean looper, Pseudoplusia includens (Walker), threecornered alfalfa hopper, Spissistilus festinus (Say), and whitefringed beetles, Graphognathus spp , demonstrated no varietal preference in this study. Few weed treatment differences were observed, but if present on certain sampling dates, then pest numbers were higher in plots where weeds were reduced (either postemergence herbicides or preplant herbicide plus postemergence herbicide). The exception to this weed treatment effect was grasshoppers, which were more numerous in weedy plots when differences were present. In post emergence herbicide plots, there were no differences in insect pest densities between the conventional herbicides (e.g., Classic, Select, Cobra, and Storm) compared with specific gene-inserted herbicide-tolerant materials (i.e., Roundup and Liberty). Defoliation, primarily by velvetbean caterpillar, was different between soybean varieties at some test sites but not different between herbicide treatments. We did not observe differences in seasonal abundance of arthropod pests between conventional and transgenic herbicide-tolerant soybean.     

Effects of weed density on the dispersal of Orius majusculus Reuter (Heteroptera Anthocoridae) within maize

Orius majusculus Reuter (Heteroptera: Anthocoridae) is the most common and abundant generalist predator in Spanish maize crops and is sensitive to drastic changes in weed density. We carried out a 2‐year study in the NE Iberian Peninsula to examine the dispersal of O. majusculus in maize plots with moderately high and low weed density. Insects were collected using yellow sticky traps and/or a bug‐vac aspirator. Dispersal was assessed using rubidium as a marker. Dispersal rate of O. majusculus differed between sampling periods, with a maximum between the 16 unfolded leaves (V16) to grain milky (R3) maize growth stages. However, we detected no differences in the distance moved by male and females of O. majusculus from rubidium‐marked areas in plots with moderately high or low weed density suggesting that changes in weed density do not affect the dispersal of O. majusculus within a maize field.     

Environmental impact of herbicide regimes used with genetically modified herbicide-resistant maize

With the potential advent of genetically modified herbicide-resistant (GMHR) crops in the European Union, changes in patterns of herbicide use are predicted. Broad-spectrum, non-selective herbicides used with GMHR crops are expected to substitute for a set of currently used herbicides, which might alter the agro-environmental footprint from crop production. To test this hypothesis, the environmental impact of various herbicide regimes currently used with non-GMHR maize in Belgium was calculated and compared with that of possible herbicide regimes applied in GMHR maize. Impacts on human health and the environment were calculated through the pesticide occupational and environmental risk (POCER) indicator. Results showed that the environmental impact of herbicide regimes solely relying on the active ingredients glyphosate (GLY) or glufosinate-ammonium (GLU) is lower than that of herbicide regimes applied in non-GMHR maize. Due to the lower potential of GLY and GLU to contaminate ground water and their lower acute toxicity to aquatic organisms, the POCER exceedence factor values for the environment were reduced approximately by a sixth when GLY or GLU is used alone. However, the environmental impact of novel herbicide regimes tested may be underestimated due to the assumption that active ingredients used with GMHR maize would be used alone. Data retrieved from literature suggest that weed control efficacy is increased and resistance development delayed when GLY or GLU is used together with other herbicides in the GMHR system. Due to the partial instead of complete replacement of currently used herbicide regimes, the beneficial environmental impact of novel herbicide regimes might sometimes be reduced or counterbalanced. Despite the high weed control efficacy provided by the biotechnology-based weed management strategy, neither indirect harmful effects on farmland biodiversity through losses in food resources and shelter, nor shifts in weed communities have been demonstrated in GMHR maize yet. However, with the increasing adoption rate of GMHR maize and their associated novel herbicide regimes, this situation is expected to change in the short-term. An erratum to this article can be found at     

Epigeic spiders are not affected by the genetically modified maize MON 88017

The genetically modified (GM) maize MON 88017 facilitates weed management owing to its tolerance to glyphosate, and resists western corn rootworm (WCR), Diabrotica virgifera virgifera, owing to the expression of Cry3Bb1 toxin. MON 88017 could therefore contribute to the solution of two major problems of European agriculture: continuous WCR spreading and high use of herbicides. To assess possible unwanted environmental impacts of MON 88017, we compared communities of spiders in plots planted in three successive years with this maize, its near isogenic non‐GM cultivar treated or not treated with an insecticide and two unrelated maize cultivars. Each of the five treatments was applied on five 0.5 ha plots in a 14 ha field. Spiders were collected in five pitfall traps per plot five times per year. Upon reaching the waxy ripening stage, all plants of first‐year cultivation were shredded to small pieces and ploughed into the soil in the respective plot, whereas in the 2nd and 3rd year the harvest was used for biogas production and only digestate was returned to the field. Out of 79 spider species, Pardosa agrestis, Pachygnatha degeeri and Oedothorax apicatus made up 28%, 25% and 23% of the total spider count in the 1st year of study; 2%, 8% and 84% in the 2nd; and 40%, 8% and 35% in the 3rd year. Statistical analysis did not reveal any influence of GM maize on the spider abundance and biodiversity. The abundance, and in two years also the species diversity, was insignificantly higher on the plots with GM maize than on plots with the insecticide‐treated non‐GM maize. The composition and size of spider community varied year to year, probably reflecting weather conditions and differences in field fertilization with organic matter.     

Bt rice in China — focusing the nontarget risk assessment

Bt rice can control yield losses caused by lepidopteran pests but may also harm nontarget species and reduce important ecosystem services. A comprehensive data set on herbivores, natural enemies, and their interactions in Chinese rice fields was compiled. This together with an analysis of the Cry protein content in arthropods collected from Bt rice in China indicated which nontarget species are most exposed to the insecticidal protein and should be the focus of regulatory risk assessment.     

Effects of weed harrowing frequency on beneficial arthropods,plants and crop yield

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Design and selection of trap color for capture of the tea leafhopper,Empoasca vitis,by orthogonal optimization

The tea leafhopper, Empoasca vitis (Göthe) (Hemiptera: Cicadellidae), is a major pest of the tea plant, Camellia sinensis (L.) O. Kuntze (Theaceae). In this study, the RGB color model was used to describe the colors of sticky traps. The most effective color for attraction of E. vitis was investigated by orthogonal optimization. The selected color was verified in tea gardens and the most effective height for positioning of color sticky traps for capturing tea leafhoppers was investigated. After the determination of the effect of the three color parameters and their interactions by orthogonal optimization, the color gold (RGB: 255, 215, 0) was selected as the most effective color to trap tea leafhoppers. In tea gardens, more leafhoppers were captured using gold sticky traps (RGB: 226, 204, 4) than using commercially available yellow sticky traps. The most effective height of gold sticky traps for trapping leafhoppers was 40–60 cm above the tea canopy. Few lady beetles were captured at this height. We conclude that the orthogonal optimization method is a convenient and efficient method to screen digitally generated colors for attracting and trapping of pests.     

Management of winter weeds affects Frankliniella fusca (Thysanoptera: Thripidae) dispersal

Frankliniella fusca (Hinds) naturally disperses from winter weeds to crops in spring, causing direct and indirect damage. Field preparation before planting includes use of herbicides or cultivation to kill unwanted vegetation, which adversely affects F. fusca host plants and potentially influences F. fusca dispersal. Common chickweed, Stellaria media (L.), infested with F. fusca, was used as a model to study effects of timing and type of vegetation management on adult dispersal. Infested weeds were caged and F. fusca weekly dispersal was monitored using sticky traps. Weed management treatments performed at an early (14 April-11 May) or late (2 wk after early treatment) date consisted of glyphosate, paraquat, disking, hoeing, or untreated control. Late glyphosate and hoeing treatments resulted in cumulative dispersal statistically similar to or greater than from control plots. Compared with the control, significantly more F. fusca dispersed from the glyphosate and hoeing plots during the 3 wk after treatment. More thrips dispersed from the late paraquat treatment 1 wk post-application than from the control. Dispersal from the disked treatment and early paraquat treatment was similar to that of the control 1- to 3-wk post-treatment. Early treatments resulted in significantly smaller cumulative dispersal than the control in all but one instance. Late disking and paraquat treatments resulted in cumulative F. fusca captures that were statistically similar or less than that in the control. Winter weed management type and timing affect F. fusca dispersal magnitude and duration.     

Impact of mowing and weed control on broadleaf weed population dynamics in turf

Abstract

Various turf management activities may influence weed population dynamics and interfere with weed control. The effects of a biocontrol agent, Sclerotinia minor, a chemical herbicide, Killex?, and mowing height on broadleaf weed dynamics were examined in two turfgrass stands for two consecutive years. Mowing did not reduce the population densities of dandelion or the ground cover of broadleaf weeds. In the second year, mowing significantly reduced white clover density, but significantly increased broadleaf plantain density, particularly at the closest mowing height (3–5 cm). Apart from the close height, the S. minor and Killex? treatments were equally effective in suppression of dandelion, white clover, broadleaf plantain, and prostrate knotweed in the second year. Common mallow increased in the herbicide treated plots and other species including yellow woodsorrel, yellow toadflax and lambsquarters increased in abundance in plots mowed at the 3–5 cm height and in plots treated with Killex?. Significant differences between the Killex? and S. minor treatments on dandelion population dynamics were rarely present and did not favour either treatment. S. minor did not damage the turfgrass, but Killex? reduced turf quality in 25% of the plots. The application of S. minor with a regular, medium height (～7 cm) mowing regime was highly effective in controlling broadleaf weeds in temperate Kentucky bluegrass turf.     

Impacts of Bt maize inoculated with rhizobacteria on development and food utilization of Mythimna separata

The current trend of increasing proportion of cultivation of transgenic Bt crops is pushing towards dramatic destabilization of the agroecosystem, thus raising severe concerns about the sustainability of transgenic Bt crops as an effective management tool for the control of target insect pests in the future. Rhizobacteria is the key biological regulator to ameliorate soil‐nitrogen utilization efficiency of crop plants, especially transgenic Bt crops. A laboratory study quantified the impacts of transgenic Bt maize (Line IE09S034 with Cry1Ie vs. non‐Bt maize cv. Xianyu335) inoculated with Azospirillum brasilense (AB) and Azotobacter chroococcum (AC) on the growth, development and food utilization of a target lepidopteran insect, Mythimna separata. The results showed that the inoculation of rhizobacteria significantly prolonged the larval lifespan and pupal duration, increased RCR and AD, reduced pupal weight, pupation rate, fecundity, RGR, ECD and ECI, and shortened adult longevity of M. separata fed on transgenic Bt maize, while exact opposite trends were found in these measured indexes of growth, development and food utilization for M. separata fed on non‐Bt maize inoculated with AB and AC compared with the buffer control in both years. Thus, the results clearly depicted that the inoculation of rhizobacteria had opposite influences on the growth, development and food utilization of M. separata fed on transgenic Bt maize. Presumably, rhizobacteria inoculation can be used to stimulate plant–soil‐nitrogen uptake and promote plant growth for transgenic Bt maize and non‐Bt maize, simultaneously increasing Bt toxin production and enhancing resistance efficiency against target lepidopteran pests for transgenic Bt maize.     

Mapping Grey Willow (Salix cinerea) stand architecture using airborne laser scanning: implications for large‐scale tree weed control

We investigated the potential of airborne laser scanning (ALS) for mapping the stand architecture of Grey Willow (Salix cinerea), an invasive wetland weed in New Zealand. In particular, we focused on two metrics, tree height and canopy density, both of which influence the efficacy and nontarget impacts of herbicides aerially broadcast by helicopter to control tree weeds. We compared ground‐based measures of Grey Willow height and canopy density with ALS‐derived data, and the relationship between canopy density as estimated by each method and aerial herbicide deposition at three wetland sites in New Zealand. Analysis revealed strong linear relationships between ground‐based and ALS metrics, indicating that ALS data could be used to generate accurate, high‐resolution digital maps of Grey Willow height and canopy density. These maps coupled with computer‐guided variable flow rate technologies, which enable optimal placement of herbicide, could maximise Grey Willow mortality while reducing the mortality of nontarget indigenous plants. We recommend the application of ALS‐derived maps and computer‐guided variable flow rate technology is investigated for more targeted large‐scale tree weed control.     

Does feeding on Bt-maize affect the slug Arion vulgaris (Mollusca: Arionidae)?

Via expression of Cry-proteins, toxic for specific insect groups, genetically modified Bacillus thuringiensis (Bt) maize offers an effective protection against insect pests. In a laboratory experiment with two transgenic and two non-transgenic maize varieties, a potential impact of Bt-maize was examined for the non-target slug Arion vulgaris. Lifetime after field collection, weight change and oviposition was examined for slugs fed with Bt-maize, non Bt-maize or dandelion (Taraxacum officinale). Test parameters were neither significantly different between transgenic and non-transgenic varieties nor among the maize varieties overall. Slugs fed with dandelion showed a significantly longer lifetime after field collection, gained significantly more weight and laid eggs. The results did not show a Bt-effect but indicated the general poor quality of maize as food resource for slugs.     

Commercially formulated glyphosate can kill non‐target pollinator bees under laboratory conditions

The use of glyphosate‐based herbicides in agroecosystems has increased over the past few years because of the advent of genetically modified glyphosate‐resistant crops and resistant weeds. This is alarming because of potential damaging effects on non‐target organisms. In sub‐Saharan Africa, for example Ghana, many rural farmers have not received training in the use of glyphosate‐based herbicides, thus tend to apply higher than recommended concentrations on farms. Therefore, this study investigated the effect of glyphosate‐based herbicides on beneficial insects under laboratory conditions, using Apis mellifera L. (Hymenoptera: Apidae, Apini) and Hypotrigona ruspolii (Magretti) (Hymenoptera: Apidae, Meliponini) as models. The bees were put in contact for 24 h with the recommended concentration of Sunphosate 360 SL, a glyphosate‐based herbicide, 2× the recommended concentration, or distilled water as control. The effect of the herbicide on the bees was compared to the effect of a lambda‐cyhalothrin insecticide. Generally, more bees died after contact with plants freshly sprayed with the herbicide than on herbicide‐treated filter paper. In both cases, more bees died after contact with the higher concentration of the herbicide. These findings suggest that beneficial insects, specifically A. mellifera and H. ruspolii, may get killed if they are sprayed upon or come into contact with plants that have been freshly sprayed with (more than) the recommended concentration of glyphosate‐based herbicides. Therefore, it is important to restrict access and use of such herbicides to trained personnel who will comply with spraying guidelines, that is, recommended concentrations and timing of spray. Spraying at a time when insects are flying about may be detrimental to beneficial insects such as pollinator bees, parasitoids, and predators.     

The impact of plant associations on Macrosteles quadrilineatus management in carrots

Habitat diversification can influence the interactions of insects with plants and this can be used in agroecosystems for the management of pest populations. Plant diversification can be achieved through planting crops, such as trap crops, or by adjusting weed management. Aster leafhopper, Macrosteles quadrilineatus Forbes (Hemiptera: Cicadellidae), is a polyphagous species that uses cereals, vegetables, and weeds as host plants. The influence of weeds on M. quadrilineatus abundance was investigated experimentally in carrot [Daucus carota L. cv. Canada (Apiaceae)] field plots by adjusting the level of management of two groups of weeds (broadleaf and grass) and by comparing it to weed‐free plots. The preference of M. quadrilineatus for different cereal and weed species relative to carrots was tested in choice test assays. Habitat context influenced the abundance of M. quadrilineatus in the field experiments. The presence of border crops such as oat, rye, barley, wheat, and triticale did not significantly attract or repel this insect to carrot plots compared to the no‐border treatment. However, spelt‐bordered plots had 42% fewer M. quadrilineatus than three treatments, triticale, wheat, and barley, that had the highest insect abundance. The type of weed management affected M. quadrilineatus abundance in carrot plots, but not the frequency of herbicide application. Plots that had carrot growing with broadleaf‐weeds had about 59% fewer M. quadrilineatus compared with those growing with crabgrass or carrot alone. In the greenhouse choice tests, grasses (e.g., cereals) attracted and broadleaf‐weeds repelled M. quadrilineatus relative to carrots. In summary, carrot growers may be able to manage this pest by reducing the interaction of cereal cover crops with carrots and eliminating grassy weeds in commercial production fields.