To avoid major negative impacts of the widespread adoption of biofuel species, whether they are exotic species, natives, or novel constructs, we need a system for screening their weed potential. Australia is an important global center of biodiversity and also has major cropping industries to protect. Prevention of the entry of further weeds is therefore a major national priority. The Weed Risk Assessment (WRA) system was developed and implemented for importation decisions in 1997; it has since been introduced into other countries and is probably as good as any system currently in operation. However, we need to be aware of the limitations of any system, to address these, and to work toward improved or alternative systems. WRA is a very simple spreadsheet requiring answers to questions about a species' life-history traits, dispersal, habitat suitability, impacts on other species, and history overseas, which are then added together and compared with numerical decision criteria. Its predictive powers are limited by this simplicity and by the complexity of human attitudes toward risk and impact. Alternative risk-management methods are available but, even so, the capacity for improvement is limited. It is quite possible, therefore, that in using any trait-based system to assess the negative risks of importation or interstate translocation of biofuel species, we will wrongly reject a valuable species or approve a species that turns out to be a major weed. It is suggested that, rather than attempting to improve a single-tiered decision-support system (the quarantine “sieve”), a multitiered system (nested sieves) would lead to a more effective system and greater cost-effectiveness. The key to this would be a postentry screening process for those species that have successfully passed through the WRA system.

Field experiments were conducted near Blackville, SC, and Tifton, GA, in 2004 and 2005, to evaluate the effect of wild radish and rye cover crops on weed control and sweet corn yield when used in conjunction with lower-than-recommended herbicide rates. Cover crop treatments included wild radish, rye, and no cover crop, alone and in conjunction with half and full rates of atrazine (0.84 and 1.68 kg ai ha−1) plus S-metolachlor (0.44 and 0.87 kg ai ha−1) applied before sweet corn emergence. Florida pusley, large crabgrass, spreading dayflower, ivyleaf morningglory, and wild radish infested the test sites. Wild radish and rye cover crops without herbicides reduced total weed density by 35 and 50%, respectively, at 4 wk after planting (WAP). Wild radish in conjunction with the full rate of atrazine plus S-metolachlor controlled Florida pusley, large crabgrass, and ivyleaf morningglory better than rye or no cover crop treated with a full herbicide rate in 2004 at Blackville. In 2005, at Blackville, weed control in sweet corn following wild radish cover crop plots alone was not different from that following rye. Wild radish or rye in conjunction with a half or full rate of atrazine and S-metolachlor controlled > 95% Florida pusley, wild radish, and large crabgrass in sweet corn at Tifton during both years. Ten glucosinolates, potential allelopathic compounds, were identified in wild radish, including glucoiberin, progoitrin, glucoraphanin, glucoraphenin, glucosinalbin, gluconapin, glucotropaeolin, glucoerucin, glucobrassicin, and gluconasturtin. Sweet corn yields at Blackville and Tifton following wild radish or rye cover crops were similar between the half and full rates of atrazine plus S-metolachlor. Sweet corn in wild radish or rye cover crop plots without herbicides produced less-marketable ears than herbicide-treated plots, indicating that a combination of cover crops and herbicides are required to optimize yields and to obtain desirable weed control.

Most nonnative plants that have become naturalized and even invasive were deliberately introduced into their new range—prompting the quip that we have often “invited trouble” by enthusiastically importing species as putative sources of food, fiber, or fuel without assessing their potential damage. Gant reed is a case in point: a large, rapidly growing grass introduced long ago in the United States that has already become a riparian invader in California and Texas. Concern about the ability of giant reed to wreak environmental damage has taken on new urgency as it is now being touted as a potential biofuel feedstock. Ambitious proposals call for creation of huge plantations devoted to the grass's cultivation. Needed is neutral, comprehensive, transparent accounting of the pros and cons (literally, the credits and debits) of the widespread planting of nonnative biofuel candidates, especially giant reed. Otherwise, the United States could embark on plans to introduce giant reed throughout a much larger new range, while simultaneously paying for its removal—obviously conflicted policies.

Experiments were initiated to determine if the tropical soda apple (TSA) biological control agent, Tobacco mild green mosaic tobamo virus (TMGMV), could be mixed with synthetic herbicides to provide effective broad-spectrum weed control. When TMGMV was mixed with 2,4-D ester or amine, metsulfuron, or hexazinone, TSA control ranged between 80 and 100%. On average, TMGMV increased TSA control by 81% as compared to these herbicides applied alone. Treatment applications were made by rubbing only three leaves, not as a broadcast application. Although this is not the optimum method for herbicide application, it does indicate the level of control the herbicide alone potentially provided relative to the herbicide/TMGMV mixture. Results indicate that the majority of TSA control was due to virus and that the herbicides mixed with TMCMV did not interfere with the virus's ability to infect TSA. Additions of organosilicone adjuvants or low rates of crop oil or nonionic adjuvants to TMGMV solutions resulted in greater infection of TSA. The finding that TMGMV remains infective when mixed with herbicides will allow greater flexibility for landowners attempting to control TSA and other troublesome weeds.

An overview of bioinformatics is presented with an emphasis on describing a set of tools, databases, and ontologies useful to the weed science community. These tools can be used to identify genes whose product may be the target site of a herbicide or in the degradation pathway of a xenobiotic. They may identify receptors responsible for pathogen recognition or enzymes in the metabolic pathway for allelopathic compounds. Whatever the gene of interest, bioinformatics allows researchers to assemble complete or partial genes from expressed sequence tags (ESTs), complete cDNAs, or complete genomes and then translate them into their corresponding amino acid sequences. Similarity searches can be used to find other proteins with homology to the gene of interest, which can provide clues to its function from the annotation of these database hits. The use of protein domain databases can also provide insight into the functional capabilities of the protein in question and delineate those portions essential for activity. Enzyme Commission (EZ) numbers or gene ontology (GO) descriptors allow placement of the protein within the larger network context of a biological system. These capabilities allow the scientist to probe deeper into the function of their protein of interest to gain a novel understanding of the biology.

Invasive plants can respond to injury from natural enemies by altering the quantity and distribution of biomass among woody materials, foliage, fruits, and seeds. Melaleuca, an Australian tree that has naturalized in south Florida, has been reunited with two natural enemies: a weevil introduced during 1997 and a psyllid introduced during 2002. We hypothesized that herbivory from these and other adventive organisms (lobate-lac scale and a leaf-rust fungus) would alter the distribution and allocation of biomass on melaleuca trees. This hypothesis was tested by temporally assessing changes in aboveground biomass components in conjunction with the presence of natural enemies and their damage to melaleuca trees. Melaleuca trees of different diameters representing the range (1 to 33 cm diam at 1.3 m height) within study sites were harvested during 1996, prior to the introduction of herbivorous insects, and again during 2003 after extensive tree damage had become apparent. Aboveground biomass, partitioned into several components (woody structures, foliage, fruits, and seeds), was quantified both times in Broward, Miami–Dade, and Palm Beach county sites located in south Florida. The two harvests within each site were performed in closely-matched melaleuca stands, and changes in biomass components were compared between years. Total biomass and woody portions decreased in Broward, whereas they increased in Miami–Dade and Palm Beach sites. Reductions in foliage (on all trees) and seed biomass (among seed-bearing trees) were greatest at Broward and least at Miami–Dade County site. Hence, overall seed and foliage production was severely reduced at the Broward site where both the natural enemy incidence and damage were more abundant compared to other sites. We therefore attribute the reduced foliar biomass and reproductive capability of melaleuca trees to infestations of natural enemies. These findings highlight the role that natural enemies can play in the long-term management of invasive tree species.

Vineyard weed communities were examined under four dormant-season cover-crop systems representative of those used in the north-coastal grape-growing region of California: no-till annuals (ANoT) (rose clover, soft brome, zorro fescue), no-till perennials (PNoT) (blue wildrye, California brome, meadow barley, red fescue, yarrow), tilled annual (AT) (triticale), and a no-cover-crop tilled control (NoCT). Treatments were carried out for 3 yr in the interrows of a wine grape vineyard. Glyphosate was used to control weeds directly beneath the vines, in the intrarows. Treatments significantly impacted weed biomass, community structure, and species diversity in the interrows. Orthogonal contrasts showed that tillage, and not the presence of a cover crop, impacted interrow weed biomass. Distance-based redundancy analyses (db-RDA) revealed significant effects of the cover-crop systems and of tillage on weed community structure in the interrows. For scarlet pimpernel and spiny sowthistle, the combination of ANOVA and orthogonal contrasts confirmed their association with the tilled treatments, as revealed by db-RDA. This same approach identified the association between California burclover and the no-till treatments. Our findings of no significant effects of the cover-crop systems on weed biomass, community structure, or diversity in the intrarows demonstrate that the impacts the cover-crop management systems had on the interrows did not carry over to adjacent intrarows. In addition, the fact that the cover crops did not affect vine yield, growth, or nutrition relative to the no-cover-crop control suggests that cover crops are likely to minimize soil erosion from winter rains, which is the primary purpose of vineyard cover cropping in northern California, without adversely affecting vine health or weed control.

Research was initiated in March 2005 to test various integrated purple nutsedge management strategies over two growing seasons in an organic production system in which bell pepper was grown as a fall crop. Main plots consisted of integrated purple nutsedge management strategies from mid-March through July 2005 and 2006. The main-plot factors were (1) green polyethylene film, (2) clear polyethylene film, (3) turnip followed by (fb) green polyethylene film, (4) turnip fb clear polyethylene film, (5) tillage every 3 wk, and (6) fallow. Subplots consisted of hand-weeding, mulching with wheat straw, and no weeding following bell pepper transplanting in early August. Purple nutsedge tuber density was determined in March, August, and November each year. Viable tubers were categorized into three sizes: small (0.1 to 0.25 g), medium (0.26 to 0.50 g), and large (> 0.50 g). The initial tuber density averaged 500 small, 300 medium, and 110 large tubers m−2 in mid-March 2005 (910 total tubers m−2). Total tuber density increased to > 5,400 tubers m−2 in fallow, nonweeded plots by November 2006. Yearly tuber density remained relatively constant over the 2 yr when the fallow period was fb hand-weeding in the bell pepper crop. Density of large and medium tubers in the season-long management systems remained stable, whereas small tubers were prone to depletion over time. Frequent tillage or use of a polyethylene film with or without turnip resulted in a lower density of large tubers in November 2006 relative to fallow treatments, regardless of management intensity in bell pepper. The density of large tubers after 2 yr was similar among treatments involving frequent tillage or use of a polyethylene film with or without turnip, regardless of subplot treatment; this was also observed for medium tubers, but not for small tubers. All hand-weeded plots had comparable densities of small tubers, ranging from 25 to 194 viable tubers m−2. Intensive management involving frequent tillage or use of a translucent polyethylene film with or without turnip fb hand-weeding was not effective in eradicating purple nutsedge over two growing seasons. Purple nutsedge management costs calculated for each main-plot treatment revealed that use of a translucent polyethylene film alone was at least 4.5-fold more costly than frequent tillage. This research demonstrates that season-long management is essential to prevent purple nutsedge proliferation over time.

Field experiments were conducted in northern Greece during 2001 and repeated in 2002 and 2004 to evaluate the effects of pronamide on sugar beet. Total leaf area, leaf area index (LAI), leaf and root dry weights, photosynthetic yield (quantum yield of photochemical energy conversion in photosystem II), chlorotic index, and yield components of sugar beet were monitored after pronamide application. Three sugar beet cultivars, ‘Avantage’, ‘Dorothea’, and ‘Bianca’, requiring short, intermediate, and long vegetative periods, respectively, were subjected to treatment. Pronamide was applied on sugar beet either as a double application of 0.63 kg ai ha−1 at the two- to four-leaf and 0.63 kg ai ha−1 at the four- to six-leaf stage or as a single application of 1.26 kg ai ha−1 performed at the latter leaf stage. Both application procedures were combined with a split application of phenmedipham at 0.04 kg ai ha−1 plus desmedipham at 0.04 kg ai ha−1 plus metamitron at 0.70 kg ai ha−1 plus ethofumesate at 0.10 kg ai ha−1 plus mineral oil at 0.50 L ha−1 applied POST at the cotyledon–to–two-leaf as well as at the four-leaf growth stages. Pronamide (both single and double application) initially caused chlorosis and reduction of sugar beet growth. LAI and photosynthetic yield were also significantly affected for a 2-mo period following the final application, after which the negative effects caused by pronamide were ameliorated. At harvest, sugar beet root and sugar yield, sucrose, K+, Na+, and N-amino acid concentrations were not affected by the herbicide treatments compared with those produced in weed-free and herbicide-free plots, indicating that all cultivars managed to overcome the transient pronamide stress. Regarding sugar beet cultivars, root and sugar yield of Avantage and Dorothea at harvest were higher than that of Bianca, whereas sucrose concentration of Avantage was the lowest. There was not an apparent relationship between the order of sugar yield per cultivar (Dorothea > Avantage > Bianca) and the length of the vegetative period (Avantage < Dorothea < Bianca).

Understanding the spatial variability of herbicide sorption to soil is important in determining the bioavailability as well as leaching potential of the chemical across a field. Multiple methods have been used to estimate herbicide sorption variability at the macroscale, but it has been difficult to measure soil heterogeneity or herbicide sorption at the individual field level. One method to determine soil heterogeneity is to create zones within a field based on maps of the apparent bulk soil electrical conductivity (ECa). These zones can be used to direct soil sampling to determine the fraction of organic carbon (foc) of each zone. The foc, in turn, can be used to predict the variability of herbicide binding among zones. Surface (0 to 30 cm) bulk-soil electrical conductivity (ECs) maps were made for three sandy fields in eastern Colorado, and soil samples were taken from the ECs zones within each field. The foc, and the soil–water partition coefficient (Kd) for EPTC, metribuzin, and metolachlor were determined for each sample. There were significant correlations between ECs and foc (R = 0.75) and between foc and Kd for EPTC, metribuzin, and metolachlor (R = 0.66, 0.61, and 0.71, respectively) across all three fields. Additional soil samples taken from the ECs zones located in previously unsampled areas of the three fields showed that one could reasonably predict Kd values for metribuzin, metolachlor, and possibly, EPTC based on the foc zones derived from ECs maps.

Genome sequencing of many model systems, including the human, yeast, Arabidopsis, and rice genomes, has been completed. As a complement to genomic techniques, proteomics has emerged to study the composition, structure, function, and interaction of the expressed proteins or proteome in a given cell, tissue, or organism. During the past several years, tremendous progress has been made with proteomic techniques in human and yeast, but progress has been slower in plants due to several factors. Proteomic techniques have been used in plants, especially in agriculturally important crops and weeds, to understand mechanisms of herbicide tolerance and weed resistance. Proteomic techniques, starting from protein extraction to protein identification, have been developed and advanced for large-scale proteomics studies, but limitations and problems for these techniques still exist for plant proteomics. Further technological improvements are needed to enhance quantitative and comparative large-scale proteomics studies. Applications of these techniques may help weed scientists to understand stress tolerance in crops and investigate weediness traits further. Proteomic techniques have unique strengths but also offer several challenges. Together with transcriptomics and metabolomics, these techniques for analyzing global patterns of gene expression offer new and novel techniques for better understanding biological questions of interest to weed scientists in the future.

A standard method for evaluating weed seed predation is needed to facilitate generalizations across studies. Identification of general trends could allow practical recommendations for enhancing weed seed predation in agricultural systems. The objective of this study was to compare the commonly used sandpaper and soil substrate methods for offering weed seeds when assessing seed predation rates. Invertebrate seed predators and associated weed seed predation levels were measured in June to July, August, and September of 2005 and 2006 within a conventionally managed corn system. Seed predation levels of three common weed species, velvetleaf, giant foxtail, and common lambsquarters, were estimated using feeding trials in which 40 seeds of each species were offered over a 48 h period using the two substrates. Exclosures were used to distinguish total predation from predation by invertebrates alone. In addition, we investigated the use of geospatial analysis to estimate spatial autocorrelation of invertebrate populations and seed removal rates. Results suggest caution in using synthetic substrates, such as sandpaper, when assessing seed predation, especially when investigating small-seeded species (< 1 mg seed−1) or when seed predators are predominantly invertebrates. By contrast, predation of the larger-seeded species, velvetleaf, was less affected by substrate, perhaps because of removal predominately by vertebrates. One way to overcome problems with the sandpaper substrate method is for studies to include some soil substrate samples for on-site calibration of the sandpaper substrate. If necessary, data could then be corrected by multiplying by the ratio of soil substrate measured-predation rate to sandpaper measured-predation rate. Spatial autocorrelation explained between 6 and 9% of the variation in giant foxtail and common lambsquarters removal rates attributed to invertebrates alone. Researchers should, therefore, be careful not to neglect the impact of clustered invertebrate populations and associated seed removal rates.

Genome sequences and genome-wide transcript profiles are becoming increasingly available, opening a way to use this information in analyzing how groups of genes are connected in pathways or “regulons” that might explain how organisms accomplish the integration on an organismal level. We have begun to explore the large datasets that are available for transcripts of the best characterized plant model, Arabidopsis thaliana, setting up a gene network using clustering methods. A network, based on the Graphical Gaussian Model (GGM), describes coregulation of genes under a variety of external factors: abiotic, biotic, and chemical treatments. In its present structure, the network reveals coregulation for more than 7,000 genes in the Arabidopsis genome. The network appears to be particularly suited to reveal the regulatory structure of biochemical pathways and environmental stress responses. Examples describe network predictions centered on a trehalose-6-phosphate phosphatase, an Arabidopsis response regulator and EPSPS. Results from the statistical analysis and bioinformatics of large data sets provide hypotheses that must be checked by additional studies. However, networks, which should be expanded from transcripts to also include proteins and metabolites, can be expected to explain not only how the Arabidopsis gene network is structured, but also provide insight in how similar networks in weed species might deviate or show correspondence and overlap.

Diclofop-resistant Italian ryegrass is a major weed problem in wheat production. This study aimed to determine the resistance pattern of diclofop-resistant Italian ryegrass accessions from the southern United States to the latest commercialized herbicides for wheat production, pinoxaden and mesosulfuron, and to other acetolactate synthase (ALS) and acetyl-CoA carboxylase (ACCase) inhibitors. Twenty-nine of 36 accessions were resistant to the commercial dose of diclofop. The majority (80%) of diclofop-resistant accessions were also resistant to clodinafop. Of 25 diclofop-resistant accessions, 5 were resistant to pinoxaden. All accessions tested were susceptible to the commercial dose of clethodim and sethoxydim. The cross-resistance pattern of diclofop-resistant Italian ryegrass to other ACCase inhibitors was 20% for pinoxaden and none with clethodim or sethoxydim. One accession was resistant to mesosulfuron but not to diclofop. This mesosulfuron-resistant accession was cross-resistant to sulfometuron but not to imazamox. All diclofop-resistant accessions tested were susceptible to ALS inhibitors, mesosulfuron, sulfometuron, and imazamox. Therefore, diclofop-resistant Italian ryegrass in Arkansas can be controlled with imazamox (in Clearfield wheat) and can mostly be controlled with mesosulfuron and pinoxaden. It could also be controlled by other selective grass herbicides in broadleaf crops.

Control of weeds growing around field edges to limit seed production is an important component of preventative weed management. POST herbicide rates that are effective on weeds growing within a dense corn or soybean canopy may not be high enough to control weeds at the edge of a field. A study was conducted from 2004 through 2006 to compare velvetleaf growth and fecundity at the edge of the field as opposed to within the crop in response to a range of glyphosate rates. Treatments included position (plot center or edge), time of emergence (VE or V4 crop growth stage) and glyphosate rate (0 to 900 g ae ha−1). Without herbicide application, velvetleaf plants grown on the edge flowered earlier, had thicker stems, and produced more seed capsules than plants grown in the center of the plots. At glyphosate application rates of 200 to 900 g ha−1, the percentage of plants surviving and reproducing was higher on the edge than within the crop. Edge plants treated with 900 g ha−1 of glyphosate produced more seeds than center plants that received no herbicide. Dose–response curves were used to estimate the glyphosate rate that would reduce seed production of surviving plants to 80% of the untreated plants. Plants emerging at the VE stage were estimated to require 300 g ha−1 within the corn or soybean canopy and 668 g ha−1 on the crop edge, whereas plants emerging at the V4 stage would require 0 g ha−1 within the canopy and 280 g ha−1 on the crop edge.

Genetic markers have been used in horticulture and conservation biology to identify breeding lines, assess genetic diversity, and examine gene flow. In weed science, analysis of genetic markers is not as common, as the focus often lies in the development of control methods. This is unfortunate, because advances in genetic marker techniques may lead to innovative methods in controlling weedy plants. Microsatellites, random amplified polymorphic DNA (RAPDs), intersimple sequence repeats (ISSRs), amplified fragment length polymorphisms (AFLPs), DNA sequences, single nucleotide polymorphisms (SNPs), and derived cleaved amplified polymorphic sequences (dCAPS) have been used in studying genetics of weedy plants. Beyond assessing genetic diversity of weeds, markers have been used to examine gene flow, patterns of dispersal, ploidy levels, and relationships of weedy and nonweedy species, as well as identifying founder populations. Identification of closely related species may indicate the potential for hybridization, cross reactivity of chemical applications, or nontarget biological control effects. Furthermore, markers have been used in identification of mutations conferring herbicide resistance and identification of regions correlating fitness of weedy and hybrid plants in new habitats. Knowledge from genetic markers provides fundamental information that can be used in advancing chemical and biological control in weed management. This article serves as a review of these marker types and their application to weed science.

Restoring range sites dominated by western juniper is central to maintaining healthy functioning shrub–steppe ecosystems. On sites without adequate species composition to respond favorably to juniper controlled by fire, revegetation is necessary. We tested the following two hypotheses related to restoration after juniper control: (1) higher seeding rates would translate into higher density of seeded species, and (2) a rich seeding mixture would provide higher density and biomass than monocultures. Western juniper control was done by cutting 25% of the trees in 2002, allowing cut trees to dry for one year, followed by a broadcast fire applied in October 2003 which killed the remaining live juniper trees. Seeding treatments were applied in 2003 and included seeding six native species in monocultures, seeding a mixture of all six species at four rates (16.8, 22.4, 28.0, or 33.6 kg ha−1 of pure live seeds), and a nonseeded control. Treatments were applied on a Sagebrush/bunchgrass and Snowberry/fescue site. We found that bluebunch wheatgrass, Idaho fescue, big bluegrass, and western yarrow density ranged from 450 to 700 plants m−2, which was over six-fold that of the control in 2004 at both sites. Only arrowleaf balsamroot did not establish successfully. The density of big bluegrass nearly doubled from 2004 to 2005. The highest plant density resulted from the highest seeding rate. The highest biomass production was combination seeding at 22.4 kg ha−1 on the Sagebrush/bunchgrass site and 33.6 kg ha−1 on the Snowberry/fescue site. Seeding a combination of species resulted in a moderate to high density of plants and optimized plant diversity and richness over seeding monocultures.