Reports arose from major Chinese wheat production regions that flixweed was not controlled by tribenuron after the herbicide was continuously used for several years. Flixweed seeds were collected from wheat fields that had been treated with tribenuron repeatedly over 3 to 15 yr or from road sides and remote hills that had never received tribenuron in Jiangsu, Hebei, Shanxi, Sichuan, Shandong, Shaanxi, and Henan provinces, and Tianjin and Beijing metropolises in China. The response of various biotypes to tribenuron was determined by whole plant experiments in the greenhouse. The experiments demonstrated that 11 of 32 flixweed biotypes were susceptible to tribenuron. The remaining 21 biotypes expressed moderate to high levels of tribenuron resistance with resistance indices ranging from 4 to > 1,500. DNA sequence analysis of acetolactate synthase (ALS) genes of selected biotypes 6, 7, 27, and 29 revealed a point mutation at position 197 of the ALS gene, as numbered relative to the protein sequence of Arabidopsis, where proline was substituted by leucine in biotype 7 and by threonine in biotype 29. These mutations are known to confer resistance to ALS-inhibiting herbicides and are responsible for the high resistance of these biotypes to tribenuron. The results also indicate that tribenuron resistance in flixweed is widespread in China and management programs to control these resistant populations are warranted.

Nomenclature: Tribenuron; flixweed, Descurainia sophia (L.) Webb ex Prantl DESSO; Arabidopsis, Arabidopsis thaliana (L.) Heynh. ARBTH; wheat, Triticum aestivum L.

Laboratory studies were conducted in 2006 and 2007 to evaluate the effects of temperature and propanil on alligatorweed control with penoxsulam. Biomass reduction of alligatorweed at 42 d after treatment (DAT) compared to nontreated was greatest at 21/11 C (day/night) compared to 26/18 C or 30/25 C for all treatments. Propanil plus penoxsulam reduced biomass less than penoxsulam applied alone, independent of temperature. At 21 and 27 C, delaying propanil application 3 d after penoxsulam provided similar biomass reduction to penoxsulam applied alone. At 27 C and 30 C, delaying propanil application 10 d after treatment was required to achieve biomass reduction greater or equal to penoxsulam applied alone. Absorption and translocation of ¹⁴C penoxsulam indicated that propanil reduced absorption of penoxsulam into the treated leaf of alligatorweed 48 h after treatment. This research demonstrates the potential for propanil to antagonize penoxsulam when applied to alligatorweed. Under the most severe antagonistic conditions (30 C) propanil applications following penoxsulam needed to be delayed 10 d to avoid antagonism.

Nomenclature: Penoxsulam; propanil; alligatorweed, Alternantherea philoxeroides (Mart.) Griseb. ALRPH.

Several field studies have observed increased foramsulfuron efficacy for the control of dallisgrass when foramsulfuron is applied after MSMA. Therefore, laboratory studies were conducted with mature dallisgrass to study the absorption and translocation of ¹⁴C-foramsulfuron, and then examine the impact of preliminary applications (preapplications) of MSMA or foramsulfuron on herbicide absorption and movement. Herbicide absorption increased rapidly through 4 h, and by 8 h, differences in absorption between pretreated and control plants were evident. After 48 h, foramsulfuron absorption in non-pretreated plants was 55%, whereas plants that received either pretreatment absorbed 70% of the herbicide. Translocation above (younger tissue) and below (older tissue) the treated leaf was 0.65 and 0.62% for non-pretreated plants, respectively. Pretreatment with foramsulfuron resulted in the translocation of 2.12 and 1.55% of applied radioactivity above and below the treated leaf, respectively. Pretreatment with MSMA resulted in the translocation of 2.33 and 2.34% of applied radioactivity above and below the treated leaf, respectively. These data indicated that pretreatment of mature dallisgrass with either foramsulfuron or MSMA results in an increase in both uptake and translocation of foramsulfuron applied 2 wk after pretreatment. The increase in absorption and translocation of foramsulfuron in the pre–MSMA-treated plants may explain the increase in control observed in the field when comparing it to the pre–foramsulfuron-treated dallisgrass plants.

Nomenclature: Foramsulfuron; MSMA; dallisgrass, Paspalum dilatatum Poir. PASDI.

Fifty corn poppy populations originating from three counties of northern Greece were evaluated for resistance to tribenuron. Twelve of the populations (six sampled from cereal fields and six from margins) were sampled from the county of Thessaloniki, 15 (13 sampled from wheat fields and two from margins) from Kilkis, and 23 (21 sampled from cereal fields and two from margins) from Serres. Fifty, 39, and 95% of the populations sampled from winter wheat fields originating from Thessaloniki, Kilkis, and Serres were resistant (R), respectively. However, all populations sampled from margins of the same areas were susceptible (S). All populations examined were susceptible to 2,4-D and bromoxynil. The level of resistance to tribenuron varied among populations with the herbicide dose required to reduce growth by 50% (GR₅₀) ranging from 41 g ha⁻¹ (R/S, resistance ratio 137) for the least resistant to over 720 g ha⁻¹ (R/S greater than 2,400) for the most resistant populations. Fresh weight accumulation, seed production, and capsule number of eight R populations grown under field conditions were similar to those recorded for eight S populations originating from sites with high proximity of their respective R populations. However, the estimated mean growth rate (MGR) indicated significant differences due to the resistance trait and the population's origin. In particular, the R populations that originating from Thessaloniki and Serres had MGR 1.3 to 4.3 times lower than the respective S populations, whereas the R populations from Kilkis had similar or higher MGR values compared to the respective S populations. The populations with the highest R/S (greater than 2,400) had low MGR values, and the populations with R/S ranging from 1,437 to 2,227 had high MGR values.

Nomenclature: Bromoxynil; tribenuron; corn poppy, Papaver rhoeas L. PAPRH.

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.

Nomenclature: Thifensulfuron; tribenuron; kochia, Kochia scoparia (L.) Schrad. KCHSC, synonym: Bassia scoparia (L.) A.J. Scott

The transfer of the imazethapyr-resistant gene from Clearfield™ (CL) rice to red rice is an ecological risk. Flowering synchronization and genetic compatibility between cultivated rice and red rice could influence gene transfer. We examined the (1) variability in maximum outcrossing rate between 12 red rice biotypes and ‘CL161’ rice during their peak flowering overlap in the field and (2) genetic compatibility of red rice biotypes with CL161 rice. Experiments were conducted at Stuttgart, AR, and Fayetteville, AR, from 2005 to 2007. To evaluate the flowering synchrony of red rice and CL161 rice as well as its impact on outcrossing rate, field experiments were conducted at four planting times from early April to late May. The red rice biotypes were planted in the middle row of nine-row CL161 plots and flowering was monitored. Outcrosses were evaluated in subsequent years by herbicide response and simple-sequence-repeat marker assays. To determine compatibility, manual crosses were performed between 12 red rice biotypes and CL161 rice in the greenhouse. The flowering duration of all red rice types ranged from 5 to 16 d after the onset of flowering in contrast to 6 d in CL161 rice. Ten of the twelve types of red rice had ≥ 70% overlap in flowering time with CL161 rice in at least one planting date. The maximum field outcrossing rate between red rice biotypes and CL161 ranged from 0.03 to 0.25%. The field outcrossing rate between red rice biotypes differed (P < 0.01), but flowering synchronization was not directly related to outcrossing rate. Manual crosses resulted in seed sets of 49 to 94%. The majority of red rice biotypes had similar compatibility with CL161 rice. Thus, other factors must contribute to hybridization rates in the field. Follow-up experiments should investigate other plant factors and environmental influence on hybridization rate.

Nomenclature: Imazethapyr; red rice, Oryza sativa L. ORYSA; rice Oryza sativa ‘CL161’.

Nalta jute and redweed are widespread and significant broadleaf weed species of the tropics. Experiments were conducted to determine the effects of various environmental factors on seed germination and seedling emergence of these species. Light was not required for germination in either species. Germination was stimulated by seed scarification, suggesting that inhibition of germination in these species is mainly due to the hard seed coat. Scarified seeds of both species germinated over a wide range of alternating temperatures (25/15, 30/20, and 35/25 C). Both species were moderately tolerant of salt and osmotic stress, but nalta jute tolerated more stresses than redweed. Seedling emergence of nalta jute and redweed was greater than 87 and 93%, respectively, at soil depths of 0 to 2 cm but decreased as depth increased, with no emergence at 8 cm. Seedling emergence of both species was reduced by the addition of rice straw, though a high amount (4 to 6 t ha⁻¹) of straw was required to suppress emergence significantly. The information gained from this study could facilitate the development of effective weed control programs.

Nomenclature: Nalta jute, Corchorus olitorius L.; redweed, Melochia concatenata L.; rice, Oryza sativa L.

Chinese sprangletop is a grass weed that has the ability to grow in both flooded and upland conditions, which makes it a widespread and abundant weed in rice and many other crops. Experiments were conducted to study the germination of this weed in the Philippines. Germination was strongly stimulated by light and warm fluctuating temperatures, suggesting high emergence of Chinese sprangletop on bare ground such as a crop seedbed. A high level of germination (95%) immediately after seed harvest suggests that the soil seed bank of this species could be depleted by stale-seedbed strategies. Seed burial depth in soil strongly influenced emergence of this weed, and no seedlings emerged from seeds buried at depths of ≥ 0.5 cm. Maximum emergence (80%) from seeds placed on the soil surface suggests that no-till practices would enhance the emergence of seedlings. Seedling emergence from surface-sown seeds was similar (80 to 82%) between saturated and aerobic-moist soil, demonstrating that this weed does not require a saturated soil and that it can emerge from a moist soil. Flooding, even though not continuous or deep, had a suppressive effect on the emergence and dry matter of Chinese sprangletop. Germination responses to light and seed burial depth were different between our study in the Philippines and the study conducted with seeds of an Italian population, suggesting that Chinese sprangletop might be polymorphic. The implications of this information for weed management strategies are discussed.

Nomenclature: Chinese sprangletop, Leptochloa chinensis (L.) Nees. LEFCH; rice, Oryza sativa L.

Twenty-day cohorts of corn poppy were grown in the presence or absence of barley, and seedling survival, biomass accumulation and allocation, plant reproduction, and seed dormancy were measured. Seedling survivorship and biomass accumulation differed strongly among cohorts and were influenced by crop competition. In the absence of crop competition, plants from the first three cohorts (emerging October to January) had 900% higher biomass and 160% more seeds per plant than later cohorts (emerging January to April). Crop competition reduced cohort fitness; for example, in 2003 to 2004, corn poppy biomass was reduced 57 to 96%, and seed production 77 to 97%. Seeds collected from plants that had emerged in spring were less dormant, and thus, germination and emergence of these seeds were higher (25% higher and 200 to 600% higher, respectively) than those for seeds collected from other cohorts. Environmental factors at the time of seed formation may be responsible for the observed differences in dormancy. Cohort-dependent emergence, growth, reproduction, and dormancy have relevant implications for corn poppy management and demography in agricultural systems in northeastern Spain. The dormant seeds produced by autumn to winter cohorts will be the main contributors to the seed bank and weed population shift in subsequent generations. For efficient corn poppy management, the control of cohorts emerging before or with the crop in a cereal field is essential.

Nomenclature: Corn poppy, Papaver rhoeas L.; barley, Hordeum vulgare L., ‘Graphic’.

The primary defense against seed mortality, the seed coat, is maternally derived. Hence, weed seed mortality in the soil seedbank is likely to be influenced by the maternal environment and genetics. We hypothesized that seed accessions from contrasting maternal environments (seed lots) exhibit different rates of seed mortality and that the relative differences among seed lots remain consistent across burial environments. Velvetleaf and giant foxtail annual seed mortality rates were studied in field experiments in Hickory Corners, MI, and Wooster, OH, using seed lots collected from the same locations. Seeds enclosed within mesh bags and unenclosed seeds (“seeded cores”) exhibited similar levels of seedbank persistence (r  =  0.90, P < 0.001) and seed mortality (r  =  0.65, P  =  0.006). Annual seed mortality rates ranged from 16 to 56% and 27 to 91% for seed lots of velvetleaf and giant foxtail, respectively. Relative differences among velvetleaf seed lots were consistent across burial environments in both years, whereas giant foxtail differences were consistent in only 1 of 2 yr. The relative ranks among velvetleaf seed lots varied between years, indicating that maternal environment may have influenced seed persistence more than seed-lot genetics. Within years, variation in seed mortality was predicted by changes in soil moisture in the burial environment (R²  =  0.47, P < 0.001 for velvetleaf; R²  =  0.34, P  =  0.007 for giant foxtail). Accelerated seed mortality was associated with moist soils (soil water potential  =  −6 kPa for velvetleaf, −7 kPa for giant foxtail). These results suggest that agronomic practices affecting the maternal environment and moisture levels in the soil seedbank may promote weed seed mortality in the soil seedbank.

Nomenclature: Giant foxtail, Setaria faberi Herrm. SETFA; velvetleaf, Abutilon theophrasti Medik. ABUTH.

There is little information available on performance interactions for tank mixtures of topramezone and acetolactate synthase (ALS)-inhibiting herbicides. Controlled-environment and field experiments were conducted in 2006 and 2007 to determine the interactions of topramezone when tank-mixed with ALS-inhibiting herbicides. Controlled-environment experiments were conducted on four annual grass species treated at the five- to six-leaf stage. Dose–response curves for large crabgrass, barnyardgrass, yellow foxtail, and green foxtail were generated for nicosulfuron or foramsulfuron alone and in combination with label rates of topramezone or mesotrione (with or without atrazine). Eight field experiments were conducted using registered rates of two ρ-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting and three ALS-inhibiting herbicides alone and in combination. All herbicide treatments in the field were applied at the two- to three-leaf and five- to six-leaf stages of barnyardgrass, green foxtail, giant green foxtail, and witchgrass. In both the controlled environment and field experiments, antagonistic interactions were found to be species specific. In the controlled environment, nicosulfuron antagonized topramezone for the control of large crabgrass and barnyardgrass, but did not influence control of yellow or green foxtail. This antagonism was overcome with the addition of atrazine or an increased dose of nicosulfuron. Antagonism was not observed with tank mixtures of topramezone and foramsulfuron on the species tested under controlled-environment or field conditions. In the field, antagonism was not influenced by growth stage of the annual grasses. Antagonistic interactions were observed when topramezone was tank-mixed with nicosulfuron or nicosulfuron rimsulfuron for the control of barnyardgrass and, to a lesser extent, giant green foxtail. Similar tank mixtures did not reduce control of green foxtail or witchgrass. HPPD-inhibiting herbicides are known to antagonize the activity of ALS-inhibiting herbicides for the control of annual grasses. This is the first report in the literature that an ALS-inhibiting herbicide can antagonize an HPPD-inhibiting herbicide. Thus, the chemistries of these herbicides exhibit a two-way antagonistic interaction.

Nomenclature: Atrazine; foramsulfuron; mesotrione; nicosulfuron; rimsulfuron; topramezone; barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; giant green foxtail, Setaria viridis var. major (Gaudin) Pospichel. SETVM; green foxtail, Setaria viridis (L.) Beauv. SETVI; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; yellow foxtail, Setaria glauca (L.) Beauv. SETLU; witchgrass, Panicum capillare L. PANCA.

Mesotrione is an effective herbicide for volunteer potato control but is not selective in several crops, including onion and carrot. Studies were conducted in 2006 to evaluate the effectiveness of wiper-applied mesotrione for control of volunteer potato in a potato crop. Surprisingly, nontreated potatoes growing adjacent to mesotrione-treated plants exhibited bleaching symptoms resembling mesotrione injury. Additional field trials confirmed injury to nontreated plants growing within 26 cm of potatoes treated with mesotrione applied with a wiper at 0.25, 0.5, and 1% (v/v) solutions. Greenhouse bioassays confirmed that mesotrione applied to potato leaves moved down through the plant and was exuded into perlite potting medium in sufficient quantities to injure potato plants that were exposed to the leachate from the perlite pots. In tracer studies, 52% of ¹⁴C-labeled mesotrione applied to potato leaves was absorbed into the potato plant by 15 d and 15% of the absorbed ¹⁴C-mesotrione was exuded into the soil and soil leachate. Mesotrione applied to potato by the wick application method has potential to injure neighboring susceptible plants from root uptake of exuded mesotrione.

Nomenclature: Mesotrione; carrot, Daucus carota L.; onion, Allium cepa L.; potato, Solanum tuberosum L.

Yellow nutsedge infests a large number of hectares in the Treasure Valley of eastern Oregon and western Idaho. Much of its continued expansion appears to be related to onion production in the valley. Fall applications of metham often produce inconsistent results when used to control yellow nutsedge before planting an onion crop. Trials were conducted in the laboratory to determine the influence on yellow nutsedge control of metham dose, duration of exposure, temperature during exposure, and tuber conditioning by washing and chilling at 3 C. All factors influenced metham efficacy against yellow nutsedge tubers. The dose causing 50% reduction in sprouting tubers (I₅₀) for metham ranged from 22 to 76 mg kg⁻¹ of soil and was lower for conditioned tubers than nonconditioned tubers across all conditions, except when tubers were exposed at 25 C for 3 d. Nonconditioned tubers were unaffected by metham after 1 d exposure at 5 C. Increasing exposure temperature or increasing exposure duration decreased sprouting for nonconditioned tubers. As exposure duration and exposure temperature increased, differences among conditioned and nonconditioned tubers were less. Temperature and exposure duration affects metham efficacy against yellow nutsedge, and the condition of the tubers at the time of treatment also has a significant effect. Applications of metham at a time when yellow nutsedge tubers are not dormant may improve yellow nutsedge control.

Nomenclature: Metham; yellow nutsedge, Cyperus esculentus L.; onion, Allium cepa L.

An important factor in controlling invasive plant infestations is frequently the acceleration of the deterioration of their persistent seed bank, which is often associated with physical dormancy mechanisms. We hypothesized that breaking dormancy by heat would enhance the vulnerability of the nondormant seeds to hydrothermal stresses. The aim of the present study was to examine the effect of soil solarization treatments (heating the soil by means of polyethylene mulching) on buried Australian Acacia seeds, with emphasis on Acacia saligna L. The results of three field experiments indicate that soil solarization treatments caused an almost complete eradication of buried seeds of Acacia saligna and two other Australian Acacia species, Acacia murrayana and Acacia sclerosperma. The killing mechanism of solarization was further studied in laboratory experiments. We observed two phases of the heat-induced deterioration of seed persistence: breaking the dormancy of the seeds and exposing the “weakened seeds” to lethal temperatures. From an ecological perspective of conservation, the present study shows for the first time the possible utilization of solar energy, by means of soil solarization, for reducing persistent seed banks of invasive woody plants.

Nomenclature: Acacia saligna L.

Modern invasion biology is a new science, with the holy grail of being able to predict the trajectory of particular invasions. Although this goal has yet to be achieved, there has been much progress through experimental research and meticulous study of the scope and mechanisms of existing invasions. Several well-established patterns are relevant to potential biofuel feedstocks: (1) ca. half of all damaging plant invaders were deliberately introduced, not accidental hitchhikers or escapees; (2) some native plants have become invasive; coevolution with native community members was not proof against unexpected damage; (3) many introduced plants were innocuous for decades or even centuries in their new locations before suddenly exploding across the landscape; lack of current observed impact does not guarantee safety; and (4) control or even eradication of widespread invaders is sometimes possible, but it is far from certain and it is often very expensive. We cannot count on effectively managing an introduction gone awry. Because much invasion biology is targeted at developing methods of preventing anthropogenic movement or establishment of species, invasion biologists have occasionally been assailed as obstructionists by various interests who fear their livelihoods will be impeded: the seed and horticulture trades, foresters, the pet industry, fish and game biologists, etc. A fringe group of philosophers, sociologists, landscape architects, and others have even taken to calling invasion biology a thinly veiled form of xenophobia. Some biofuels advocates have joined this litany, accusing invasion biologists of playing on the emotions of an uneducated public by raising fears of a new kudzu. Invasion biologists need not be cast in this role. In collaboration with agronomists, geneticists, physiologists, and other scientists, they have much to offer in understanding the risks posed by particular feedstocks and developing approaches that would minimize these risks and mitigate unforeseen consequences.

Nomenclature: Kudzu, Pueraria lobata (Willd.) Ohwi. PUELO.

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.

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.

Nomenclature: Giant reed, Arundo donax L.

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.

Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; giant foxtail, Setaria faberi Herrm. SETFA; velvetleaf, Abutilon theophrasti Medik. ABUTH; corn, Zea mays L.