Field trials were conducted in 2004 and 2005 to identify sulfonylurea (SU) herbicides that would provide improved weed control, minimal soil residual, and crop safety to SU-resistant chicory. SU-resistant chicory had previously been selected in vitro for resistance to chlorsulfuron. Our research evaluated three commercial, nonresistant and three breeding lines of SU-resistant chicory. Each of the cultivars was treated POST at the two true-leaf growth stage with either foramsulfuron, rimsulfuron, rimsulfuron plus thifensulfuron, tribenuron, thifensulfuron, thifensulfuron plus tribenuron, triflusulfuron, flumetsulam, or imazamox at normal use rates. Established plant densities and root yields of SU-resistant chicory breeding lines were greater than or equal to the densities and root yields of commercial cultivars. The plant density of commercial chicory cultivars was reduced by rimsulfuron, rimsulfuron plus thifensulfuron, tribenuron, and thifensulfuron plus tribenuron, but SU-herbicides did not reduce the density of SU-resistant breeding lines. SU-resistant chicory differed in cross-resistance to SU-herbicides, with tribenuron causing the most crop injury and thifensulfuron, the least. Weed control varied between the SU-herbicides. The greatest reduction in weed biomass occurred with tribenuron, thifensulfuron plus tribenuron, and rimsulfuron plus thifensulfuron; the least reduction occurred with triflusulfuron, foramsulfuron, and rimsulfuron. Chicory root yields comparable to the hand-weeded treatment were achieved with rimsulfuron plus thifensulfuron and thifensulfuron plus tribenuron treatments. The SU herbicides that met the initial project objectives of crop tolerance and improved weed control were combinations of rimsulfuron plus thifensulfuron and thifensulfuron plus tribenuron.

Sulfentrazone adsorption and mobility in six soils with varying soil properties were evaluated under laboratory conditions. Adsorption was evaluated using a modified slurry technique. Mobility was evaluated using packed-soil columns under saturated flow conditions. The order of adsorption to soil was Sequatchie loam > Dothan loamy sand = Bosket fine sandy loam > Malden loamy sand > Commerce silty clay loam > Harkey clay loam. Greater sulfentrazone adsorption occurred in soils with lower pH. Sulfentrazone movement under saturated flow conditions in 27-cm soil-packed columns was greater in soils with low adsorption, high pH, and coarse texture. Sulfentrazone movement was limited in the Sequatchie loam but was greater in the other soils examined. No clear relationship was evident between sulfentrazone mobility and adsorption in these soils.

Field studies were conducted from 2003 through 2006 to evaluate bundleflower tolerance to several postemergence (POST) herbicides commonly used in pastures. All herbicides except imazapic, metsulfuron, and 2,4-DB injured bundleflower at least 88% when rated 4 wk after treatment (WAT). When rated 8 WAT, metsulfuron, picloram, and picloram plus 2,4-D injured bundleflower greater than 90%. Imazapic stunted bundleflower (10 to 35% injury) throughout the growing season. When rated 52 WAT, dicamba plus 2,4-D, picloram alone, and picloram plus 2,4-D injured bundleflower at least 97% in one of two years. Emergence of bundleflower with picloram-containing treatments ranged from 16 to 67% of the nontreated control, whereas emergence after dicamba-containing treatments ranged from 67 to 97%.

Dry peas (pea) usually require early and effective weed management for optimum yields. However, it is not always possible to control all weeds with a single herbicide application. In experiments at Lacombe and Lethbridge, Alberta, Canada, we determined the relative importance of controlling redstem filaree or wild oat, or both species. Bentazon, sethoxydim, or a imazethapyr/imazamox mixture was applied to control redstem filaree, wild oat, or both weeds, respectively. None of the herbicides caused visually detectable crop injury. Time of weed removal effects on pea yield were inconsistent. In addition, applying half or full herbicide rates did not usually influence weed biomass, pea yield, or pea seed weight. Averaged across all variables except herbicide, pea yield losses due to competition from redstem filaree, wild oat, or both species averaged 31, 47, or 53%, respectively. When redstem filaree and wild oat were controlled with imazethapyr/imazamox, pea yields were the same as weed-free check plots in three of four location-years (89% of weed-free yields for all four location-years). Optimal pea yields in weed communities with redstem filaree and wild oat as dominant species were more dependent upon selecting an herbicide that controlled both species than a specific time of weed removal or herbicide rate.

The annual Southern Weed Contest has been a valuable asset for training graduate students in the applied aspects of weed science since its inception in 1980. Recently, participation in the contest has declined, which spurred the need to assess the contest's utility. Past participants in the contest from 1980 through 2004 were surveyed (1) to determine their perception of the importance, impact, and need for a weed contest activity in the southern region; and (2) to determine whether participation in the contest is contingent upon availability of study material resources and level of emphasis placed on the contest at each university. A total of 88 of 134 electronic surveys was returned, with at least 1 survey from each of the 14 universities in the southern region. Most participants (93%) expressed having had a pleasurable experience in the contest. Fifty-five percent of the respondents indicated that the contest either “increased” or “may have increased” their employment opportunities. Ninety-two percent of the respondents indicated that they had access to “excellent” or “adequate” resources to prepare for the contest. Ninety-eight percent of the respondents felt that the contest is still needed. Faculty involvement in student preparation was closely linked to team performance in the contest. There were numerous ideas put forth to increase participation along with ways to make the contest more interesting and relevant with the changing times. With less than 25% of the graduate students in the southern region competing in the contest for the last 3 years, there is obviously a disconnect between the apparent benefits of participation and the number of students taking advantage of it. However, participation alone without preparation does little to instill within students the confidence and knowledge necessary to make the contest an enjoyable experience. Ultimately, the future of the Southern Weed Contest rests on weed science faculty involvement from each university in the southern region and on recruitment of graduate students.

Field research was conducted to evaluate plant growth-regulator efficacy for tall fescue growth and seedhead suppression applied using application placement equipment. Specially designed equipment outfitted with fluid application systems applies low-volume plant growth regulator directly on plant foliage, reducing opportunity for drift and visible application. Wet-blade mowers are equipped to apply plant growth regulators and mow in a single pass, whereas rotary-wick applicators simply wipe chemicals directly on uncut vegetation. Therefore, a wet-blade, rotary-wick, and broadcast sprayer system were chosen to apply imazapic at three rates (9, 35, and 53 g ai/ha), and a mefluidide + chlorsulfuron tank mix at 7 + 140 g ai/ha to tall fescue roadsides for vegetative growth and seedhead suppression. Experiments were conducted during the spring and summer of 2004 in central and western North Carolina. Tall fescue was slightly injured and discolored by all treatments but fully recovered by 2 mo after treatment. Imazapic suppressed new vegetative growth 3 mo after treatment compared with the nonmowed–nontreated control (16.1 cm of growth) and the mowed–nontreated control (21.1 cm) when applied with the rotary-wick applicator (8.5 cm) and broadcast sprayer (6.2 cm). However, differences in vegetative height primarily occurred when application placement equipment treatments were compared with nontreated vegetation as opposed to mowed–nontreated plants. Although mowed–nontreated and wet-blade–treated plots had more new vegetative growth, nonmowed–nontreated plots still consistently had the greatest vegetative height. Seedhead suppression ranged from 87 to 100% when compared with the nonmowed–nontreated control, with wet-blade treatments consistently providing the least-effective seedhead suppression. Overall, application placement equipment did not improve plant growth-regulator efficacy when compared with the foliar broadcast spray.

Control of common lambsquarters with glyphosate in Michigan soybean fields has been inconsistent. Stem-boring insects and evidence of insect tunneling were found inside the stems of common lambsquarters plants not controlled with glyphosate. In 2004 and 2005, field surveys and studies were conducted to identify and evaluate the prevalence of stem-boring insects in common lambsquarters in Michigan and Indiana soybean fields to determine whether tunneling by insects occurred before or following POST glyphosate applications and to evaluate the effect of glyphosate rate, application timing, and insect tunneling on the control of common lambsquarters with glyphosate. Two insect species, the beet petiole borer (Cosmobaris americana) from the Curculionidae family and an unidentified leafminer fly larvae from the Agromyzidae family were found inside common lambsquarters stems. Leafminer larvae were present in Michigan soybean fields in mid- to late-June, when most POST glyphosate applications are made in Michigan and Indiana; however, beet petiole borer larvae were not found in common lambsquarters stems until mid-July and would only be present in common lambsquarters plants if glyphosate applications occurred at that time. Results from three field experiments in East Lansing, MI, demonstrated the variability in common lambsquarters control. Control ranged from 79 to 98%, 75 to 99%, and 49 to 97% from glyphosate applied at 0.84 kgae/ha to 10-, 25-, and 46-cm common lambsquarters, respectively. In general, applying glyphosate to common lambsquarters plants 10 cm or less, or increasing the glyphosate rate beyond 0.84 kgae/ha, improved common lambsquarters control. Insect tunneling by leafminer and beet petiole borer larvae did not contribute to reduced common lambsquarters control with glyphosate applied to 10- and 25-cm common lambsquarters.

Corn and soybean growers across Indiana were surveyed to assess their perceptions about the importance of preplant and POST weed control timing, focusing mainly on soybean production. Despite studies demonstrating the importance of planting into a clean field, almost a third of Indiana growers do not think it is important to plant into a weed-free seedbed and 74% do not use residual herbicides in glyphosate-resistant soybean production systems. Growers who farmed less than 200 ha were more likely to overestimate the ability of soybean to tolerate weed interference than growers who farmed more hectares. Growers who manage smaller farms were also more likely to use a one-pass weed control program than larger growers. This suggests that yield losses to weed interference may be greater for smaller farms than for larger farms. Weed size and density were the most common criteria used by growers to decide when to apply herbicides. This suggests that field scouting plays an important role in the decision-making process of growers. However, a substantial proportion of growers apply POST herbicides to large common lambsquarters and giant ragweed in an attempt to minimize the number of trips across the field for weed control. Delayed control of these species likely contributes to reduced crop yields, higher application rates, and to the survival of treated plants. Opportunities to improve control and increase yields through more optimal herbicide use appear possible for Indiana corn and soybean growers.

Voucher specimens and herbarium collections provide the foundation for many aspects of research in the plant sciences. Available for study and verification by contemporary and future workers, voucher specimens promote reproducibility in scientific method because permanent records document identification, distribution, and interspecific and intraspecific variation of species. The utility and importance of voucher specimens and herbarium collections in supporting research in weed science are discussed, and the collection, preparation, documentation, storage, and shipment of voucher specimens are detailed.

Base temperature (Tb) for leaf appearance and the thermal time interval between appearance of successive leaves (phyllochron) were determined for six common weed species from a series of growth chamber experiments. Mean leaf appearance Tb values for giant ragweed, velvetleaf, redroot pigweed, large crabgrass, woolly cupgrass, and wild-proso millet were 1.3, 8.0, 8.5, 4.5, 2.2, and 5.1 C, respectively, and mean phyllochron values were 37.2, 34.4, 17.3, 42.2, 65.2, and 34.2 growing degree-days per leaf, respectively. Phyllochron values increased slightly with mean temperature for each weed species. To our knowledge, these are the first reported leaf appearance Tb and phyllochron values for giant ragweed, woolly cupgrass, and wild-proso millet. The results confirm leaf appearance Tb and phyllochron values reported previously for velvetleaf and redroot pigweed. However, large crabgrass leaf appearance Tb and phyllochron values in our study varied somewhat from those reported previously. The results provide information needed for parameterization of plant growth models that predict leaf development based on thermal time.

New hybrid bluegrass cultivars have been bred for increased heat and drought tolerance compared with traditional Kentucky bluegrass cultivars. Research was conducted to evaluate hybrid bluegrass tolerance and smooth crabgrass and goosegrass control with mesotrione and quinclorac during seeded establishment. Mesotrione applied as a single application 14, 28, or 42 d after emergence (DAE) injured hybrid bluegrass acceptably from 1 to 11% 7 d after treatment (DAT). A sequential mesotrione application at 0.14 kg/ha 28 DAE did not injure hybrid bluegrass greater than the initial 14 DAE application; however, a sequential application at 0.28 kg/ha 28 DAE injured hybrid bluegrass greater than the initial 14 DAE application. Three sequential mesotrione applications did not reduce hybrid bluegrass ground cover 63 DAE. Quinclorac applied singly at 1.68 kg/ha 14 DAE and sequentially at 0.84 kg/ha 14 and 28 DAE injured hybrid bluegrass that continued throughout the rating period resulting in decreased ground cover at 63 DAE. Quinclorac at 0.84 kg/ha plus mesotrione at 0.28 kg/ha injured hybrid bluegrass < 20% throughout the rating period but reduced ground cover 63 DAE. All quinclorac-containing treatments controlled smooth crabgrass ≥ 92%. All mesotrione sequential-application treatments controlled smooth crabgrass and goosegrass ≥ 87%. These data indicate that sequential mesotrione applications can be used for smooth crabgrass and goosegrass control during seeded hybrid bluegrass establishment. Quinclorac should be applied according to label recommendations at 0.84 kg/ha no earlier than 28 DAE.

Weed management is a perennial challenge for growers, and continual innovation is essential to maintain the effectiveness of management technologies. The first generation of herbicide-resistant crops revolutionized weed control. However, weeds are adapting to crop systems that rely on a single mode of herbicide action. Crops with resistance to multiple modes of herbicide action could help maintain weed management. GAT/HRA is a new multiple herbicide–resistance technology for corn, soybean, and other crops. GAT/HRA combines metabolic glyphosate inactivation with an acetolactate synthase (ALS) enzyme that is insensitive to ALS-inhibiting herbicides. The mechanism to inactivate glyphosate is the glyphosate N-acetyltransferase enzyme, which transforms glyphosate into a nonphytotoxic metabolite. The gat gene is derived from a naturally occurring soil bacterium and optimized by repetitive gene shuffling and screening. The resistance mechanism to ALS-inhibiting herbicides is a double-mutant, highly resistant ALS (HRA) that is insensitive to all five classes of ALS herbicides. GAT/HRA crops will maintain natural tolerance to selective herbicides and thus provide more weed management options for growers to help deter weed spectrum shifts and delay the evolution of herbicide-resistant weeds.

Autoradiography is a radioisotope-based technique that allows absorbed and translocated herbicide to be visualized. Autoradiographs are traditionally produced with X-ray film and exposure times of several weeks. Phosphorescence imaging (PI) was investigated as an alternative autoradiography procedure. Smallflower morningglory plants were root-exposed to a series of 14C-atrazine concentrations, producing a series of increasing foliar radioactivity concentrations (i.e., dosage) that ranged from marginal to excessive with respect to autoradiography. Autoradiographs were subsequently produced from these 14C-atrazine-dosed plants using both the X-ray film and the PI technique. Autoradiographs from both techniques were of excellent quality and nearly identical when the dosage was ∼20 to 70 Bq/mg. However, PI produces an acceptable image in dosages either above or below this optimum range. A 1-d exposure time was sufficient with PI, and longer exposure times were not detrimental to image quality. In contrast, a 3-wk exposure time was required with X-ray film. Autoradiographs of selected herbicides are presented to further demonstrate the utility of PI.

The vast majority of crop hectares in the United States are treated with chemical herbicides annually. The adoption of herbicides for weed control was rapid in the 1950s and 1960s. Herbicides replaced the use of millions of workers to pull and hoe weeds by hand and greatly reduced the use of tillage for weed control. Costs of production were reduced and crop yields increased because herbicides were cheaper and more effective than hand weeding and cultivation. Organic crop growers cite weed control as their greatest difficulty in crop production because they are not permitted the use of chemical herbicides. They substitute hand weeding and cultivation for herbicides at a greatly increased cost and with reduced effectiveness. Aggregate studies that estimate the value of herbicides assume that growers would substitute a certain amount of hand weeding and tillage if chemicals were not used, which would not be sufficient to prevent yield losses totaling about 20% of U.S. crop production.

Considerable discussion has occurred among the weed science community regarding the potential benefits and limitations of integrated approaches to crop and pest management. This discussion also needs to occur in our weed science classrooms, where students from a wide range of academic disciplines are trained in the fundamentals of weed ecology and management. Although the inherent complexity of integrated crop and pest management can make this adaptation to our weed science courses challenging, the use of experiential learning techniques provides an effective means to promote understanding and retention of these concepts. This paper outlines several classroom activities based on the experiential learning approaches that have been implemented by the authors. The activities focus on (1) weed identification and natural history, (2) weed population processes, and (3) integrated management systems. For each activity, we offer our rationale for the exercise, an example of its implementation in the classroom setting, potential pitfalls, and student feedback regarding their perceptions of the activity's educational value. With this paper, we hope to provide examples that may be useful to other weed science educators wishing to incorporate more experiential learning activities into their courses and to initiate a dialogue between educators that can help our community improve and enliven weed science education.

Cogongrass is a highly invasive perennial grass that threatens agriculture, forestry, and native plant assemblages in many regions of the world. Cogongrass is a prolific seed producer, but the ecological importance of seeds as a vector of invasion has not been adequately addressed. Propagule pressure plays a key role in many successful invasions and the relative importance of propagule pressure across environmental gradients is an area of research that is quickly becoming important in understanding invasion success. The present study was conducted to test the effects of varying propagule density upon the ability of cogongrass seedlings to grow and establish across experimentally manipulated light and soil gradients. Seedlings growing in high-nutrient soil performed the best regardless of the amount of available light, but overall biomass was always greatest in high-light environments. Cogongrass showed a very strong trend in biomass allocation, with seedlings in reduced light environments partitioning more biomass to aboveground tissue. The data provided no evidence that initial propagule density affected the growth and establishment of cogongrass seedlings, but growth and biomass production were positively correlated with final seedling density.

The difficulty of monitoring growth parameters of climbing invasive plants subjected to different control options can be overcome by using standardized support structures (trellises). The utility of such support structures on aboveground biomass accumulation and fruit production was demonstrated using the invasive climber, bridal creeper in three invaded nature reserves near Perth in Western Australia. Mean above-ground plant biomass for plots provided with trellises ranged from 204 ± 38 g/m2 to 336 ± 31 g/m2, whereas it ranged from 66 ± 10 g/m2 to 118 ± 10 g/m2 in plots with no trellises. The mean number of fruits/m2 produced on shoots in plots provided with trellises ranged from 424 ± 159 to 3,787 ± 873 and was up to almost four orders of magnitude greater than the number of fruits produced on plants in plots with no trellis (ranging from 0 to 5.25 ± 7.9). The use of standardized trellises also showed that fruit volume and fruit seed number can vary significantly between sites. Standardized trellises have been installed at sites across Australia to assess the long-term impact of biological control agents introduced to manage bridal creeper.

Eradication is often stated as an essential element of weed management. Assessing the costs and benefits of eradication programs is often difficult because doing so requires speculation about the impacts and spread of weeds if eradication measures were not undertaken. The objective of this article is to describe and assess the Montana Dyer's Woad Cooperative Project, a program aimed at eradicating dyer's woad from Montana. The Project comprises four key components: early detection, treatment technologies, repeated site visits with monitoring, and education. To evaluate the success of the Montana Dyer's Woad Cooperative Project, we used monitoring data to observe the change in the number of counties where dyer's woad is present, plotted the trend in population size over time, and evaluated change in infestation size. We also predicted population spread based on the 1999 population size and demographic characteristics of dyer's woad. Dyer's woad has been eradicated from 9 of 13 infested counties in Montana, and infestation sizes have decreased in the remaining infested counties. In some counties, a containment effort was needed in conjunction with repeated inventories and treatment applications to prevent spread while depleting the seedbank to the point where eradication is possible. If not for the Project, our analysis suggests that some dyer's woad populations might consist of millions of plants, potentially covering 39,021 ha in Montana and costing $1.9 million/yr to manage. In comparison, the Project has reduced the total area infested in Montana to 2.6 ha and cost the state only $142,000 for the past 7 yr of management. In Montana, dyer's woad eradication from individual counties has been successful because of persistence and ongoing cooperative efforts.

There are nearly 75 species in the genus Amaranthus, part of the Amaranthaceae family, worldwide. In this large genus, there is a distinct group of 10 species that are dioecious (separate male and female plants). In contrast to the monoecious Amaranthus spp. which are represented by species endemic to every continent, the dioecious Amaranthus spp. are all native to North America. The Amaranthus spp. have a long documented history of being fellow travelers with humans. In recent years, three dioecious Amaranthus spp.: Palmer amaranth (Amaranthus palmeri S. Wats.), common waterhemp (Amaranthus rudis Sauer), and tall waterhemp [Amaranthus tuberculatus (Moq) Sauer] have become major weeds to row crops in North America. Palmer amaranth has become a very troublesome weed to cotton (Gossypium hirsutum L.), corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] production in large parts of the southern United States, and the waterhemp complex is now a major weed pest in corn and soybean production in the midwestern United States (Horak and Loughin 2000; King 1966; Mabberly 1997; Robertson 1981; Sauer 1950, 1955, 1972; Wax 1995).

Certified Crop Advisors of Arkansas and members of the Arkansas Crop Consultants Association were surveyed in Fall 2006 through direct mail to assess current weed management practices and needs in cotton from both a research and educational perspective. Consultants reported scouting 162,300 of the possible 473,700 ha of cotton grown in Arkansas. Collectively, glyphosate-resistant and enhanced glyphosate-resistant cultivars were reported grown on 98% of the cotton hectares. Ninety-five percent of the consultants believe the planting of enhanced glyphosate-resistant cultivars will increase over the next 5 yr. All consultants indicated a “moderate” to “high” level of concern with herbicide-resistant weeds in cotton, and 79% of the consultants suspect herbicide resistance in the fields they scout, predominately glyphosate-resistant horseweed. Horseweed, Palmer amaranth, and morningglories were the three most problematic weeds in cotton. A continued focus on resistant weed management was the most frequent research and educational request by consultants.