Weed Management Programs Research Articles

Seeding plants for long-term multiple ecosystem service goals

The historical management of agroecological systems, such as California's rangelands, have received criticism for a singular focus on agricultural production goals, while society has shifting expectations to the supply of multiple ecosystem services from these working landscapes. The sustainability and the multiple benefits derived from these complex social-ecological systems is increasingly threatened by weed invasion, extreme disturbance, urban development, and the impacts of a rapidly changing and increasingly variable climate. California's grasslands, oak savannas, and oak woodlands are among the most invaded ecosystems in the world. Weed eradication efforts are rarely combined with seeding on these landscapes despite support for the inclusion of the practice in a weed management program. Depending on seed mix choice, cost and long-term uncertainty, especially for native seed, is an impediment to adoption by land managers. We investigated four seeding mixes (forage annual, native perennial, exotic perennial, and exotic-native perennial) to evaluate how these treatments resist reinvasion and support the delivery of simultaneous multiple ecosystem services (invasion resistance, native richness, nitrogen fixing plants, pollinator food sources, plant community diversity, forage quality, and productivity). We found the increase of exotic and native perennial cover will drive resistance to an invading weedy summer flowering forb Centaurea solstitialis but provides a mixed response to resisting invasive annual grasses. The resistance to invasion is coupled with little tradeoff in forage productivity and quality and gains in plant diversity and native cover.

Opportunities and challenges for harvest weed seed control in global cropping systems.

The opportunity to target weed seeds during grain harvest was established many decades ago following the introduction of mechanical harvesting and the recognition of high weed-seed retention levels at crop maturity; however, this opportunity remained largely neglected until more recently. The introduction and adoption of harvest weed seed control (HWSC) systems in Australia has been in response to widespread occurrence of herbicide-resistant weed populations. With diminishing herbicide resources and the need to maintain highly productive reduced tillage and stubble-retention practices, growers began to develop systems that targeted weed seeds during crop harvest. Research and development efforts over the past two decades have established the efficacy of HWSC systems in Australian cropping systems, where widespread adoption is now occurring. With similarly dramatic herbicide resistance issues now present across many of the world's cropping regions, it is timely for HWSC systems to be considered for inclusion in weed-management programs in these areas. This review describes HWSC systems and establishing the potential for this approach to weed control in several cropping regions. As observed in Australia, the inclusion of HWSC systems can reduce weed populations substantially reducing the potential for weed adaptation and resistance evolution. © 2017 Society of Chemical Industry.

Weeds and ground-dwelling predators' response to two different weed management systems in glyphosate-tolerant cotton: A farm-scale study.

The use of glyphosate, as a post-emergence broad-spectrum herbicide in genetically modified glyphosate-tolerant (GT) cotton, supposes a big change in weed management programs with respect to a conventional regime. Thus, alterations in arable flora and arthropod fauna must be considered when evaluating their potential impacts. A 3-year farm-scale study was conducted in a 2-ha GT cotton crop, in southern Spain, to compare the effects of conventional and glyphosate herbicide regimes on weed abundance and diversity and their consequences for ground-dwelling predators. Surveys reveal that weed density was relatively low within all treatments with a few dominant species, with significantly higher weed densities and modifications of the floristic composition in glyphosate-treated plots that led to an increase in the abundance of Portulaca oleracea and to a reduction in plant diversity. The activity-density of the main predatory arthropod taxa (spiders, ground beetles, rove beetles and earwigs) varied among years, but no significant differences were obtained between conventional and glyphosate herbicide regimes. However, significant differences between treatments were obtained for ground beetles species richness and diversity, being higher under the glyphosate herbicide regime, and a positive correlation with weed density could be established for both parameters. The implications of these findings to weed control in GT cotton are discussed.

Evaluating Mustard Seed Meal for Weed Suppression in Potato (Solanum tuberosum)

Mustard seed meal (MSM) derived from Sinapis alba controls weeds for several weeks following application to soil, but also has potential to injure the planted crop. Producers of certified organic potatoes typically utilize a combination of cover crops, soil hilling, harrowing, and cultivation for weed control. Once the potato canopy nears row closure, most late emerging weeds are suppressed by the dense potato canopy. MSM may have value for early season weed suppression in potato, but has not been previously tested. Our objectives were to determine the weed control efficacy and potato tolerance to MSM. We evaluated response of potatoes and weeds to MSM applied at 1.1, 2.2, and 4.5 MT ha-1 applied in a band on the potato hill just after a shallow harrowing and prior to potato emergence as part of an integrated weed management program in potatoes. MSM applied at 2.2 and 4.5 MT ha-1 reduced early season grass and broadleaf weed density 73 to 99% and 54 to 98%, respectively, in potato and reduced late season broadleaf weed biomass 71 to 94% in all three years tested. Early season grass weed density in potato was reduced by MSM at 2.2 and 4.5 MT ha-1. Late season grass weed biomass was reduced by the highest rate of 4.5 MT ha-1. MSM at 4.5 MT ha-1 caused minor injury to potato (3 to 15%) at 3 weeks after emergence, but did not reduce total tuber yields or percentage of US No.1 tubers. MSM could be a component of an integrated weed control program in potato.

Comparing Canopy Hyperspectral Reflectance Properties of <i>Palmer amaranth</i> to Okra and Super-Okra Leaf Cotton

Palmer amaranth (Amaranthus palmeri S. Wats.) is a major weed problem of cotton (Gossypium hirsutum L.) production systems in the southern United States. Hyperspectral remote sensing has shown promise as a tool for crop weed discrimination, and there is a growing interest in using this technology for identifying weeds in cotton production systems. Information is lacking on differentiating Palmer amaranth from cotton with an okra leaf structure based on canopy hyperspectral reflectance properties. Two greenhouse studies were conducted to compare canopy hyperspectral reflectance profiles of Palmer amaranth to canopy hyperspectral reflectance profiles of okra and super-okra leaf cotton and to identify optimal regions of the electromagnetic spectrum for their discrimination. Ground-based hyperspectral measurements of the plant canopies were obtained with a spectroradiometer (400 - 2350 nm range). Analysis of variance (ANOVA, p ≤ 0.05), Dunnett’s test (p ≤ 0.05), and difference and sensitivity measurements were tabulated to determine the optimal wavebands for Palmer amaranth and cotton discrimination. Results were inconsistent for Palmer amaranth and okra leaf cotton separation. Optimal wavebands for distinguishing Palmer amaranth from super-okra leaf cotton were observed in the shortwave infrared region (2000 nm and 2180 nm) of the optical spectrum. Ground-based and airborne sensors can be tuned into the shortwave infrared bands identified in this study, facilitating application of remote sensing technology for Palmer amaranth discrimination from super-okra leaf cotton and implementation of the technology as a decision support tool in cotton weed management programs.

Multiscale Invasive Plant Monitoring: Experiences from the Greater Everglades Restoration Area

AbstractObtaining spatially explicit, cost-effective, and management-relevant data on invasive plant distributions across large natural areas presents considerable challenges. This is especially true when multiple monitoring objectives exist, because the utility of different monitoring methodologies varies with scale, logistical considerations, and information needs. The Florida Everglades is a vast wetland landscape with widespread invasive plant infestations and multiple management jurisdictions. A multi-agency team Working Group conducted a workshop in 2013 to explore opportunities to enhance the performance of a regional weed control program. Among the most important developments occurring at this meeting was the recognition that relevant management questions are scale-dependent. This led the team to define multiple monitoring objectives. Essential for conveying the success of the weed management program is quantifying large-scale patterns of change, as are quantifying fine-scale patterns informing control activities, defining mechanisms of spread, recognizing accelerating rates of spread, and detecting patterns of occupancy immediately before management intervention. The group’s deliberation resulted in the emergence of a multiscale monitoring program utilizing several distinct monitoring protocols, including systematic landscape-level reconnaissance, a sample-based spatially stratified monitoring system, detailed inventories in planned treatment areas, and a set of methods focused solely on early detection and rapid response. Here we provide an overview of the Everglades multiscale invasive plant monitoring program, highlight benefits and challenges of each program component, and discuss how this program has improved regional invasive plant management.

Cereal Rye Cover Crop Suppresses Winter Annual Weeds

Cover crop (CC) adoption has increased in North America corn and soybean production areas. The objective was to evaluate the impact of cereal rye CC on winter annual weeds. Cereal rye reduced winter annual weed density and biomass by >90% at time of spring termination, showing potential as a component of an integrated weed management program.

Seed Dormancy and Seed Morphology Related to Weed Susceptibility to Biofumigation

Biofumigation is practiced to control soilborne pests and weeds in agronomic fields. The objectives of this research were to assess the dose response of weed seeds to Indian mustard biofumigation and associate responses to seed dormancy state, initial dormancy, and seed parameters. A petri dish biofumigation methodology was developed to expose seeds of common lambsquarters, bird vetch, wild carrot, common ragweed, green foxtail, velvetleaf, hairy galinsoga, and red clover to allelochemicals produced after rehydrating 0 (control), 1.94, 2.90, 5.81, 11.61, and 17.41 mg cm−2of dried mustard powder. Weed species expressed specific dose responses, estimated ED50, LD50, and maximal mortality. Hairy galinsoga and wild carrot were consistently the most affected by biofumigation, with maximal mortality reaching 97% and 95%, ED50values for germination were 1.91 and 2.68 mg cm−2, and LD50values were 3.31 and 3.69 mg cm−2of dried mustard tissue, respectively. Initial dormancy was assessed by germination and tetrazolium tests. Seed parameters such as testa thickness, relative weight of the testa, and seed size were measured directly by manual dissection, weighing seed structures, and stereomicroscopic imaging software measurements. Linear regression analyses revealed initial dormancy to be positively related to ED50and LD50values with a significant interaction with seed surface and seed width, respectively. Exposure to 5.81 mg cm−2of dried mustard powder increased common ragweed seed mortality for after-ripened seeds by 293% and by 58% for primary dormant seeds compared with untreated seeds. Mortality of common lambsquarters secondary and primary dormant seeds increased by 730% and 106%, respectively, and for wild carrot by 1,193 and 156%, respectively. Results underline the potential to incorporate biofumigation into weed management programs for repression of susceptible weed species.

Pulse Crop Tolerance and Weed Control with Fall‐Applied Soil‐Residual Herbicides

Core Ideas Limited weed control tools is a challenge for pulse production in the northern Great Plains. Soil‐applied residual herbicides are an important component of integrated weed management programs. Most herbicide programs adequately controlled kochia and Russian‐thistle in the pulse crops. Season‐long control of kochia and Russian thistle in dry pea, lentil, and chickpea. Weed management is a challenge for pulse producers in the northern Great Plains (NGP). Multi‐location trials were conducted in Montana to evaluate crop safety and weed control in spring‐planted pulse crops from soil‐residual herbicides applied the previous fall in postharvest wheat (Triticum aestivum L.) stubble. Dry pea (Pisum sativum L.), lentil (Lens culinaris L.), and chickpea (Cicer arietinum L.) were planted the subsequent spring in herbicide‐treated plots. Metribuzin (210 or 420 g ha−1), flumioxazin (107 or 214 g ha−1), pyroxasulfone (119 or 238 g ha−1) + carfentrazone (8 or 16 g ha−1), pendimethalin (532 or 1064 g ha−1) + dimethenamid‐P (945 or 1890 g ha−1), sulfentrazone (164 or 328 g ha−1) + carfentrazone (18 or 36 g ha−1), sulfentrazone (101 or 202 g ha−1) + metribuzin (151 or 302 g ha−1) applied the previous fall had no significant visual injury (≤8% early‐season) or yield reductions in dry pea and chickpea. However, sulfentrazone‐based programs caused unacceptable crop injury (up to 75% early‐season) and yield reductions in lentil. Unacceptable early season injury and yield reductions were observed in pulse crops with thiencarbazone + isoxaflutole‐based programs. Metribuzin or pyroxasulfone + carfentrazone at twice the recommended fall‐use rate(s) and flumioxazin, sulfentrazone + carfentrazone, or sulfentrazone + metribuzin even at the recommended fall‐use rate(s) provided 75 to 99% end‐season control of kochia [Kochia scoparia (L.) Shrad.] and Russian‐thistle (Salsola tragus L.). These herbicide programs will provide new tools for weed control in pulse crops.

Double-Mutated 5-Enol Pyruvylshikimate-3-phosphate Synthase Protein Expressed in MZHG0JG Corn (Zea mays L.) Has No Impact on Toxicological Safety and Nutritional Composition.

MZHG0JG corn will offer growers the flexibility to alternate between herbicides with two different modes of action in their weed-management programs, helping to mitigate and manage the evolution of herbicide resistance in weed populations. The proteins conferring herbicide tolerence in MZHG0JG corn, double-mutated 5-enol pyruvylshikimate-3-phosphate synthase protein (mEPSPS) and phosphinothricin acetyltransferase (PAT), as well as the MZHG0JG corn event, have been assessed by regulatory authorities globally and have been determined to be safe for humans, animals, and the environment. In addition to the safety data available for these proteins, further studies were conducted on MZHG0JG corn to assess levels of mEPSPS as compared to previously registered genetically modified (GM) corn. The results support the conclusion of no impact on toxicological safety or nutritional composition.

Can alternating temperatures be used to estimate base temperature for seed germination?

SummaryModelling weed seedling emergence pattern appears to be a promising approach in the development of effective weed management programmes based on the selection of optimal timing of control operations. Thermal and hydrothermal time models propose that seed germination rates are proportional to the amount by which temperature and water potential exceed threshold values for these environmental factors. Hence, base temperature for seed germination is a fundamental biological parameter for the prediction of weed emergence. A series of laboratory experiments were conducted to estimate base temperature in three weed species belonging to the Asteraceae family, predominant in conservation tillage fields in north‐eastern Italy. The traditional method based on germination assays at constant temperatures was compared with a method based on assays at alternating temperatures. The latter might represent an alternative to the former for those species which do not germinate or only poorly under constant temperatures. Base temperature was estimated by regressing the reciprocal of the median germination time on temperature comparing two functions, a broken‐stick and an exponential‐type model. Both models showed good fit to all data in the whole temperature range and in almost all cases provided similar estimates of base temperature. The main result is that, for the weed species examined in this study, the use of alternating temperatures for base temperature estimation appears to be possible. However, further research is required to test if the use of germination assays performed at alternating temperatures can be a suitable method to estimate base temperature of species that have too low germination at constant temperatures.

Tolerance and Suppression of Weeds Varies among Carrot Varieties

Slow carrot emergence and canopy development render the crop a poor competitor with weeds. In this study, the ability to suppress weeds and maintain yield in the presence of weeds was compared among nine carrot varieties that included those selected by plant breeders for rapid vegetative canopy development compared to traditional varieties. Two weed management treatments were compared: handweeding for 21 d after carrot seeding versus handweeding for the entire carrot season. In years and locations with low to moderate weed pressure, such as in the 2014 study, differences among carrot varieties in weed competitiveness or tolerance were less apparent and therefore less relevant. Maximum carrot yield loss to weed competition among varieties was 28% in 2014. Yield loss in the presence of weeds was 15% or less with six of the nine carrot varieties. However, when weed pressure was intense in the 2015 study, both carrot plant density and carrot canopy development were inversely related to weed biomass. Carrot yield loss in the presence of weeds ranged from 38 to 87%. Despite correcting seeding populations for differences in germination among carrot varieties, carrot stand establishment varied greatly and would likely affect subsequent weed control measures such as timely cultivation or herbicide application. Future research efforts are warranted that consider carrot stand establishment factors and their relationship with integrated weed management programs.

Phenological behaviour of Parthenium hysterophorus in response to climatic variations according to the extended BBCH scale

AbstractConsidering the importance of ecological and biological traits in imparting invasive success to the alien species, the phenological behaviour of an alien invasive weed Parthenium hysterophorus was documented according to the extended BBCH scale in four different seasons. A phenological calendar was prepared using both two‐ and three‐ digit coding system, precisely describing the developmental stages of the weed. The phenological documentation is further supplemented with the dates corresponding to a particular growth stage, pictures of the representative growth stages and meteorological data of all the four seasons. Results revealed that the phenology of the weed altered in response to the changing temperature and humidity conditions but no apparent climatic condition could inhibit its germination or flowering. However, the emergence of inflorescence was highly sensitive to the temperature/photoperiodic conditions. Variations in the phenological traits of P. hysterophorus with changing environmental conditions explain the acclimatisation potential of the weed permitting its vast spread in the non‐native regions. Since the given phenological illustrations are accurate, unambiguous and coded as per an internationally recognised scale, they could be exploited for agronomic practices, weed management programmes, and research purposes.

Comparative Programs for Arthropod, Disease and Weed Management in New York Organic Apples.

Organic apple production in the eastern US is small and is mostly based on existing varieties, which are susceptible to scab, and rootstocks, which are susceptible to fire blight. This requires numerous sprays per year of various pesticides to produce acceptable fruit. From 2014 to 2016, we tested different arthropod, disease and weed management programs in an advanced tall spindle high-density production system that included disease-resistant cultivars and rootstocks, in an organic research planting of apples in Geneva, New York. Arthropod and disease management regimens were characterized as Advanced Organic, Minimal Organic, or Untreated Control. Results varied by year and variety, but, in general, the Advanced program was more effective than the Minimal program in preventing damage from internal-feeding Lepidoptera, plum curculio, and obliquebanded leafroller, and less effective than the Minimal program against damage by foliar insects. Both organic programs provided comparable control of sooty blotch, cedar apple rust, and fire blight, with some variability across cultivars and years. The advanced selection CC1009 and Modi seemed to possess complete resistance to cedar apple rust, while Pristine had partial resistance. For weed control, bark chip mulch, organic soap sprays, and limonene sprays tended to be most effective, while mechanical tillage and flame weeding had lower success.

Weed Management Programs with Pyroxasulfone in Field Corn (Zea mays)

Field experiments were conducted in Louisiana and Mississippi from 2011 through 2013 to evaluate crop injury, weed control, and yield in field corn following pyroxasulfone applied PRE and POST. Pyroxasulfone PRE or POST did not injure corn at any evaluation. Barnyardgrass control was not improved with the addition of any POST treatment to pyroxasulfone alone or atrazine plus pyroxasulfone PRE; however, all POST treatments increased barnyardgrass control to at least 95% at all evaluations following atrazine PRE. All treatments that contained a PRE followed by POST application controlled browntop millet ≥90% at all evaluations. All POST treatments increased ivyleaf morningglory control to ≥92% following atrazine or pyroxasulfone alone PRE. However, control with atrazine plus pyroxasulfone PRE was similar or greater 28 d after POST than all treatments that received a POST application. In the absence of a POST treatment, pyroxasulfone or atrazine plus pyroxasulfone PRE controlled Palmer amaranth 93 to 96% at all evaluations, but atrazine alone PRE provided 84, 82, and 66% control 7, 14, and 28 d after POST, respectively. All programs that contained a PRE followed by POST herbicide treatment controlled Palmer amaranth >90% at all evaluations. Corn yield following all treatments except atrazine alone PRE and the nontreated were similar and ranged from 10990 to 12330 kg ha−1. This research demonstrated that pyroxasulfone can be a valuable tool for weed management in a corn weed management program.

Weed control in minor crops in Spain after adoption of European regulation 1107/2009/EC and directive 2009/128/EC

Vegetable crops have become a source of great economic importance to many countries, particularly Spain. Crops should be protected from weeds in their early stages of development to prevent yield loss. It must be noted that there are limited registered herbicides for minor regional horticultural crops that generate little commercial interest. In this article, we discuss the implementation of European Regulation (Directive on Sustainable Use of Pesticides 2009/128/EC) in National Action Plans regarding horticultural minor use crops and the use of plant protection products with reference to evidence from Spain. The Spanish National Action Plan for the Sustainable Use of Plant Protection Products was implemented in 2012 by the Ministry of Agriculture, Food and Environment. Studies of the critical period of competition for weed control are a key component to help in developing a clear scheme that can be used for the design of effective integrated weed management programs. We highlight the urgent need for research and investigation into these areas and specifically ‘minor use’ crops due to the significant reduction of active substances approved in the European Union.

Effects of Environmental Conditions on the Fitness Penalty in Herbicide Resistant Brachypodium hybridum.

Herbicide-resistance mutations may impose a fitness penalty in herbicide-free environments. Moreover, the fitness penalty associated with herbicide resistance is not a stable parameter and can be influenced by ecological factors. Here, we used two Brachypodium hybridum accessions collected from the same planted forest, sensitive (S) and target-site resistance (TSR) to photosystem II (PSII) inhibitors, to study the effect of agro-ecological parameters on fitness penalty. Both accessions were collected in the same habitat, thus, we can assume that the genetic variance between them is relatively low. This allow us to focus on the effect of PSII TSR on plant fitness. S plants grains were significantly larger than those of the TSR plants and this was associated with a higher rate of germination. Under low radiation, the TSR plants showed a significant fitness penalty relative to S plants. S plants exhibiting dominance when both types of plants were grown together in a low-light environment. In contrast to previous documented studies, under high-light environment our TSR accession didn’t show any significant difference in fitness compared to the S accession. Nitrogen deficiency had significant effect on the R compared to the S accession and was demonstrated in significant yield reduction. TSR plants also expressed a high fitness penalty, relative to the S plants, when grown in competition with wheat plants. Two evolutionary scenarios can be suggested to explain the coexistence of both TSR and S plants in the same habitat. The application of PSII inhibitors may have created selective pressure toward TSR dominancy; termination of herbicide application gave an ecological advantage to S plants, creating changes in the composition of the seed bank. Alternatively, the high radiation intensities found in the Mediterranean-like climate may reduce the fitness penalty associated with TSR. Our results may suggest that by integrating non-herbicidal approaches into weed-management programs, we can reduce the agricultural costs associated with herbicide resistance.

Response of Alectra vogelii Benth to Different Crop Root Exudates

Aims: The aim of the study was to evaluate the effect of root exudates from cowpea, groundnut, maize, sorghum and pearl millet genotypes on the germination and attachment of Alectra vogelii. It also aimed to identify functional groups in the powdered root samples that stimulate A. vogelli germination. Study Design: In the laboratory, a Complete Randomised Design (CRD) replicated six times with six treatments; cowpea (IT18, CBC2 and CBC3); groundnuts (Nyanda), maize (PAN 413), sorghum (Landrace) pearl millet (Landrace) and a negative control (distilled water) were used. Place and Duration of Study: Department of Agronomy Laboratory, Midlands State University Gweru, Zimbabwe (19°25’S and 29°50’E), between March 2014 to May 2014. Methodology: To assess the germination and attachment of A. vogelii seeds, three seeds from each genotype were placed on a moistened filter paper in a petri dish with 0,01 g of preconditioned A. vogelii seeds. Identification of functional groups from the powdered root samples of all the crop genotypes using the FT-IR spectroscopy was also done. Results: Significant differences (P<.05) in the germination of A. vogelii were observed among the crop genotypes. All Cowpea genotypes and groundnut showed no statistical differences and had the highest germination percentages ranging between 72%-80%. The pearl millet landrace (62%) and groundnut (72%) also showed no statistical differences. Sorghum and maize allowed for low germination percentages (29.6% and 24.5%, respectively) Significant differences were noted among attachment counts (P<.05), however, with no statistical differences noted among the three cowpea varieties, which had the highest counts recorded on attachments (123-139 attachments). Significantly low counts on attachment were recorded in groundnut and all the cereals, ranging between 9-15 counts. The FT-IR spectra obtained from the root samples showed differences and similarities as revealed by the peaks (groundnut, CBC2 and PAN 413 - 8 peaks; IT 18, CBC3 and sorghum – 7 peaks; pearl Millet – 5 peaks). Conclusion: Groundnut and pearl millet genotypes caused effective suicidal germination of A. vogelii seeds and therefore can be used as trap crops in Integrated Weed Management Program. Maize and sorghum did not effectively support germination or attachment. Use of High Performance Liquid Chromatography (HPLC) and mass spectrometry to identify and quantify the strigolactones in each genotype is highly recommended.

The Eco-Evolutionary Imperative: Revisiting Weed Management in the Midst of an Herbicide Resistance Crisis

Modern weed science is at a crossroads. Born out of advances in chemistry, it has focused on minimizing weed competition with genetically uniform crops and heavy reliance on herbicides. Paradoxically, the success obtained with such an approach and the reluctance to conduct integrated and multidisciplinary research has resulted in unintended, but predictable, consequences, including the selection of herbicide resistant biotypes. Advances in eco-evolutionary biology, a relatively recent discipline that seeks to understand how local population dynamics arise from phenotypic variation resulting from natural selection, habitat distribution, and propagule dispersal across the landscape are transforming our understanding of the processes that regulate agroecosystems. Within this framework, complementary tactics to develop alternative weed management programs include the following: (1) weed scientists must recognize that evolution occurs within crop fields at ecologically-relevant time scales and is rooted in the inherent variation that exists in all populations; (2) weed management should recognize that the probability of a resistant mutant is directly related to the population size; (3) farmers need to acknowledge that herbicide resistance transcends any one farm and should coordinate local practices with regional actions; (4) incentives should be developed and implemented to help the adoption of eco-evolutionary management programs; and (5) risk analysis can help incorporate an eco-evolutionary perspective into integrated weed management programs.

Evaluation of Season-Long Weed Management Programs in Red Beet

Red beet growers have expressed interest in adopting the microrate herbicide approach originally implemented in sugarbeet to achieve season-long weed management. Several red beet herbicides were first labeled for use in sugarbeet and lack substantial residual weed control. In response, red beet herbicide programs were evaluated that included a PRE application followed by up to three POST applications of various herbicide combinations. This research, however, indicated that herbicide programs that included PRE herbicides followed by as few as one or two POST applications that involve multiple active ingredients can provide season-long weed control. This observation was consistent across a broad spectrum of weeds, between two study locations that varied in soil type, and during two growing seasons. Herbicide programs that included only a PRE and six-leaf red beet growth stage application were successful at two locations in maintaining weed control and crop yield relative to hand-weeded red beet. Furthermore, these herbicide programs reduced the number of applications by 50% compared with the full programs, reducing crop injury risk and grower cost.