Weed management is a challenge in all agroecosystems. Given the negative consequences associated with herbicide-based weed management, it is important to consider integrated weed management options with emphasis on strategies such as biological control. Postdispersal weed seed predation by granivorous and omnivorous carabid beetles results in substantial natural suppression of weed populations. Although the role of ground beetles as “generalist predators” in various agroecosystems is known, their contribution to weed management is not well recognized. In this context, this review presents an account of carabids and their granivorous nature, the importance of a seed diet in the life histories of different carabid groups, factors affecting granivory, and their potential role in weed seed management. Below, we discuss the interrelationships among various factors influencing weed seed consumption by carabids, its consequences for weed management, and the need for future research.

When herbicides are sprayed in the field, a proportion of the herbicide falls onto leaves and soil surfaces, where it can be exposed to sunlight, generating photoproducts that can be more toxic and/or persistent than the parent substance and affect human health and the environment. The aim of this study was to identify the photoproducts of the herbicide alloxydim in leaf and soil model systems and to perform phytotoxicity studies. Alloxydim was rapidly photodegraded in systems simulating plant cuticles and soil surfaces, with half-lives ranging from 1 to 30 min. The main by-product, identified by LC-Qtof-MS as deallyoxylated alloxydim, was more stable than the active substance. The EC₅₀ values on root lengths of different varieties of wheat plants and one grass weed ranged from 0.38 to 0.50 mg L⁻¹ for alloxydim. In contrast, the EC₅₀ values for deallyoxylated alloxydim ranged from 94 to 600 mg L⁻¹ in the same species and in crops where the herbicide was applied. Special attention should be given to alloxydim degradation products because of the rapid degradation of this herbicide. Comparative bioassay studies between alloxydim and its photostable by-product showed that the by-product presents low phytotoxicity, whereas alloxydim can cause injury to neighboring and succeeding cereal crops.

Nomenclature: Alloxydim.

Annual bluegrass is a problematic weed of Kentucky bluegrass turf that can be selectively controlled with POST applications of primisulfuron-methyl. The objective of this research was to evaluate physiological behavior of primisulfuron-methyl attributed to selectivity in these species. In application placement experiments, annual bluegrass shoot weight reductions from the nontreated from high to low were treatments including: foliar soil ≥ soil only ≥ foliar. Annual bluegrass averaged 33 and 52% shoot weight reductions from the nontreated after 4 wk from primisulfuron-methyl at 40 and 80 g ha⁻¹, respectively. Kentucky bluegrass shoot weight was not reduced from the nontreated, and application placements were similar. From five harvests ranging 1 to 168 h after treatment (HAT), annual and Kentucky bluegrass absorbed up to 25 and 32% of foliar applied ¹⁴C-primisulfuron-methyl, respectively. Both grasses distributed 15% of foliar absorbed ¹⁴C to nontreated shoots with minimal translocation (≤ 2%) to roots after 168 h. Annual bluegrass translocated 2 times more root-absorbed ¹⁴C to shoots than Kentucky bluegrass at 24, 72, and 168 HAT. From foliar uptake, the time required for annual and Kentucky bluegrass to degrade 50% of the absorbed herbicide to the major metabolite detected (R_f 0.1) measured > 168 and 93 h, respectively. In root metabolism experiments, annual bluegrass had ≈ 3 times and 2 times more primisulfuron acid in roots and shoots, respectively, than Kentucky bluegrass at 24, 72, and 168 HAT. The isolated acetolactate synthase (ALS) enzymes from the two grasses were equally susceptible to inhibition by primisulfuron-methyl. Overall, selectivity of primisulfuron-methyl for annual bluegrass control in Kentucky bluegrass is attributed to differential translocation and metabolism between species.

Nomenclature: Annual bluegrass (Poa annua L.); Kentucky bluegrass (Poa pratensis L.) ‘Midnight’.

A waterhemp population (MCR) previously characterized as resistant to 4-hydroxyphenylpyruvate dioxygenase and photosystem II inhibitors demonstrated both moderate and high levels of resistance to acetolactate synthase (ALS) inhibitors. Plants from the MCR population exhibiting high resistance to ALS inhibitors contained the commonly found Trp574Leu ALS amino acid substitution, whereas plants with only moderate resistance did not have this substitution. A subpopulation (JG11) was derived from the MCR population in which the moderate-resistance trait was isolated from the Trp574Leu mutation. Results from DNA sequencing and ALS enzyme assays demonstrated that resistance to ALS inhibitors in the JG11 population was not due to an altered site of action. This nontarget-site ALS-inhibitor resistance was characterized with whole-plant dose–response experiments using herbicides from each of the five commercialized families of ALS-inhibiting herbicides. Resistance ratios ranging from 3 to 90 were obtained from the seven herbicides evaluated. Nontarget-site resistance to ALS has been rarely documented in eudicot weeds, and adds to the growing list of resistance traits evolved in waterhemp.

Nomenclature: Waterhemp, Amaranthus tuberculatus (Moq.) Sauer var. rudis (Sauer) Costea and Tardif AMATU.

Acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicides affect fatty acid biosynthesis in plants and are widely used to control smooth and hare barley in dicot crops in Australia. Recently, growers have experienced difficulty in controlling smooth and hare barley with herbicides from this mode of action. Dose–response experiments conducted on five suspected resistant populations confirmed varying levels of resistance to quizalofop and haloxyfop. The level of resistance in these populations was greater than 27-fold to quizalofop and greater than 15-fold to haloxyfop. The quizalofop dose required to reduce shoot biomass by 50% (GR₅₀) for the resistant populations varied from 52.6 to 111.9 g ha⁻¹, and for haloxyfop from 26.5 to 71.3 g ha⁻¹. Sequencing the CT domain of the ACCase gene from resistant plants of different populations confirmed the presence of previously known mutations Ile1781Leu and Gly2096Ala. Amino acid substitution at the 2096 position conferred a greater level of resistance to haloxyfop than the substitution at the 1781 position. This study documents the first known case of field-evolved target-site resistance to ACCase-inhibiting herbicides in Australian populations of smooth barley.

Nomenclature: Quizalofop; haloxyfop; smooth barley, Hordeum glaucum (Steud.) Tzvelev; hare barley, Hordeum leporinum (Link) Arcang.

Shortawn foxtail is a competitive annual grass weed widely spread in east, south-central, and southwest China and parts of the Yellow River basin. One shortawn foxtail population (JSQT-1) resistant to fenoxaprop was identified in Jiangyan, Jiangsu province. Whole-plant experiments determined that the resistant population conferred high-level resistance to fenoxaprop (93-fold), clodinafop (21-fold), sethoxydim (107-fold), mesosulfuron (41-fold), and pyroxsulam (12-fold); moderate-level resistance to haloxyfop (8-fold), clethodim (9-fold), and pinoxaden (8-fold), and no resistance to isoproturon. Molecular analyses confirmed that the Ile-1781-Leu mutation was present in the resistant population. A dCAPS marker was used to detect the Ile-1781-Leu mutation. All 97 plants of the resistant population analyzed were homozygous mutants at the 1781 position. Our study established the first case of fenoxaprop resistance in shortawn foxtail, determined cross resistance to other herbicides, and elucidated that the molecular basis of resistance resulted from, at least partly, an Ile to Leu mutation at amino acid position 1781 in the plastid ACCase.

Nomenclature: Clethodim; clodinafop; fenoxaprop; haloxyfop; isoproturon; mesosulfuron; pinoxaden; pyroxsulam; sethoxydim; shortawn foxtail, Alopecurus aequalis Sobol.; wheat, Triticum aestivum L.

A segment of the debate surrounding the commercialization and use of glyphosate-resistant (GR) crops focuses on the theory that the implementation of these traits is an extension of the intensification of agriculture that will further erode the biodiversity of agricultural landscapes. A large field-scale study was initiated in 2006 in the United States on 156 different field sites with a minimum 3-yr history of GR-corn, -cotton or -soybean in the cropping system. The impact of cropping system, crop rotation, frequency of using the GR crop trait, and several categorical variables on seedbank weed population density and diversity was analyzed. The parameters of total weed population density of all species in the seedbank, species richness, Shannon's H′ and evenness were not affected by any management treatment. The similarity between the seedbank and aboveground weed community was more strongly related to location than management; previous year's crops and cropping systems were also important while GR trait rotation was not. The composition of the weed flora was more strongly related to location (geography) than any other parameter. The diversity of weed flora in agricultural sites with a history of GR crop production can be influenced by several factors relating to the specific method in which the GR trait is integrated (cropping system, crop rotation, GR trait rotation), the specific weed species, and the geographical location. Continuous GR crop, compared to fields with other cropping systems, only had greater species diversity (species richness) of some life forms, i.e., biennials, winter annuals, and prostrate weeds. Overall diversity was related to geography and not cropping system. These results justify further research to clarify the complexities of crops grown with herbicide-resistance traits to provide a more complete characterization of their culture and local adaptation to the weed seedbank.

Nomenclature: Glyphosate; corn, Zea mays L.; cotton, Gossypium hirsutum L.; soybean, Glycine max (L.) Merr.

Little published information is available related to seed germination and seedling establishment of Asia Minor bluegrass, a problematic grass weed in some regions of China. The objective of this study was to examine the effects of different environmental factors on Asia Minor bluegrass seed germination. The optimum temperature for germination was around 10 to 20 C, and more than 90% of seeds germinated under 20/10 and 25/15 C temperature regimes. Also, light and pH did not appear to have any effect on seed germination. Asia Minor bluegrass was sensitive to osmotic stress, but tolerant of NaCl. No seedlings emerged when seeds were buried 4 cm deep. The result suggested that Asia Minor bluegrass has the potential to spread into a large area in China. To prevent its spreading, measures such as soil cultivation can be used to limit seed germination from increased burial depth and/or nonselective herbicides can be applied to kill early-germinating weed seedlings in late summer.

Nomenclature: Asia Minor bluegrass, Polypogon fugax Nees ex Steud.

Due to the looming water and labor crisis, farmers are adopting dry-seeded rice establishment, in which Chinese sprangletop is becoming a major weed. Concerns about the excessive use of herbicides in controlling Chinese sprangletop highlight the need for cultural weed management strategies. Such strategies require an adequate understanding of Chinese sprangletop response to rice plant density, nutrition, and water regime. Therefore, a greenhouse study was conducted to determine the effect of water regime (aerobic and saturated), nitrogen (N) fertilization (50 and 150 kg ha⁻¹), and rice density (0, 160, and 640 plants m⁻²) on the growth and reproduction of Chinese sprangletop. Chinese sprangletop plants were taller than rice in aerobic conditions than in saturated conditions. All growth parameters (shoot, root, and inflorescence biomass and leaf area, leaf weight, and inflorescence weight ratio) of Chinese sprangletop were higher in aerobic conditions than in saturated conditions when grown without rice. However, no difference was observed for these parameters between water regimes when Chinese sprangletop was grown with rice. Chinese sprangletop growth and seed production was not affected, but rice growth was affected by N rates. Irrespective of N rate and water regime, Chinese sprangletop height (34 to 59%), tiller number (87 to 92%), leaf number (83 to 89%), shoot biomass (93 to 99%), and inflorescence biomass (95 to 99%) decreased as rice density increased from 0 to 640 plants m⁻². The ability of Chinese sprangletop to grow taller and produce more plant biomass (107%) and inflorescence biomass (183%) under aerobic than saturated conditions suggests the need for integrated weed management strategies for controlling weeds under water-limited environments. Such strategies might include the use of weed-competitive and drought-tolerant rice cultivars, high seeding rates, and optimum rate of fertilizer application.

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

Crop yields can be similar in organic and conventional systems even when weed biomass is greater in organic systems. Greater weed tolerance in organic systems may be due to differences in management-driven soil fertility properties. The goal of this experiment was to determine whether soil collected from a long-term organic cropping system with a diverse crop rotation and organic fertility inputs would support higher soil nitrogen (N) resource partitioning, as indicated by overyielding of corn–weed mixtures, than a cropping system with a less diverse crop rotation and inorganic N inputs. A replacement series greenhouse experiment was conducted using corn : smooth pigweed and corn : giant foxtail proportions of 0 : 1, 0.25 : 0.75, 0.5 : 0.5, 0.75 : 0.25, and 1 : 0 and harvested at 29, 40, or 48 d after experiment initiation (DAI). The monoculture density of corn was 4 plants pot⁻¹ and the monoculture density of each weed species was 36 plants pot⁻¹. Corn was consistently more competitive than both weed species at 40 and 48 DAI when soil inorganic N was limiting to growth. Corn–smooth pigweed mixtures had greater shoot biomass and shoot N content than expected based on the shoot biomass and shoot N content of monocultures (i.e., overyielding) at the onset of soil inorganic N limitation, providing some evidence for N resource partitioning. However, soil management effects on overyielding were infrequent and inconsistent among harvest dates and corn–weed mixtures, leading us to conclude that management-driven soil fertility properties did not affect corn–weed N resource partitioning during the early stages of corn growth.

Nomenclature: Giant foxtail, Setaria faberi Herrm. SETFA; smooth pigweed, Amaranthus hybridus L. AMACH; corn, Zea mays L.

Insufficient weed control is a major constraint to adoption of reduced-tillage practices for organic grain production. Tillage, cover crop management, and crop planting date are factors that influence emergence periodicity and growth potential of important weed species in these systems. We assessed two hairy vetch cover crop management practices, disk-kill and roll-kill, across a range of corn planting dates from early May to late June in three experiments in Beltsville, MD. Patterns of seed dormancy, emergence, and early weed growth were determined for overseeded populations of common ragweed, giant foxtail, and smooth pigweed, three important species in the Mid-Atlantic states that represent early to late emergence. Common ragweed emergence was lowest and dormancy was highest of the three species across all planting dates. Giant foxtail emergence was higher than the other species in roll-killed hairy vetch and included a significant number of seeds that germinated before rolling operations in late June. Smooth pigweed had the highest emergence and lowest dormancy in disk-killed hairy vetch in June. Individual giant foxtail plant weight was higher in roll-killed than disk-killed hairy vetch in 2 of 3 yr, whereas that of smooth pigweed plants was higher in disk-killed than roll-killed vetch in 2 of 3 yr. Giant foxtail was the dominant species in roll-killed hairy vetch (averaged 79% of total weed biomass at corn silking), probably because of early germination and establishment before rolling operations. Smooth pigweed was the dominant species in disk-killed hairy vetch at June planting dates (averaged 77% of total weed biomass), probably because of high growth rates under warm conditions in tilled soil. This research demonstrated that cover crop management practices and the timing of planting operations can shift the dominant species of weed communities in organic farming systems and must be considered in long-term weed management planning.

Nomenclature: Common ragweed, Ambrosia artemisiifolia L. AMBEL; giant foxtail, Setaria faberi Herrm. SETFA; smooth pigweed, Amaranthus hybridus L. AMACH; corn, Zea mays L.; hairy vetch, Vicia villosa Roth.

This study was conducted in the laboratory and screenhouse to determine the effects of temperature, light, osmotic stress, salt stress, burial depth, use of crop residues as mulch, depth of flooding, and use of POST herbicides on the emergence, survival, and growth of doveweed. In the light/dark regime, germination was higher at alternating day/night temperatures of 35/25 C (95%) than at 30/20 C (72%), and no germination occurred at 25/15 C. Light strongly influenced germination (95%) and dark completely inhibited germination. No germination occurred at an osmotic potential of −0.8 MPa and a salt concentration of 150 mM and above. The highest germination (91%) was observed from the seeds sown on the soil surface and emergence decreased by 78, 86, and 92% when burial depths were increased to 0.5, 1, and 2 cm, respectively. No seedlings emerged from seeds buried at depths of more than 2 cm. The use of rice residues as mulch significantly reduced the emergence and growth of doveweed seedlings. The amount of residue required to suppress 50% of the maximum biomass was 2.5 t ha⁻¹. Flooding had a more pronounced effect on seedling biomass than seedling emergence. Biomass was reduced by 78, 92, and 96% when flooding depths increased from 0 to 2, 4, and 6 cm, respectively, for the seeds placed on the soil surface, whereas for the seeds buried at 0.5 cm, these values were 78, 100, and 100%. Bentazon (100 g ha⁻¹) and bispyribac-sodium (30 g ha⁻¹) provided 100% control of doveweed when applied at the three-leaf stage. Doveweed control was less than 31% with glyphosate rates up to 2,000 g ha⁻¹. The application of 2,4-D (500 g ha⁻¹) provided 100% control of doveweed even when applied at the seven-leaf stage. The information from this study could help in developing more sustainable and effective integrated weed management strategies for the control of this weed and weeds with similar response in dry-seeded rice systems.

Nomenclature: Bispyribac-sodium; bentazon; 2,4-D ester; glyphosate; doveweed, Murdannia nudiflora (L.) Brenan. MUDNU; rice, Oryza sativa L.

Spotted spurge, a C₄ species, is a summer annual weed, introduced to the Golestan province of Iran in 2006. A series of laboratory experiments were conducted at the Faculty of Agriculture, Ferdowsi University of Mashhad, Iran, to evaluate the influence of environmental factors on seed germination of spotted spurge. Seeds germinated over a constant temperature range of 25 to 45 C with a 14-h photoperiod and at 30 to 50 C in continuous darkness. Seeds germinated at alternating day/night temperature regimes of 25/15 to 45/35 C, with maximum germination (> 80%) at alternating day/night temperatures of 35/25, 40/30, and 45/35C. Germination increased from 23.5 to 98% as water potential increased from −0.6 to 0 MPa (control). Germination was > 85% at sodium chloride (NaCl) concentrations up to 80 mM, with no germination at 160 mM NaCl. Germination was not affected by pH, and it was > more than 95% at pH ranging from 4 to 9. The germination of seeds submerged in water for a period less than 3 wk was > 60%, whereas no germination was observed after 9 wk of submergence in water. The results of our study could help to develop effective management strategies for this species. The results also suggest that spotted spurge could invade most tropical regions of Iran.

Nomenclature: Spotted spurge, Chamaesyce maculata (L.) Small EPHMA; soybean, Glycine max (L.) Merr.

Waterhemp resistance to foliar applications of protoporphyrinogen oxidase (PPO)–inhibiting herbicides has become increasingly disconcerting given the widespread distribution of glyphosate resistance. Fortunately, soil-residual PPO-inhibiting herbicides remain efficacious in waterhemp populations resistant to PPO-inhibiting herbicides; however, these herbicides should theoretically select for the resistant biotype as herbicide concentrations diminish in the soil. Accordingly, the objectives of this research were twofold: (1) evaluate the efficacy of three PPO-inhibiting herbicides, foliar- and soil-applied, on PPO-resistant (PPO-R) and PPO-susceptible (PPO-S) waterhemp, and (2) investigate the differential effects of PPO-inhibiting herbicides on an R biotype and an S biotype during several discrete developmental events relevant to soil–residual herbicide activity (i.e., radicle protrusion, radicle elongation, and waterhemp emergence). Greenhouse and growth chamber experiments indicated that the R biotype was least sensitive to the diphenylether herbicide fomesafen, followed by sulfentrazone and flumioxazin; however, fomesafen plus s-metolachlor improved soil-residual efficacy over fomesafen alone. Growth stage considerably influenced the R : S ratio, decreasing from 38× to 3.4×, when comparing ratios generated from foliar applications and soil-residual applications measuring radicle protrusion, respectively. Overall, this research supports the use of full soil-residual herbicide rates, reinforcing the importance of best management practices to manage the spread of herbicide resistance.

Nomenclature: Flumioxazin; fomesafen; glyphosate; s-metolachlor; sulfentrazone; tall waterhemp, Amaranthus tuberculatus (Moq.) Sauer (syn. rudis) AMATA.

Knowledge of economic threshold level and growth habits of weeds in chickpea is essential to implement timely, effective, and economical weed control treatments. The effect of weed density on growth and yield performance in chickpea using dragon spurge as a test weed was investigated for 2 consecutive yr. Dragon spurge density levels of 5, 10, 15, 20, 25, 30, 35, and 40 plants m⁻² were compared with weed-free plots. Each increment in densities of dragon spurge from 5 to 40 plants m⁻² reduced plant height, number of fruits, seeds, and dry weight per plant. Chickpea grain yield losses varied between 1 to 63% with dragon spurge density ranging from 5 to 40 plants m⁻². The seed protein content of chickpea was found to be significantly reduced above a weed density of 25 plants m⁻². Maximum N, P and K uptake by dragon spurge was 1,520, 1,020, and 7,350 mg m⁻², respectively. Thus, dragon spurge should be controlled at densities above 5 plants m⁻² to achieve optimum chickpea yield.

Nomenclature: Chickpea, Cicer arietinum L.; Euphorbia dracunculoides Lam.

The extensive use of foliar-applied protoporphyrinogen oxidase (PPO)-inhibiting herbicides indisputably contributes to the continued selection of waterhemp resistant to PPO-inhibiting herbicides (PPO-R). However, the role of soil-residual applications of PPO-inhibiting herbicides in the selection of PPO-R has been clouded by the efficacy that these herbicides have on PPO-R waterhemp. The aim of the present study was to understand if soil-residual PPO-inhibiting herbicides have the potential to influence the proportion of resistant waterhemp in emerging plants as herbicide concentrations diminish in the soil. Greenhouse and field experiments were conducted in a PRE dose-response experiment testing fomesafen or fomesafen plus s-metolachlor in the presence of mixed seed populations of PPO-R and -susceptible (S) waterhemp. The first 20 (greenhouse) or 10 (field) waterhemp plants that survived the residual herbicide treatment were sampled for genotypic analysis to detect the presence of the allele responsible for PPO-R in waterhemp (ΔG210). Relative to the nontreated control, the highest rate of fomesafen increased the frequency of resistance (FOR) by 70% in the greenhouse experiments and 20% in the field experiments. The addition of s-metolachlor did not reduce the fomesafen-induced increase in the FOR in the surviving plants from field or greenhouse experiments. However, the additional herbicide from an alternate site of action (s-metolachlor) substantially improved soil-residual herbicide efficacy over fomesafen alone, which limited the number of waterhemp plants surviving the herbicide application. Thus, the selection for resistance can be delayed with the addition of a herbicide from an alternative site of action by postponing and/or reducing waterhemp emergence. These data strongly suggest that soil-residual PPO-inhibiting herbicides can influence the FOR in a field population, placing even greater importance on the implementation of best management practices such as full herbicide use rates and using herbicides from multiple sites of action to mitigate the risk of selecting for herbicide-resistant weed biotypes.

Nomenclature: Fomesafen; s-metolachlor; waterhemp, Amaranthus tuberculatus (Moq.) Sauer (syn. rudis) AMATA.

Common lespedeza is a problematic summer annual weed in bermudagrass lawns, with limited PRE herbicides available for control. Dithiopyr is a pyridine herbicide primarily used for PRE grassy weed control but has shown potential efficacy for controlling annual legumes. The objectives of this research were to evaluate efficacy and behavior of dithiopyr in common lespedeza. In a 3-yr field experiment, sequential dithiopyr applications at 0.42 or 0.56 kg ai ha⁻¹ beginning in late winter and single applications of dithiopyr at 0.56 kg ai ha⁻¹ in spring controlled common lespedeza ≥ 88%. Single and sequential applications of indaziflam at 0.035 and 0.053 kg ai ha⁻¹ provided poor control (< 70%) of common lespedeza by late summer. In laboratory experiments, bermudagrass and common lespedeza had similar foliar absorption of ¹⁴C-dithiopyr, averaging 10% of the ¹⁴C applied, and both species retained > 80% of ¹⁴C in the treated leaf at 72 h after treatment (HAT). Common lespedeza translocated 6 times more root-absorbed ¹⁴C to shoots than bermudagrass and had 2.8 times greater absorption (Bq mg⁻¹) at 72 HAT. In metabolism experiments, parent herbicide levels measured ≥ 84% of extracted ¹⁴C in both species at 1, 3, and 7 d after treatment. Overall, dithiopyr effectively controls common lespedeza in bermudagrass as a PRE treatment in spring. Susceptibility of common lespedeza to dithiopyr is associated with acropetal translocation and greater herbicide concentrations compared with a tolerant species, bermudagrass.

Nomenclature: Common lespedeza (Kummerowia striata (Thunb.) Schindl.) ‘Kobe’; bermudagrass (Cynodon dactylon × C. transvaalensis Burtt-Davy) ‘Princess 77’.

Although herbicide tolerance is not usually evaluated until the final stages of breeding programs, this trait is very important for grower adoption of new peanut cultivars. Understanding herbicide tolerance of breeding lines could help breeders develop selection strategies that maximize herbicide tolerance in new commercial cultivars. However, little is known about herbicide tolerance variability in peanut germplasm. Thirty-five randomly selected breeding lines from the peanut mini-core collection and cultivars ‘Florida-07’ and ‘Georgia-06G’ were evaluated for tolerance to 11 herbicides under greenhouse conditions. Variation among peanut lines in herbicide tolerance, measured as dry weight reductions (DWR), was similar across herbicides and was normally distributed. Florida-07 and Georgia-06G were in the lower two quartiles of injury and DWR among the evaluated peanut lines. Dose–response experiments showed that the most tolerant breeding lines had I₅₀ (the rate required to cause 50% injury) and GR₅₀ (the rate required to reduce dry weight 50%) values 0.4 to 2.5 times higher than the most susceptible lines, depending on the herbicide. A breeding line had a dicamba GR₅₀ 13 times higher than the most susceptible line and 2.8 and 4.7 times higher than Florida-07 and Georgia-06G, respectively. The most tolerant lines were consistently tolerant to herbicides with different mechanisms of action, suggesting that nontarget site mechanisms are more likely to be responsible for the tolerance than target-site mutations. These results confirmed peanut-breeding programs would greatly benefit from screening breeding lines for tolerance to key herbicides and developing an herbicide-tolerance catalog. This information can be used when designing new crosses to reduce the risk of developing cultivars with low herbicide tolerance especially considering that one-half of the breeding lines exhibited lower tolerance than the commercial cultivars.

Nomenclature: Dicamba; peanut, Arachis hypogaea L. ‘Florida-07’ and ‘Georgia-06G’.

Pendimethalin is commonly applied for PRE weed control in container nursery production. Field and laboratory trials were conducted to determine herbicide effectiveness and leaching of two pendimethalin formulations in pine bark, the primary component used in the growing medium of container-grown plants in the South. The microencapsulated (ME) formulation of pendimethalin gave lower control of southern crabgrass and leached deeper than the emulsifiable concentrate (EC) formulation in pine bark. The EC formulation controlled southern crabgrass 93% compared with only 70% with the ME formulation at 4.48 kg ai ha⁻¹. After applying 3.4 kg ai ha⁻¹ pendimethalin and 17.8 cm of irrigation water, the ME formulation showed greater leaching into the 3- to 6- and 6- to 9-cm depths than the EC formulation on the basis of a southern crabgrass bioassay. Using a microwave extraction method, only 0.91 mg kg⁻¹ pendimethalin was found in the 3- to 6-cm pine bark depth compared with 4.0 mg kg⁻¹ for the ME formulation. Below the 6-cm depth, no pendimethalin was detected when the EC formulation was applied, but 0.5 ppm was found for the ME formulation. No pendimethalin was detected in effluent collected from irrigation water for the EC; however, 3.0 mg kg⁻¹ was collected from leachate for the ME formulation. Pendimethalin ME is leaching much deeper than the EC formulation in the pine bark profile, which results in lower weed control. This extensive leaching of ME formulation may be due to capsule movement with the irrigation water, combined with a delayed release of pendimethalin, which then binds to the pine bark much lower in the container profile.

Nomenclature: Pendimethalin; southern crabgrass, Digitaria ciliaris (Retz.) Koel.