Rice is a principal source of food for more than half of the world population, and more than 90% of rice worldwide is grown and consumed in Asia. A change in establishment method from manual transplanting of rice seedlings to dry-seeded rice (DSR) has occurred in some countries as growers respond to increased costs or decreased availability of labor or water. However, weeds are a major constraint to DSR production because of the absence of the size differential between the crop and the weeds and the suppressive effect of standing water on weed growth at crop establishment. Herbicides are used to control weeds in DSR, but because of concerns about the evolution of herbicide resistance and a scarcity of new and effective herbicides, there is a need to integrate other weed management strategies with herbicide use. In addition, because of the variability in the growth habit of weeds, any single method of weed control cannot provide effective and season-long control in DSR. Various weed management approaches need to be integrated to achieve effective, sustainable, and long-term weed control in DSR. These approaches may include tillage systems; the use of crop residue; the use of weed-competitive cultivars with high-yield potential; appropriate water depth and duration; appropriate agronomic practices, such as row spacing and seeding rates; manual or mechanical weeding; and appropriate herbicide timing, rotation, and combination. This article aims to provide a logical perspective of what can be done to improve weed management strategies in DSR.

Nomenclature: Rice, Oryza sativa L.

Conventional grain sorghum is highly susceptible to POST grass control herbicides. Development of aryloxyphenoxypropionate-resistant grain sorghum could provide additional opportunities for POST herbicide grass control in grain sorghum. Field experiments were conducted at Hays and Manhattan, KS, to determine the effect of quizalofop rate and crop growth stage on injury and yield of aryloxyphenoxypropionate-resistant grain sorghum. Quizalofop was applied at 62, 124, 186, and 248 g ai ha⁻¹ at sorghum heights of 8 to 10, 15 to 25, and 30 to 38 cm, which corresponded to early POST (EPOST), mid-POST (MPOST), and late POST (LPOST) application timings, respectively. Grain sorghum injury ranged from 0 to 68% at 1 wk after treatment (WAT); by 4 WAT, plants generally recovered from injury. The EPOST and MPOST applications caused 9 to 68% and 2 to 48% injury, respectively, whereas injury from LPOST was 0 to 16%, depending on rate. Crop injury from quizalofop was more prominent at rates higher than the proposed use rate in grain sorghum of 62 g ha⁻¹. Grain yields were similar in treated and nontreated plots; applications of quizalofop at different timings did not reduce yield except when applied MPOST at the Manhattan site.

Nomenclature: Quizalofop; sorghum, Sorghum bicolor (L.) Moench. SORBI.

Field experiments were conducted in 2006, 2007, and 2008 at the Louisiana State University Agricultural Center's Northeast Research Station near St. Joseph, LA, to evaluate imazosulfuron programs involving rate, application timings, and tank mixes for PRE and POST broadleaf weed control in drill-seeded rice. Imazosulfuron showed residual activity against both Texasweed and hemp sesbania. PRE-applied imazosulfuron at 168 g ai ha⁻¹ and higher rates provided 83 to 93% Texasweed control at 4 WAP. At 12 WAP, Texasweed control with 168 g ha⁻¹ and higher rates was 92%. Hemp sesbania control with 168 g ha⁻¹ and higher rates was 86 to 89% at 4 WAP and 65 to 86% at 12 WAP. Imazosulfuron at 224 g ha⁻¹ applied EPOST provided 84 to 93% Texasweed control and 82 to 87% hemp sesbania control, and it was as effective as its tank mixture with bispyribac-sodium. When applied LPOST, four- to five-leaf Texasweed, imazosulfuron alone at 224 g ha⁻¹ was not effective against Texasweed and hemp sesbania, but did improve weed control when mixed with bispyribac-sodium at 17.6 g ai ha⁻¹.

Nomenclature: Imazosulfuron; bispyribac-sodium; hemp sesbania, Sesbania herbacia (L.) SESEX; Texasweed, Caperonia palustris (L.) St. Hil. CNPPA; rice, Oryza sativa L. ORYSA.

Field studies were conducted in Crowley, LA, and Stoneville, MS, in drill-seeded rice to evaluate economical returns of weed control with imazethapyr. Red rice and barnyardgrass control was evaluated with imazethapyr alone at various rates and application timings. Imazethapyr, averaged across rate, controlled red rice 89% and barnyardgrass 90% when the initial application of imazethapyr was applied at emergence followed by a second application of imazethapyr 2 wk later. No difference in red rice and barnyardgrass control was observed with imazethapyr, averaged across timing. Yield and economical returns were maximized when the initial application of imazethapyr was applied at rice emergence followed by a second application of imazethapyr 2 wk later.

Nomenclature: Imazethapyr; barnyardgrass, Echinochloa crus-galli (L.) Beauv.; red rice, Oryza sativa L.; rice, Oryza sativa L.

Selection for biotypes of common ragweed expressing resistance to acetolactate synthase (ALS)–inhibiting herbicides has increased in North Carolina and surrounding states. Research was conducted in North Carolina to confirm common ragweed resistance to diclosulam and to compare herbicide programs designed to control ALS-resistant common ragweed in corn, cotton, peanut, and soybean. In greenhouse experiments, 50% inhibition values following POST application of diclosulam for mortality of plants, visual estimates for percentage of control, and percentage of reduction in plant fresh weight were 557- to 653-fold higher for the suspected ALS-resistant biotype compared with a suspected ALS-susceptible biotype. Herbicides with different modes of action, including atrazine, dicamba, and glyphosate in corn; fomesafen, glyphosate, MSMA, and prometryn in cotton; bentazon, flumioxazin, and lactofen in peanut; and flumioxazin, glyphosate, and lactofen in soybean controlled common ragweed more effectively than programs relying on cloransulam-methyl (soybean), diclosulam (peanut), thifensulfuron (corn), and trifloxysulfuron (cotton), which typically control nonresistant common ragweed populations. Applying tank-mix or sequential applications of herbicides with different modes of action was effective in controlling ALS-resistant common ragweed in all crops.

Nomenclature: Atrazine; cloransulam-methyl; dicamba; diclosulam; flumioxazin; fomesafen; glyphosate; lactofen; prometryn; trifloxysulfuron; common ragweed, Ambrosia artemisiifolia L.; corn, Zea mays L.; cotton, Gossypium hirsutum L.; peanut, Arachis hypogaea L.; soybean, Glycine max (L.) Merr.

Field studies were conducted in Louisiana and Mississippi in 2009 and 2010 to evaluate PRE herbicide treatments containing isoxaflutole or a prepackaged mixture of thiencarbazone-methyl ∶ isoxaflutole (TCM ∶ isoxaflutole) for weed control in corn. PRE treatments included the premix of TCM ∶ isoxaflutole alone (30 ∶ 80 g ai ha⁻¹) and with atrazine (1,120 g ai ha⁻¹), isoxaflutole alone (90 g ai ha⁻¹) and with atrazine (1,120 g ai ha⁻¹), and the premix of atrazine plus S-metolachlor (1,820 plus 1,410 g ai ha⁻¹). POST treatments included glufosinate (450 g ai ha⁻¹) or glyphosate (870 g ae ha⁻¹) applied to 30-cm corn along with a no POST treatment. All PRE treatments controlled barnyardgrass, entireleaf morningglory, rhizomatous johnsongrass, Palmer amaranth, and velvetleaf 87 to 95% 4 wk after planting (WAP) and browntop millet and hophornbeam copperleaf were controlled 86 to 95% 8 WAP. Weed control was improved 8 and 20 WAP when either POST treatment was applied. TCM ∶ isoxaflutole plus atrazine controlled barnyardgrass, entireleaf morningglory, Palmer amaranth, and velvetleaf at least 90% 20 WAP regardless of POST treatment. TCM ∶ isoxaflutole plus atrazine provided greater control of browntop millet (90%) than isoxaflutole alone or with atrazine and atrazine plus S-metolachlor where control was 86% 20 WAP. Pooled across POST treatments, all PRE treatments containing isoxaflutole or TCM ∶ isoxaflutole controlled rhizomatous johnsongrass better (74 to 76%) than atrazine plus S-metolachlor (67%). Corn yield following herbicide treatments ranged from 9,280 to 11,040 kg ha⁻¹ compared with 9,110 kg ha⁻¹ for the nontreated. Results indicate that TCM ∶ isoxaflutole or isoxaflutole PRE is an option for use in a corn weed management program and may prolong the use of atrazine where weed resistance may be an issue. Where rhizomatous johnsongrass is a problem, TCM ∶ isoxaflutole or isoxaflutole PRE can provide better control than atrazine plus S-metolachlor PRE. Without PRE treatments, glufosinate or glyphosate was needed for season-long weed control.

Nomenclature: Atrazine; glufosinate; glyphosate; isoxaflutole; S-metolachlor; thiencarbazone-methyl, methyl 4-[(4,5-dihydro-3-methoxy-4-methyl-5-oxo-1H-1,2,4-triazol-1-yl)carboxamidosulfonyl]-5-methylthiophene-3-carboxylate; barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; browntop millet, Urochloa ramosa (L.) Nguyen PANRA; entireleaf morningglory, Ipomoea hederacea (L.) Jacq. var. integriuscula Gray IPOHG; hophornbeam copperleaf, Acalypha ostryifolia Riddell ACCOS; johnsongrass, Sorghum halepense (L.) Pers. SORHA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; velvetleaf, Abutilon theophrasti Medik ABUTH; corn, Zea mays L.

Studies were conducted in Oklahoma and Arkansas to evaluate the tolerance of nine advanced cowpea breeding lines and one cultivar treated PRE with halosulfuron at 1× (0.054 kg ha⁻¹) and 2× ( 0.107 kg ha⁻¹) rates. The breeding lines, developed by the University of Arkansas, included 01-103, 01-111, 01-117, 01-140, 01-174, 01-180, 01-181, 01-184, and 01-198. ‘Early Scarlet’ was also included as the standard commercial cultivar. Halosulfuron did not reduce the emergence of the breeding lines and Early Scarlet in Oklahoma, but reduced cowpea emergence 14% at the 2× rate in Arkansas. All breeding lines and Early Scarlet had similar emergence capacity in both locations. Higher injury (crop stunting, up to 59% at the 2× rate) and reduction in flowering (up to 83% points at the 1× rate) were observed in Arkansas, but not in Oklahoma. Averaged over herbicide rate, yield was higher and did not differ among cultivars in Arkansas (0.89 to 1.18 Mg ha⁻¹) versus Oklahoma (0.36 to 0.82 Mg ha⁻¹). The highest yield in Oklahoma was obtained from 01-174, 01-103, and 01-117. Despite the observed phytotoxicity symptoms, halosulfuron did not reduce cowpea yield. Halosulfuron is safe to use with these breeding lines and cultivar, at the 0.054 kg ha⁻¹ rate, but may delay cowpea maturity almost 1 wk in soils of close to neutral pH or higher.

Nomenclature: Halosulfuron-methyl; cowpea, Vigna unguiculata L. Walp.

Indaziflam controls annual grassy weeds by inhibiting cellulose biosynthesis. Research was conducted from 2008 to 2011 in Tennessee, Texas, and Georgia evaluating the efficacy of indaziflam for PRE and POST control of annual bluegrass in bermudagrass turf. In Texas, indaziflam at 30, 40, 50, and 60 g ai ha⁻¹ applied PRE provided 93 to 100% annual bluegrass control through 28 wk after treatment. When applied PRE at 80 g ai ha⁻¹ and at 4, 8, and 12 wk after PRE (WAP), indaziflam controlled annual bluegrass 67 to 100% 32 wk after initial treatment (WAIT) in Tennessee; however, reduced efficacy was observed with 12 WAP treatments in a single year of a 2-yr study. Similarly, annual bluegrass control with PRE applications or with 4 and 8 WAP applications of indaziflam at 35 and 52.5 g ai ha⁻¹ ranged from 88 to 100% at 30 WAIT in Tennessee. In Georgia, these rates of indaziflam applied PRE and 4 WAP controlled annual bluegrass 96 to 100% on all evaluation dates and resulted in 97 to 100% reduction in plant counts relative to the untreated control at 30 WAIT. When applied 8 WAP, the 35 and 52.5 g ai ha⁻¹ rates of indaziflam controlled annual bluegrass only 51 to 71% at 30 WAIT in Georgia. Although increasing the application rate of indaziflam treatments 8 WAP provided greater annual bluegrass control, each rate provided significantly lower control when applied 8 WAP compared with PRE or at 4 WAP. No bermudagrass injury was observed in this research. Results suggest indaziflam provides effective PRE and early POST control of annual bluegrass in bermudagrass turf. However, additional research is needed to determine the effects of plant size and maturity on indaziflam efficacy for POST annual bluegrass control.

Nomenclature: Annual bluegrass, Poa annua L.; bermudagrass, Cynodon dactylon (L.) Pers.

The continued phase-out of methyl bromide (MBr) challenges vegetable growers' abilities to control weeds in plasticulture production. Herbicides, such as EPTC (S-ethyl dipropylthiocarbamate), may be needed as part of a MBr alternative system. An experiment was conducted during the springs of 2008 and 2009 in Ty Ty, GA, to determine tomato, pepper, eggplant, and watermelon tolerance to EPTC applied under mulch. Treatments consisted of a factorial arrangement of four rates of EPTC (0, 2, 3, or 4 kg ai ha⁻¹) and two plastic mulch types (low density polyethylene [LDPE] mulch or a high barrier mulch [HBM]). Each crop was planted 28 d after applying herbicides and laying mulch. EPTC, regardless of rate, applied under LDPE mulch did not impact plant growth, fruit number produced, or fruit weights for any crop. Conversely, pepper, tomato, and eggplant heights were reduced 65 to 72%, 30 to 75%, and 9 to 32%, respectively, by EPTC at 2 to 4 kg ai ha⁻¹ when applied under HBM. Similar trends were observed for crop yield; fruit number and weight were reduced by 71 to 84% for pepper, 36 to 76% for tomato, and 7 to 15% for eggplant when EPTC was applied at 2 to 4 kg ai ha⁻¹ as compared to the no EPTC HBM control. Watermelon stem lengths, fruit number, and fruit weights were not impacted by EPTC applied under HBM mulch. It appears as though HBMs reduce the loss of EPTC through volatilization, thereby increasing the dose present at time of planting. EPTC could be included as part of a MBr alternative system for tomato, pepper, eggplant, and watermelon when applied under LDPE mulch, and may also be applied at labeled rates with the HBM utilized in this experiment for watermelon.

Nomenclature: S-ethyl dipropylthiocarbamate (EPTC); bell pepper, Capsicum annuum L. CPSAN; eggplant, Solanum melongena L. SOLME; tomato Solanum lycopersicum L. LYPES; watermelon, Citrullus lanatus L. CITLA.

Experiments were conducted during 2007 and 2008 to evaluate various herbicide treatment regimes for POST purple nutsedge and false-green kyllinga control. Evaluated herbicides included halosulfuron, sulfentrazone, sulfosulfuron, and trifloxysulfuron. Evaluated treatments did not cause objectionable bermudagrass injury at any time. Results were variable across years, likely due to reduced rainfall in 2007 causing reduced purple nutsedge and false-green kyllinga growth. In 2007, averaged across herbicide rate and number of applications, sulfosulfuron provided greater purple nutsedge control than trifloxysulfuron. Sulfosulfuron and trifloxysulfuron provided similar levels of control in 2008, although both were less effective than in 2007. In 2007, sulfosulfuron and trifloxysulfuron provided excellent (> 90%) false-green kyllinga control, and trifloxysulfuron provided greater control (80%) compared to sulfosulfuron (61%) in 2008. Sulfentrazone provided < 30 and 60% purple nutsedge and false-green kyllinga control, respectively. A sequential application applied 6 wk after initial treatment provided the highest level of purple nutsedge and false-green kyllinga control with evaluated herbicides. Tank-mix partners to enhance purple nutsedge control with sulfentrazone provided inconsistent results. Sulfosulfuron and trifloxysulfuron offer acceptable POST perennial sedge control in tolerant warm-season turfgrasses.

Nomenclature: Halosulfuron; sulfentrazone; sulfosulfuron; trifloxysulfuron; false-green kyllinga, Kyllinga gracillima L.; purple nutsedge, Cyperus rotundus L.; bermudagrass, Cynodon spp.

Giant reed has been proposed as a bioenergy crop in the sugarcane production region of south Florida, where it has a high invasive potential. In an effort to limit future invasion of giant reed escapes in sugarcane, currently labeled sugarcane herbicides asulam and trifloxysulfuron were evaluated for its management. Greenhouse and field dose–response studies were conducted at the Everglades Research and Education Center in Belle Glade, FL, between 2010 and 2011. Herbicides were applied at rates ranging from 0.46 to 7.4 kg ha⁻¹ asulam and 2 to 32 g ha⁻¹ trifloxysulfuron, which represent 0.125× to 2× sugarcane labeled use rates, respectively. In the greenhouse, asulam and trifloxysulfuron reduced giant reed relative shoot dry weight by a maximum of 50% at 21 d after treatment (DAT). The probability of giant reed resprouting 35 d following herbicide treatment was greater for trifloxysulfuron when compared with asulam. In the field, it was predicted that a maximum of 69 and 55% giant reed control occurred with application of asulam and trifloxysulfuron, respectively, at 14 DAT. Relative shoot dry weight of giant reed treated with asulam and trifloxysulfuron was reduced by a maximum of 43% at 42 DAT. Application of asulam and trifloxysulfuron did not provide complete control of giant reed at twice the labeled sugarcane use rate, indicating that control of established giant reed in sugarcane with currently available herbicides would not be an option.

Nomenclature: Asulam; trifloxysulfuron; giant reed, Arundo donax L.; sugarcane, Saccharum spp. hybrids.

Morningglories are summer annual or perennial dicots, and are troublesome weeds in sugarcane cultivated in northern India. If not controlled, they may compete with sugarcane, interfere in the harvest operation, and reduce yields. Managing morningglories in sugarcane continues to be a serious challenge for sugarcane growers. Field experiments were conducted during the 3-yr period from 2007 to 2009 to evaluate herbicides applied PRE and POST for control of morningglories in sugarcane. The herbicides applied PRE included diuron, metribuzin, and atrazine at 1.6, 1.4, and 1.0 kg ai ha⁻¹, respectively, applied alone or followed by 2,4-D amine salt (0.58 or 1.16 kg ae ha⁻¹) or 2,4-D sodium salt (0.8 or 1.6 kg ae ha⁻¹) applied POST. Herbicides applied PRE controlled morningglories ≤ 87% at 15 d after treatment (DAT); however, control reduced to ≤ 56% at 90 DAT. Control improved when herbicides applied PRE were followed by POST application of 2,4-D amine or sodium salt. For example, diuron applied PRE followed by 2,4-D amine salt applied POST at any rate provided 100% control of morningglories at 15 and 30 DAT. At 90 d after POST application, control ranged from 68 to 82% with the PRE followed by POST herbicides, compared to 0% control when metribuzin or atrazine were applied PRE alone. The density and biomass of morningglories was also reduced to zero in treatments that included 2,4-D amine salt. The number of millable canes, cane height, and single cane weight was superior in PRE followed by POST herbicide treatments compared to herbicides applied PRE alone. Maximum cane yield was recorded for the treatments that included 2,4-D amine or sodium salt compared to only PRE treatments, and it was usually comparable with the nontreated weed-free control. It is concluded that a combination of PRE and POST herbicides were effective for control of morningglories; however, more research is required to evaluate other herbicides and their tank mix partners for control of morningglories in sugarcane.

Nomenclature: Japanese morningglory, Ipomoea nil (L.) Roth.; obscure morningglory, Ipomoea obscura L. Ker Gawl.; sugarcane, Saccharum spp.

An experiment was conducted on a specially designed hard surface to study the impact of time interval between flaming treatments on the regrowth and flower production of two grass weeds. The goal of this experiment was to optimize the control of annual bluegrass and perennial ryegrass, both species that are very difficult to control without herbicides. Aboveground biomass from 72 plants per treatment was harvested and dry weights were recorded at regular intervals to investigate how the plants responded to flaming. Regrowth of the grasses was measured by harvesting aboveground biomass 2 wk after the second flaming treatments that were implemented at different time intervals. Flaming treatments decreased plant biomass of both species and also the ratio of flowering annual bluegrass plants. However, few plants were killed. The first flaming treatment affected aboveground biomass more than the second flaming treatment. A treatment interval of 7 d provided the greatest reduction in regrowth of perennial ryegrass, whereas the effect of treatment interval varied between the first and second repetitions of this experiment for annual bluegrass. In general, short treatment intervals (3 d) should be avoided, as they did not increase the reduction of aboveground biomass compared with the 7-d treatment interval. Knowledge on the regrowth of grass weeds after flaming treatments provided by this study can help improve recommendations given to road keepers and park managers for management on these weeds.

Nomenclature: Annual bluegrass, Poa annua L.; perennial ryegrass, Lolium perenne L.

Alligatorweed is subject to an eradication program in Victoria, Australia. In aquatic situations, the herbicides glyphosate and metsulfuron are used. Alligatorweed has been shown to break up soon after the application of these herbicides, resulting in the production of many stem fragments that are viable and capable of downstream colonization, compromising the effectiveness of the eradication program. This paper reports on an experiment to investigate the usefulness of commercially available plant growth regulators (PGRs) in reducing the number of viable propagules produced post-herbicide application. Three herbicide treatments (no herbicide, glyphosate, and metsulfuron) and four PGR treatments (no PGR, aviglycine [AVG], naphthalene acetic acid [NAA], and 2,4-D) were investigated in a factorial experiment. Chemicals were applied to alligatorweed growing in separate aquaria, the resulting stem fragments were collected and counted, and a subset was tested for viability. There was no evidence of PGRs having any effect on the total number of viable stem fragments produced. However, AVG reduced the total number of fragments produced. PGRs in combination with herbicide treatment had an antagonistic effect on the efficacy of the herbicides. PGRs increased belowground biomass of alligatorweed, as well as the number of apical growing tips present. Results indicate that although PGRs, particularly AVG, may be of benefit in reducing the number of alligatorweed propagules produced post-herbicide application, at the application rates tested here there would be no benefit from incorporating them into herbicide control programs for alligatorweed.

Nomenclature: Glyphosate; metsulfuron; aviglycine; naphthalene acetic acid; 2,4-D; alligatorweed, Alternanthera philoxeroides (Mart.) Griseb. ALRPH.

Greenhouse studies were conducted to evaluate the influence of selected adjuvants on glyphosate efficacy on yellow nutsedge and tuber production. Glyphosate was applied at 0, 0.25, 0.43, 0.87, 1.26 (1× rate), and 1.74 kg ae ha⁻¹ at 31 d after yellow nutsedge was planted. Each rate was mixed with one of the following adjuvants: ammonium sulfate (AMS), AMS plus nonionic surfactant (NIS), or AMS plus an experimental adjuvant (W-7995) plus NIS. Plants were evaluated for injury and for the number and size of tubers produced. Dose–response curves based on log-logistic models were used to determine the effective glyphosate rate plus adjuvant that provided both 90% effective dose (ED₉₀) for yellow nutsedge injury and reduced tuber production. Addition of NIS to glyphosate plus AMS resulted in the greatest yellow nutsedge injury at 28 d after treatment (DAT). Addition of the experimental adjuvant plus NIS resulted in injury similar to NIS alone. The ED₉₀ for injury at 28 DAT was 2.12 kg ha⁻¹ with glyphosate plus AMS and NIS compared with 2.18 kg ha⁻¹ for W-7995 plus NIS and 3.06 kg ha⁻¹ with AMS alone. The ED₉₀ rates with different adjuvants represent 168%, 173%, and 243% of the highest glyphosate rate (1.26 kg ha⁻¹) labeled for application on many glyphosate-resistant crops. However, the estimated ED₉₀ to reduce small, medium, large, and total tubers were 1.60, 1.50, 1.63, and 1.66 kg ha⁻¹, respectively. Increases in labeled rates of glyphosate may be required to reduce yellow nutsedge tuber production in field conditions. Use of lower glyphosate rates should be discouraged because it may increase tuber production and exacerbate yellow nutsedge expansion in infested fields.

Nomenclature: Glyphosate; yellow nutsedge, Cyperus esculentus L. CYPES.

Management of weeds is often a barrier to conversion from conventional to organic agriculture. Tef is a C₄ annual cereal that is valued for its small seeds, rapid establishment, and wide adaptation. The objective of this study was to evaluate tef as a smother crop for management of weeds during transition to organic production. Greenhouse and field trials were conducted in 2008 and 2009 to evaluate the growth of eight tef varieties and their effect on Canada thistle and annual weeds. In greenhouse studies, tef decreased the biomass of Canada thistle shoots and roots 44 to 74%, depending on variety. Emergence of Canada thistle shoots was affected by the planting depth of their roots. Tef variety Corvalis suppressed Canada thistle biomass and accumulated more biomass than most other tef varieties. In field studies, tef varieties suppressed annual weed biomass by 35 to 54% with varieties Corvalis, Dessie, and VA-T1 being least suppressive in 2008, but there were no differences between varieties in 2009. Canada thistle growth was suppressed an average of 73% by tef in 2008 and 37% in 2009, a year of cooler temperatures and unseasonal rainfall. Differences between varieties in suppressing Canada thistle and annual weeds were mostly inconsistent between years. However, tef variety Tiffany did consistently suppress biomass, height, and percentage cover of Canada thistle and other weeds in the field study in 2008 and 2009.

Nomenclature: Tef, Eragrostis tef (Zucc.) Trotter; Canada thistle, Cirsium arvense (L.) Scop.

Sustainable weed management strategies are needed for organic orchard systems. A study was conducted in an almond orchard in Fresno, CA from 2009 to 2011. Treatment comparisons included steam, flame, and broad applications of either lemongrass oil or d-limonene. An untreated control was also included. The experimental design was a randomized complete block with four replications. Weekly evaluations on percent weed control were taken and weed biomass was sampled 4 to 8 wk after treatment (WAT). Weed control and biomass differed between seasons but, in general, steam and flame provided as much as 95% control 1 WAT. However, the effects lasted only 3 to 4 wk as new weeds emerged or the treated weeds overcame the suppressive effects of the thermal treatments. Weed biomass was 95% lower in the steam- and flame-treated plots compared with the untreated plots in summer. Both steam and flame were more effective on certain erect-growing broad-leaved weed species than on prostrate-growing weeds and grasses. Lemongrass oil provided very little weed control. However, d-limonene provided up to 95% weed control 1 WAT and in one experiment 53% control was observed up to 5 WAT. This herbicide also resulted in lower weed biomass than the untreated and the thermal-treated plots. Monthly applications of steam or flame or applications of d-limonene every 5 to 6 wk may have to be made to adequately suppress weeds in organic almond orchards. Cost estimates of propane use were $41 to 56 ha⁻¹ and $26 ha⁻¹ for the steam and flame treatments, respectively. The cost of d-limonene was estimated as $275 ha⁻¹. To optimize weed control and costs, these tools may need to be used in combination rather than by themselves.

Nomenclature: Greenmatch EX 50% lemongrass oil; Greenmatch d-limonene 55%.

Alternaria cassiae and Colletotrichum truncatum are bioherbicidal pathogens of sicklepod, and hemp sesbania, respectively. The effects of simulated rainfall followed by 12 h simulated dew application, immediately or delayed by 1 to 4 h, on disease severity and weed control were studied for each pathogen on its weed host under greenhouse conditions. After each simulated rainfall event, treated plants were placed in a dew chamber for 12 h. Regardless of rainfall amount and/or timing, only slight differences occurred on A. cassiae disease severity and sicklepod control (85 to 100% for both parameters). However, when similar tests were imposed on C. truncatum, disease severity and hemp sesbania control were highly variable, ranging from 5 to 100%. Regardless of rainfall amount, disease development and control of hemp sesbania were greatly reduced (60%) when dew application was delayed by only 1 h following inoculation, regardless of rainfall treatment. Rainfall at 1.27 and 2.58 cm had little effect on disease development and control in hemp sesbania, but the effect of transfer time to dew application exhibited a greater role on these parameters. Thus the time between bioherbicide application and dew application was more important for C. truncatum than for A. cassiae. These results indicate that rainfall amounts and the timing of dew application caused differential effects on disease severity and weed control after application of these bioherbicides to their target weeds.

Nomenclature: Hemp sesbania [Sesbania exaltata (Rydb.)] ex A.W. Hill sicklepod [Senna obtusifolia (L.) Irwin & Barneby]; Alternaria cassiae Jurair & Khan; Colletotrichum truncatum (Schw.) Andrews and Moore.

Greenhouse, growth chamber, and field studies were conducted at Stoneville, MS, in 2000 to 2008, to determine the growth rate, reproductive and overwintering potential, and control of deeproot sedge. In growth chamber studies, deeproot sedge growth rate (ht) and plant dry wt were greatest at 25/35 C (night/day temperatures), when compared with regimes of 5/15, 15/25, and 20/30 C. Based on the average number of scales (fruiting sites per spikelet), spikelets per inflorescence, and culms per plant, deeproot sedge reproductive potential was 2.6-, 6.2-, and 17.4-fold greater than Surinam, green, and knob sedges, respectively. A single deeproot sedge plant produced an average of 85,500 achenes annually. Mowing at 15-cm ht weekly prevented achene production but did not kill deeproot sedge plants. The average number of inflorescences produced on mowed plants was 1.2 to 4 times greater in 2- and 1-yr-old deeproot sedge plants, respectively, when compared with unmowed plants. Mature deeproot sedge achenes were produced between monthly mowings. In a 3-yr field study, glyphosate, glufosinate, hexazinone, and MSMA provided more than 85% control of deeproot sedge, and above the soil, live deeproot sedge plant dry wt was reduced by 50, 64, 68, 72, 86, and 93% by dicamba, halosulfuron-methyl, MSMA, hexazinone, glufosinate, and glyphosate, respectively. All (100%) deeproot sedge plants 1 yr old or older overwintered at Stoneville, MS, at 33°N latitude.

Nomenclature: 2,4-D; dicamba; glufosinate; glyphosate; halosulfuron-methyl; hexazinone; imazapic; MSMA; picloram; triclopyr; deeproot sedge, Cyperus entrerianus Boeck. CYPEN; green sedge, Cyperus virens Michx. CYPVI; knob sedge, Cyperus pseudovegetus Steud. CYPPV; Surinam sedge, Cyperus surinamensis Rottb. CYPSU.

Avena spp. are world weeds with many cases of evolved herbicide resistance. In Australia, Avena spp. (wild oat and sterile oat) are a major problem, especially in grain crops. Acetyl-CoA carboxylase (ACCase)–inhibiting herbicides have been used extensively since the late 1970s for Avena spp. control. However, continued reliance on these herbicides has resulted in the evolution of resistant Avena spp. populations. Resistance across many ACCase-inhibiting herbicides was characterized in four Avena spp. populations from the Western Australian grain belt. Dose–response experiments were conducted to determine the level of resistance to the aryloxyphenoxypropionates and cyclohexanediones and to the phenylpyrazoline herbicide pinoxaden. On the basis of resistance index values, all four resistant populations exhibited high-level diclofop resistance but varied in the level of resistance to other ACCase-inhibiting herbicides tested. It is evident that Avena spp. populations from the Western Australian grain belt have evolved resistance to a number of ACCase-inhibiting herbicides.

Nomenclature: Diclofop; pinoxaden; sterile oat, Avena sterilis L. AVEST; wild oat, Avena fatua L. AVEFA.

Field studies were conducted near College Station, TX, in 2006 and 2007 to evaluate the economic impact of common sunflower interference in field corn. A density of one common sunflower per 6 m of crop row caused a yield loss of 293 kg ha⁻¹. Estimated losses at a net corn price of $0.08 kg⁻¹ was $92 ha⁻¹ for infestation levels of four common sunflower plants per 6 m of row. Corn yield was increased by 32 kg ha⁻¹ by each 1,000 plant ha⁻¹ increase in corn planting density. Corn planting densities of 49,400 and 59,300 plants ha⁻¹ provided the greatest net returns with or without the presence of common sunflower competition. Corn yields were reduced by extended duration of sunflower competition, with losses exceeding 1,500 kg ha⁻¹ per week and increasing in magnitude at a decreasing rate throughout the growing season. Herbicide treatments provided net returns of $600 to $1,300 ha⁻¹ above no weed control in both 2006 and 2007. Net returns of $609 and $653 ha⁻¹ were obtained without the use of any herbicide for sunflower control. Determining the economic impact of common sunflower interference in field corn allows producers to estimate the overall net return on the basis of duration of common sunflower interference and density, while considering varying net corn prices, crop planting density, and herbicide application costs.

Nomenclature: Common sunflower, Helianthus annuus HELAN; corn, Zea mays L. ‘DLP 69-71’.

Annual bluegrass is a troublesome weed in golf course putting greens. The objective of this research was to evaluate creeping bentgrass putting green tolerance to bispyribac-sodium tank-mixed with paclobutrazol in the transition zone. Field trials with four replications were conducted in Oklahoma during 2009 and 2010 and in Missouri during 2010. The results of this study suggest that tank-mixing bispyribac-sodium with paclobutrazol may discolor creeping bentgrass putting greens but will not reduce turf quality below acceptable levels. Normalized vegetative difference index readings indicated no treatment differences in turf greenness at 4 and 8 wk after initial treatment. Weekly application of bispyribac-sodium at 12.4 g ha⁻¹ or biweekly application at 24.8 g ha⁻¹ alone or with monthly applications of paclobutrazol at 224 g ha⁻¹ did not cause unacceptable injury to creeping bentgrass putting greens during the spring.

Nomenclature: Bispyribac-sodium {2,6-bis[(4,6-dimethoxypyrimidin-2-yl)oxy] benzoic acid}; paclobutrazol; trinexapac-ethyl; annual bluegrass, Poa annua L. POAAN; creeping bentgrass, Agrostis stolonifera L. AGSST, ‘Penncross’.

Cleavers species (false cleavers and catchweed bedstraw) are among the top 10 most abundant weeds across the prairie region of western Canada, and are increasing in relative abundance at the fastest rate since the 1970s. In 2008, two false cleavers populations from Tisdale and Choiceland, Saskatchewan, were suspected of acetolactate synthase (ALS) –inhibitor resistance. Dose-response experiments were conducted with the use of imazethapyr and florasulam, both ALS inhibitors, as well as fluroxypyr, a synthetic auxin. Additionally, a 1,954–base-pair region of the ALS gene including sites known to confer ALS resistance were sequenced. Both populations were highly resistant to imazethapyr (resistance factors greater than 100), one population (Tisdale) was highly resistant to florasulam (Choiceland population susceptible, although a second, larger screening of 200 individuals indicated low frequency [2%] florasulam resistance), and both populations were susceptible to fluroxypyr. All sequenced Tisdale individuals screened with imazethapyr posessed the Trp₅₇₄Leu mutation. In contrast, three point mutations were found for Choiceland individuals sequenced: Ser₆₅₃Asn, Trp₅₇₄Leu, and Asp₃₇₆Glu. These ALS target-site mutations have not been documented previously in this species.

Nomenclature: Florasulam; fluroxypyr; imazethapyr; catchweed bedstraw, Galium aparine L.; false cleavers, Galium spurium L. GALSP.

Wild buckwheat is the most abundant broadleaf weed across the Prairie region of western Canada. Acetolactate synthase (ALS)-inhibiting herbicides are commonly used to control this species and other broadleaf weeds in cereal crops. A field survey in Alberta in 2007 identified a single population that was putatively resistant to ALS-inhibiting herbicides. In herbicide resistance screening in the greenhouse, all F₁ progeny tested were resistant to the ALS-inhibiting herbicides thifensulfuron/tribenuron, a sulfonylurea herbicide, or florasulam, a triazolopyrimidine herbicide; dose response of shoot biomass indicated the population was 10- and 20-fold less sensitive to thifensulfuron/tribenuron and florasulam, respectively, than a susceptible control population. ALS gene sequencing of 24 F₁ progeny indicated that the Trp₅₇₄Leu target-site mutation was responsible for conferring ALS-inhibitor resistance in this biotype, the first global report of ALS-inhibitor resistance for this species. Because this mutation typically endows high-level resistance across all five ALS-inhibitor classes, this wild buckwheat biotype may only be controlled by a different site-of-action herbicide.

Nomenclature: Florasulam; thifensulfuron; tribenuron; wild buckwheat, Polygonum convolvulus L. POLCO.

Organic growers need additional tools for weed control. A new technique using abrasive grit propelled by compressed air was tested in field plots. Grit derived from corncobs was directed at seedlings of summer annual weeds growing at the bases of corn plants when the corn was at differing early stages of leaf development. Season-long, in-row weed control exceeded 90% when two or three abrasion events were coupled with between-row cultivation. Timing of weed abrasion was critical, with highest levels of control corresponding to the one- and five-leaf stages or the one-, three-, and five-leaf stages of corn development. Corn yields associated with these treatments were equivalent to those of hand-weeded controls in which no abrasive grit was applied. Thus, air-propelled abrasive grit applications at the one-, three-, and five-leaf stages of corn controlled weeds sufficiently to prevent weed-induced reductions in corn grain. Additionally, these applications were not harmful to corn plants. This new concept for weed control may be of interest to organic crop managers.

Nomenclature: Corn, Zea mays L. ‘Croplan 294RR' and ‘3114RR’.