Weeds are a major biotic constraint to aerobic rice production in Asia. Research is needed on the effects of cultural practices on weed management in aerobic rice, including techniques such as planting pattern and competitive cultivars. Field experiments were conducted in Punjab, India, in the wet seasons of 2008 and 2009 to study the growth of weeds and two rice cultivars [PR 115 and Punjab (P.) Mehak 1] in relation to planting pattern (uniform rows [23-cm row spacing] and paired rows [15-, 30-, and 15-cm row spacings]) under aerobic conditions. Junglerice and rice flatsedge were the dominant weed species during the early stages of the crop, while Chinese sprangletop and large crabgrass were the predominant species during flowering stage of the crop. Weed dry matter was not affected by planting pattern of P. Mehak 1; however, for PR 115, weed dry matter was greater in rice grown in uniform rows (244 g m⁻²) than in paired rows (183 g m⁻²). Planting patterns did not affect weed-free crop growth and yield, but weeds tended to be more abundant in the uniform planting system, particularly under cultivar PR 115. Consequently, this cultivar grew and yielded better under the paired rows when weeds were present. The cultivar PR 115 had greater yield potential than P. Mehak 1, but growth and productivity of P. Mehak 1 were unaffected by the planting patterns, suggesting better competitive ability against weeds than PR 115. The results imply that yield of some aerobic rice cultivars may be improved by exploring competitiveness of rice cultivars through paired row planting patterns. There is a need to study plasticity changes for cultivars which respond with more competiveness in paired rows. The identified traits could be useful as selection criteria for screening weed-competitive cultivars in paired row pattern.

Nomenclature: Junglerice, Echinochloa colona (L.) Link ECHCO; rice flatsedge, Cyperus iria L. CYPIR; Chinese sprangletop, Leptochloa chinensis (L.) Nees LEFCH; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; rice, Oryza sativa L.

Research was conducted at experimental research stations near Keiser and Marianna (Marianna-A), AR, in 2007, and in a grower's field near Marianna (Marianna-B), AR, in 2008, to compare herbicide programs, including POST application(s) of glyphosate/glufosinate alone or in combination with residual herbicides applied as PRE, mid-POST (MPOST), or layby POST-directed (PD) in enhanced glyphosate- and glufosinate-resistant cotton. Weed species evaluated included Palmer amaranth, pitted morningglory, hemp sesbania, barnyardgrass, and a mixture of large crabgrass and goosegrass. At Marianna-B, AR, the Palmer amaranth population was a mixture of glyphosate-resistant and -susceptible plants. For both cotton cultivars and at all locations, inclusion of S-metolachlor plus fluometuron PRE increased weed control and/or decreased the number of glufosinate or glyphosate applications needed in-season. At Marianna-B, AR, PRE residual herbicides and/or glufosinate were required to control glyphosate-resistant Palmer amaranth. Addition of pyrithiobac to glufosinate or glyphosate did not increase weed control. A layby PD application of flumioxazin plus MSMA was required to increase late-season control of all weed species in POST glufosinate-only programs, but not in POST glyphosate-only programs. None of the programs caused > 5% injury to either cotton cultivar. Seed-cotton yield was similar in all herbicide programs at Keiser, AR, and Marianna-A, AR, except for the POST glyphosate-only program, which yielded less than the PRE followed by POST programs in glyphosate-resistant cotton at Keiser, AR. In general, PRE herbicides did not increase cotton yield but did improve early and late-season control of glyphosate-susceptible and -resistant weeds in both cotton cultivars.

Nomenclature: Flumioxazin; fluometuron; glufosinate; glyphosate; MSMA; pyrithiobac; S-metolachlor; barnyardgrass, Echinochloa crus-galli (L.) Beauv.; goosegrass, Eleusine indica (L.) Gaertn.; hemp sesbania, Sesbania herbacea (P. Mill.) McVaugh; large crabgrass, Digitaria sanguinalis (L.) Scop.; Palmer amaranth, Amaranthus palmeri S. Wats.; pitted morningglory, Ipomoea lacunosa L.; cotton, Gossypium hirsutum L.

With the number of glyphosate-resistant weed species increasing in North America and a lack of new herbicide chemistries being developed, growers are shifting toward using older herbicides that are more expensive and may be less environmentally friendly. Therefore, to determine which weed management strategies are most cost effective and have the lowest impact on the environment we evaluated the efficacy, environmental impact, and the profitability of several weed management strategies in glyphosate-resistant soybean over a 3-yr period (2007 to 2009) at three locations in southwestern Ontario, Canada. No visible injury to soybean was observed with the herbicide treatments evaluated. A sequential application of glyphosate consistently provided high levels of weed control (99 to 100%) at 56 d after treatment in comparison with one- or two-pass herbicide programs. Soybean yield did not differ between the two-pass herbicide programs and glyphosate applied early POST; however, a yield benefit was found with a sequential application of glyphosate or a PRE herbicide followed by glyphosate compared with glyphosate applied only at late POST. The two-pass herbicide programs had higher environmental impact (EI) (> 23) than the one-pass herbicide programs (< 15), except when imazethapyr was followed by or tank-mixed with glyphosate, which had an equivalent EI (∼ 14) to the one-pass herbicide programs. Not surprisingly because of the low purchase price of glyphosate, gross margins were highest for treatments that included glyphosate. However, to reduce the selection pressure on glyphosate-resistant weed biotypes, to reduce environmental impact, and to increase gross margins a combination of glyphosate with another mode of action would be most beneficial. In this study glyphosate imazethapyr was the best alternative to a sequential two-pass glyphosate program.

Nomenclature: Flumetsulam; glyphosate; imazethapyr; s-metolachlor; soybean, Glycine max L.; common lambsquarters, Chenopodium album L. CHEAL; common ragweed, Ambrosia artemisiifolia L. AMBEL; green foxtail, Setaria viridis (L.) Beauv. SETVI; redroot pigweed, Amaranthus retroflexus L. AMARE; velvetleaf, Abutilon theophrasti Medic. ABUTH.

A field experiment was conducted during three cropping seasons to compare weed control and cotton yield provided by conventional (CV), glufosinate-resistant (LL), and glyphosate-resistant (RR) weed management systems under standard (102 cm) and narrow (38 cm) row spacing grown in conventional and conservation tillage systems. The conventional tillage and/or CV cotton received a PRE application of pendimethalin. The CV, LL, and RR cotton varieties received two POST applications of pyrithiobac, glufosinate, and glyphosate, respectively, at two- and four-leaf cotton growth stages. A final (LAYBY) application of trifloxysulfuron was applied to 38-cm row cotton while a LAYBY POST-directed spray of prometryn plus MSMA was used in 102-cm row cotton. The LL and RR weed management systems controlled at least 97% of large crabgrass, Palmer amaranth, sicklepod, and smallflower morningglory, while the CV system controlled 89, 73, and 87 to 98% of large crabgrass, smallflower morningglory, and Palmer amaranth, respectively. Sicklepod control increased from 85% in 102-cm rows to 95% in 38-cm rows in the CV herbicide system. Yellow nutsedge and pitted morningglory control exceeded 98% and was not affected by tillage, row spacing, or weed management system. Cotton yield was not affected by row spacing any year, by tillage in 2005, or by weed management system in 2004 and 2005. In 2006, yield in the RR weed management system was 27 and 24% higher than LL and CV weed management systems, respectively. In 2004, yield of conventional tillage cotton was 18% higher than conservation tillage cotton, but in 2006 the yield in conservation tillage was 12% higher than conventional tillage.

Nomenclature: Glufosinate; glyphosate; monosodium methanearsonate (MSMA); pendimethalin; prometryn; pyrithiobac; trifloxysulfuron; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; sicklepod, Senna obtusifolia (L.) H.S. Irwin & Barneby SENOB; smallflower morningglory, Jacquemontia tamnifolia (L.) Griseb. IAQTA; yellow nutsedge, Cyperus esculentus L. CYPES; cotton, Gossypium hirsutum L.

Research was conducted in 2009 and 2010 to evaluate influence of imazosulfuron rate and application timing on weed control in drill-seeded rice at Stuttgart, AR, and to evaluate imazosulfuron-containing herbicide programs in drill-seeded rice at Keiser and Stuttgart, AR. Weed species evaluated included barnyardgrass, broadleaf signalgrass, hemp sesbania, and yellow nutsedge. Imazosulfuron applied at 224 and 336 g ai ha⁻¹ during PRE, early POST (EPOST), or preflood (PREFLD) growth periods provided similar control of all weeds. Imazosulfuron applied EPOST or PREFLD controlled hemp sesbania and yellow nutsedge ≥ 93% both years at 5 and 7 wk after planting (WAP), except in 2009 when hemp sesbania control was ≤ 79% at 7 WAP. In 2010, because of inadequate rainfall, hemp sesbania and yellow nutsedge control with PRE-applied imazosulfuron was ≤29% at 5 and 7 WAP. Imazosulfuron plus clomazone PRE followed by (fb) quinclorac plus propanil EPOST and imazosulfuron plus quinclorac EPOST fb thiobencarb plus propanil PREFLD programs controlled hemp sesbania and barnyardgrass (in at least two site-years), and yellow nutsedge and broadleaf signalgrass (in at least one site-year) greater than or equal to clomazone plus quinclorac PRE fb propanil plus halosulfuron PRELD (standard program). No rice injury was observed with any herbicide program. Rice yield with all imazosulfuron-containing herbicide programs (6,630 to 8,130 kg ha⁻¹) was similar to the standard herbicide program (7,240 kg ha⁻¹). Imazosulfuron in mixture with clomazone, propanil, or quinclorac can be incorporated into herbicide programs of mid-South rice production for the control of broadleaf weeds and sedges.

Nomenclature: Clomazone; halosulfuron; imazosulfuron; propanil; quinclorac; thiobencarb; barnyardgrass, Echinochloa crus-galli (L.) P. Beauv.; broadleaf signalgrass, Urochloa platyphylla (Griseb.) Nash.; hemp sesbania, Sesbania herbacea (P. Mill.) McVaugh; yellow nutsedge, Cyperus esculentus L.; rice, Oryza sativa L.

Whether season-long weed control can be achieved in a furrow-irrigated rice system with similar herbicide inputs to that of a flooded system is not known. Field experiments were conducted in 2007 and 2008 at Pine Tree, AR to evaluate different herbicide programs on the weed control efficacy and rice grain yield in furrow-irrigated and flooded rice production systems. Six herbicide programs were evaluated with and without additional late-season “as-needed” herbicide treatments. Minor injury to rice was noted for quinclorac plus propanil. However, the injury was transient and the plants fully recovered. Overall weed control was greater in the flooded system compared with the furrow-irrigated system (up to 20% greater), because flooding effectively prevented the emergence of most terrestrial weeds. In addition, rice grain yields were 13 to 14% greater in flooded compared with furrow-irrigated plots. Irrespective of the irrigation system, herbicide programs that contained a PRE-applied herbicide provided greater weed control and resulted in greater yield compared with those that did not contain PRE-applied herbicide, indicative of the importance of early-season weed control in achieving higher grain yields. On the basis of weed control, yield, and weed treatment cost, the herbicide program with clomazone PRE followed by propanil at four- to five-leaf rice was more efficient than other programs evaluated in both irrigation systems. However, furrow-irrigated plots required as-needed herbicide applications, which were applied after the four- to five-leaf rice stage when two or more plots within a program exhibited ≤ 80% control for any of the weed species. This suggests that furrow-irrigated rice production demands additional weed management efforts and thereby increases production costs. There is also a possibility for substantial yield reduction in the furrow-irrigated system compared with the flooded system. Nevertheless, furrow-irrigated rice production can still be a viable option under water-limiting situations and under certain topographic conditions.

Nomenclature: Clomazone; propanil; quinclorac; rice, Oryza sativa L. ‘XL723’ ORYZA.

Field studies were conducted to compare the effectiveness of PRE and POST applications of a prepackaged mixture of flufenacet plus metribuzin with that of diclofop for winter wheat tolerance and control of Italian ryegrass. Additional studies investigated the effectiveness of reduced rates of flufenacet plus metribuzin applied POST to Italian ryegrass when wheat was in the spike stage. All PRE and POST applications of flufenacet plus metribuzin produced similar or greater injury to wheat and more consistent control of Italian ryegrass than PRE or POST applications of diclofop. PRE applications of flufenacet plus metribuzin controlled Italian ryegrass 73 to 77%, whereas POST applications controlled Italian ryegrass 77 to 99%. PRE applications of diclofop controlled Italian ryegrass 57%; POST application controlled Italian ryegrass 78%. Wheat injury from flufenacet plus metribuzin applications varied with application rate, cultivar, and year of application.

Nomenclature: Diclofop; flufenacet; metribuzin; Italian ryegrass, Lolium perenne L. ssp. Multiflorum (Lam.) Husnot winter wheat, Triticum aestivum L.

Experiments were conducted in North Carolina during 2005, 2006, and 2007 to determine peanut and weed response when peanut was planted in strip tillage after desiccation of cereal rye, Italian ryegrass, oats, triticale, wheat, and native vegetation by glyphosate and paraquat before planting with three in-season herbicide programs. Control of common ragweed and yellow nutsedge did not differ among cover crop treatments when compared within a specific herbicide program. Applying dimethenamid or S-metolachlor plus diclosulam PRE followed by imazapic POST was more effective than a chloroacetamide herbicide PRE followed by acifluorfen, bentazon, and paraquat POST. Incidence of spotted wilt in peanut (caused by a Tospovirus) did not differ when comparing cover crop treatments, regardless of herbicide program. Peanut yield increased in all 3 yr when herbicides were applied POST, compared with clethodim only. Peanut yield was not affected by cover crop treatment. Response to cover crop treatments was comparable, suggesting that growers can select cereal rye, Italian ryegrass, oats, or triticale as an alternative to wheat as a cover crop in peanut systems without experiencing differences associated with in-season weed management.

Nomenclature: Acifluorfen; bentazon; glyphosate; imazapic; paraquat; common ragweed, Ambrosia artemisiifolia L.; yellow nutsedge, Cyperus esculentus L.; cereal rye, Secale cereale L.; Italian ryegrass, Lolium multiflorum Lam.; oats, Avena sativa L.; peanut, Arachis hypogaea L.; triticale, Triticale hexaploide Lart.; wheat, Triticum aestivum L.

Aminocyclopyrachlor (AMCP) is labeled for use on zoysiagrass, but some injury has been observed. Differential zoysiagrass cultivar response to herbicide treatment has been previously reported. This greenhouse study evaluated the response of ‘BK-7’, ‘Cavalier’, ‘Emerald’, ‘Empire’, ‘Meyer’, and ‘Zorro’ zoysiagrass to 0, 0.005, 0.02, 0.11, 0.52, and 2.4, 11 kg ai ha⁻¹, AMCP. Visual estimation of percent necrosis and normalized difference vegetative index (NDVI) analysis were conducted. Based on rating dates and data types three tolerance groups were established: Cavalier, Meyer, and Zorro are the most tolerant; Emerald and Empire are intermediate; and BK-7 is the least tolerant to AMCP. All zoysiagrass cultivars had sufficient tolerance at the labeled rate. Visual and NDVI analyses were highly correlated; however, NDVI data were subject to greater standard error and pseudo R² values.

Nomenclature: Aminocyclopyrachlor, DPX-MAT28; zoysiagrass, Zoysia japonica Steud. ‘Empire’, ‘Meyer’; Z. matrella (L.) Merr. ‘Cavalier’, ‘Zorro’; Z. japonica Steud. × Z. pacifica Goudsw. ‘Emerald’, ‘BK-7’.

Quinoclamine is used in Europe, and was under evaluation in the Unites States for the control of liverwort in nursery crops. Liverwort is a nonvascular, chlorophyll-containing plant that can be problematic in greenhouse and nursery crops. POST-applied quinoclamine controls liverwort. However, liverwort structures vary in their sensitivity to POST-applied quinoclamine. Specifically, archegonial receptacles (female) are much more tolerant of quinoclamine than either antheridial receptacles (male) or thalli (leaflike structures). A series of studies were conducted to, first, document the degree of differential sensitivity between tissues to quinoclamine, and second, to determine the basis of this differential sensitivity. The dose that results in 50% of the population being controlled (I₅₀) of antheridial receptacles and juvenile thalli were estimated to be 1.60 and 1.27 kg·ha⁻¹, respectively. The I₅₀ of archegonial receptacles could not be estimated, but exceeded 10.45 kg·ha⁻¹. Chlorophyll content varied between liverwort tissues, but the content did not correlate to quinoclamine sensitivity. Absorption of ¹⁴C after application of radiolabeled quinoclamine was less in archegonial receptacles than in either antheridial receptacles or thalli. Scanning electron microscopy of the surface of the liverwort tissues revealed that archegonial receptacles had smaller pores (equivalent to stomata in higher plants) than either antheridial receptacles or thalli. The tolerance of archegonial receptacles to quinoclamine can be partially, but not exclusively, attributed to reduced absorption. This reduced absorption may be attributed to the limited pore size and less total pore area of the archegonial receptacles.

Nomenclature: Liverwort, Marchantia polymorpha L.; quinoclamine.

Field studies were conducted in 2010 in Ontario, OR, to evaluate the response of direct-seeded dry bulb onion, sugar beet, and pinto beans to imazosulfuron soil residues 12 mo after application to control weeds in potato. The studies were organized as randomized complete block designs with three replications each. Imazosulfuron was applied alone PRE at 224 and 450 g ai ha⁻¹, sequentially at 224 g ha⁻¹ PRE and POST, or in tank mixture with S-metolachlor 1,060 g ha⁻¹. Very few onion plants emerged in plots previously treated with imazosulfuron at 224 g ha⁻¹, regardless of timing. Emerged onion plants were severely injured and never matured. No onions emerged from residues of imazosulfuron applied at 450 g ha⁻¹. A few sugar beet plants emerged from 224 g ha⁻¹ but were severely stunted and never grew beyond the first set of leaves. There was no sugar beet emergence from imazosulfuron sequential applications, regardless of the rate and application timing. However, imazosulfuron residues did not affect pinto beans, which emerged and produced marketable yield, similar to grower standard and nontreated plots. The results suggest sensitivity of direct-seeded dry bulb onion and sugar beet, but not pinto beans, to imazosulfuron residues 12 mo after application.

Nomenclature: Imazosulfuron; onion, Allium cepa L. ‘Vaquero’; pinto beans, Phaseolus vulgaris ‘GTS-900’; potato, Solanum tuberosum L., ‘Ranger Russet’; sugar beet, Beta vulgaris L., ‘HM91122RR’.

Bermudagrass is a troublesome weed of zoysiagrass golf-course fairways. Field research was conducted in 2009 and 2010 evaluating bermudagrass suppression with applications of fluazifop plus triclopyr at various timings. Three rates of fluazifop (0.10, 0.21, and 0.32 kg ai ha⁻¹) were applied with triclopyr (1.12 kg ae ha⁻¹) once six thresholds of growing-degree-day accumulation (GDD_10C) had been reached: 200, 450, 825, 1,275, 1,775, and 2,250 GDD_10C. Yearly accumulated GDD_10C values were calculated with a base temperature of 10 C beginning on 1 January. Applications at 200 and 2,250 GDD_10C suppressed bermudagrass ≥ 90% at 5 WAT each year. Increased rates of fluazifop did not provide additional bermudagrass suppression at these timings. Cooling accumulation models may be needed to time fall applications, as the 1,775 GDD_10C timing in 2009 provided similar bermudagrass suppression to the 2,250 GDD_10C timing in 2010. Late-spring and midsummer applications at 450 GDD_10C, 825 GDD_10C, and 1,275 GDD_10C only suppressed bermudagrass 4 to 16% at 6 wk after treatment (WAT) in 2009 and 0 to 57% at 6 WAT in 2010. Zoysiagrass injury measured < 25% for all timings and decreased to 0 to 7% by 5 WAT each year. Future studies should evaluate bermudagrass suppression with other herbicides with the use of growing-degree-day and cooling accumulation models.

Nomenclature: Fluazifop; triclopyr; bermudagrass (Cynodon dactylon L. Pers.) ‘Riviera’; zoysiagrass (Zoysia japonica Steud.) ‘Zenith’.

We conducted a field experiment in 2007 and 2008 and repeated it in a separate field in 2008 and 2009 to test the effectiveness of two herbicides applied at two different times on weed control during switchgrass establishment. At 4 and 6 wk after switchgrass planting (WAP), sulfosulfuron was applied at 0.04 and 0.07 kg ai ha⁻¹ with nonionic surfactant and quinclorac was applied at 0.28, 0.42, and 0.56 kg ai ha⁻¹ with methylated seed oil. Herbicides applied at 4 WAP tended to be more effective than at 6 WAP. Sulfosulfuron provided greater control of smooth pigweed; however, quinclorac provided greater control of yellow foxtail, a grass weed that has traditionally been difficult to control with herbicides in switchgrass. Average yellow foxtail control was 73, 87, and 93% for quinclorac at 0.28, 0.42, and 0.56 kg ha⁻¹, respectively, compared to 62 and 60% for sulfosulfuron at 0.04 and 0.07 kg ha⁻¹, respectively. Switchgrass injury (chlorosis and height reduction relative to the untreated control) was observed, but most symptoms were not detectable by 8 wk after treatment (WAT) for most treatments. Plots that received quinclorac at 0.56 kg ha⁻¹ at 6 WAP tended to have relatively low weed biomass and high total aboveground yield in the establishment year and relatively high total aboveground yield in the year after establishment.

Nomenclature: Quinclorac; sulfosulfuron; smooth pigweed, Amaranthus hybridus L.; yellow foxtail, Setaria pumila (Poir.) Roemer & J.A. Schultes; switchgrass, Panicum virgatum L.

Amicarbazone is a photosystem II (PSII) inhibiting herbicide of the triazolinone herbicide family. Greenhouse experiments were conducted to compare the effects of amicarbazone and atrazine on annual bluegrass control and quantum yield (Φ_PSII) when applied at three treatment placements (soil-only, foliage-only, and foliage soil). Herbicide rates for amicarbazone and atrazine were 0.53 and 2.25 kg ha⁻¹, respectively. Amicarbazone applied soil-only and foliage soil controlled annual bluegrass 57 and 59%, respectively, 1 wk after treatment (WAT). Atrazine applied to foliage soil controlled annual bluegrass 48% at 1 WAT. All soil-only and foliage soil treatments were similar 2 WAT. Foliage-only application of amicarbazone provided significantly less control than other amicarbazone treatments throughout the study. Amicarbazone applied soil-only and foliage soil controlled annual bluegrass 100% at 3 WAT. Soil-only and foliage soil applications of atrazine and amicarbazone had similar reductions in quantum yield (Φ_PSII) at 1 to 3 WAT. Foliar-applied amicarbazone reduced Φ_PSII 78, 84, and 86% at 1, 2, and 3 WAT, respectively. The rapid reduction in annual bluegrass Φ_PSII and the increase in control resulting from soil contact of amicarbazone indicate root exposure of amicarbazone is beneficial for annual bluegrass control.

Nomenclature: Amicarbazone, 4-amino-N-(1,1-dimethylethyl)-4,5-dihydro-3-(1-methylethyl)-5-oxo-1H-1,2,4-triazole-1-carboxamide; annual bluegrass, Poa annua L.

Flue-cured tobacco is sensitive to foliar and soil residues of off-target synthetic auxin drift. Aminocyclopyrachlor is a newly developed synthetic auxin herbicide that may be used in right-of-way applications for broadleaf weed and brush control. Aminocyclopyrachlor is considered a reduced-risk alternative in rights-of-way compared with similar compounds because of its low application rate and volatility risk. However, no research is available on the response of field-grown, flue-cured tobacco to aminocyclopyrachlor drift exposure. Research was conducted in 2009 and 2010 at the Border Belt Tobacco Research Station in Whiteville, NC, to determine the response of ‘NC 71’ flue-cured tobacco to five simulated drift rates of aminocyclopyrachlor (0.31, 1.6, 3.1, 15.7, and 31.4 g ae ha⁻¹) and one aminopyralid (6.1 g ae ha⁻¹) simulated drift rates applied pretransplant incorporated, pretransplant unincorporated, 3 wk after transplant, and 6 wk after transplant. All herbicide rates and application timings caused significant visual tobacco injury, ranging from slight to severe with increasing herbicide drift rates. Tobacco plant heights and fresh weights were reduced at all application timings receiving ≥ 15.7 g ha⁻¹ aminocyclopyrachlor and the comparative aminopyralid rate.

Nomenclature: Aminocyclopyrachlor, 6-amino-5-chloro-2-cyclopropyl-4-pyrimidine-carboxylic acid; aminopyralid 4-amino-3,6-dichloro-2-pyridinecarboxylic acid; tobacco, Nicotiana tabacum L. ‘NC-71’.

The use of aminopyralid combined with metsulfuron for western snowberry control was evaluated with field trials conducted near Rushville, NE. Herbicides treatments consisted of aminopyralid plus metsulfuron, aminopyralid plus metsulfuron plus 2,4-D, 2,4-D alone, and metsulfuron plus chlorsulfuron plus 2,4-D plus dicamba. All treatments were applied in May and June. Sixty days after treatment (DAT) western snowberry control with aminopyralid plus metsulfuron at 0.073 0.012 kg ai ha⁻¹ applied in May was 64%, whereas when applied in June, control was 97%. Meanwhile control with 2,4-D was 99 and 78% for the May and June applications, respectively. No major differences between application timings were observed 60 DAT for the rest of the treatments, with control levels ranging from 85 to 99%. One year after application, differences in control between application timings only persisted for 2,4-D. At 365 DAT, western snowberry control with aminopyralid plus metsulfuron at 0.073 0.012 kg ai ha⁻¹ was 76 and 78% for May and June applications, respectively. The addition of 2,4-D at 1.1 kg ai ha⁻¹ to aminopyralid plus metsulfuron provided excellent control and was similar to the combination of metsulfuron, chlorsulfuron, 2,4-D, and dicamba for both May and June applications. Grass production and animal carrying capacity were higher after western snowberry control with the majority of the treatments. Aminopyralid plus metsulfuron applied at the lower rate was the exception. The increase in the carrying capacity after western snowberry control ranged from 2.2 to 4.5 animal unit month (AUM). The control of western snowberry resulted in an increase in net income per hectare when compared with the untreated checks, ranging from $4 to $47.9 ha⁻¹. Several options are available for effective western snowberry control during a broader time of application with increased grass production.

Nomenclature: 2,4-D; aminopyralid; chlorsulfuron; dicamba; metsulfuron; western snowberry, Symphoricarpos occidentalis Hook.

Conventional lentil, because it is relatively noncompetitive, requires effective weed control. In conventional lentil, metribuzin should be applied by the four-node stage to avoid crop injury. This is earlier than the critical period of weed control (CPWC) of lentil, which is between the five- and 10-node stage. However, imidazolinone herbicides potentially can be applied later in imidazolinone-resistant lentil, which might allow lentil to be kept weed-free for the CPWC. The objective of this experiment was to determine the best herbicide choice and application timing necessary to achieve the CPWC in lentil. To do this we tested herbicides differing in efficacy and residual control. The herbicides imazethapyr/imazamox, imazamox, and metribuzin sethoxydim were applied at the two- and six-node lentil stage. Of the three herbicide treatments, metribuzin sethoxydim resulted in grain yield that was on average 31% lower than the other herbicides. This occurred because of greater broadleaf biomass (composed primarily of wild mustard) in lentils treated with these herbicides regardless of application timing. Because of this, the CPWC was not attained with metribuzin sethoxydim. Late applications of imazethapyr/imazamox or imazamox resulted in grain yields 30% higher than with early application of these herbicides. Early applications of the imidazolinone herbicides gave poor control of grass weeds (wild oat and green foxtail), but late applications resulted in grass weed control equivalent to metribuzin sethoxydim. Imazethapyr/imazamox or imazamox should be applied at the five- to six-node stage of lentil to achieve the CPWC.

Nomenclature: Imazamox; imazethapyr; metribuzin; sethoxydim; green foxtail, Setaria viridis (L.) Beauv.; wild mustard, Sinapis arvensis L.; wild oat, Avena fatua L.; lentil, Lens culinaris Medik. ‘CDC Impact’.

Catbriar can be problematic to ranchers who graze rangeland. Five field studies of 2 yr duration were conducted during the 2007 to 2010 growing seasons to evaluate the effects of mowing and foliar-applied herbicides on the control of catbriar in Oklahoma rangeland. Without mowing, a formulated mixture of triclopyr and fluroxypyr (2.7 and 0.9 g ae L⁻¹) and triclopyr alone (2.4 g ae L⁻¹) applied at a volume of approximately 720 L ha⁻¹ twice over 2 yr consecutively controlled catbriar 69 and 71% (visual rating), respectively. Relative to the untreated control, these two treatments reduced the number of live catbriar stems 53 and 64% at the final evaluation, respectively. Mowing without herbicide was equally as effective as any herbicide treatment in reducing the catbriar population. The effects of herbicide were independent of mowing (i.e., the two experimental variables were noninteractive). If infested areas can be mowed, adding herbicide is not necessary to reduce catbriar population.

Nomenclature: Fluroxypyr; triclopyr; catbriar, Smilax bona-nox L.; rangeland.

Field experiments were conducted to evaluate the efficacy of herbicides and soil sterilants for the fairway conversion of ‘Tifway’ bermudagrass to ‘Zorro’ zoysiagrass. Treatments included glyphosate (4.48 kg ae ha⁻¹), EPTC (7.84 kg ai ha⁻¹), dazomet (338 kg ai ha⁻¹), siduron (13.4 kg ai ha⁻¹), glyphosate plus ETPC (4.48 7.84 kg ha⁻¹), glyphosate plus dazomet (4.48 338 kg ha⁻¹), EPTC plus siduron (7.84 13.4 kg ha⁻¹), and dazomet plus siduron (338 13.4 kg ha⁻¹). Glyphosate treatments were applied 5 wk prior to establishment (WPE), dazomet and EPTC treatments were applied 3 WPE, and siduron was applied at establishment. Dazomet and EPTC treatments were incorporated to a depth of 10 to 15 cm with a rotary tiller and rolled with a weighted roller to reduce losses from volatilization after application. Zorro zoysiagrass was established in June 2008 and 2009 using a mixture of rhizomes and stolons at a rate of 76 cm³ m⁻². Results indicate that glyphosate dazomet, glyphosate EPTC, dazomet siduron, and EPTC siduron were equally effective at controlling Tifway bermudagrass. EPTC and dazomet controlled bermudagrass more effectively when used in combination with glyphosate or siduron. There were no significant differences in bermudagrass cover between the EPTC combinations with glyphosate or siduron and dazomet applied with glyphosate or siduron. Comparing EPTC- and dazomet-alone, EPTC yielded less bermudagrass cover (32%) than dazomet (71%). At present, research is limited on using EPTC for controlling perennial grasses in turfgrass systems. Data from these studies demonstrate the potential use of EPTC as a preplant soil herbicide to control hybrid bermudagrass during zoysiagrass renovation.

Nomenclature: Dazomet; EPTC; glyphosate; siduron; hybrid bermudagrass, Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy ‘Tifway’; zoysiagrass or Manilagrass, Zoysia matrella (L.) Merr. ‘Zorro’.

Field studies were conducted in 2008 in Ontario, OR and Paterson, WA to determine the effect of simulated glyphosate drift on ‘Ranger Russet’ potato, including visual injury, shikimic acid accumulation, and tuber yield. Glyphosate was applied at 8.5, 54, 107, 215, and 423 g ae ha⁻¹; which corresponds to 0.01, 0.064, 0.126, 0.254, and 0.5 of the lowest recommended (846 g ha⁻¹) single application dose for glyphosate-resistant corn and sugar beet. Glyphosate was applied when potato plants were at 10-cm height, stolon hooking, tuber initiation, or bulking stage. The greatest visual foliar injury was observed when glyphosate was applied at a dose of 54 g ha⁻¹ or greater and potato plants were at the hooking stage. The lowest foliar injury was observed when glyphosate was applied to potato plants at the bulking stage. The I₅₀ glyphosate dose at 42 d after treatment (DAT) was estimated to be 167 g ha⁻¹ for potatoes sprayed at the hooking stage. The corresponding glyphosate dose to result in 50% injury for potatoes sprayed at tuber initiation, 10-cm height, and bulking stages were 129%, 338%, and 438%, respectively, greater than hooking stage. The U.S. No.1 potato yield was inversely related to vine injury and shikimic acid accumulation. Shikimic acid accumulation increased when glyphosate was applied at 107 g ha⁻¹ or greater. U.S. No.1 potato yield was reduced by 46% and 84% relative to the untreated control (55 and 76 T/ha) when glyphosate was applied at 107 g ha⁻¹ to plants in the hooking stage at Ontario and Paterson, respectively. Tuber yields at both sites were lowest when glyphosate was applied at hooking and tuber initiation stages.

Nomenclature: Glyphosate; potato, Solanum tuberosum L. ‘Ranger Russet’, SOLTU.

The feasibility of visual detection of weeds for map-based patch spraying systems needs to be assessed for use in large-scale cropping systems. The main objective of this research was to evaluate the reliability and profitability of using maps of Johnsongrass patches constructed at harvest to predict spatial distribution of weeds during the next cropping season. Johnsongrass patches visually were assessed from the cabin of a combine harvester in three corn fields and were compared with maps obtained in the subsequent year prior to postemergence herbicide application. There was a good correlation (71% on average) between the position of Johnsongrass patches on the two maps (fall vs. spring). The highest correlation (82%) was obtained with relatively large infestations, whereas the lowest (58%) was obtained when the infested area was smaller. Although the relative positions of the patches remained almost unchanged from 1 yr to the next, the infested area increased in all fields during the 4-yr experimental period. According to our estimates, using a strategy based on spraying full rates of herbicides to patches recorded in the map generated in the previous fall resulted in higher net returns than spraying the whole field, either at full or half rate. This site-specific strategy resulted in an average 65% reduction in the volume of herbicide applied to control this weed.

Nomenclature: Johnsongrass, Sorghum halepense (L.) Pers. SORHA; corn, Zea mays L.

Chinese sprangletop, a C₄ species, is one of the most important grass weeds of seeded rice in Asia. Chinese sprangletop biology was studied by growing it alone and in competition with 4 and 12 rice plants. Rice competition did not affect the height of Chinese sprangletop, and the weed grew taller than rice, regardless of the competition. Compared with Chinese sprangletop grown alone, competition from rice reduced Chinese sprangletop leaf number, leaf production rate, tiller number, tiller production rate, leaf area, shoot biomass, relative growth rate, and net assimilation rate. Leaf area and shoot biomass of Chinese sprangletop when grown in competition with 12 rice plants was only 16% and 13%, respectively, of the leaf area and biomass of the weed grown alone.

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

Diclofop-resistant Italian ryegrass is widespread in southwestern North Carolina, and growers have resorted to using acetolactate synthase (ALS) inhibitors such as mesosulfuron and pyroxsulam to control this weed in wheat. In the spring of 2007, mesosulfuron failed to control Italian ryegrass in several wheat fields. Seed were collected from six fields in two counties and greenhouse studies were conducted to determine response to mesosulfuron and the acetyl-CoA carboxylase (ACCase) inhibitors diclofop and pinoxaden. All populations were resistant to diclofop and cross-resistant to pinoxaden. Five of the six populations were resistant to diclofop, pinoxaden, and mesosulfuron. An additional study with two biotypes confirmed cross-resistance to the ALS inhibitors imazamox, mesosulfuron, and pyroxsulam. Resistance to mesosulfuron was heritable.

Nomenclature: Diclofop; imazamox; mesosulfuron; pinoxaden; pyroxsulam; Italian ryegrass, Lolium perenne L. subsp. multiflorum (Lam.) Husnot.; wheat, Triticum aestivum L.

Texasweed is an annual broadleaf plant belonging to the Euphorbiaceae family and is an emerging problem in southern U.S. rice fields. Field studies were conducted in 2008 and 2009 to study the effect of flood depth on Texasweed survival and growth. The trearments were five flood depths: 0, 10, 15, 20, and 30 cm and two Texasweed growth stages: two- to three-leaf stage and four- to five-leaf stage. The experiment was conducted in a completely randomized split-plot design with three replications. Flooding conditions were created by placing potted plants in 1.3 m by 0.7 m by 0.7 m polyvinyl chloride troughs. The effect of flood depth on Texasweed growth and fruit production was evaluated using ANOVA and regression analysis. Texasweed plants were able to survive in floods up to 30 cm; however, growth and fruit production were reduced. Increasing flood depths resulted in increased plant height and greater biomass allocation to stem. Texasweed plants produced adventitious roots and a thick spongy tissue, secondary aerenchyma, in the submerged roots and stem, which may play a role in its survival under flooded conditions. The recommended flood depth for rice in Louisiana is 5 to 10 cm. A 10-cm flood in the present study caused about 30 and 15% biomass reduction in two- to three-leaf and four- to five-leaf stage Texasweed, respectively. The results, thus, suggest that flooding alone may not be a viable option for Texasweed management in drill-seeded rice. However, appropriate manipulation of flooding could enhance the effectiveness of POST herbicides. This aspect needs further investigation.

Nomenclature: Texasweed, Caperonia palustris (L.) St. Hil. CNPPA; rice, Oryza sativa L. ORYSA.

In 2007, populations of Italian ryegrass were observed surviving applications of glyphosate under field conditions in southeast Arkansas. At least 10 reports of Italian ryegrass escaping glyphosate applications followed in subsequent years in Arkansas. These were unconfirmed reports of resistance from county agents, consultants, and farmers. The objectives of this research were to confirm resistance to glyphosate in a suspected resistant population collected in 2007 (Desha 2007) and to determine the level of resistance of a putative glyphosate-resistant population collected in 2009, both from Desha County, AR. Other objectives were to determine the resistance frequency in these populations, to determine whether the 2009 population was also acetolactate synthase (ALS) or acetyl-CoA carboxylase (ACCase-resistant), and to determine the effect on plant size as it relates to dose–response to glyphosate. The Desha, AR, 2007 population exhibited a low level of resistance to glyphosate. The estimated glyphosate dose that would control this population 50% was 1,260 g ae ha⁻¹, compared with 190 g ae ha⁻¹ for the susceptible check. In 2009, a population of Italian ryegrass (Des03) was identified that survived a glyphosate application of 1,740 g ae ha⁻¹ made in the field, which is twice the commercial use rate for glyphosate. Dose–response experiments determined that an estimated 3,890 g ae ha⁻¹ glyphosate was required to obtain 50% biomass reduction of Des03; this was 23 times that of the susceptible standard. Neither growth stage nor glyphosate rate evaluated affected the level of resistance observed in the Des03 population. This population was determined to be more than 70% resistant at the levels reported. In addition to glyphosate, Des03 was also resistant to diclofop, a commonly used herbicide in wheat in Arkansas and other areas. As a result, alternative management strategies for Italian ryegrass are currently being explored.

Nomenclature: Glyphosate; Italian ryegrass, Lolium perenne L. ssp. multiflorum (Lam.) Husnot; wheat, Triticum aestivum L.

Agroecosystems are inherently complex, and practices aimed at managing one component of the system can have unintended consequences for other components of the system. Management decisions, therefore, can be improved by assessing and understanding the multivariate nature of agricultural systems and the multifunctional character of particular agricultural management practices. The act of simultaneously assessing and evaluating multiple characteristics or functions in agriculture also can be a valuable education and extension activity, because it draws on active and experiential methods of learning and because the process effectively reveals important functions and tradeoffs associated with agroecosystems and their management. Here we introduce a tool (the spider plot) and present a case-study exercise in which we used this tool to evaluate the multiple characteristics and functions of different cover crops within a field day workshop format. We also provide examples of how this approach could be used to assess other management practices or properties of agroecosystems and communicate multivariate concepts within a weed science classroom or extension environment.

Seashore paspalum has high salinity tolerance, suggesting sodium chloride might have potential as a selective grassy weed herbicide. The objective of this research was to investigate sodium chloride rate and application timing for smooth crabgrass control and seashore paspalum and common bermudagrass injury. Five rates of sodium chloride (244, 488, 976, 1,952, or 3,904 kg ha⁻¹) were compared with quinclorac at 0.84 kg ai ha⁻¹ for controlling multileaf or multitiller smooth crabgrass. Sodium chloride at ≥ 976 kg ha⁻¹ provided excellent control (90 to 100%) of multitiller smooth crabgrass from 7 to 28 d after treatment, but ≥ 1,952 kg ha⁻¹ was required to achieve excellent control of multileaf populations. Furthermore, 976 kg ha⁻¹ of sodium chloride applied to multitiller smooth crabgrass caused minimal seashore paspalum injury (0 to 6%), comparable to quinclorac, but was more injurious when applied earlier in the spring for multileaf smooth crabgrass control. Common bermudagrass injury increased with sodium chloride rate and was > 20% from sodium chloride at 488 and 976 kg ha⁻¹ at both application timings. Overall, sodium chloride was most effective and safe on seashore paspalum when applied for smooth crabgrass control at the multitiller growth stage, whereas bermudagrass injury might be excessive at minimum rates required for control.

Nomenclature: Smooth crabgrass, Digitaria ischaemum (Schreb) Schreb. ex Muhl.; common bermudagrass, Cynodon dactylon L. (Pers.); seashore paspalum, Paspalum vaginatum (Sw.).

Common purslane is a widely distributed summer annual weed. It can reproduce vegetatively from stem cuttings by forming adventitious roots from the cut end of the stem. Apart from large stem cuttings, it is unclear whether purslane cuttings of various plant tissues differ in their ability to reproduce asexually. The objective of the study was to determine the survival and asexual reproductive capacity of purslane cuttings. A greenhouse study evaluated three cuttings from two stem locations and a leaf from one stem location for their survival and new leaf growth after 21 d. Cuttings included a stem node with either leaves attached or removed and a stem internode, all from proximal and distal stem locations relative to the root crown, and a leaf from a proximal stem node. Stem node cuttings had ≥ 70% survival, whereas internodes had 0% survival. Nodes with leaves attached further increased survival by > 20%. The location of the cutting on the main stem did not affect survival. Only noded cuttings produced new leaves, and cuttings with leaves attached produced the most new leaves. For purslane to vegetatively reproduce, nodes on stem cuttings are required, and the presence of leaves on the cutting improves the survival and new leaf growth of cuttings. Therefore, mechanical methods of weed control that chop and spread purslane leaves and stems might not be effective and could ultimately increase weed populations.

Nomenclature: Common purslane, Portulaca oleracea L. POROL.