Herbicide resistance in rigid ryegrass is an escalating problem in grain-cropping fields of southeastern Australia due to increased reliance on herbicides as the main method for weed control. Weed surveys were conducted between 1998 and 2009 to identify the extent of herbicide-resistant rigid ryegrass across this region to dinitroaniline, and acetolactate synthase- and acetyl coenzyme A (CoA) carboxylase-inhibiting herbicides. Rigid ryegrass was collected from cropped fields chosen at random. Outdoor pot studies were conducted during the normal winter growing season for rigid ryegrass with PRE-applied trifluralin and POST-applied diclofop-methyl, chlorsulfuron, tralkoxydim, pinoxaden, and clethodim. Herbicide resistance to trifluralin in rigid ryegrass was identified in one-third of the fields surveyed from South Australia, whereas less than 5% of fields in Victoria exhibited resistance. In contrast, resistance to chlorsulfuron was detected in at least half of the cropped fields across southeastern Australia. Resistance to the cereal-selective aryloxyphenoxypropionate-inhibiting herbicides diclofop-methyl, tralkoxydim, and pinoxaden ranged between 30 and 60% in most regions, whereas in marginal cropping areas less than 12% of fields exhibited resistance. Resistance to clethodim varied between 0 and 61%. Higher levels of resistance to clethodim were identified in the more intensively cropped, higher-rainfall districts where pulse and canola crops are common. These weed surveys demonstrated that a high incidence of resistance to most tested herbicides was present in rigid ryegrass from cropped fields in southeastern Australia, which presents a major challenge for crop producers.

Nomenclature: Chlorsulfuron; clethodim; diclofop-methyl; pinoxaden; tralkoxydim; trifluralin; rigid ryegrass, Lolium rigidum Gaudin; canola, Brassica napus L.

Glyphosate-resistant (GR) alfalfa offers growers new options for weed control in alfalfa. One potential benefit of using GR alfalfa is increased longevity of an alfalfa stand under frequent harvests. It was hypothesized that GR alfalfa would have a greater longevity because of removal of weed interference with minimal crop injury. To study GR alfalfa yield, weed invasion, alfalfa stand persistence, and relative forage quality (RFQ), a field experiment with three weed control methods (no herbicide, glyphosate, and hexazinone) under two harvest frequencies (high and moderate) was established in August 2003 at the Michigan State University Agronomy Farm in East Lansing, MI. Forage yield of established alfalfa was not adversely affected by herbicide treatments. There were no differences in weed biomass between alfalfa treated with glyphosate and that treated with hexazinone, except in 2007. Average GR alfalfa stand density decreased approximately 90% (from 236 to 27 plant m⁻²), and yield decreased approximately 30% (from 11.04 to 7.87 Mg ha⁻¹) during the 7-yr period (2004 to 2010) of the experiment. Stand density of GR alfalfa showed natural thinning during the 7-yr period regardless of harvest intensity or herbicide treatment. In most production years (4 out of 5 yr), relative forage quality of GR alfalfa was higher under a high-intensity harvesting system (4 to 5 harvests yr⁻¹) than it was with a moderate intensity harvesting system (3 to 4 harvests yr⁻¹). Relative forage quality was not affected by weed removal with herbicides in most years. Weed removal and harvest intensity in established GR alfalfa had no effect on stand persistence.

Nomenclature: Glyphosate; hexazinone; alfalfa, Medicago sativa L.

Inability to control Italian ryegrass in soft red winter wheat can result in reduced yields, reduced quality, or both and cause double-crop planting to be inefficient. Experiments were conducted at Plains, GA, to evaluate diclofop-susceptible Italian ryegrass control in a single-gene imidazolinone (IMI)-resistant wheat using imazamox, mesosulfuron, and diclofop. Treatments were applied at variable rates and tank mixtures to the IMI-resistant soft red winter wheat ‘AGS CL7’ at Feekes' stages 1 (EMERG) or 2 (POST). Lower Italian ryegrass control of 78% or less was observed with single treatments of EMERG or POST herbicide applications. Diclofop provided maximum Italian ryegrass control of 79% or greater with minimal injury to wheat cultivar AGS CL 7. Sequential applications of diclofop at EMERG followed by imazamox, mesosulfuron, or diclofop POST provided maximum Italian ryegrass control at 86% or greater. The efficacy of the acetolactate synthase (ALS)–inhibiting herbicides registered for wheat weed control for AGS CL7 and ‘AGS 2000’ (conventional) was also evaluated. Mesosulfuron at 40 g ai ha⁻¹ resulted in 17% injury at 7 d after application (DAA), tribenuron at 40 g ai ha⁻¹ caused 9% injury 7 DAA, and pyroxsulam at 190 g ai ha⁻¹ caused 7% injury at 7 DAA, but was transient and not observed after heading or at harvest. No yield differences were noted between the nontreated control for AGS 2000 and AGS CL 7 for chlorsulfuron, mesosulfuron, thifensulfuron, tribenuron, prosulfuron, and pyroxsulam.

Nomenclature: Chlorsulfuron; dicoflop; imazamox; mesosulfuron; prosulfuron, N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]-2-(3,3,3-trifluoropropyl)benzenesulfonamide; pyroxsulam, N-(5,7-dimethoxy[1,2,4]triazolo[1,5-a]pyrimidin-2-yl)-2-methoxy-4- (trifluoromethyl)-3-pyridinesulfonamide; thifensulfuron; tribenuron; Italian ryegrass, Lolium perenne L. ssp. multiflorum (Lam.) Husnot LOLMU; wheat, Triticum aestivum L., ‘AGS 2000’, ‘AGS CL 7’.

Field studies were conducted in 2008 and 2009 near Crowley, LA to evaluate the addition of a herbicide with soil-residual activity in mixture with imazethapyr applied very early POST followed by an application of imazethapyr or imazamox 2 wk after the initial application. Weeds evaluated included red rice, barnyardgrass, and alligatorweed. Weed control with treatments including a herbicide with soil-residual activity was equivalent to or higher than imazethapyr applied alone followed by imazethapyr or imazamox. Yield and economical returns were maximized with quinclorac or penoxsulam mixed with imazethapyr followed by imazethapyr or imazamox. The addition of quinclorac or penoxsulam proved to be beneficial in a total weed management program.

Nomenclature: Imazamox; imazethapyr; penoxsulam; quinclorac; alligatorweed, Althernanthera philoxeroides (Mart.) Griseb.; barnyardgrass, Echinochloa crus-galli (L.) Beauv; red rice, Oryza sativa L.

Undesirable stands of hybrid corn often result in a decision to replant; removal of the initial corn is recommended to reduce competition for available resources. Because much of the hybrid corn is glyphosate-resistant (GR), the particular herbicide and timing for control is challenging. No-till field trials were established in central and northeast Missouri in 2009 and 2010 to determine the efficacy of glufosinate POST in glufosinate-resistant corn or imazethapyr plus imazapyr POST in imidazolinone-resistant corn for the control of GR corn. Separate blocks of glufosinate-resistant and imidazolinone-resistant corn were planted in 76 cm rows, with GR corn established between rows at densities of 1 (low) and 4 (high) plants m⁻². Herbicides were broadcast at corn heights of 10, 20, and 40 cm. Visual estimates of control rated 5 wk after treatment were highest for the 20 cm application height, ranging from 81 to 84% and 72 to 79% with glufosinate or imazethapyr plus imazapyr, respectively. Control was unacceptable at 10 and 40 cm, ranging from 26 to 62% and 24 to 83%. Dry weights per plant indicated that applications at all heights reduced GR corn biomass a minimum of 94 and 82% with glufosinate or imazethapyr plus imazapyr, respectively. Although control of GR corn with single applications of glufosinate and imazethapyr plus imazapyr was unacceptable for two of three application heights, reductions in corn biomass indicate applications were effective.

Nomenclature: Glufosinate; imazapyr; imazethapyr; corn, Zea mays L.

Glyphosate-resistant (GR) giant ragweed has been confirmed in Ontario, Canada. Giant ragweed is an extremely competitive weed and lack of control in soybean will lead to significant yield losses. Seed companies have developed new herbicide-resistant (HR) crop cultivars and hybrids that stack multiple HR traits. The objective of this research was to evaluate the efficacy of glyphosate and glyphosate plus dicamba tank mixes for the control of GR giant ragweed under Ontario environmental conditions in dicamba-tolerant (DT) soybean. Three field trials were established over a 2-yr period (2010 and 2011) on farms near Windsor and Belle River, ON. Treatments included glyphosate (900 g ae ha⁻¹), dicamba (300 g ae ha⁻¹), and dicamba (600 g ha⁻¹) applied preplant (PP), POST, or sequentially in various combinations. Glyphosate applied PP, POST, or sequentially provided 22 to 68%, 40 to 47%, and 59 to 95% control of GR giant ragweed and reduced shoot dry weight 26 to 80%, 16 to 50%, and 72 to 98%, respectively. Glyphosate plus dicamba applied PP followed by glyphosate plus dicamba applied POST consistently provided 100% control of GR giant ragweed. DT soybean yield correlated with GR giant ragweed control. This is the first report in Canada of weed control in DT soybean, specifically for the control of GR giant ragweed. Results indicate that the use of dicamba in DT soybean will provide an effective option for the control of GR giant ragweed in Ontario.

Nomenclature: dicamba; glyphosate; giant ragweed, Ambrosia trifida L.; soybean, Glycine max (L.) Merr.

Recent shifts in the peanut cultivars commercially grown have led to a renewed interest in the tolerance of these new cultivars to herbicides. Field experiments were conducted in Georgia from 2008 to 2011 to evaluate the effects of chlorimuron on the incidence of tomato spotted wilt virus (TSWV) and yield of ‘Florida-07’, ‘Georgia-06G’, and ‘Tifguard’. Chlorimuron at 9 g ai ha⁻¹ was applied at 60 to 69, 70 to 79, 90 to 99, and 100 to 109 d after peanut emergence (DAE). TSWV was increased by only 3% when chlorimuron was applied to Tifguard at 60 to 69 DAE. Yields of Florida-07 were not influenced by any timing of chlorimuron. Chlorimuron applied 60 to 69, 70 to 79, and 90 to 99 DAE caused yield reductions when applied to Georgia-06G. Yields of the cultivar Tifguard were reduced when chlorimuron was applied 70 to 79, 90 to 99, and 100 to 109 DAE. Yield losses from chlorimuron ranged from 7 to 11%.

Nomenclature: Chlorimuron; peanut, Arachis hypogaea L.

Inadequate corn stands due to extreme weather conditions may require producers to replant their corn fields. The use of GR corn, however, can result in difficulty in managing replanted corn without experiencing yield loss. Therefore, the objectives of this research were to evaluate the herbicide options for control of GR corn in a corn replant situation and to determine the effect of corn replanted into various initial corn stands on grain yield. Two field studies were conducted to accomplish the objectives. The first experiment was designed to identify the most efficacious herbicide treatment for GR corn removal in a corn replant situation. Clethodim (51 g ai ha⁻¹) applied 6 d prior to replanting, paraquat (700 g ai ha⁻¹) plus metribuzin (160 g ai ha⁻¹) applied at replanting, and glufosinate (450 g ai ha⁻¹) applied at replanting along with a sequential treatment 3 wk later provided 96 to 100% control of the initial corn stand and resulted in the highest yield. If corn from the first planting remains, the interaction between different sized plants can reduce yield of corn. Thus, a second field experiment was conducted to evaluate the influence on grain yield of corn replanted into various initial corn stands. Corn stands of 0, 20,000, 40,000, 60,000, 80,000, and 100,000 plants ha⁻¹ were established and either followed by a corn replant at 80,000 seeds ha⁻¹ or not replanted. Initial stands ≥ 60,000 plants ha⁻¹ did not require a replant to maximize yield. Initial corn stands ≤ 40,000 plants ha⁻¹ required a replant with initial stand control to maximize grain yield. The percent yield contribution from an initial stand of 20,000 plants ha⁻¹ was 20% greater than the same population replanted a few weeks later, which showed the competitive advantage to earlier planting even at the lowest initial corn stand. Because of this competitive advantage, an initial stand must be removed to maximize corn yield in a replant situation.

Nomenclature: Clethodim; glufosinate; metribuzin; paraquat; corn, Zea mays L.

Dry pea improves corn yield and tolerance to weed interference compared with soybean, spring wheat, or canola as preceding crops. To understand this synergy between dry pea and corn, growth and nutrient concentration of corn were examined following dry pea or soybean in sequence. Each corn plot was split into weed-free and weed-infested subplots, with foxtail millet established at one density to provide uniform weed interference. Compared with soybean, dry pea improved corn grain yield 10% in weed-free conditions and corn tolerance to weed interference more than twofold. Dry pea synergy to corn in weed-free conditions was not related to differences in corn development, height, or nutrient status of corn seedlings. When foxtail millet was present, dry pea increased corn height and rate of development late in the growing season compared with soybean. Improved corn tolerance to weed interference was not related to seedling emergence or growth of foxtail millet, as these parameters did not vary with preceding crop. Other biological factors must be involved in dry pea synergy to corn.

Nomenclature: Canola, Brassica napus L.; corn, Zea mays L.; dry pea, Pisum sativum L.; foxtail millet, Setaria italica (L.) Beauv.; soybean, Glycine max (L.) Merr.; spring wheat, Triticum aestivum L.

Field and greenhouse studies were conducted in Belle Glade, FL, in 2010 and 2011 to evaluate saflufenacil and glyphosate efficacy on POST burndown of ragweed parthenium. Log-logistic models were used to determine the herbicide dose required to produce 90% control (ED₉₀). The ED₉₀ for rosette ragweed parthenium control in the greenhouse was saflufenacil at 8.0 g ai ha⁻¹ at 14 d after treatment. The rate required to cause 90% growth reduction of rosette ragweed parthenium at 14 d after treatment was 8.9 g ha⁻¹ of saflufenacil. The probability of rosette ragweed parthenium survival decreased with increasing rates of saflufenacil. The ED₉₀ value for bolted ragweed parthenium control in the field was 5.7 g ha⁻¹ of saflufenacil at 21 d after treatment. Ragweed parthenium had no response to glyphosate either in the field or in the greenhouse studies. This demonstrates that saflufenacil can be used as a POST burndown of ragweed parthenium populations that have no response to glyphosate.

Nomenclature: Glyphosate; saflufenacil; ragweed parthenium, Parthenium hysterophorus L.

Methyl bromide has been widely used for weed control in polyethylene-mulched tomato production. With the phaseout of methyl bromide in the United States, an effective alternative is needed. Field experiments were conducted in 2007 and 2009 to determine if allyl isothiocyanate (ITC) would provide substantive weed control in tomato along with crop tolerance under low-density polyethylene (LDPE) and virtually impermeable film (VIF) mulch. Treatment factors included two mulch types (LDPE and VIF) and six rates of allyl ITC (0, 15, 75, 150, 750, 1,500 kg ha⁻¹). A standard treatment of methyl bromide ∶ chloropicrin (67 ∶ 33%) at 390 kg ha⁻¹ under LDPE mulch was also established. Allyl ITC was broadcast applied and incorporated in soil before forming raised beds and laying plastic mulch. Tomatoes were transplanted 3 wk after applying allyl ITC or methyl bromide treatments. Tomato injury was ≤ 8% in all treatments at 2 wk after transplanting (WATP). Allyl ITC at 913 (± 191) kg ha⁻¹ was required to control yellow nutsedge, Palmer amaranth, and large crabgrass equivalent to methyl bromide at 6 WATP and maintain marketable tomato yield equivalent to methyl bromide treatment. VIF mulch was not effective in increasing weed control or improving the marketable yield of tomato over LDPE mulch. This research demonstrates that allyl ITC under an LDPE mulch can have a practical application for weed control in polyethylene-mulched tomato in the absence of methyl bromide.

Nomenclature: Allyl isothiocyanate; methyl bromide; large crabgrass, Digitaria sanguinalis (L) Scop. DIGSA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; yellow nutsedge, Cyperus esculentus L. CYPES; tomato, Lycopersicon esculentum Mill. ‘Amelia’.

Herbicides used to control many forb species in pastures may injure desirable native grass species. Buffalograss, a major component of shortgrass rangeland, often is injured by some growth regulator herbicides, such as 2,4-D and dicamba. Aminocyclopyrachlor (formerly known as DPX-MAT28 and herein termed ACPCR), a new synthetic auxin herbicide chemistry for control of broadleaf weeds, was investigated for injury to buffalograss and control of forbs in shortgrass prairie at varying rates of application. In the season of application, ACPCR at rates of 140 g ai ha⁻¹ or less caused buffalograss injury that was either negligible or short-lived, and visual estimates of grass injury were 8% or less at the end of the growing season. At ACPCR rates of 280 g ha⁻¹, more injury was evident at 3 wk after treatment (WAT) than at the end of the season if adequate precipitation was available for new leaf growth. When precipitation was lacking, evidence of injury persisted through to the end of the season when treated at the greatest rate of ACPCR. Buffalograss injury was mainly in the form of browned leaf tips, but total buffalograss dry matter yield was not different between any treatments in either year. The year after treatment, no buffalograss injury was evident from any of the herbicide rates. Final forb control was 97% or greater each year for ACPCR at the 140 and 280 g ha⁻¹ rates. In this experiment, rates as low as ACPCR at 140 g ha⁻¹ provided excellent forb control and maintained buffalograss productivity.

Nomenclature: 2,4-D; aminocyclopyrachlor; dicamba; buffalograss, Bouteloua dactyloides (Nutt.) J.T. Columbus BUCDA.

Studies were conducted in 2007 and 2008 to evaluate herbicides having both PRE and POST activity for selective weed control in bald cypress plantings. Five herbicides were applied at two or three rates at two different timings. The first timing was to dormant seedlings without foliage and prior to weed emergence (i.e., PRE). The second timing was to foliated seedlings with established weed seedlings present (i.e., POST). Herbicide treatments included aminopyralid at 70 and 120 g ae ha⁻¹, hexazinone at 420 and 560 g ai ha⁻¹, imazapyr at 140 and 210 g ae ha⁻¹, sulfometuron methyl at 110, 160, and 210 g ai ha⁻¹, and flumioxazin at 290 and 430 g ai ha⁻¹. Herbicide rate had little effect on vegetation control. PRE-applied sulfometuron methyl was most effective, providing nearly complete control of graminoids and broadleaves at 60 d after treatment (DAT). POST-applied treatments were generally less effective, though in the 2008 study imazapyr and sulfometuron methyl resulted in approximately 60% bare ground at 60 DAT. Growth of bald cypress seedlings was enhanced by both PRE- and POST-applied sulfometuron methyl, flumioxazin, or hexazinone and by PRE imazapyr. The best bald cypress growth response followed POST-applied sulfometuron methyl at 210 g ha⁻¹, which resulted in 63 cm³ mean volume index, more than fivefold greater than the nontreated check. Aminopyralid caused severe and lasting seedling injury. POST-applied imazapyr resulted in fasciculation and no growth benefit, despite providing the most efficacious weed control among POST treatments. Survival and growth of bald cypress can be greatly enhanced with a single selective herbicide treatment using sulfometuron methyl, flumioxazin, or hexazinone applied before or following foliation in the spring.

Nomenclature: Aminopyralid; flumioxazin; hexazinone; imazapyr; sulfometuron methyl; bald cypress, Taxodium distichum (L.) Rich var. distichum.

Dermatitis from poison ivy is a significant health problem. Considerable effort is devoted to the control of this invasive and virulent weed in urban areas. Glyphosate, triclopyr, 2,4-D, a 1 ∶ 1 mixture of glyphosate and 2,4-D, and a 9 ∶ 1 mixture of glyphosate and triclopyr were evaluated for poison ivy control. Each of these three herbicides and two mixtures were applied at nine or ten rates, which ranged in phytotoxicity from none to death. Poison ivy plants had been propagated and container-grown. Percent control, as determined from plant fresh weight reduction, was determined at 1 and 4 mo after treatment (MAT). Data were subjected to ANOVA followed by nonlinear regression. Rates required for 95% control at 1 and 4 MAT and the associated costs were determined for each of the three herbicides and two mixtures. Acceptable control (i.e., ≥ 95%) at 1 and 4 MAT could be obtained at a much lower cost with either triclopyr or 2,4-D than with either glyphosate alone or with the two glyphosate-containing mixtures. Nonlinear regression also was used to evaluate whether the two mixtures were interactive (i.e., synergistic or antagonistic) or not (i.e., additive). Glyphosate plus triclopyr was synergistic for control at both 1 and 4 MAT. Glyphosate plus 2,4-D was synergistic for control at 4 MAT only. However, for both mixtures, synergism was only evident at rates that controlled poison ivy ≤ 80%. Both mixtures were noninteractive at rates required for acceptable control.

Nomenclature: 2,4-D amine; glyphosate; triclopyr; poison ivy Toxicodendron radican (L.) Kuntze.

Studies were conducted in 2008 and 2009 to determine the effect of S-metolachlor rate and application time on sweetpotato cultivar injury and storage root shape under conditions of excessive moisture at the time of application. S-metolachlor at 1.1, 2.2, or 3.4 kg ai ha⁻¹ was applied immediately after transplanting or 2 wk after transplanting (WATP) to ‘Beauregard’, ‘Covington’, ‘DM02-180’, ‘Hatteras’, and ‘Murasaki-29’ sweetpotato. One and three d after S-metolachlor application plots received 1.9 cm rainfall or irrigation. S-metolachlor applied immediately after transplanting resulted in increased sweetpotato stunting 4 and 12 WATP, decreased no. 1 and marketable sweetpotato yields, and decreased storage root length to width ratio compared with the nontreated check. Sweetpotato stunting, no. 1 and marketable yields, and storage root length to width ratio in treatments receiving S-metolachlor 2 WATP were similar to the nontreated check. In 2008, Covington and Hattaras stunting 12 WATP was greater at 2.2 and 3.4 kg ha⁻¹ (11 to 16%) than 1.1 kg ha⁻¹ (1 to 2%). In 2009, S-metolachlor at 3.4 kg ha⁻¹ was more injurious 4 WATP than 2.2 kg ha⁻¹ and 1.1 kg ha⁻¹. While cultivar by treatment interactions did exist, injury, yield, and storage root length to width ratio trends were similar among all cultivars used in this study.

Nomenclature: S-metolachlor; sweetpotato, Ipomoea batatas L. Lam. ‘Beauregard’, ‘Covington’, ‘DM02-180’, ‘Hatteras’, and ‘Murasaki-29’.

The objective of this study was to determine whether a junglerice population from the tropical Ord River region of northwest Australia was glyphosate resistant, and whether alternative herbicides labeled for junglerice control were still effective. Seed samples collected from the field site were initially screened with glyphosate in the glasshouse, and surviving individuals were self-pollinated for subsequent glyphosate dose-response studies. Glyphosate resistance was confirmed, as the suspected resistant population was found to be 8.6-fold more resistant to glyphosate than a susceptible population based on survival (LD₅₀ of 3.72 kg ha⁻¹), and 5.6-fold more resistant based on biomass reduction (GR₅₀ of 1.16 kg ha⁻¹). The glyphosate-resistant population was susceptible to label-recommended doses of all other herbicides assessed, including three acetyl-CoA carboxylase (ACC) –inhibiting herbicides (fluazifop-P, haloxyfop, and sethoxydim), two acetolactate synthase (ALS) –inhibiting herbicides (imazamox and sulfometuron), paraquat, and glufosinate. Glyphosate resistance has previously evolved in numerous species found in glyphosate-resistant cropping systems, no-till chemical fallow, fence line, and perennial crop situations. Here we report the evolution of glyphosate resistance in a cropping system that included annual tillage. The evolution of glyphosate resistance in junglerice from a tropical cropping system further demonstrates the need for improved glyphosate stewardship practices globally.

Nomenclature: Fluazifop-P; glufosinate; glyphosate; haloxyfop; imazamox; paraquat, sethoxydim; sulfometuron; junglerice, Echinochloa colona (L.) Link.

Dodder seeds are physically dormant because of hard seed coats and do not readily germinate without scarification. Reliable methods of scarification for small lots of dodder seed are needed to facilitate laboratory, greenhouse, and field research projects. Dodder seed was scarified for varying times using a handheld rotary tool at the 10,000 rpm setting with a conical grinding-stone bit attached. Percentage of germination and weight change of seeds were assessed using scarification times between 0 and 4 min at 0.5-min increments. Mean seed weight loss and mean number of germinated seeds increased quadratically as scarification time increased. Scarifying for 2.5 min was judged the shortest time with maximal germination. Another study evaluated the effect of seed number (100 to 400 seeds sample⁻¹) on the efficacy of rotary tool scarification when scarification time was held constant at 2.5 min. Percentage of germination decreased linearly as seed batch size increased. The handheld rotary tool provides consistent and repeatable scarification of dodder seed with germination rates greater than 80%.

Nomenclature: Dodder, Cuscuta spp.; cranberry, Vaccinium macrocarpon Ait.

Conservation agriculture (CA) practices are threatened by glyphosate-resistant Palmer amaranth. Integrated control practices including PRE herbicides and high-residue CA systems can decrease Amaranthus emergence. Field experiments were conducted from autumn 2006 through crop harvest in 2009 at two sites in Alabama to evaluate the effect of integrated weed management practices on Amaranthus population density and biomass, cotton yield, and economics in glyphosate-resistant cotton. Horizontal strips included four CA systems with three cereal rye cover crop seeding dates and a winter fallow (WF) CA system compared to a conventional tillage (CT) system. Additionally, vertical strips of four herbicide regimes consisted of: broadcast, banded, or no PRE applications of S-metolachlor (1.12 kg ai ha⁻¹) followed by (fb) glyphosate (1.12 kg ae ha⁻¹) applied POST fb layby applications of diuron (1.12 kg ai ha⁻¹) plus MSMA (2.24 kg ai ha⁻¹) or the LAYBY application alone. Early-season Amaranthus density was reduced in high-residue CA in comparison to the CA WF systems in 2 of 3 yr. Amaranthus densities in herbicide treatments that included a broadcast PRE application were lower at three of five sampling dates compared to banding early-season PRE applications; however, the differences were not significant during the late season and cotton yields were not affected by PRE placement. High-residue conservation tillage yields were 577 to 899 kg ha⁻¹ more than CT, except at one site in 1 yr when CT treatment yields were higher. CA utilizing high-residue cover crops increased net returns over CT by $100 ha⁻¹ or more 2 out of 3 yr at both locations. High-residue cover crop integration into a CA system reduced Amaranthus density and increased yield over WF systems; the inclusion of a broadcast PRE application can increase early-season Amaranthus control and might provide additional control when glyphosate-resistant Amaranthus populations are present.

Nomenclature: Diuron; glyphosate; MSMA; S-metolachlor; Palmer amaranth, Amaranthus palmeri S. Wats.; cotton, Gossypium hirsutum L; rye, Secale cereale L.

Greenhouse and field experiments were conducted to evaluate the use of a carbon band to provide a “safe zone” for seedling emergence and growth of three native grass species. ‘KIKA677’ streambed bristlegrass germplasm, ‘Alamo’ switchgrass, and ‘Waelder’ shortspike windmillgrass germplasm were used in combination with several PRE- and POST-applied herbicides including cloransulam, flumioxazin, imazapic, imazethapyr, and 2,4-D. In a greenhouse experiment, switchgrass emergence was improved when a carbon band was used with imazapic or imazethapyr at 0.04 and 0.07 kg ai ha⁻¹ or 2,4-D at 2.12 kg ae ha⁻¹. Windmillgrass emergence was improved when carbon was used in combination with flumioxazin at 0.05 and 0.1 kg ai ha⁻¹, imazapic at 0.04 and 0.07 kg ha⁻¹, imazethapyr at 0.07 kg ha⁻¹, and 2,4-D at 1.06 kg ha⁻¹, whereas bristlegrass emergence was improved when carbon was used in combination with flumioxazin at 0.1 kg ai ha⁻¹, imazapic at both rates, and imazethapyr at 0.04 kg ha⁻¹. Field studies indicated that flumioxazin at 0.05 and 0.1 kg ha⁻¹, imazapic at 0.04 kg ha⁻¹, and imazethapyr at 0.04 and 0.07 kg ha⁻¹, were safened for bristlegrass and switchgrass emergence when used with carbon. Windmillgrass emergence and growth were improved when carbon was used in combination with flumioxazin at 0.1 kg ha⁻¹.

Nomenclature: Cloransulam; 2,4-D; flumioxazin; imazapic; imazethapyr; switchgrass, Panicum virgatum L. ‘Alamo’; streambed bristlegrass, Setaria leucopila (Scribn. & Merr.) K. Schum. ‘KIKA677’; shortspike windmillgrass, Chloris subdolichostachya Nash ‘Waelder’.

The biology of purple nutsedge was studied by growing it alone and in competition with 12 and 24 rice plants in a pot experiment. Compared with the weedy plants grown alone, competition from rice reduced purple nutsedge leaf number, shoot number, tuber production rate, and leaf biomass. At 10 wk after planting, interference from 12 and 24 rice plants reduced purple nutsedge leaf area by 79 and 86%, respectively, compared with weedy plants grown without rice interference. On the same date, purple nutsedge aboveground shoot biomass was 26.8 g plant⁻¹ without interference, whereas in interference with 12 and 24 rice plants, purple nutsedge produced aboveground biomass of 4.8 and 2.2 g plant⁻¹, respectively. A total of 95 tubers plant⁻¹ were produced by purple nutsedge when grown alone. Growth with 12 and 24 rice plants reduced tuber production to 33 and 17 tubers plant⁻¹, respectively. Without interference, purple nutsedge produced 40 g plant⁻¹ of total biomass of tuber plus root plus rhizome, whereas in interference with 12 and 24 rice plants, purple nutsedge produced 14 and 5 g plant⁻¹ of total belowground biomass, respectively.

Nomenclature: Purple nutsedge, Cyperus rotundus L. CYPRO; rice, Oryza sativa L.

Despite the abundance of common ragweed in crops and the potency of ragweed pollen as an allergen, pollen production in agricultural fields has hardly been evaluated. Our goal was to evaluate pollen and seed production of early- (i.e., plants missed by weed control) and late- (i.e., after weed control) emerging common ragweed growing in corn and soybean. Allocation and gender distribution were also evaluated. The experiment included 2 yr (2008, 2009), three competition treatments, two seeding/emergence dates, three densities, and four replicates. Competition treatments (main plots) included no crop or weeds (bare), corn, or soybean. Crops were glyphosate resistant. Subplots were seeded with common ragweed before or after glyphosate application at densities of 1 (4 m⁻²), 3 (12 m⁻²), or 6 (24 m⁻²) plants per plot. Ragweed plants were harvested in mid-October and measured (aboveground biomass, length of all male inflorescences, stem diameter, and seed production). Based on our estimates, mean (backtransformed from ln[x 1]) pollen production values were: 6.25 (bare), 0.74 (corn), and 1.13 (soybean) × 10⁸ pollen grains per ragweed. Biomass and diameter were good predictors of ragweed male and female fitness. Plant height was not correlated with maleness. In crops, ragweed gender distribution was shifted toward maleness. Estimations indicate early-emerging (June 18 to 23) ragweed produced three times more pollen than late (July 7 to 11) plants.

Nomenclature: Glyphosate; common ragweed, Ambrosia artemisiifolia L. AMBEL; corn, Zea mays L.; soybean, Glycine max (L.) Merr.

Research was conducted to evaluate the weed suppression potential of ‘Rondo’ (4484-1693; PI 657830), a sister line (4484-1665), and other indica rice lines against barnyardgrass in field plots in Stuttgart, AR, using minimal herbicide inputs in two separate 3-yr experiments. Under weed pressure, Rondo and the sister line (4484-1665) generally produced yields that were comparable to those of weed-suppressive indica standards and approximately 50% greater than those of the least-suppressive commercial cultivars, such as ‘Kaybonnet’, ‘Katy’, and ‘Lemont’. Rice yield under weed pressure was correlated with weed-free yield and harvest height. Indica lines tended to produce more tillers than did the commercial cultivars. Tillering potential under weed-free conditions was not correlated with weed suppression or yield loss; however, tillering under weed pressure was strongly correlated with weed suppression and biomass, and yield and yield loss under the weed densities in these experiments. Rondo is presently being used for commercial organic rice production in Texas, in part due to its high yield potential and ability to suppress or tolerate rice pests, including weeds. Our results suggest that the weed-suppressive ability of Rondo and the other indica lines evaluated in these experiments is superior to that of many commercial cultivars.

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

Almost 1,650 corn, cotton, and soybean growers in 22 states participated in a 2010 telephone survey to determine their attitudes with regard to which weed species were most problematic in glyphosate-resistant (GR) crop production systems for corn, cotton, and soybean. The survey is a follow-up to a previous 2005 to 2006 survey that utilized a smaller set of growers from fewer states. In general, growers continued to estimate weed populations as low and few challenges have been created following adoption of GR cropping systems. Pigweed and foxtail species were dominant overall, whereas other species were more commodity and state specific. Corn, cotton, and soybean growers cited velvetleaf, annual morningglory, and waterhemp, respectively, as predominant weeds. Growers in the South region were more likely to report pigweed and waterhemp (Amaranthus spp.), whereas growers in the East and West reported horseweed. When growers were asked with which GR weeds they had experienced personally, horseweed was reported in all regions, but growers in the South more frequently reported pigweed, whereas growers in the East and West regions more frequently reported waterhemp. Comparisons with the previous 2005 survey indicated that more growers believed they were experiencing GR weeds and were more aware of specific examples in their state. In particular, the Amaranthus complex was of greatest concern in continuously cropped soybean and cotton.

Nomenclature: Glyphosate; horseweed, Conyza canadensis (L.) Cronq.; velvetleaf, Abutilon theophrasti Medic.; waterhemp, Amaranthus tuberculatus (Moq.) Sauer; corn, Zea mays L.; cotton, Gossypium hirsutum L.; soybean, Glycine max (L.) Merr.

A 2010 survey of 1,299 corn, cotton, and soybean growers was conducted to determine their attitudes and awareness regarding glyphosate-resistant (GR) weeds and resultant implications on weed management practices. An additional 350 growers included in the current study participated in a 2005 survey, and these answers were compared across time so that cross-sectional and longitudinal comparisons of responses could be made. Most growers surveyed in 2010 were aware of the potential for weeds to evolve resistance to glyphosate; however, many growers were not aware of glyphosate resistance in specific weeds in their county or state. Growers in the South were different from growers in other geographic regions and were significantly more aware of local cases of GR weeds. Awareness of GR weeds did not increase appreciably from 2005 to 2010, but the percentage who reported GR weeds as problematic was significantly higher. Grower reports of GR weeds on-farm in 2010 were up considerably from 2005, with growers in the South reporting significantly more instances than growers in other regions. Growers in the South were also more likely to consider glyphosate resistance a serious problem. Overall, 30% of growers did not consider GR weeds to be a problem. It appears that most growers received information about glyphosate resistance from farm publications, although in the South this percentage was less than for other geographic regions. Growers in the South received more information from universities and extension sources.

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

Approximately 1,300 growers from 22 states were surveyed during 2010 to determine herbicide use. Cropping systems included continuous glyphosate-resistant corn, cotton, and soybean, and various combinations of these crops and rotations with non–glyphosate-resistant crops. The most commonly used herbicide for both fall and spring applications was glyphosate followed by synthetic auxin herbicides. Herbicide application in spring was favored over application in the fall. The percentage of growers in a glyphosate-only system was as high as 69% for some cropping systems. Excluding glyphosate, the most frequently used herbicides included photosystem II, mitotic, and protoporphyrinogen oxidase inhibitors. A higher percentage of growers integrated herbicides other than glyphosate during 2010 compared with 2005. Extensive educational efforts have promoted resistance management by increasing the diversity of herbicides in glyphosate-resistant cropping systems. However, a considerable percentage of growers continued use of only glyphosate from the period of 2005 to 2010, and this practice most likely will continue to exert a high level of selection for evolved glyphosate-resistant weed species.

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

In 2010, a grower survey was administered to 1,299 growers in 22 states to determine changes in weed management in the United States from 2006 to 2009. The majority of growers had not changed weed management practices in the previous 3 yr; however, 75% reported using weed management practices targeted at glyphosate-resistant (GR) weeds. Growers were asked to rate their efforts at controlling GR weeds and rate the effectiveness of various practices for controlling/preventing GR weeds regardless of whether they were personally using them. Using the herbicide labeled rate, scouting fields, and rotating crops were among the practices considered by growers as most effective in managing GR weeds. Sixty-seven percent of growers reported effective management of GR weeds. Between the 2005 and 2010 Benchmark surveys, the frequency of growers using specific actions to manage GR weeds increased markedly. Although the relative effectiveness of practices, as perceived by growers, remained the same, the effectiveness rating of tillage and the use of residual and POST herbicides increased.

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

Ground ivy and khakiweed are troublesome broadleaf weeds of warm-season turfgrass. Field studies were conducted in Tennessee (TN) and Texas (TX) from 2008 to 2010 to evaluate the efficacy of sulfentrazone plus metsulfuron and carfentrazone plus metsulfuron tank mixtures compared with metsulfuron alone for control of ground ivy and khakiweed. In TN, sulfentrazone plus metsulfuron and carfentrazone plus metsulfuron provided accelerated control of ground ivy compared with metsulfuron alone. Over a 2-yr period, ground ivy control with metsulfuron at 10, 21, and 42 g ai ha⁻¹ ranged from 0 to 5% 7 d after treatment (DAT) and 12 to 60% 14 DAT. Ground ivy control with mixtures of sulfentrazone plus metsulfuron ranged from 40 to 72% 7 DAT and 87 to 100% 14 DAT. Similarly, carfentrazone plus metsulfuron controlled ground ivy 5 to 32% 7 DAT and 23 to 93% 14 DAT. In TX, carfentrazone plus metsulfuron and sulfentrazone plus metsulfuron controlled khakiweed greater than metsulfuron alone 7 and 14 DAT as well. Few differences in ground ivy and khakiweed control were detected 56 DAT because metsulfuron applied alone at 21 g ai ha⁻¹ controlled both weeds > 77%, similar to each mixture. These data indicate that when applied in mixtures, sulfentrazone and carfentrazone accelerate ground ivy and khakiweed control with metsulfuron but do not affect long-term efficacy.

Nomenclature: Carfentrazone; metsulfuron; sulfentrazone; ground ivy, Glechoma hederacea L.; khakiweed; Alternanthera pungens Kunth.

Largeleaf lantana is a perennial shrub that commonly infests pastures, roadsides, and natural areas. Many experiments have been conducted to manage this weed, but few successful herbicides have been found. Little information is available for the effectiveness of fluroxypyr, aminopyralid, or aminocyclopyrachlor on largeleaf lantana. Experiments were conducted in central Florida on dense, natural infestations of largeleaf lantana. Aminopyralid (0.12 kg ha⁻¹), fluroxypyr (0.56 kg ha⁻¹), and aminocyclopyrachlor (0.2 kg ha⁻¹) were either applied in the fall (approximately 2 mo before frost) or in the fall followed by a spring application. Aminopyralid was ineffective on largeleaf lantana, and neither one nor two applications resulted in > 20% control 1 yr after treatment (YAT). Fluroxypyr applied once in the fall resulted in 12% control at 1 YAT, but two applications resulted in 80% control after 1 yr. The combination of fluroxypyr aminopyralid, applied twice, resulted in approximately 90% control 1 YAT. A single application of fluroxypyr aminopyralid failed to provide greater than 20% control. Conversely, aminocyclopyrachlor applied once in the fall provided 98% control of largeleaf at 1 YAT. Where aminocyclopyrachlor was applied twice, largeleaf lantana control was 100%. From these data, largeleaf lantana can be effectively controlled by two applications of fluroxypyr, two applications of fluroxypyr aminopyralid, or a single application of aminocyclopyrachlor. Individual plant treatments were also investigated using herbicides applied as basal or cut surface applications. At 1 YAT, only triclopyr aminopyralid provided > 90% control as a basal application. The other herbicide combinations appeared to be effective earlier, but significant regrowth had occurred by 1 YAT. Cut surface applications were similar with triclopyr aminopyralid and triclopyr fluroxypyr providing effective control. Neither triclopyr alone nor imazapyr provided effective control for 1 YAT with basal or cut surface applications.

Nomenclature: Aminocyclopyrachlor; aminopyralid; fluroxypyr; imazapyr; triclopyr; largeleaf lantana, Lantana camara L. LANCA.

Fruit trees in orchards of the mid-Atlantic region of the United States are often planted in vegetation-free rows alternating with grass alleys. Grass managed to suppress weeds but to compete minimally with fruit trees may be an alternative to herbicide and tillage. This research was conducted in the greenhouse and field to assess five different grasses that may suppress weeds without reducing yield of fruit trees. In the greenhouse with high seeding rates, red fescue competed more effectively than did chewings fescue, tall fescue, and perennial ryegrass with three weeds (damesrocket, cornflower, and chicory). However, with reduced seeding rates, similar to rates used in the field, grass competitiveness with weeds was similar between red fescue, tall fescue, and perennial ryegrass. Similar results were obtained during a 4-yr field experiment; roughstalk bluegrass competed least effectively with weeds but the other four grasses provided similar weed suppression—generally providing as much weed suppression as traditional herbicides. None of the candidate grasses significantly reduced yields of 10-yr-old apple and peach trees, although fruit size was affected by some grasses. The grass that was least suppressive of yield, roughstalk bluegrass, was the least effective in controlling weeds. Annual mowing in combination with four of the grasses tested is one option to manage the orchard floor with reduced herbicides, but fruit size may decrease.

Nomenclature: Chicory, Cichorium intybus L.; cornflower, Centaurea cyanus L.; damesrocket, Hesperis matronalis L.; apple, Malus × domestica Borkh.; chewings red fescue, Festuca rubra var. commutata L. Gaudin; peach, Prunus persica (L.) Batch; perennial ryegrass, Lolium perenne L.; red fescue, Festuca rubra L.; roughstalk bluegrass, Poa trivialis L.; tall fescue, Lolium arundinaceum (Schreb.) S.J. Darbyshire.

Calendula is an alternative oilseed crop whose seed oil is valued as a substitute for tung oil and a replacement for petroleum-based volatile organic compounds in paints and other coatings. Calendula tolerances to most POST-applied herbicides are unknown. Two POST-applied herbicides were tested for tolerance by calendula. Imazamethabenz at 0.44 kg ai ha⁻¹ plus surfactant and desmedipham plus phenmedipham at 0.36 0.36 kg ai ha⁻¹ were tolerated by calendula, but the latter herbicide must be applied after the four–leaf-pair stage of growth to avoid severe injury. Neither herbicide adversely affected calendula seed yield if applied at the four–leaf-pair stage. Because these herbicides can control several weed species, calendula tolerance to them may encourage more growers and crop advisors to test this new oilseed crop on commercial farms.

Nomenclature: Desmedipham; imazamethabenz; phenmedipham; calendula, Calendula officinalis L.

This greenhouse experiment examined the response of homozygous susceptible and acetolactate synthase (ALS) inhibitor–resistant plants from six Canadian kochia accessions with the Pro197 or Trp574 mutation to six alternative herbicides of different sites of action. The null hypothesis was ALS-inhibitor–resistant and –susceptible plants from within and across accessions would respond similarly to herbicides of different sites of action. This hypothesis was accepted for all accessions except that of MBK2 with the Trp574 mutation. Resistant plants of that accession were 80, 60, and 50% more sensitive than susceptible plants to pyrasulfotole, mesotrione (hydroxyphenylpyruvate dioxygenase [HPPD] inhibitors), and carfentrazone (protoporphyrinogen oxidase [PPO] inhibitor), respectively. However, no differential dose response between resistant and susceptible plants of this kochia accession to bromoxynil, fluroxypyr, or glyphosate was observed. A previous study had found marked differences in growth and development between resistant and susceptible plants of this accession, but not of the other accessions examined in this experiment. Negative cross-resistance exhibited by resistant plants of accession MBK2 to PPO and HPPD inhibitors in this experiment may be a pleiotropic effect related to the Trp574 mutation.

Nomenclature: Bromoxynil; carfentrazone; fluroxypyr; glyphosate; mesotrione; pyrasulfotole; kochia, Kochia scoparia (L.) Schrad. KCHSC, synonym: Bassia scoparia (L.) A.J. Scott.

Weed management is a common practice in golf courses, home lawns, and sod production systems. Sulfonylurea (SU) herbicides were initially introduced in the agricultural market in 1982; however, SUs were also evaluated for control of weeds and overseeded grasses. Later, SUs were evaluated for selective control of broadleaf weeds, sedges, and kyllinga species in cool- and warm-season turfgrasses. In the 1990s, chlorsulfuron and metsulfuron were registered for selective control of broadleaf weeds, such as wild garlic, spotted spurge, and difficult-to-control grasses, such as bahiagrass in turfgrass. Now, there are several SUs registered for specific weed management in both cool- and warm-season turfgrasses. The current status of SUs, along with potential benefits and drawbacks in using these herbicides for weed management practices, are discussed. The research findings, possible recommendations in relation to the safety of turfgrass (established and overseeding stands), environmental concerns (persistence and lateral movement), and management practices in cool- and warm-season turfgrasses are discussed, including the potential evolution of weed resistance.

Nomenclature: Chlorsulfuron; metsulfuron; bahiagrass, Paspalum notatum Fluggé; spotted spurge, Chamaesyce maculata (L.) Small; wild garlic, Allium vineale L.

Sulfonylurea herbicides used in turfgrass—including chlorsulfuron, flazasulfuron, foramsulfuron, halosulfuron, metsulfuron, rimsulfuron, sulfometuron, sulfosulfuron, and trifloxysulfuron—are all weak acids, with disassociation constants ranging from 3.3 to 5.2. Sulfonylureas are used at low rates ranging from 4 to 280 g ha⁻¹. Although these use rates put their soil concentration in parts per billion, they still have residual activity with variable persistence. They have limited susceptibility to soil leaching with weak adsorption to soil clay minerals. Sulfonylurea herbicides used in turfgrass have variable soil organic matter adsorption, which is soil dependent. The persistence and activity of these sulfonylureas are affected by soil pH. At soil pH of 7.0 and greater, some of these sulfonylurea herbicides tend to persist for longer periods with half-lives extending into years rather than days. In normal use patterns with soil pH of 7.0 and less, dissipation occurs via chemical hydrolysis and microbial degradation with half-lives ranging from days to months. Overall, sulfonylurea herbicide adsorption is negatively correlated to increasing pH (increased persistence) and positively correlated to increased organic matter (decreased activity).

Nomenclature: Chlorsulfuron, flazasulfuron, foramsulfuron, halosulfuron, metsulfuron, rimsulfuron, sulfometuron, sulfosulfuron, trifloxysulfuron.

Broadleaf weeds are common and troublesome pests in cool-season turfgrass species such as tall fescue, Kentucky bluegrass, perennial ryegrass, and creeping bentgrass. Broadleaf weeds are primarily managed in these grasses through POST applications of growth regulator herbicides in the phenoxy, benzoic acid, and pyridine chemical classes. There are disadvantages to use of these chemicals, including nontarget plant damage and limited residual control. Certain annual broadleaf weeds can be controlled through application of isoxaben or a PRE crabgrass herbicide, but these herbicides do not control emerged broadleaf weeds. There are advantages to use of sulfonylurea herbicides, including PRE and POST control of annual and perennial weeds, a different mode of action, and these herbicides have low vapor pressure, reducing the potential for offsite movement. There are disadvantages to the use of sulfonylurea herbicides, including limited spectrum of broadleaf weed species controlled and limited tolerance in cool-season turfgrass species. The primary sulfonylurea herbicides used in cool-season turfgrass are chlorsulfuron, halosulfuron, metsulfuron, and sulfosulfuron. There have been specialized uses for primisulfuron and tribenuron-methyl.

Nomenclature: Chlorsulfuron; halosulfuron; metsulfuron; primisulfuron; sulfosulfuron; tribenuron-methyl; creeping bentgrass, Agrostis stolonifera L.; tall fescue, Festuca arundinacea Schreb.; perennial ryegrass, Lolium perenne L.; Kentucky bluegrass, Poa pratensis L.

Dose–response analysis is widely used in biological sciences and has application to a variety of risk assessment, bioassay, and calibration problems. In weed science, dose–response methodologies have typically relied on least squares estimation under the assumptions of normal, homoscedastic, and independent errors. Advances in computational abilities and available software, however, have given researchers more flexibility and choices for data analysis when these assumptions are not appropriate. This article will explore these techniques and demonstrate their use to provide researchers with an up-to-date set of tools necessary for analysis of dose–response problems. Demonstrations of the techniques are provided using a variety of data examples from weed science.

Soil-applied herbicides are commonly used for broad-spectrum residual weed control in Florida citrus. Groundwater contamination from some soil-applied herbicides has been reported in citrus growing areas in Florida. Indaziflam is a new soil-applied herbicide recently registered for broad-spectrum weed control in Florida citrus. There is no information available on leaching behavior of indaziflam in sandy soil. Experiments were conducted to compare leaching of indaziflam with five commercially used residual herbicides in a Florida Candler soil under simulated rainfall of 5 or 15 cm ha⁻¹. Herbicide movement down soil columns was measured by visually evaluating injury and harvesting aboveground biomass of the bioassay species annual ryegrass. Ryegrass was not injured and plant biomass was not affected beyond 30 cm when indaziflam at a recommended rate of 73 g ai ha⁻¹ was leached through the soil column. Leaching of indaziflam increased with increasing amounts of rainfall. For example, indaziflam leached up to 12.2 ± 0.8 cm (values are expressed ± SD) and 27.2 ± 2.6 cm at 5 and 15 cm ha⁻¹ rainfall, respectively. The herbicide ranking from high to low mobility at 15 cm ha⁻¹ of rainfall was bromacil  =  norflurazon > indaziflam > simazine  =  pendimethalin > diuron. Overall results suggested that indaziflam leaching was limited in Florida Candler soil in this study; however, field experiments are required to confirm the leaching of indaziflam under natural rainfall situation.

Nomenclature: Bromacil; diuron; indaziflam {N-[(1R, 2S)-2,3-dihydro-2,6-dimethyl-1H-inden-1-yl]-6-[(1RS)-1fluoroethyl]-1,3,5-triazine-2,4-diamine}; norflurazon; pendimethalin; simazine; annual ryegrass, Lolium multiflorum L.