Greenhouse studies were initiated to evaluate glyphosate alone and tank-mixed with acifluorfen, CGA 277476, chlorimuron, cloransulam-methyl, fomesafen, imazaquin, or pyrithiobac on seedling johnsongrass, broadleaf signalgrass, pitted morningglory, and hemp sesbania. Johnsongrass and broadleaf signalgrass control by glyphosate was not affected by the selective herbicides applied in mixtures. Pitted morningglory control by glyphosate ranged from 0% with 280 g ai/ha to 67% with 840 g/ha. There was an additive effect when selective herbicides were added to 280 g/ha glyphosate 2 wk after treatment (WAT). When acifluorfen was added to 560 g/ha glyphosate, pitted morningglory control 2 WAT increased to 100% compared with 55% with glyphosate alone. Similarly, the addition of fomesafen or acifluorfen to 840 g/ha glyphosate controlled pitted morningglory 2 WAT by 90 and 98%, respectively, compared with 67% with glyphosate alone. Only tank mixtures of acifluorfen, CGA 277476, or fomesafen, and 840 g/ha glyphosate reduced fresh weight compared with glyphosate alone 4 WAT. Acifluorfen, CGA 277476, and fomesafen controlled pitted morningglory by 85 to 100% when added to 1,120 g/ha glyphosate. Both acifluorfen and fomesafen effectively controlled hemp sesbania without the addition of glyphosate 2 WAT. Chlorimuron and pyrithiobac added to 1,120 g/ha glyphosate increased hemp sesbania control to 88 and 99%, respectively, compared with 45% with glyphosate alone 2 WAT. CGA 277476, cloransulam-methyl, imazaquin, and pyrithiobac were antagonistic to hemp sesbania fresh weight reduction when compared with the expected response, but fresh weights were still reduced more than with the same rate of glyphosate alone.

Nomenclature: Acifluorfen; CGA-277476, 2-[[[[(4,6-dimethyl-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-3-oxetanyl ester; chlorimuron; cloransulam-methyl; fomesafen; glyphosate; imazaquin; pyrithiobac; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash. #³ ECHCG; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex. A. W. Hill # SEBEX; johnsongrass, Sorghum halepense (L.) Pers. # SORHA; pitted morningglory, Ipomoea lacunosa L. # IPOLA.

Additional index words: Additive effects, herbicide antagonism, tank mixtures.

Abbreviations: ALS, acetolactate synthase; WAT, weeks after treatment.

A field experiment was conducted in 1998 and 1999 at Keiser, AR, to evaluate glyphosate timing and soybean population in reducing hemp sesbania and pitted morningglory interference with dryland and irrigated glyphosate-resistant soybean under a narrow row, no-till production system. Soybean densities following emergence were 247,000, 475,000, and 729,000 plants/ha. Glyphosate was applied at 0.56 kg ai/ha at the V2; V4; V2 and V4; and V2, V4, and R2 stages of soybean. In dry portions of the growing season, glyphosate increased moisture availability for dryland soybean because of control of hemp sesbania and pitted morningglory. As soybean population increased from 247,000 to 729,000 plants/ha, pitted morningglory and hemp sesbania control increased from 60 to 91%, respectively, for the V2 glyphosate application. Control of both species at 14 wk after emergence was at least 90% following the V4 alone treatment and sequential applications, with no differences in control among soybean populations. Untreated, irrigated hemp sesbania produced up to 32 million seeds/ha in 1999. Irrigation did not influence pitted morningglory seed production either year, and untreated pitted morningglory produced a maximum of 1 million seeds/ha in 1998 at 247,000 soybean plants/ha. Three sequential applications of glyphosate reduced pitted morningglory seed production to 9,000 seeds/ha and eliminated hemp sesbania seed production. Soybean yielded 1,297 kg/ha greater under irrigated than dryland conditions, whereas increasing soybean density from 247,000 to 729,000 plants/ha resulted in 416 kg/ha improvement in seed yield. At the densities of pitted morningglory and hemp sesbania present in this study, seed yield of drill-seeded soybean can be maximized following a V4 alone treatment or sequential glyphosate applications.

Nomenclature: Glyphosate; hemp sesbania, Sesbania exaltata (Raf.) Rybd. Ex A. W. Hill #³ SEBEX; pitted morningglory, Ipomoea lacunosa L. # IPOLA; soybean, Glycine max (L.) Merr. ‘Delta King 5961 Roundup Ready®’.

Additional index words: Light interception, soil moisture, transgenic soybean, weed competition.

Abbreviations: DAE, days after emergence; PAR, photosynthetically active radiation; WAE, weeks after emergence; WAT, weeks after treatment.

Broomsedge control studies were conducted on six broomsedge-infested pastures in southeastern Oklahoma from 1995 to 1997. Glyphosate applied in spring at 2.24 kg ai/ha decreased broomsedge plant density by 58% 3 mo after treatment (MAT), on areas where the previous year's forage was grazed, and by 95% 3 MAT, where spring fire had removed the old top-growth before glyphosate application. Broomsedge plant density was not affected where glyphosate was applied in spring to sites with old-standing top-growth. Paraquat applied in spring at 0.56 kg ai/ha and spring burning without a herbicide treatment had no effect on broomsedge plant density. Glyphosate at 0.56 and 1.12 kg ai/ha applied in late summer reduced the number of broomsedge stems 1 yr after treatment (YAT) by an average of 65 and 80%, respectively. Paraquat at 0.56 kg/ha applied in late summer of 1995, followed by burning 1 wk after treatment (WAT), decreased broomsedge stem density by more than 60% 1 YAT at four of six locations when compared with mowing in late summer. Burning in November after an October frost decreased broomsedge stem density by more than 47% 1 YAT at four locations. Two consecutive years of burning after frost and paraquat applied in late summer followed by burning 1 WAT reduced broomsedge dry matter production by 68 and 96%, respectively, when compared with mowing in late summer. These data suggest that good to excellent control of established broomsedge is possible with herbicides alone, with a combination of herbicides and late-summer burning, and with fall burning after an early frost in a dry fall. However, broomsedge control was short-lived with all the treatments because of the establishment of new broomsedge seedlings. Thus, it will be important to integrate the destruction of broomsedge plants with proper fertility and grazing management in order to provide satisfactory broomsedge control.

Nomenclature: Glyphosate; paraquat; broomsedge, Andropogon virginicus L. #³ ANOVI.

Additional index words: CYNDA, Cynodon dactylon, mowing, prescribed fire.

Abbreviations: DM, dry matter; MAT, months after treatment; WAT, weeks after treatment; YAT, years after treatment.

Five weed management systems utilizing combinations of cover crops, herbicides, and cultivation were tested in potato in 1994 and 1995 in central Washington. A standard herbicide treatment of metribuzin applied preemergence (PRE) at 0.4 kg ai/ha (standard herbicide weed management system [STD]) was compared with (1) fall-planted winter rye followed by metribuzin at 0.4 kg/ha applied in a band in the potato hill, followed by reservoir tillage (rye cover crop with herbicide-banded and reservoir-tilled weed management system [RYESTD]); (2) cultivation with tine-tooth harrow followed by hilling with shovels and rolling cultivators (total-cultivation weed management system [CULT]); (3) fall-planted rapeseed followed by reservoir tillage (rapeseed cover crop and reservoir-tilled weed management system [RPSD]); and (4) reservoir tillage alone (reservoir-tilled weed management system [RESTIL]). In both years, early-season weed density and final weed biomass were lower in the STD, RYESTD, and CULT systems than in RPSD and RESTIL. Total tuber yield and yield of U.S. #2 or better were greatest in the RYESTD and STD systems in both years. The CULT system reduced early-season weed densities, but tuber yield was reduced 15% in 1994, and yield of U.S. #2 or better was reduced 25% in 1995 compared with the STD system. The RPSD system reduced early-season in-row weed density from 60 to 70% and final weed biomass from 29 to 40% compared with a nontreated check, i.e., a no–cover crop, no-cultivation, no-herbicide weed management system, but tuber yield was 27 to 30% lower than in the STD system. The RYESTD system was an effective alternative weed management strategy that controlled weeds, decreased PRE-applied herbicide inputs 66%, and maintained tuber yield.

Nomenclature: Metribuzin; potato, Solanum tuberosum L.; rapeseed, Brassica napus; rye, Secale cereale L.

Additional index words: Banding, cover crops, cultivation, integrated weed management, glyphosate, reservoir tillage, tillage.

Abbreviations: BR, between row; CHECK, no–cover crop, no-cultivation, no-herbicide weed management system; CULT, total-cultivation weed management system; IR, in row; PRE, preemergence; RESTIL, reservoir-tilled weed management system; RPSD, rapeseed cover crop and reservoir-tilled weed management system; RYESTD, rye cover crop with herbicide-banded and reservoir-tilled weed management system; STD, standard herbicide weed management system.

Experiments were conducted at three locations in North Carolina in 1999 and 2000 to evaluate weed management systems in strip-tillage peanut. Diclosulam was evaluated with standard preemergence (PRE), early postemergence, and postemergence (POST) herbicide systems in a factorial treatment arrangement. Preemergence treatments that contained diclosulam controlled common lambsquarters, common ragweed, and eclipta by 100%. Diclosulam PRE controlled entireleaf morningglory by 88%, ivyleaf morningglory by ≥ 90%, pitted morningglory by ≥ 81%, and prickly sida by ≥ 94%. Yellow nutsedge control with diclosulam ranged from 65 to 100% depending on location, whereas POST systems containing imazapic controlled yellow nutsedge by at least 89%, regardless of PRE herbicides. Peanut yields and net returns were reflective of levels of weed management. Systems that included diclosulam PRE plus POST herbicides consistently provided high yields and net returns. Clethodim late POST was required for full-season control of annual grasses, including broadleaf signalgrass, goosegrass, large crabgrass, and Texas panicum.

Nomenclature: Clethodim; diclosulam; imazapic; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash #³ BRAPP; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; eclipta, Eclipta prostrata L. # ECLAL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; Texas panicum, Panicum texanum Buckl. # PANTE; yellow nutsedge, Cyperus esculentus L. # CYPES; peanut, Arachis hypogaea L. ‘NC 10C’ and ‘NC 12C’.

Additional index words: Economic analysis.

Abbreviations: EPOST, early postemergence; fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Epicuticular wax is a major barrier to the movement of foliar-applied herbicides into plant leaves. Many researchers have evaluated the penetration of herbicides in plants using similar methods. However, the methods used to remove unabsorbed herbicide from the leaf surface have been inconsistent among scientists. Laboratory experiments were conducted to evaluate the effectiveness of various compounds as a leaf wash for removing unabsorbed ¹⁴C-labeled herbicides from shattercane and velvetleaf leaves. Product B and Product C provided poor results as a leaf wash compared with water, chloroform, methanol, and Product A. Product A increased the amount of ¹⁴C-bentazon removed from velvetleaf by 26% compared with the amount removed by chloroform, methanol, or water. Removal of ¹⁴C-nicosulfuron was not different between chloroform, Product A, methanol, or water. Although water was the best treatment for the two salts of ¹⁴C-glyphosate, Product A was as good or better than chloroform and methanol.

Nomenclature: Bentazon; glyphosate; nicosulfuron; shattercane, Sorghum bicolor L. #³ SORBI; velvetleaf, Abutilon theophrasti L. # ABUTH.

Additional index words: Epicuticular wax, leaf wash, radiolabeled herbicides.

Abbreviations: IPA, isopropylamine; LSS, liquid scintillation spectrometry; TMS, trimethylsulfonium.

Plot-scale field studies were conducted to evaluate the efficacy of steam for the control of cropland weeds in comparison with common herbicides. Weed densities, biomass, or emergence after treatment were measured. Steam (3,200 kg/ha, energy dosage equivalent to 890 kJ/m², speed of 0.8 m/s) and glyphosate (560 g ai/ha) gave similar control (> 90%) of seedling common lambsquarters and seedling redroot pigweed. Applied at heading, steam was comparable to glyphosate in reducing green foxtail biomass at heading 2 wk after application. Steam applied at a rate of 3,200 kg/ha significantly reduced weed biomass (mixed stand, treated at seedling stage) 9 wk after application compared with the control, whereas steam applied at a rate of 1,600 kg/ha (1.6 m/s) did not. Biomass of downy brome treated with steam was reduced more at anthesis than at the seedling growth stage. Emergence of common lambsquarters, redroot pigweed, and black nightshade was not affected by steam application. Amount of steam applied, weed species, and growth stage are key factors in determining control effectiveness.

Nomenclature: Glyphosate; black nightshade, Solanum nigrum L. #³ SOLNI; downy brome, Bromus tectorum L. # BROTE; common lambsquarters, Chenopodium album L. # CHEAL; green foxtail, Setaria viridis L. # SETVI; redroot pigweed, Amaranthus retroflexus L. # AMARE.

Additional index words: Kochia scoparia L. Schrad., KOCSC, paraquat, pelargonic acid, SALIB, Salsola iberica Sennen & Pau.

Auxin-type herbicides such as 2,4-D and dicamba are commonly used to control kochia in small grain production areas, but poor kochia control with these herbicides has been reported. Several auxinic herbicide-resistant kochia inbreds were evaluated for their response to 2,4-D or dicamba and to alternative herbicide treatments. Values of the dose of the herbicide causing 50% visible injury to test plants (I₅₀) from week 1 to week 4 after treatment with 2,4-D were unchanged for six of the seven 2,4-D–resistant inbreds, indicating that these plants may recover to produce seeds. In contrast, the corresponding I₅₀ values for dicamba decreased for five of the six dicamba-resistant inbreds, indicating that kochia was not recovering from the treatment. Postemergence treatments with atrazine, carfentrazone, fluroxypyr, bromoxynil plus MCPA, nicosulfuron plus dicamba, and nicosulfuron plus dicamba plus atrazine, all provided adequate to excellent control of resistant kochia inbreds. Alternative chemical control options are available for managing auxinic herbicide-resistance in kochia.

Nomenclature: Atrazine; bromoxynil; carfentrazone; 2,4-D; dicamba; fluroxypyr; MCPA; nicosulfuron; kochia, Kochia scoparia (L.) Schrad. #³ KOCSC.

Additional index words: Herbicide resistance.

Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); dma, dimethylamine; I₅₀, dose of the herbicide causing 50% visible injury to test plants; WAT, weeks after treatment.

Field studies were conducted from 1998 to 2000 in Beltsville, MD, to evaluate the effects of preemergence (PRE) applications of BAY FOE 5043 metribuzin, s-metolachlor, and diclofop on crop injury, yield, and control of diclofop-tolerant Italian ryegrass in winter wheat. No injury was observed in 1999. In 2000, minor stunting of wheat plants was observed where high rates of BAY FOE 5043 metribuzin and s-metolachlor were utilized. Wheat plants outgrew the stunting and grain yields were not affected. High rates of BAY FOE 5043 metribuzin and s-metolachlor provided equally effective Italian ryegrass control in 1999, averaging 85% or greater in June. In 2000, all rates of BAY FOE 5043 metribuzin provided 93% or greater Italian ryegrass control, whereas s-metolachlor at 0.43 kg/ha or greater provided 85% Italian ryegrass control or greater when evaluated in June. In 1999, wheat yields from plots treated with BAY FOE 5043 metribuzin, or s-metolachlor at 0.43, 0.56, or 0.84 kg/ha, were higher than from the nontreated control. In 2000, all wheat yields from plots treated with BAY FOE 5043 metribuzin and s-metolachlor were higher than from the nontreated control.

Nomenclature: BAY FOE 5043; diclofop; metribuzin; s-metolachlor; Italian ryegrass, Lolium multiflorum Lam. #³ LOLMU; wheat, Triticum aestivum L. ‘Jackson’.

Additional index words: Herbicide-resistant weeds.

Abbreviations: EP, early postemergence; POST, postemergence; PRE, preemergence.

A bioassay, based on seedling shoot inhibition with difenzoquat at 10 mg/L, provides a rapid means of predicting hard red spring wheat (HRSW) cultivar response to foliar-applied difenzoquat. The tolerance of several cultivars to difenzoquat was determined by shoot length inhibition in the laboratory, and by visible crop injury and shoot dry weight in the greenhouse. Of the 19 cultivars tested, one cultivar that was susceptible in the laboratory assay was intermediate in tolerance to difenzoquat in the greenhouse assay; two cultivars that were tolerant in the laboratory bioassay were of intermediate tolerance in the greenhouse assay. Results from laboratory and greenhouse studies both identified cultivars distinctly susceptible to difenzoquat. Shoot inhibition indicated that HRSW cultivar susceptibility to difenzoquat involves continuous variation from tolerant to susceptible. This may explain why some cultivars show differential responses to difenzoquat under different environmental conditions.

Nomenclature: Difenzoquat; hard red spring wheat, Triticum aestivum L.

Additional index words: Herbicide tolerance, root length, shoot length.

Abbreviation: HRSW, hard red spring wheat.

Field trials were conducted in 1999 and 2000 to determine the influence of weed size and the number of glyphosate or glufosinate applications on weed control and sugarbeet yield. Glyphosate at 840 g/ha or glufosinate at 390 g/ha was applied one, two, or three times, beginning when the average weed height was 3, 10, 15, or 25 cm. Two sequential applications of glyphosate applied to 10-cm weeds or three sequential applications of glufosinate applied to 3-cm weeds provided weed control comparable to three sequential applications of desmedipham plus phenmedipham plus triflusulfuron plus clopyralid. Weed control and sugarbeet root yield were optimal for two postemergence applications of glyphosate and for three applications of glufosinate. Glyphosate provided greater control of redroot pigweed and common lambsquarters than glufosinate. Sugarbeet sucrose yield with both glyphosate and glufosinate weed control programs was nearly 10,000 kg/ha. Compared with two sequential applications of glyphosate, sucrose yield of glyphosate-resistant sugarbeet was reduced 15% by three sequential applications of desmedipham plus phenmedipham plus triflusulfuron plus clopyralid. Sucrose yields were similar between three sequential applications of glufosinate and three applications of desmedipham plus phenmedipham plus triflusulfuron plus clopyralid.

Nomenclature: Clopyralid; desmedipham; glufosinate; glyphosate; phenmedipham; triflusulfuron; common lambsquarters, Chenopodium album L. #³ CHEAL; redroot pigweed, Amaranthus retroflexus L. # AMARE; sugarbeet, Beta vulgaris L. ‘HM 1605RR’, ‘HM 1640RR’, ‘Beta 1399LL’, ‘Beta 4546LL’.

Additional index words: Setaria viridis, SETVI, Solanum sarrachoides, SOLSA.

The relationship between surface activity and weed control efficacy of diuron spray solution (0.075 kg ai/ha) with 12 adjuvants (0.1% v/v) was studied in the laboratory and the greenhouse. Organosilicone adjuvants reduced surface tension (ST) and contact angle (CA) of diuron spray solutions to a greater extent than did nonsilicone adjuvants. Three organosilicone adjuvants significantly increased the control and reduced the fresh weight of barnyardgrass. Contact angle was more closely correlated with diuron efficacy than ST, and the coefficient of determination between the CA and the fresh weight or control percent of barnyardgrass was 0.41. Kinetic® applied before or in combination with diuron significantly enhanced diuron efficacy. However, Kinetic sprayed after diuron did not affect the efficacy. Kinetic influenced the retention and absorption of diuron rather than its deposition and translocation.

Nomenclature: Diuron; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCR.

Additional index words: Adjuvant, Amaranthus retroflexus, AMARE, Chenopodium album, CHEAL, contact angle, organosilicone, Setria glauca, SETGL, surface tension, surfactant.

Abbreviations: CA, contact angle; ST, surface tension; WAT, weeks after treatment.

The biological activity of rimsulfuron applied with 33 alcohol ethoxylate surfactants was determined on six economically important weed species. The surfactants had hydrophobes ranging from 6 to 24 carbons and hydrophiles ranging from 3 to 32 ethylene oxides (EOs), and the weeds had different leaf orientations, surface characteristics, and chemical compositions. In general, similar activity was observed among weed species with correlation coefficients ranging from 0.62 to 0.94. A few distinct species-specific differences were identified. For example, increasing surfactant size generally increased rimsulfuron activity on velvetleaf, but activity was reduced on giant foxtail with surfactants having the longest alkyl chain and the highest number of EO units. Increasing surfactant size increased common cocklebur control if the right balance between the hydrophobic and hydrophilic group was maintained. The optimum surfactant type with rimsulfuron across six species from both the empirical and the modeling results ranged from a hydrophobe with 17 carbons and a hydrophilic group with 20 to 30 EOs to 24 carbons and 13 EOs.

Nomenclature: Rimsulfuron; common cocklebur, Xanthium strumarium L. #³ XANST; giant foxtail, Setaria faberi Herrm # SETFA; velvetleaf, Abutilon theophrasti Medicus # ABUTH.

Additional index words: Adjuvant, nonionic surfactant, species specificity, structure–activity.

Abbreviations: EO, ethylene oxide; HLB, hydrophilic–lipophilic balance.

Lawn burweed is a serious problem in warm-season golf courses, sports fields, and residential turfgrass. Field studies were conducted at three sites in Florida to evaluate herbicides applied postemergence for control of lawn burweed. Mecoprop 2,4-D dicamba provided > 95% control of lawn burweed when evaluated 47 to 55 d after treatment (DAT). MCPA triclopyr dicamba in either ester or amine forms, 2,4-D triclopyr dicamba, triclopyr, 2,4-D, and bromoxynil provided 88 to 100% control 40 to 55 DAT. Although triclopyr clopyralid provided > 90% control in one study, it was not consistent and controlled < 75% of the lawn burweed present in another experiment. Simazine was unacceptable for lawn burweed control. Bermudagrass turf was not injured by any of the treatments evaluated. Mecoprop 2,4-D dicamba caused minimal short-term injury to centipedegrass.

Nomenclature: Bromoxynil; clopyralid; 2,4-D; dicamba; MCPA; mecoprop; simazine; triclopyr; common bermudagrass, Cynodon dactylon (L.) Pers. #³ CYNDA; common centipedegrass, Eremochloa ophioroides (Munro) Hack. # ERLOP; hybrid bermudagrass, Cynodon dactylon × C. transvaalensis Burtt-Davy ‘Tifway’; lawn burweed, Soliva pterosperma (Juss.) Less. # SOVPT.

Additional index words: Atrazine, bentazon, postemergence, preemergence.

Abbreviations: DAT, days after treatment; FWBGC, Fort Walton Beach Golf Club; WCHS, Whitfield Community Home Site; WFREC, West Florida Research and Education Center.

Herbicides were evaluated for weed control and crop response in conventional and no-tillage dry pea production. Preplant or preemergence (PRE) applications of imazethapyr, sulfentrazone, flumetsulam, cloransulam, and BAY FOE 5043 metribuzin did not show crop injury within the locations, years, and tillage systems where applied. Postemergence applications of cloransulam had crop injury in excess of 60% where applied, and injury with flumiclorac and fomesafen ranged from 0 to greater than 40% with differences in crop injury as a result of dry pea growth stage at the time of application and surfactant use. Imazamox injury was as great as 24% when applied at a more advanced dry pea growth stage and was not different from 0% when applied at an earlier growth stage. Dry pea injury with bentazon was not significant, with an exception at one of the six locations where injury was 14%. Common lambsquarters was best controlled (80 to 90%) with sulfentrazone and imazamox. Preplant and PRE applications of sulfentrazone consistently provided the greatest mayweed chamomile control across tillage systems (control ranged from 59 to 93%), whereas bentazon provided the greatest postemergence (POST) control of mayweed chamomile (control ranged from 46 to 84%). Prickly lettuce control with preplant or PRE treatments was greatest with sulfentrazone (74 to 85%), whereas the greatest POST control was with imazamox in combination with urea-ammonium nitrate solution and surfactant or bentazon and crop oil concentrate (71 to 92%). Dry pea yields with herbicide treatments were not always greater than the nontreated and were often affected by crop injury.

Nomenclature: BAY FOE 5043, N-(4fluorophenyl)-N-(1-methylethyl)-2-[[5-(trifluoromethyl)-1,3,4-thiadiazol-2-yl]oxy]acetamide; bentazon; cloransulam; flumetsulam; flumiclorac; fomesafen; imazamox; imazethapyr; metribuzin; sulfentrazone; common lambsquarters, Chenopodium album L. #³ CHEAL; dry pea, Pisum sativum L., ‘Columbia’, ‘Phantom’; mayweed chamomile, Anthemis cotula L. # ANTCO; prickly lettuce, Lactuca serriola L. # LACSE.

Additional index words: Conservation tillage, herbicide efficacy, pea yield.

Abbreviations: COC, Crop Oil Concentrate; DAT, days after treatment; FPP, fall preplant; NIS, nonionic surfactant; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; SPP, spring preplant; UAN, urea-ammonium nitrate solution.

Laboratory and greenhouse studies were conducted to determine if the reported red morningglory control failures with atrazine in sugarcane are caused by triazine-resistant mutants. Plants were grown from seeds collected at 24 locations in Louisiana and Arkansas where atrazine had never been used, and where it had been used in sugarcane with poor results. Terminal fluorescence of leaf material from all locations increased after treatment with 10⁻³ M atrazine, indicating electron transport inhibition and, hence, triazine susceptibility. However, small differences in the magnitude of fluorescence increase were observed among populations, possibly indicating the existence of biotypes with slightly different inherent tolerances to atrazine. Some phenotypic differences were observed among the red morningglory populations. In a separate study, postemergence application of atrazine at 1.1 kg ai/ha plus nonionic surfactant controlled greenhouse-grown plants from all populations at least 99%, which supports the findings of the fluorescence assay. This research was unable to verify that reduced red morningglory control with atrazine was the result of an altered binding site mutation, even in populations exposed to atrazine annually for more than 10 yr. Other factors should be evaluated to determine their impact on atrazine performance.

Nomenclature: Atrazine; red morningglory, Ipomoea coccinea L. #³ IPOCC; sugarcane, Saccharum interspecific hybrids.

Additional index words: Chlorophyll fluorescence, herbicide resistance, IPOCC, photosynthesis inhibition, photosystem II, triazine resistance, weed biotypes.

Abbreviations: CRF, change in relative fluorescence; DAT, days after treatment; F_T, terminal fluorescence; POST, postemergence; PRE, preemergence.

Jointed goatgrass is a problem weed in winter wheat production areas of the Great Plains. Winter wheat seeding rates are easily adjusted by the growers and influence competition by some weeds. Field experiments were initiated in Kansas, Nebraska, and Wyoming using winter wheat cultivars selected from leading adapted cultivars from each region to determine the effect of wheat plant density in the fall on jointed goatgrass competitiveness. Three winter wheat seeding rates (50, 67, and 84 kg seeds/ha) were used at Hays, KS, and Sidney, NE, and four seeding rates (33, 50, 67, and 101 kg seeds/ha) were used at Torrington and Archer, WY. An analysis of covariance model was fit with winter wheat fall plant density as the covariate. In 1996, winter wheat grain contamination (dockage) was reduced at the rate of about 6% for every 10 additional wheat plants/m² above the threshold density of 70 plants/m² at Archer, WY, and at the rate of about 0.5% for every 10 additional wheat plants/m² above the threshold density of 110 plants/m² at Hays, KS. At Hays the reduction occurred only with the semidwarf cultivar ‘Vista’. Increased wheat density reduced jointed goatgrass reproductive tillers in four out of six location–year combinations and biomass in two out of four location–year combinations. Despite the lack of a consistent reduction in jointed goatgrass competitiveness as the result of increased wheat density, increased seeding rates may be a good, low-cost, long-term investment as part of an integrated jointed goatgrass control program in winter wheat.

Nomenclature: Jointed goatgrass, Aegilops cylindrica Host. #³ AEGCY; winter wheat, Triticum aestivum L.

Additional index words: Interference; plant competition.

Field trials were conducted in 1998 and 1999 to determine the influence of harvest-aids on dry bean desiccation, seed yield, and quality. Light Red Kidney and Great Northern dry beans were pulled from the soil and placed on the soil surface to dry or treated with glufosinate at 440 g ai/ha, with glyphosate at 840 g ae/ha, or with paraquat at 560 g ai/ha at three stages during the maturation process. Dry bean seed weight and seed yield were reduced by all harvest-aid treatments applied when only 5 to 7% of the seedpods were yellow. Herbicides did not affect dry bean seed yield, weight, or germination if treatments were delayed until 77 to 85% of the seedpods had turned yellow. Application of harvest-aids at early stages of the maturation process enhanced desiccation of dry bean plants, pods, and seeds, but reduced yield. Herbicides applied at later stages of the maturation process avoided seed yield reductions, but were not as effective in desiccating plants. Therefore, applying glufosinate, glyphosate, or paraquat to reduce the time from dry bean maturation to harvest may not be beneficial when the crop is grown on the high plains of the United States.

Nomenclature: Glufosinate; glyphosate; paraquat; dry bean, Phaseolus vulgaris L.

Additional index words: Great Northern ‘Beryl’, Light Red Kidney ‘Sacramento’.

Abbreviations: DAT, days after treatment.

Littleseed canarygrass, a troublesome wheat weed, has developed resistance against isoproturon in India. Laboratory, pot, and field experiments were conducted to quantify the level of isoproturon resistance in various littleseed canarygrass biotypes and to evaluate the response of isoproturon-resistant littleseed canarygrass to alternate herbicides. For quantification of resistance, 10 littleseed canarygrass biotypes were collected from fields with a varied history of cropping and herbicide use. Pot studies indicated that 6 out of the 10 biotypes tested were resistant to isoproturon. The resistant (R) biotypes had 50% growth reduction values, 5 to 10 times greater than that of the most susceptible biotype. The R biotypes were from areas where isoproturon had been used continuously for more than 10 yr in wheat under a continuous rice–wheat cropping system. The isoproturon resistance was not detected where crops and herbicides were rotated. Under field conditions, postemergence isoproturon at 1,000 g/ha 32 d after sowing failed to control littleseed canarygrass and as a result wheat grain yield decreased by 65% compared with the weed-free control. The herbicides observed to be effective in wheat against isoproturon-resistant littleseed canarygrass were CGA 184927 (50 to 60 g ai/ha), fenoxaprop-p-ethyl (100 to 120 g/ha), ICIA 0604 (350 g ai/ha), and MON 37503 (25 g ai/ha). The use of these herbicides increased the grain yield by 200% or more when compared with the weedy check. Among the herbicides tested, MON 37503 at 25 g ai/ha was the best because of complex weed flora control and produced wheat yield similar to that of the weed-free control. Based on this study, the absence of resistance when herbicides and crops were rotated indicates that growers should follow herbicide and crop rotation in order to avoid development of herbicide resistance in the near future. The integration of this system (crop and herbicide rotation) with cultural and mechanical means of weed control could be further targeted as a long-term strategy for resistance management.

Nomenclature: CGA 184927 (proposed common name, clodinafop), 2-propynyl-(R)-2-[4-(5-chloro-3-fluoro-2-pyridyloxy)phenoxy]propionate; fenoxaprop-p-ethyl; ICIA 0604 (proposed common name, tralkoxydim), 2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethyl phenyl)cyclohex-2-enone; MON 37503 (proposed common name, sulfosulfuron), 1-(2-ethylsulfonylimidazol[1,2-a]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl)urea; littleseed canarygrass, Phalaris minor Retz #³ PHAMI; rice, Oryza sativa L.; wheat, Triticum aestivum L.

Additional index words: Biotype, competition, cross-resistance, germination, herbicide resistance.

Abbreviations: CRD, completely randomized design; DAS, days after sowing; GR₅₀, 50% growth reduction; R, resistant; RI, resistance index; S, susceptible.

Glyphosate-resistant canola has been widely adopted in western Canada. This has prompted producer interest in the timing of glyphosate application, particularly under zero tillage, where glyphosate is often applied preseeding. Field experiments were conducted at Lacombe, Edmonton, and Beaverlodge in Alberta in 1997, 1998, and 1999 to determine the importance of preseeding glyphosate and the most effective growth stage to apply glyphosate to canola to optimize yield and weed management. Treatments consisted of zero-tillage systems, with and without preseeding glyphosate, and a conventional-tillage system involving preseeding tillage operations. Glyphosate was applied at the one- to two-, three- to four-, or five- to six-leaf stages of canola in each tillage system. Canola yield and weed dry weight were largely unaffected by the tillage system. In most instances, the highest canola yields occurred when glyphosate was applied early to the crop. The opposite occurred at Lacombe and Edmonton in 1999, however, where canola yield increased as glyphosate was applied at later crop growth stages. This yield benefit likely resulted from the control of late-emerging weeds that exerted competitive pressure on canola. Early glyphosate timing in glyphosate-resistant canola may eliminate the need for preseeding glyphosate in zero-tillage systems, and optimize yield and weed control.

Nomenclature: Glyphosate; canola, Brassica napus L. ‘Quest’.

Additional index words: Critical period of weed control, direct seeding, preseeding glyphosate application, reduced tillage, zero tillage.

Studies were conducted with one glyphosate-resistant and three conventional soybean cultivars to determine the effects of reducing row spacing from 76 to 38 and 19 cm, in combination with increased soybean population and herbicide applications (single and sequential), on sicklepod control and soybean yield. ‘Hutcheson’ was the only cultivar, and only under adverse conditions (1998), for which the 19-cm rows provided greater sicklepod control than the 38-cm rows. It was only under optimum conditions (1997), and only with conventional cultivars and sequential herbicide applications, that the 19-cm–row yield of 3,350 kg/ha was 21% greater than the 38-cm–row yield in medium population (455,375 plants/ha), and 21 and 64% greater than the 19- and 76-cm–row yield in low populations (241,000 plants/ha), respectively. In 1998, the same treatment showed similar late-season sicklepod control (> 80%) and a yield of 1,890 kg/ha, with no difference between the 19- and the 38-cm rows; but the yields were 15 and 24% greater than the yield of the narrow (19 and 38 cm) and that of the 76-cm row in low populations, respectively. Low populations with sequential applications in narrow rows and in the 76-cm row showed similar late-season sicklepod control (59 to 70%) and yield in 1998; but in 1997, the narrow rows showed 18 and 32% greater late-season control and yield than the 76-cm row, respectively. In 1997 and 1998, for ‘Hartz 5088RR’ (glyphosate resistant) with medium population and narrow rows, the single and sequential applications provided similar late-season sicklepod control (> 80%) and yield, and at least 10 and 24% greater yield than the narrow and the 76-cm rows in low populations, respectively.

Nomenclature: Glyphosate; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby #³ CASOB; soybean, Glycine max (L.) Merr.

Additional index words: Chlorimuron, flumetsulam, glyphosate-resistant soybean, metolachlor, sequential herbicide applications.

Abbreviations: MG, maturity group; POST, postemergence; PRE, preemergence; WAP, weeks after planting.

A field study was conducted over 2 yr to evaluate red morningglory control and sugarcane injury with herbicides applied below the sugarcane canopy in late May to early June following the layby cultivation. Rainfall to activate herbicides was received within the first 2 wk after application at the two sites in 1997, but not at the two sites in 1998. Red morningglory control for most herbicides 21 d after treatment (DAT) in both years was at least 90% and was attributed to postemergence activity of the herbicides and limited weed reinfestation following cultivation and herbicide application. At 45 DAT, red morningglory control with sulfentrazone was maximized (87 to 100%) at 0.14 kg ai/ha at three of four sites. Control with azafeniden was less consistent and, to achieve the same level of control as for sulfentrazone, 0.42 kg ai/ha azafeniden was needed in 1997 and 0.84 kg/ha in 1998. The currently registered herbicides atrazine, diuron, metribuzin, and terbacil controlled red morningglory no more than 83%, 45 DAT at three of the four sites. Of these herbicides, terbacil was the least effective. Even in 1997 at one site when the herbicide was rainfall activated early, red morningglory control with sulfentrazone at 0.14 kg/ha and azafeniden at 0.42 kg/ha 45 DAT was still greater than with the currently registered herbicides. Sugarcane injury expressed as foliage discoloration 21 DAT was 7 to 18% for sulfentrazone at 0.14 kg/ha and 15 to 31% for azafeniden at 0.42 kg/ha. Plant recovery was rapid and none of the herbicide treatments evaluated reduced sugarcane stalk height or population in September.

Nomenclature: Atrazine; azafeniden; diuron; metribuzin; sulfentrazone; terbacil; red morningglory, Ipomoea coccinea L. #³ IPOCC; sugarcane, Saccharum spp. # SACCH, ‘LCP 85-384’, ‘CP 70-321’.

Additional index words: Crop tolerance, final interrow cultivation, layby.

Abbreviations: DAT, days after treatment; POST, postemergence; PRE, preemergence.

Field experiments were conducted in 1999 and 2000 to evaluate reduced-rate split-applied treatments of imazamethabenz and ICIA 0604 for wild oat control in hard red spring wheat. Single herbicide treatments were applied at standard timing to wild oat at the two- to four-leaf stage. The first split-applied treatments were made when most of the wild oat had emerged but prior to the two-leaf stage. The second split-applied treatments were made after the surviving wild oat had visibly recovered and prior to the two-leaf stage of late-emerging wild oat. Split applications of imazamethabenz or ICIA 0604 allowed the herbicide rate to be reduced by half while maintaining or improving wild oat control. Both imazamethabenz and ICIA 0604 were most effective with methylated vegetable oil adjuvants. Wheat yield and net returns were greatest for half-rate split applications of imazamethabenz and ICIA 0604 in both years, likely because of less early-season wild oat competition and reduced wheat injury caused by ICIA 0604.

Nomenclature: Imazamethabenz; ICIA 0604 (proposed name, tralkoxydim), 2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl)cyclohex-2-enone; wild oat, Avena fatua L. #³ AVEFA; hard red spring wheat, Triticum aestivum L.

Additional index words: Adjuvant, application timing.

Abbreviations: MVO, methylated vegetable oil; NIS, nonionic surfactant; SC, Supercharge.

A population model was constructed to simulate the development of imazamox-resistant jointed goatgrass (AEGCY) in imazamox-resistant (Clearfield^™) wheat. The model computed changes in the surface and in the buried AEGCY seed banks for both resistant and susceptible biotypes. Simulations started with an initial density of 1,000 susceptible and zero resistant seeds/m² in each seed bank. Simulation of continuous, no-till Clearfield wheat production resulted in rapid development of resistant AEGCY without hybridization with wheat and in extremely rapid resistance development with hybridization. In less than 10 yr, the resistant population was growing exponentially in both simulations. Adding a fallow year with tillage into the simulated rotation did not substantially slow down the appearance of resistance but did delay the rate of resistant population increase by several orders of magnitude over 10 yr. Alternating Clearfield and a nonresistant winter wheat in combination with fallowing prevented the establishment of a significant resistant AEGCY population and prevented the susceptible seed population from increasing exponentially. These projections suggest that imazamox-resistant wheat can be a tool for managing AEGCY populations especially if combined with rotations that include fallow and crops other than Clearfield winter wheat.

Nomenclature: Imazamox; jointed goatgrass, Aegilops cylindrica Host #³ AEGCY; winter wheat, Triticum aestivum L. Clearfield^™.

Additional index words: Crop rotation, pollen flow, population model, resistance management.

Abbreviations: ALS, acetolactate synthase; BSB, buried seed bank; DSP, local seed dispersal; EST, established plant; MAT, mature plant; PRD, seed production; SDL, seedling; SSB, surface seed bank.

Two field trials were established in Virginia during 1998, 1999, and 2000 to evaluate long-term mugwort control with varying rates of dicamba, triclopyr, clopyralid, picloram, metsulfuron, glufosinate, glyphosate, and the dimethylamine salt and the isooctyl ester of 2,4-D. A logarithmic sprayer was utilized in the first field trial to evaluate mugwort control with each of these herbicides, and, except for metsulfuron, rates ranged from 0.28 to 8.9 kg ai/ha. Mugwort control with metsulfuron was evaluated at a lower rate range. In addition, mugwort control was evaluated with a logarithmic range of pelargonic acid rates in combination with constant rates of glyphosate, glufosinate, and the dimethylamine salt of 2,4-D. Complete control of mugwort plants and rhizomes was achieved at 1 yr after treatment with picloram at rates ≥ 0.28 kg ai/ha, with clopyralid at rates ≥ 4.4 kg ai/ha, and with glyphosate at 8.9 kg ai/ha. Greater than 80% mugwort control was also achieved at 1 yr after treatment with clopyralid at rates ≥ 0.28 kg/ha, with glyphosate at rates ≥ 4.4 kg/ha, and with dicamba at 8.9 kg ai/ha. However, all rates (≤ 8.9 kg ai/ha) of glufosinate, triclopyr, and the dimethylamine salt and the isooctyl ester of 2,4-D provided less than 50% mugwort control at 1 yr after treatment. Similar results were obtained with metsulfuron at rates ≤ 0.063 kg ai/ha. The addition of pelargonic acid to glyphosate, glufosinate, or the dimethylamine salt of 2,4-D did not significantly enhance mugwort control when compared with applications of these herbicides alone. Additionally, progressively higher rates of pelargonic acid in combination with glyphosate, glufosinate, or the dimethylamine salt of 2,4-D resulted in antagonism of these herbicides. In separate field trials conducted in 2000, reduced rates of picloram were evaluated. In these dose–response trials, picloram at 0.28 kg/ha was the lowest rate that consistently provided greater than 90% control of mugwort at 3 mo after treatment. Collectively, the results from both trials indicate that excellent long-term mugwort control may be achieved with relatively low use rates of picloram (0.28 kg/ha) and clopyralid (0.28 kg/ha), but higher rates were needed for glyphosate (8.9 kg/ha) and dicamba (8.9 kg/ha). Results also indicate that little to no long-term control of mugwort will be achieved with applications of glufosinate, metsulfuron, triclopyr, or the dimethylamine salt and the isooctyl ester of 2,4-D, even at exceptionally high use rates.

Nomenclature: Clopyralid; 2,4-D dimethylamine salt; dicamba; 2,4-D isooctyl ester; glufosinate; glyphosate; metsulfuron; pelargonic acid; picloram; triclopyr; mugwort, Artemisia vulgaris L. #³ ARTVU.

Additional index words: Growth regulator herbicides, logarithmic sprayer, nonselective herbicides, perennial weed control, regrowth, rhizome.

Abbreviations: MAT, month after treatment; YAT, year after treatment.

Common cocklebur is an adaptable species found in diverse environments. We grew 28 common cocklebur accessions from 14 states at Urbana, IL, to compare their growth, physiology, and morphology in a common environment to determine if regional control recommendations of specific biotypes might be practical. Accessions were evaluated for midseason and maximum heights and widths, flowering date, insect damage, and petiole color in 1998 and 1999. Weight of aboveground tissue, photosynthetic rate, stomatal conductance, chlorophyll content, and leaf and bur morphology descriptions were also taken in 1999. Midseason and maximum widths, midseason height, flowering date, and insect damage differed significantly based on the year of evaluation. The year by accession interaction was a significant source of variation for midseason and maximum heights and widths, flowering date, insect damage, and petiole color. Within each year, accessions differed significantly for all measured variables except maximum width in 1998 and stomatal conductance in 1999. Accessions from northern states usually flowered earlier, and flowering date was negatively correlated with latitude of origin (1998 r = −0.76; 1999 r = −0.60). Nevertheless, some of the earliest flowering accessions were from the southern states. Results from cluster analysis indicated that several accessions had phenotypes more similar to accessions from distant sites than to nearby accessions. We conclude that the accessions differ for traits that may affect weediness, but proximal accessions differ too frequently to recommend regional, biotype-specific control strategies.

Nomenclature: Common cocklebur, Xanthium strumarium L. #³ XANST.

Additional index words: Biotype, common garden, ecotype, intraspecies variability.

Abbreviations: P, probability level; Pn, net photosynthesis; *, significant at P ≤ 0.05; **, significant at P ≤ 0.01.

Field studies were conducted in 1998 and 1999 to evaluate the response of seven cotton cultivars to CGA-362622 applied postemergence at 7.5 and 15 g ai/ha to three- to five-leaf cotton. The cultivars evaluated included Deltapine 51, Deltapine NuCotn 33B, Paymaster 1220 RR, Paymaster 1220 BG/RR, Stoneville bromoxynil-resistant 47, Stoneville 474, and Sure-Grow 125. At 1 to 2 wk after treatment (WAT), CGA-362622 at 7.5 and 15 g/ha injured all cotton cultivars 7 to 9% and 13 to 15%, respectively. Cotton injury symptoms included chlorosis and minor stunting. At 3 to 4 WAT, injury from CGA-362622 at 7.5 and 15 g/ha was 2 to 6% and 7 to 9%, respectively. Except for Paymaster 1220 RR, Deltapine NuCotn 33B, and Stoneville 474, all cotton cultivars were injured more by the higher rate than by the lower rate of CGA-362622. Injury was not visibly apparent 6 to 8 WAT. CGA-362622 at either rate had no effect on cotton lint yield.

Nomenclature: CGA-362622 (proposed common name trifloxysulfuron), N-[(4,6-dimethoxy-2-pyrimidinyl)carbamoyl]-3-(2,2,2-trifluoroethoxy)-pyridin-2-sulfonamide sodium salt; cotton, Gossypium hirsutum L. ‘Deltapine 51’, ‘Deltapine NuCotn 33B’, ‘Paymaster 1220 RR’, ‘Paymaster 1220 BG/RR’, ‘Stoneville BXN 47’, ‘Stoneville 474’, ‘Sure-Grow 125’.

Additional index words: Crop injury, crop yield.

Abbreviations: ALS, acetolactate synthase; BXN, bromoxynil-resistant; LAYBY, late postemergence directed; POST, postemergence; WAT, weeks after treatment.

Separate field experiments were conducted to evaluate weed control and cotton response to flumioxazin in North Carolina. Flumioxazin postemergence directed (PD) at 70 g ai/ha applied alone or mixed with glyphosate or MSMA completely controlled common lambsquarters, common ragweed, entireleaf morningglory, ivyleaf morningglory, Palmer amaranth, pitted morningglory, prickly sida, sicklepod, smooth pigweed, and tall morningglory 4 wk after treatment. Glyphosate at 1,120 g ai/ha controlled sicklepod and entireleaf, ivyleaf, pitted, and tall morningglory less than flumioxazin. Weed-free experiments were conducted to evaluate cotton injury, fresh biomass reduction, and yield response to flumioxazin at 70 g ai/ha preplant (PP) and two rates PD. Nine PP applications were made at various timings between 0 and 10 wk prior to planting. Cotton was stunted 12% initially, and midseason cotton biomass was reduced when flumioxazin was applied at planting in 1 yr. Flumioxazin did not injure 15- or 30-cm–tall cotton when applied PD at 36 or 70 g/ha. Cotton yield differed between years, but was not affected by various flumioxazin treatments compared with commercial standards and nontreated controls.

Nomenclature: Flumioxazin; glyphosate; MSMA; common lambsquarters, Chenopodium album L. #³ CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; Palmer amaranth, Amaranthus palmeri S.Wats. # AMAPA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; sicklepod, Senna obtusifolia Irwin and Banaby # CASOB; smooth pigweed, Amaranthus hybridus L. # AMACH; tall morningglory, Ipomoea purpurea (L.) Roth # PHBPU; cotton, Gossypium hirsutum L. ‘Deltapine 51’, ‘Suregrow 125’.

Additional index words: Burn-down application, fresh biomass, injury, LAYBY, stale seedbed.

Abbreviations: LAYBY, the last postemergence-directed herbicide application; PD, postemergence directed; POST, postemergence; PP, preplant; PRE, preemergence; WAP, weeks after planting.

Field studies were conducted at three locations in North Carolina to evaluate clomazone preemergence (PRE) in glyphosate-tolerant cotton. Cotton was injured by fluometuron PRE at one location. Clomazone PRE controlled common ragweed, goosegrass, large crabgrass, and prickly sida better than trifluralin preplant incorporated (PPI). Trifluralin controlled Palmer amaranth better than clomazone. The addition of a late post-directed (LAYBY) treatment of cyanazine plus MSMA improved the control of goosegrass. Glyphosate at 0.8 kg ai/ha, used postemergence as needed, controlled tall morningglory and entireleaf morningglory at least 84%. Common ragweed was controlled with all herbicides, except trifluralin PPI. Prickly sida was controlled 94% or greater in glyphosate-containing systems. Cotton yields and net returns were similar for all glyphosate systems, regardless of soil-applied herbicides and LAYBY treatment options.

Nomenclature: Clomazone; cyanazine; fluometuron; glyphosate; MSMA; trifluralin; common ragweed, Ambrosia artemisiifolia L. #³ AMBEL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; Palmer amaranth, Amaranthus palmeri S.Wats # AMAPA; prickly sida, Sida spinosa L. # SIDSP; tall morningglory, Ipomoea purpurea (L.) Roth # PHBPU; cotton, Gossypium hirsutum L. ‘Paymaster 1330RR’, ‘DP5415RR’.

Additional index words: Economic analysis, herbicide-resistant crops.

Abbreviations: ANS, as needed spray; DAP, days after planting; EPOST, early postemergence; fb, followed by; LAYBY, late post directed; POST, postemergence; POT, postemergence over-the-top; PPI, preplant incorporated; PRE, preemergence.

Genetically modified, herbicide-resistant crop (HRC) cultivars, which allow for simplified weed control decisions compared with conventional cultivars, have considerable potential in Latin America. The number of herbicide applications can be reduced in HRCs, and otherwise difficult-to-control species, including red rice in rice or herbicide-resistant weeds, can potentially be managed. The American tropics include the centers of origin of several crops, such as corn and potato, and natural or agrestal floras containing wild near relatives of introduced crops, including rice and cotton, for which HRCs could be used. Potential direct impacts of HRC adoption on biodiversity in Latin America include changes in the genetic diversity of crops, increased volunteer crop problems, and invasion by resistant cultivars of natural areas beyond the farm boundary. Additionally, there is a risk associated with the escape of transgenes from HRCs, involving introgression to weedy relatives on a field scale leading to amplification effects of existing weeds or modification of gene pools of crop progenitors in the centers of origin or diversity. Possible indirect effects of HRCs include the potential expansion of agriculture into uncleared wild areas made economically attractive by the more efficient cropping system, and adverse effects on nontarget organisms and ecosystem processes. The occurrence of spontaneous hybrids of crop–weed or near-relative complexes is known in the United States for rice and sunflower, and the development of HRC–weed hybrids would provide a particularly difficult set of weed management problems. For crops in which HRCs are currently in use or under development, the greatest risks in Latin America appear to be with corn, cotton, and potato. However, some of the genetic and geographical barriers reduce the risk of hybridization between these crops and their wild relatives. Furthermore, unlike the case of feral rapeseed on road verges in Europe, there is no known example of a conventionally bred crop or interfertile hybrid with a near relative becoming established outside of cultivation in Latin America. Soybean, the most widely adopted HRC in Latin America to date, is an exotic beyond the range of its wild relatives. With the exception of O. glumaepatula, there appears to be little threat to endemic wild species from HRC rice as strong infertility barriers should prevent transgene flow, but possible transgene movement to the conspecific red rice may become an issue. Beyond the field boundary, a key question concerns the possible persistence of HRC x wild relative hybrids and the manner in which resistance traits affect their overall fitness. Designing practical risk assessment protocols on which to base HRC release approval is a considerable challenge, and it is vital that Latin American states continue to build and maintain functional biosafety regulatory structures.

Nomenclature: Sunflower, Helianthus annuus L.; rapeseed, Brassica napus L.; corn (maize), Zea mays L.; cotton, Gossypium hirsutum L.; potato, Solanum tuberosum L.; rice or wild rice, Oryza sativa L.; soybean, Glycine max (L.) Merr.

Additional index words: Bromoxynil, glufosinate, glyphosate, imazapyr, imazethapyr, propanil, transgene flow, wild relatives.

Abbreviations: GM, genetically modified; GMO, genetically modified organism; HR, herbicide resistant; HRC, herbicide-resistant crop; IWM, integrated weed management.

Herbicide-resistant crops (HRCs), particularly glyphosate-resistant soybean, are increasingly important in Latin America. Prior to commercial release of these crops, their short- and long-term risks should be thoroughly assessed. A risk assessment should include the identification and characterization of potential hazards and an estimation of the likelihood of these hazards occurring. For HRCs the agro-ecological hazards are mostly related to the occurrence of herbicide-resistant (HR) weeds and crop volunteers and the adverse effects from the use of pesticides within the agricultural area. Herbicide-resistant rice is used as a case study to visualize the key components of such a risk assessment. For this purpose, a model that simulates a typical rain-fed rice production system in Central America was developed. The model was used to investigate the selection of HR weedy rice populations under various scenarios. Scenarios included contrasting weed management practices, hybridization levels between the commercial HR cultivated and weedy rice, and seed predation rates. Because risks may become apparent only after long-term cultivation of HR rice, simulations were run for a 10-yr period. In a cropping system relying on glufosinate-resistant rice for weed control, the model predicted that resistance to glufosinate would occur after 3 to 8 yr of monoculture. Increasing the hybridization level from 1 to 5% decreased the time for resistance to occur by 1 to 3 yr. Increasing annual rate of weedy rice seed predation at the soil surface delayed the development of resistance. Tillage as a weed control tactic also delayed the occurrence of resistance when compared with a no-till situation.

Nomenclature: Glufosinate; glyphosate; red or weedy rice, Oryza sativa L. #³ ORYSA; rice (crop), Oryza sativa L; soybean, Glycine max (L.) Merr.

Additional index words: Brassica napus, Brassica rapa, ECHCE, ECHCO, Echinochloa colona, Echinochloa crus-galli, Echinochloa crus-pavonis, ecological hazard assessment, herbicide-resistant crops, herbicide-resistant rice, Latin America, ORUSA, Oryza latifolia, red rice, Sagittaria montevidensis, weedy rice.

Abbreviations: ALS, acetolactate synthase; DAS, days after sowing; FAO, Food and Agriculture Organization; GMO, genetically modified organism; HR, herbicide resistant; HRC, herbicide-resistant crop; WHO, World Health Organization.

Laboratory experiments were conducted in 55-L aquaria to evaluate the efficacy of the aquatic herbicide endothall and the fungal pathogen Mycoleptodiscus terrestris (Gerd.) Ostazeski, applied alone and in combination against hydrilla. Treatments included 0.25, 0.50, and 1.25 mg ae/L endothall, 100, 200, and 400 colony-forming units (CFU)/ml M. terrestris, simultaneous integrated treatments of 0.25, 0.50, and 1.25 endothall 100 or 200 CFU/ml M. terrestris, sequential integrated treatments of 100 and 200 CFU/ml M. terrestris 0.25 and 0.50 mg ae/L endothall, and untreated controls. By 42 d after treatment (DAT), all treatments had significantly reduced shoot biomass levels of hydrilla compared with the untreated controls. Combining the two lowest herbicide rates with M. terrestris provided better hydrilla control than either treatment alone. Based on these results, an outdoor mesocosm study was conducted to evaluate the efficacy and selectivity of endothall and the pathogen applied alone and in combination against hydrilla, Illinois pondweed, American pondweed, and vallisneria. Treatments included 0.25 and 0.50 mg ae/L endothall, 100 and 200 CFU/ml M. terrestris, integrated treatments of 0.25 and 0.50 mg ae/L endothall 100 and 200 CFU/ml M. terrestris, and untreated controls. Unlike the laboratory results, none of the treatments controlled hydrilla 100%. The combined treatments worked better than either treatment applied alone. By 42 DAT, all the combined treatments except 0.25 mg ae/L endothall 100 CFU/ml M. terrestris had reduced above-ground hydrilla biomass by ≥ 90% compared with the untreated controls. All nontarget species sustained varying amounts of injury from endothall and M. terrestris applied alone or in combination.

Nomenclature: Endothall; American pondweed, Potamogeton nodosus Poir. #³ PTMNO; hydrilla, Hydrilla verticillata (L.f.) Royle # HYLLI; Illinois pondweed, Potamogeton illinoensis Morong # PTMIL; Mycoleptodiscus terrestris (Gerd.) Ostazeski; vallisneria, Vallisneria americana Michx.

Additional index words: Aquatic plant management, integrated pest management.

Abbreviations: CFU, colony-forming units; DAT, days after treatment; DW, dry weight; ERDC, Engineer Research and Development Center; LAERF, Lewisville Aquatic Ecosystem Research Facility.

The allelopathic potential of hoary cress was evaluated by exposing the seeds and the germinated seeds of winter wheat, alfalfa, crested wheatgrass, bluebunch wheatgrass, and hoary cress to a water extract of dried, hoary cress roots under controlled conditions in an environmental chamber. Germination for all species was reduced in the hoary cress root extract when compared with distilled water, with winter wheat and hoary cress being more tolerant than the other species. Root length of all species was reduced by the extract when compared with distilled water. These data show the presence of phytotoxic chemical(s) that may inhibit germination and initial seedling growth in natural environments. Three glucosinolate compounds were identified in hoary cress root extracts.

Nomenclature: Glucosinolate; alfalfa, Medicago sativa L. ‘Latac’; bluebunch wheatgrass, Pseudoroegneria spicata (Pursh) A. Love; crested wheatgrass, Agropyron cristatum (L.) Gaertn.; hoary cress, Cardaria draba (L.) Desv., #³ CARDR; wheat, Triticum aestivum L. ‘Hill 81’.

Additional index words: Allelopathy, Brassicaceae, glucosinolates.

Autumn desiccation of warm-season perennial grasses is one method to enhance the establishment and early production of overseeded cool-season annuals. Potential herbicides were compared with paraquat, glyphosate, and dalapon to desiccate a dallisgrass–bermudagrass sod for overseeding annual ryegrass over a 2-yr period. Fluazifop-P at ≥ 0.14 kg/ha, glufosinate at ≥ 1.12 kg/ha, and haloxyfop at ≥ 0.07 kg/ha provided good dallisgrass desiccation and ryegrass yields similar to those with dalapon and glyphosate. Dallisgrass recovery was inversely related to desiccation rating for all treatments except for paraquat. None of the herbicide treatments had the desired combination of acceptable dallisgrass desiccation, improved early ryegrass production, and acceptable dallisgrass recovery.

Nomenclature: Dalapon; fluazifop-P; glufosinate; glyphosate; haloxyfop; paraquat; sethoxydim; annual ryegrass, Lolium multiflorum Lam. ‘Gulf’; bermudagrass, Cynodon dactylon (L.). Pers.; dallisgrass, Paspalum dilatatum Poir.

Additional index words: Desiccant, overseeding.

A survey was conducted to document the significance of crabgrass species among cropping systems and geographical regions in the continental United States. Surveys were mailed to 117 weed scientists, at least one in each state, including, where possible, extension weed scientists with responsibilities in each of the major agronomic and horticultural crops plus turfgrass systems. A 62% response rate was achieved. Large, smooth, and southern crabgrasses were considered at least occasionally important, with India and blanket crabgrasses considered rarely or not important. Smooth crabgrass and large crabgrass were considered to be important species in most of the latitudinal range, whereas southern crabgrass was considered to be important only in the southern states. Crabgrasses were considered to be more problematic in turf than in other cropping systems. From a regional perspective in turf, large crabgrass was the most important species in the Southeast, followed by southern crabgrass and smooth crabgrass. In the Northeast, smooth crabgrass was perceived as the more important species, but large crabgrass was more important in the north-central states.

Nomenclature: Blanket crabgrass, Digitaria serotina (Walt.) Michx. #³ DIGSO; crabgrass, Digitaria spp.; India crabgrass, Digitaria longiflora (Retz.) Pers. # DIGLO; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; smooth crabgrass, Digitaria ischaemum (Schreb.) Muhl. # DIGIS; southern crabgrass, Digitaria ciliaris (Retz.) Koel. # DIGSP.

Additional index words: Geographic distribution, turfgrass.

A tractor-mounted, air-pressurized, herbicide application system was designed and constructed for use in weed management research on cropland, pastures, and rangeland. The spray system was designed to minimize wind-induced spray pattern distortion, to enable accurate application of multiple treatments, to withstand the stresses of use on uneven and rough terrain, to apply herbicide treatments reliably, to be easy to transport, to be constructed with readily available spray system components, and to enable quick diagnosis and resolution of operational problems. The spray system has a total shield frame length of 5.2 m. The shielded frame comprises three sections. The two outside sections are connected to the center section by hinges so that they can be folded up and over the center section for transport or storage. Four spray booms are mounted inside the shield with a 50-cm distance between nozzles. Herbicides are usually applied with the bottom of the shield placed 20 cm above the soil or plant surface. This height provides 100% overlap of the spray pattern between adjacent nozzle tips. The spray system has been a durable and reliable tool that accurately and quickly applies herbicide treatments.

Additional index words: Application technology, cropland, pasture, rangeland, weed control.

Abbreviations: ID, inside diameter; PVC, polyvinylchloride.