Abstract: In 1998, field populations of wild radish suspected of being resistant to chlorsulfuron were collected and screened for resistance to this herbicide using the Quick-Test technique. This test successfully identified chlorsulfuron-resistant populations of wild radish. Detailed dose–response experiments with the progeny of these populations confirmed their resistance and validated the use of the Quick-Test for a dicot species. Subsequently in 1999, a random survey was conducted employing this test to establish the current extent of chlorsulfuron resistance in wild radish populations. The survey covered more than 200 fields in the northern, central, and eastern wheatbelt regions of Western Australia. Wild radish plants were collected from wheat crops in 133 of these fields. The Quick-Test method was used to screen these plants with the acetolactate synthase (ALS)-inhibiting herbicide chlorsulfuron. Overall, 21% of randomly collected wild radish populations were found to be resistant to chlorsulfuron.

Nomenclature: Chlorsulfuron; wheat, Triticum aestivum L.; wild radish, Raphanus raphanistrum L.

Additional index words: Herbicide resistance, Quick-Test, resistance survey.

Abbreviations: ALS, acetolactate synthase; WA, Western Australia.

Abstract: Field studies were conducted in 1997 and 1998 to evaluate tolerance of nine sweet corn cultivars to CGA 152005 postemergence at 10 and 20 g ai/ha. There was a cultivar by herbicide interaction for visible plant injury, plant height, ear weight, and yield. Sweet corn injury from CGA 152005 increased as rate increased. CGA 152005 at both rates killed ‘DelMonte 2038’. ‘Eliminator’, ‘Reward’, ‘Delectable’, and ‘Reveille’ were injured (10 to 12% plant height reduction), and the remaining cultivars (‘Challenger’, ‘Krispy King’, ‘CNS 710’, and ‘GH 2690’) were tolerant to CGA 152005 at both rates.

Nomenclature: CGA 152005 (proposed common name, prosulfuron), 1-(4-methoxy-6-methyl-triazin-2-yl)-3-[2-(3,3,3-trifluoropropyl)-phenylsulfonyl]-urea; sweet corn, Zea mays L.

Additional index words: Plant height, crop injury, sulfonylurea.

Abbreviations: DAP, days after planting; DAT, days after treatment; OM, organic matter; PRE, preemergence; POST, postemergence; SU, sulfonylurea.

Abstract: Potato crops often are grown in rotation with cereal crops such as wheat and barley. Imazamethabenz is a postemergence herbicide that selectively controls wild oat and certain other weeds in wheat and barley. Experiments were conducted at the University of Idaho Research and Extension Center, Aberdeen, ID, over a 3-yr period to evaluate the effect of irrigation management in an imazamethabenz-treated wheat crop on imazamethabenz persistence and injury in a subsequent potato crop. The experimental design was a split plot arrangement of a randomized complete block; main plots were seasonal irrigation amounts in wheat (20, 30, 40, or 50 cm), and subplots were imazamethabenz rates applied to the wheat crop (0, 0.26, 0.52, or 1.05 kg/ha). Soil analyses for imazamethabenz residues showed that herbicide degradation during the wheat growing season (i.e., 0 to 128 d after treatment [DAT]) followed first-order kinetics at all irrigation levels. Herbicide degradation rate increased with irrigation rate. Soil samples taken 338 or 351 DAT showed no detectable imazamethabenz residues (<10 ng/g) in most plots. However, some foliar injury to potato grown the year following imazamethabenz treatment was noted (<10% average injury), suggesting that potato is sensitive to imazamethabenz or imazamethabenz acid residues below the analytical detection limit. U.S. No. 1 and total potato tuber yield were not reduced by any treatment compared to the nontreated control. Therefore, under good growing conditions, potato can recover from mild imazamethabenz carryover injury without effects on tuber yield or quality.

Nomenclature: Imazamethabenz-methyl; wild oat, Avena fatua L.; barley, Hordeum vulgare L.; potato, Solanum tuberosum L.; wheat, Triticum aestivum L.

Additional index words: Irrigation management, carryover.

Abbreviations: DAT, days after imazamethabenz treatment; OC, organic carbon; OM, organic matter; POST, postemergence; PRE, preemergence.

Abstract: Goosegrass is considered tolerant to quinclorac. The purpose of this study was to determine whether there was a stage of growth at which it was susceptible. Stage of growth studies with goosegrass were conducted that evaluated quinclorac activity at rates of 0, 1, 2, 4, 8, and 16 kg ai/ha applied with 1% (v/v) Merge spray adjuvant. Quinclorac application stages evaluated included preemergence and one- to two-leaf, four- to five-leaf, and one- to two-tiller stage. The effects of root uptake from postemergence applications were also evaluated by comparing treatments with and without a vermiculite soil barrier. Goosegrass was more susceptible to quinclorac when applied preemergence or early postemergence at the one- to two-leaf stage than at later more mature stages. The importance of root uptake on quinclorac activity was also observed, particularly at the four- to five-leaf stage, where the dose required to reduce growth 50% (GR₅₀) in the absence of the soil barrier was 3.4 kg/ha vs. 16 kg/ha in the presence of a barrier. At the most advanced growth stage of one to two tillers, calculated GR₅₀ values were greater than 16 kg/ha whether a soil barrier was present or not. The lowest calculated GR₅₀ value of 2.7 kg/ha for the one- to two-leaf stage with no soil barrier was still approximately 3.5 times higher than the maximum labeled rate for turfgrass.

Nomenclature: Quinclorac; goosegrass, Eleusine indica (L.) Gaertn. #³ ELEIN.

Additional index words: Preemergence, postemergence, vermiculite soil barrier, true leaf.

Abbreviations: GR₅₀, herbicide dose that reduces growth by 50%; PPFD, photosynthetic photon flux density.

Abstract: Several commercial and experimental adjuvants were evaluated for efficacy in enhancing activity and selectivity of quinclorac in two cultivars of canola and four turfgrass species. Weed species investigated included cleavers, annual sowthistle, large crabgrass, and goosegrass. Turfgrass species evaluated included Kentucky bluegrass, perennial ryegrass, tall fescue, and creeping bentgrass. A variety of adjuvant types were selected, such as a methylated seed oil (Sunit II), a petroleum-based crop oil concentrate, the silicone-based Sylgard 309, a cationic fatty amine ethoxylate surfactant (Frigate), and modified crop oils (Dash and Merge). Adjuvant efficacy was evaluated by calculating the quinclorac rate required to reduce plant growth 50% (GR₅₀) based on rates applied at 0, 15.6, 31.2, 62.5, and 125 g ai/ha. For goosegrass, quinclorac rates evaluated were increased to 250, 500, 1,000, and 2,000 g ai/ha. All evaluated adjuvants provided similar enhancement of control for cleavers and annual sowthistle. Sylgard 309 was the least effective adjuvant for control of large crabgrass. Goosegrass was tolerant to quinclorac across the evaluated rate range regardless of adjuvant; therefore, GR₅₀ values could not be determined. None of the adjuvants alone caused phytotoxicity to canola or any turfgrass species.

Nomenclature: Quinclorac; annual sowthistle, Sonchus oleraceus L. #³ SONOL; cleavers, Galium aparine L. # GALAP; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; canola, Brassica napus L. ‘Garrison’, ‘Goldrush’; creeping bentgrass, Agrostis palustris (L.) Huds.; Kentucky bluegrass, Poa pratensis L.; perennial ryegrass, Lolium perenne L.; tall fescue, Festuca arundinacea (L.) Schreb.

Abbreviations: GR₅₀, herbicide rate required to reduce growth 50%; PPFD, photosynthetic photon flux density.

Abstract: A 3-yr study was conducted to assess cranberry bean susceptibility to mechanical weeding using a rotary hoe at preemergence, hook, cotyledon, unifoliate, and first to fourth trifoliate stages of bean development and at different combinations of stages. The experiment was conducted in a weed-free environment. Cultivation with the rotary hoe reduced bean yield only for the treatment that received four cultivations at four different bean growth stages. Three cultivations improved yield compared with no cultivation. Single cultivation done at any of the eight crop growth stages did not affect yield. Crop density at harvest was decreased 6% in the treatments receiving two cultivations and 9% in the treatments receiving four cultivations compared to no cultivation. The effects of the cultivations on grain moisture were not consistent and differed from year to year. Seed weight did not differ among treatments in either year. Because this study was conducted under weed-free conditions, the beneficial effects of cultivating with the rotary hoe are probably mostly related to breaking the soil crust, improving soil aeration, preserving soil moisture, or promoting mineralization of the nutrients required by the crop.

Nomenclature: Cranberry bean, Phaseolus vulgaris L. ‘SVM Taylor’.

Additional index words: Bentazon, cultivation, fenoxaprop-p-ethyl, mechanical weeding, physical weed control, trifluralin.

Abstract: An experiment was conducted in 1998 and 1999 in southeastern Pennsylvania to examine the effect of tillage and soybean row spacing on burcucumber emergence and growth. A second experiment evaluated postemergence (POST) soybean herbicides on burcucumber control. In the tillage and row spacing study, a glyphosate-resistant soybean variety was planted in no-till and reduced-tillage systems in 38- and 76-cm row spacings. In the POST herbicide experiment, chlorimuron, glyphosate, CGA-277476, thifensulfuron, and several combinations of these herbicides were applied at two different POST application timings in 38-cm row soybean planted in a reduced-tillage system. In the tillage and row spacing study, burcucumber emergence was greatest starting in late May through mid-June and mostly ceased by early July, regardless of tillage system or row spacing. Although there was no difference in germination period in either tillage system, preplant tillage increased the number of emerged plants by 110% in 1997 and 70% in 1998 compared to the no-till system. Row spacing had no effect on burcucumber emergence or biomass production. In general, most POST herbicide programs controlled burcucumber, and there was no difference between early POST and mid-POST application timings. Chlorimuron at 13 g ai/ha, chlorimuron plus thifensulfuron, glyphosate, glyphosate plus chlorimuron, and glyphosate plus CGA-277476 provided 87% or greater control of burcucumber 12 wk after planting. These herbicides reduced burcucumber density and biomass by more than 56% in 1997 and 96% in 1998.

Nomenclature: CGA-277476 (proposed name, oxasulfuron), 2-[[[[[4,6-dimethyl-3-pyrimidinyl]amino]carbonyl]amino] sulfonyl]benzoic acid, 3-oxetanyl-ester; chlorimuron; glyphosate; thifensulfuron; burcucumber, Sicyos angulatus L. #³ SIYAN; soybean, Glycine max (L.) Merr.

Additional index words: Cultural control, emergence period, herbicide application timing, herbicide-resistant crops.

Abbreviations: EPOST, early postemergence; GDD, growing degree days; LPOST, late postemergence; MPOST, mid-postemergence; POST, postemergence; WAP, weeks after planting.

Abstract: Field experiments were conducted in 1997 and 1998 at the Prattville Experiment Field in Prattville, AL and the Wiregrass Substation in Headland, AL to determine if ammonium thiosulfate (ATS) additions to monosodium methanearsonate (MSMA) affects weed control, reduces MSMA-induced cotton injury, lessens the fruiting and maturity delay on cotton caused by MSMA, and lessens MSMA-induced yield reductions in cotton. Treatments were applied before cotton was at the pinhead square stage and the weeds were 5 cm tall. Weeds evaluated were sicklepod, morningglory species, yellow nutsedge, and Texas panicum. ATS additions to MSMA occasionally enhanced control of all weeds 5 to 20%. However, the addition of ATS did not reduce crop injury caused by MSMA, the effects of MSMA on cotton maturity, or yield reductions caused by MSMA.

Nomenclature: MSMA, monosodium methanearsonate; morningglory species, Ipomoea spp. #³ IPOZZ; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB; Texas panicum, Panicum texanum Buckl. # PANTE; yellow nutsedge, Cyperus esculentus L. # CYPES; cotton, Gossypium hirsutum L.

Abbreviations: ATS, ammonium thiosulfate; DAT, days after treatment; POST, postemergence.

Abstract: A random survey of 264 cropping fields in the Western Australian wheat belt was conducted to determine the extent of rigid ryegrass resistance to commonly used acetolactate synthase- and acetyl-CoA carboxylase-inhibiting herbicides. Rigid ryegrass infestation density was assessed and seed samples collected and subsequently tested for resistance to diclofop-methyl, clethodim, chlorsulfuron, and sulfometuron. Of these randomly collected populations, 46% exhibited resistance to diclofop-methyl and 64% to chlorsulfuron, with 37% exhibiting multiple resistance to both herbicides. Only 28% of tested populations were classified as susceptible to both diclofop-methyl and chlorsulfuron, although all but one population were susceptible to clethodim. Large differences in the proportion of fields containing resistant populations were found between agronomic areas, reflecting different cropping and, therefore, herbicide use history. There was no significant association between resistance status and the density at which rigid ryegrass was present. Herbicide-resistant rigid ryegrass populations are now more common than susceptible populations across much of the Western Australian wheat belt.

Nomenclature: Chlorsulfuron; clethodim; diclofop-methyl; sulfometuron; rigid ryegrass, Lolium rigidum Gaud. #³LOLRI.

Additional index word: Weed density.

Abbreviations: ACCase, acetyl-CoA carboxylase; ALS, acetolactate synthase.

Abstract: The premix atrazine S-metolachlor is commonly used to control a wide range of weeds in corn, but it is weak on velvetleaf and several other broadleaf species. RPA 201772, used at reduced rates in combination with atrazine S-metolachlor, may improve the weed control spectrum. In field studies at Urbana and Dekalb in 1998 and 1999, RPA 201772 was combined with a premix of atrazine at 1,820 g ai/ha and S-metolachlor at 1,408 g ai/ha to compare RPA 201772 rate effects on corn injury, weed control, and yield. RPA 201772 was applied at 0, 26, 53, 78, 105, and 132 g ai/ha early preplant (EPP), preplant incorporated (PPI), and preemergence (PRE). Compared with atrazine S-metolachlor alone, RPA 201772 combinations did not improve giant foxtail control. However, RPA 201772 at 26 or 53 g/ha increased control of redroot pigweed, common lambsquarters, ivyleaf morningglory, common ragweed, giant ragweed, and velvetleaf in some environments. At Urbana in both years, RPA 201772 at 26 g/ha in combination with atrazine S-metolachlor increased velvetleaf control 15% compared with the premix alone. RPA 201722 at 26 to 78 g/ha decreased velvetleaf densities with all application methods. Greater weed control and higher corn yield occurred in treatments applied PRE or PPI compared with EPP applications, except where conditions were dry after PRE applications. This research demonstrates the benefit of RPA 201772 at low rates for broadleaf weed control with less potential for crop injury compared with high RPA 201772 rates.

Nomenclature: RPA 201772 (proposed common name, isoxaflutole), 5-cyclopropyl isoxazol-4-yl-2-mesyl-4-trifluoromethylphenyl ketone; common lambsquarters, Chenopodium album L. #³ CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; giant ragweed, Ambrosia trifida L. # AMBTR; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; redroot pigweed, Amaranthus retroflexus L. # AMARE; velvetleaf, Abutilon theophrasti Medicus # ABUTH; corn, Zea mays L.

Additional index words: HPPD inhibitor, isoxaflutole, reduced herbicide rates.

Abbreviations: DAE, days after emergence; DAT, days after treatment; EPP, early preplant; PPI, preplant incorporated; PRE, preemergence.

Abstract: A diagnostic test (Syngenta Quick-Test, QT) used for testing grass weed survivors to herbicides in the field for resistance was evaluated. Cuttings from grass weeds were transplanted into pots to regenerate new leaves, then treated with herbicide. In greenhouse experiments, resistance of known herbicide-resistant blackgrass biotypes to the aryloxyphenoxypropanoate herbicides CGA 184927 and fenoxaprop-ethyl and to the phenylurea herbicide isoproturon was verified by the QT. The findings were similar to those for seedlings grown from seed. Rigid ryegrass from suspect resistant fields in South Australia was sampled and sent by post to Switzerland for QT analysis. Resistance was confirmed in less than 4 wk, which verified resistance as responsible for the field failures. The added features of the QT over current resistance tests suggest a likely fit for in-season testing of surviving weeds and possible follow-up action.

Nomenclature: CGA 184927, (propynyl (R)-2-[4-(5-chloro-3-fluoro-2-pyridyloxy)phenoxy]-propanoate); fenoxaprop-ethyl; isoproturon; blackgrass, Alopecurus myosuroides Huds. #³ ALOMY; rigid ryegrass, Lolium rigidum Gaudin # LOLRI.

Additional index words: Resistance test, aryloxyphenoxypropanoate, phenylurea.

Abbreviations: ACCase, acetyl coenzyme A carboxylase (EC 6.4.1.2); APP, aryloxyphenoxypropanoate; CHD, cyclohexanedione; DAT, days after treatment; PU, phenylurea; QT, Syngenta Quick-Test; SU, sulfonylurea.

Abstract: Two field experiments were conducted to evaluate the effects of selected herbicides on Italian ryegrass, combined Italian ryegrass plus wheat forage production, and returns from hard red winter wheat grain. Herbicides included BAY FOE 5043 metribuzin (4:1 w/w premix), BAY MKH 6562, chlorsulfuron, chlorsulfuron metsulfuron (5:1 w/w premix), diclofop, MON 37560, pendimethalin, ICIA 0604, and triasulfuron. Italian ryegrass was controlled 80% or more by 28 of 34 treatments. Grain dockage was reduced by 33 of 34 treatments at both sites, and grain yield was improved at both sites by 29 of 34 treatments. No herbicide treatment decreased forage protein content, but forage yield was frequently decreased by controlling Italian ryegrass. Gross returns from wheat grain were improved over the untreated check by all but six treatments at site 1, and by all but one treatment at site 2. The data did not support the hypothesis that returns from forage plus grain could be maximized by delaying Italian ryegrass control until grazing termination.

Nomenclature: BAY FOE 5043, N-(4-fluorophenyl)-N-(1-methylethyl)-2-[[5-(trifluoromethyl)-1,3,4-thiadiazol-2-yl]oxy]acetamide; BAY MKH 6562, 1H-1,2,4-triazole-carboxamide,4,5-dihydro-3-methoxy-4-methyl-5-oxo-N-[[2-(trifluoromethoxy)phenyl]sulfonyl]-sodium salt; chlorsulfuron; diclofop; metribuzin; metsulfuron; MON 37560, 1-(4,6-dimethoxypyrimidin-2-yl)-3-[(ethanesulfonyl-imidazo[1,2-a]-pyridine-3-yl)sulfonyl]urea; pendimethalin; ICIA 0604 (proposed common name, tralkoxydim), 2-cyclohexen-1-one,2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl)-(9Cl); triasulfuron; Italian ryegrass, Lolium multiflorum Lam., Marshall #³ LOLMU; wheat, Triticum aestivum L., 2137.

Additional index words: BAY FOE 5043, BAY MKH 6562, chlorsulfuron, diclofop, metribuzin, metsulfuron, MON 37560, pendimethalin, ICIA 0604, triasulfuron, forage.

Abbreviations: DAS, days after seeding; POST, postemergence; PRE, preemergence.

Abstract: The experimental sulfonylurea herbicide ASC-67040 was evaluated preemergence (PRE) and postemergence (POST) at 25 to 100 g ai/ha and PRE at 50 g/ha followed by ASC-67040 POST at 50 g/ha for broadleaf weed control in potato and tomato. In Virginia, ASC-67040 POST at 50 and 100 g/ha gave 70 to 98% control of common lambsquarters, common ragweed, and jimsonweed with slight (0 to 6%) ‘Superior’ potato and moderate (0 to 23%) ‘Agriset’ tomato injury. This crop injury was present primarily as chlorosis in terminal growth and disappeared by 3 wk after treatment (WAT). Potato tuber and tomato fruit yields were high in ASC-67040-treated plots. In North Carolina, ASC-67040 PRE and POST at 50 and 100 g/ha controlled 10 species of annual broadleaf weeds and grasses, and at 25 g/ha ASC-67040 gave greater than 90% control of most species. ASC-67040 injured ‘Fontenot’ potato more than Superior and caused 10 to 13% injury to ‘Mountain Spring’ tomato but did not injure ‘Mountain Pride’ tomato. Mountain Spring tomato recovered rapidly and produced high yields. In the greenhouse, yellow nutsedge control by ASC-67040 POST at 25 to 100 g/ha was 59 to 86% 3 WAT and yellow nutsedge height, dry weight, and regrowth dry weight were reduced by all rates. Lower rates of ASC-67040 might control weeds and cause less injury to potato and tomato.

Nomenclature: ASC-67040 (proposed name fluazasulfuron), 1-(4,6-dimethoxypyrimidin-2-yl)-3-[3-trifluoromethyl-pyridin-2-yl)sulfonyl]urea; metolachlor; metribuzin; trifluralin; common lambsquarters, Chenopodium album L. #³ CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; jimsonweed, Datura stramonium L. # DATST; yellow nutsedge, Cyperus esulentus L. # CYPES; potato, Solanum tuberosum L. ‘Fontenot’, ‘Superior’; tomato, Lycopersicum esculentus L. ‘Agriset’, ‘Mountain Pride’, ‘Mountain Spring’.

Additional index words: Metolachlor, metribuzin, trifluralin, Ambrosia artemisiifolia, Cyperus esculentus, Datura stramonium, AMBEL, CHEAL, CYPES, DATST.

Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); DAP, days after planting; DATP, days after transplanting; DAT, days after treatment; fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE, preemergence in potato and pretransplant surface applied in tomato; WAT, weeks after treatment.

Abstract: Field experiments were conducted in 1996, 1997, and 1998 at Lacombe and Lethbridge, AB, to determine the influence of early weed competition on field pea yields. Wild oat and Tartary buckwheat were removed from plots at weekly intervals after pea emergence by hand-weeding and maintained weed-free for the remainder of the growing season. Tartary buckwheat produced slightly more biomass than wild oat at Lacombe, whereas wild oat produced much more biomass than Tartary buckwheat at Lethbridge. Weed-free pea yields at Lacombe were always two- to threefold higher than at Lethbridge. At Lethbridge, early competition with Tartary buckwheat in all years, and with wild oat in 1998, did not reduce pea yields. In 1996 and 1997 at Lethbridge, pea yield reductions due to wild oat began at 2 wk after pea emergence; for the next 2 wk yield loss was linear, decreasing at an average rate of 97 kg/ha per day. Early weed competition led to pea yield losses at Lacombe in all 3 yr. The onset of yield loss at Lacombe over the 3-yr period ranged from 1 to 2 wk after pea emergence; for the next 2 to 3 wk yield loss was linear, decreasing at an average rate of 45 kg/ha per day. Yield losses after full-season weed competition ranged from 40 to 70% at both sites. Usually, the beginning of the critical weed-free period was at 1 or 2 wk after pea emergence. Optimum pea yields usually required weed removal very early in the pea life cycle; weed removal beyond 2 wk after pea emergence often protected only suboptimal yields.

Nomenclature: Wild oat, Avena fatua L. #³ AVEFA; Tartary buckwheat, Fagopyrum tataricum (L.) J. Gaertn.; pea, Pisum sativum L. Carrera.

Additional index words: Critical weed-free period, crop-weed interference, duration of competition, AVEFA.

Abbreviations: POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Abstract: Glyphosate-resistant (Roundup Ready®) soybean is widely grown to provide broad-spectrum weed control following sequential applications of glyphosate. Studies were conducted during 1998 and 1999 at Keiser, AR, and in 1999 at Pine Tree, AR, to examine the effect of glyphosate-resistant soybean populations on the number of glyphosate applications needed to maintain 90% or greater control of all weed species and on the gross profit margin from weed management. Soybean was seeded in 19-cm rows at 12 rates ranging from 185,000 to 1,482,000 seeds/ha. Each seeding rate received a single application of 0.56 and 1.12 kg ai/ha glyphosate once weeds were 5 to 7 cm tall, followed by repeat applications when control of any species fell below 90%. Soybean yield and gross profit margin at Keiser were similar both years, and a quadratic curve best described the relationship between seed yield and seeding rate, with maximum predicted and observed yield at 988,000 seeds/ha. Soybean seeding rate affected light interception by soybean and the number of glyphosate applications needed to maintain 90% control of all species. By the later stages of vegetative development, soybean at Pine Tree achieved ≥95% light interception, maximizing yield at all seeding rates. Late-season light interception at Keiser ranged from 88 to 99%, causing soybean yield to vary by seeding rate. Three applications of 0.56 kg/ha glyphosate were needed at seeding rates of 185,000 and 247,000 seeds/ha, whereas higher seeding rates sometimes required only a single application for season-long weed control. Application and herbicide costs were offset by reduced seeding costs; thus, predicted gross profit margin from weed management was optimized at the lowest seeding rate of 185,000 seeds/ha.

Nomenclature: Glyphosate; soybean, Glycine max (L.) Merr. ‘Delta King 5961 RR’.

Additional index words: Economic analysis, light interception, photosynthetically active radiation, Digitaria sanguinalis, Echinochloa crus-gall, Euphorbia maculata, Ipomoea lacunosa, Sesbania exaltata, DIGSA, ECHCG, EUPMA, IPOLA, SEBEX.

Abbreviations: DAE, days after emergence; LAI, leaf area index; PAR, photosynthetically active radiation.

Abstract: An accession of auxinic herbicide-resistant yellow starthistle found near Dayton, WA, was tested to evaluate cross-resistance to growth regulator herbicides and susceptibility to herbicides with different modes of action. Picloram at 0.43 kg ae/ha removed susceptible (S) yellow starthistle plants from a field plot, and surviving resistant (R) plants were dug and moved to the greenhouse. Known S plants were transplanted from a pasture near the R population. The R biotype was reconfirmed as resistant to picloram in greenhouse tests, with resistance ratios of 5.6 and 3.8 for vegetative and reproductive biomass, respectively, and 10.2 for LD₅₀ (lethal dose for 50% of the treated population) data. The R biotype was also cross-resistant to clopyralid and dicamba in all responses and to 2,4-D and triclopyr in vegetative biomass and LD₅₀ data. In field trials, eight herbicides were applied alone and in various combinations with and without addition of picloram. The yellow starthistle population was apparently comprised of differing percentages of R and S plants in 1997 and 1998, as picloram alone controlled 65 to 76% of the yellow starthistle in 1997 and 96 to 97% in 1998. BAS 662 01H (dicamba SAN 836) at 0.28 or 0.42 kg ae/ha, respectively, or dicamba at 0.56 kg ae/ha were the best alternative treatments in either trial in either year, but only in 1998 did control exceed 85%. Picloram and other auxinic herbicides should continue to be useful for control of mixed R and S yellow starthistle populations. However, effective herbicides with different mode(s) of action integrated with range improvement practices and biological control must be identified for long-term yellow starthistle management.

Nomenclature: BAS 662 01H (formerly SAN 1269; contains 20% ae 2-(1-[([3, 5-difluorophenylamino] carbonyl)-hydrazono] ethyl)-3-pyridinecarboxylic acid) (formerly SAN 836 [proposed common name diflufenzopyr]) plus 50% ae dicamba; yellow starthistle, Centaurea solstitialis L. #³ CENSO.

Additional index words: Growth regulator herbicides, herbicide resistance, picloram.

Abbreviations: I₅₀, dose causing 50% reduction in vegetative or reproductive weight; POST, postemergence; R, resistant; S, susceptible,.

Abstract: Field studies were conducted from 1997 to 1999 to evaluate the influence of broadleaf herbicides on double-crop glyphosate-resistant soybean injury and yield at Belleville, IL. Diphenylether herbicides applied postemergence (POST) caused 10 to 48% necrosis 7 days after treatment (DAT). POST herbicides caused 0 to 8%, 8 to 37%, and 0 to 12% height reduction 7 DAT in 1997, 1998, and 1999, respectively. In most instances, diphenylether herbicides did not delay soybean maturity, whereas imazethapyr applied POST delayed soybean maturity in 1998 and 1999. Acifluorfen plus bentazon reduced soybean height at maturity in 1997 and 1998, whereas lactofen, imazethapyr, and imazamox reduced height only in 1998. Diphenylether herbicides did not reduce grain yield when compared to the no-herbicide hand-weeded treatment, but imazamox reduced yield by 18%. Furthermore, the soil herbicides applied preemergence and diphenylether herbicides applied POST did not reduce grain yield when compared to glyphosate alone.

Nomenclature: Acifluorfen; bentazon; glyphosate; imazamox; imazethapyr; lactofen; soybean, Glycine max (L.) Merr. ‘Asgrow 3601 RR’, ‘Asgrow 4501 RR’, and ‘Bergmann-Taylor 369 CR’.

Additional index words: Herbicide injury, preemergence, postemergence, CGA-248757, CGA-277476, cloransulam, flumiclorac, fomesafen, imazaquin, pendimethalin.

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

Abstract: Field trials were conducted in 1997 and 1998 at two locations in Israel to evaluate the efficacy of imazapic applied postemergence (POST) to sunflower for broomrape control under irrigated and nonirrigated conditions. Two sequential treatments of imazapic at 1.5 followed by (FB) 3.0, 3.0 FB 4.5, or 4.5 FB 6.0 g ai/ha on sunflower plants 12 ± 3 and 55 ± 5 cm tall, respectively, reduced sunflower broomrape throughout the growing season under irrigated and nonirrigated conditions. Sunflower growth was not affected by imazapic treatments. It was confirmed, in accordance with an earlier report, that when sequential treatments of imazapic included an application at the sunflower inflorescence developmental stage, the herbicide decreased seed yield in proportion to the applied rate.

Nomenclature: Imazapic; broomrape, Orobanche cumana Waller; sunflower, Helianthus annuus L.

Additional index words: Parasitic weed, herbicide.

Abbreviations: fb, followed by; POST, postemergence; PRE, preemergence.

Abstract: Kyllinga squamulata has become problematic in bermudagrass turf in recent years, probably related to shifts in herbicide use strategies. Preemergence and postemergence greenhouse and field herbicide studies evaluated K. squamulata control in bermudagrass turf. Excellent (≥90%) postemergence control at 6 wk after initial treatment (WAIT) followed single and sequential applications of imazaquin at 0.42 kg ai/ha, MSMA plus imazaquin at 1.12 0.42 kg ai/ha, and sulfentrazone at 0.56 kg ai/ha. In one of two experiments, unacceptable (>30%) bermudagrass injury occurred with imazaquin at 0.42 and 0.56 kg ai/ha and MSMA plus imazaquin at 1.12 0.42 kg ai/ha 1 wk after application; however, plots recovered fully by 2 wk. In the field at 18 WAIT, preemergence control of greater than 70% was obtained with a single application of oxadiazon at 1.12 or 2.24 kg ai/ha and sequential applications of 1.12 kg ai/ha each 8 wk apart. Sequential applications 8 wk apart of sulfentrazone at 0.28 followed by 0.28 kg/ha also provided greater than 70% preemergence control. In two greenhouse studies, oxadiazon at 2.24 kg/ha and sulfentrazone at 0.56 kg/ha provided greater than 90% preemergence control.

Nomenclature: Imazaquin; MSMA; oxadiazon; sulfentrazone; cock's comb kyllinga (proposed common name), Kyllinga squamulata Thonn. ex Vahl; hybrid bermudagrass, Cynodon dactylon Burtt-Davey × C. transvaalensis L. Pers. ‘Tifway’.

Abbreviations: fb, followed by, WAIT, weeks after initial treatment, WAT, weeks after treatment.

Abstract: A study was conducted in 1999 to evaluate weed control and imidazolinone-tolerant (IMI-tolerant) rice response to 140 g ai/ha imazethapyr at different application timings and to flood depths of 5, 10, and 20 cm at the Rice Research Station near Crowley, LA, and at the Northeast Research Station near St. Joseph, LA. Barnyardgrass control, rice injury, and rice yield were not influenced by flood depth; therefore, data were averaged over flood depths. Season-long barnyardgrass control was greater than 80% at both locations with imazethapyr applied preplant incorporated (PPI), early postemergence (EPOST), and mid-postemergence (MPOST). IMI-tolerant rice injury at 7 d after late postemergence (LPOST) treatment (DAT) was less than 5% for all imazethapyr treatments at Crowley and 1 to 8% for PPI, preemergence (PRE), delayed preemergence (DPRE), and EPOST timings at St. Joseph. However, IMI-tolerant rice injury was 5% or less at 42 DAT for all treatments at Crowley and St. Joseph. IMI-tolerant rice yield at Crowley was 2,780 to 3,000 kg/ha following applications of imazethapyr at PPI, PRE, DPRE, and EPOST, and these yields were higher than the yields of the MPOST and LPOST treatments. At St. Joseph, IMI-tolerant rice yields were equal for imazethapyr applied PPI, DPRE, and EPOST treatments compared with Crowley.

Nomenclature: Imazethapyr; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; rice, Oryza sativa L. imidazolinone-tolerant ‘93 AS 3510’.

Additional index words: ALS, acetolactate synthase, Clearfield rice, soil-applied herbicide, water depth.

Abbreviations: DAT, days after LPOST treatment; DPRE, delayed preemergence; EPOST, early postemergence; IMI-tolerant, imidazolinone-tolerant; LPOST, late postemergence; MPOST, mid-postemergence; PPI, preplant incorporated; PRE, preemergence; power take-off (PTO).

Abstract: We examined the effect of a postemergence application of fluazifop-P on root uptake, translocation, and metabolism of ¹⁴C-terbacil in ‘Kent’ strawberry. Fluazifop-P had no effect on uptake of ¹⁴C-terbacil from a nutrient solution over 48 h, nor did it affect the proportional distribution of ¹⁴C-label in the plants. The ¹⁴C-label was readily translocated to the foliage where it tended to accumulate in vascular tissue. Fluazifop-P reduced the overall conversion of ¹⁴C-terbacil to metabolites by about 50%. Thin layer chromatography of methanol extracts of leaflets, petioles, crowns, and roots separated the 6-hydroxymethyl derivative, and several unidentified metabolites, including a major water-soluble metabolite at the origin. At least 50% of the latter could be converted to the 6-hydroxymethyl metabolite by β-glucosidase, but other metabolites could be separated in other solvent systems. The levels of metabolites were generally two- to threefold higher in plants treated with terbacil alone than in those pretreated with fluazifop-P. Therefore, we conclude that the interaction observed between these herbicides in the field results from fluazifop-P inhibiting detoxification of terbacil by strawberry.

Nomenclature: Fluazifop-P; terbacil; strawberry, Fragaria × ananassa Duchensne ‘Kent’.

Additional index words: Herbicide interaction, synergism, root uptake.

Abbreviations: GC-ECD, gas chromatography electron capture detection; GC-MSD, gas chromatography mass spectrum detection; HPLC, high-performance liquid chromatography; LSS, liquid scintillation spectrometry; PPFD, photosynthetic photon flux density; SEM, standard error of the mean; TLC, thin layer chromatography.

Abstract: Greenhouse studies were conducted to determine yellow nutsedge response to selective placement of a 5-cm layer of norflurazon-treated soil above, below, or above plus below pregerminated nutsedge tubers. Norflurazon at 1.68 kg ai/ha applied postemergence (POST) as a foliar, soil, or foliar plus soil treatment was also evaluated. Soil concentrations of norflurazon at 1.5 mg/kg (w/w) applied below or above plus below nutsedge tubers reduced yellow nutsedge shoot numbers at least 69%, shoot height at least 71%, shoot dry weights at least 77%, and root tuber dry weights at least 89%. Yellow nutsedge growth reduction with norflurazon was greatest when norflurazon was placed in the soil profile below or above plus below the yellow nutsedge tubers. Placement of norflurazon above yellow nutsedge tubers did not reduce shoot number, height, or dry weight until the foliar portion of plants were removed 39 d after treatment. POST application of norflurazon did not reduce initial yellow nutsedge shoot number regardless of application method. Foliar-only POST application of norflurazon was less effective for reducing numbers of emerged yellow nutsedge than application to soil only or soil plus foliage.

Nomenclature: Norflurazon; yellow nutsedge, Cyperus esculentus L. #³ CYPES.

Additional index words: Application method, herbicide placement, timing, herbicide concentration, cotton, Gossypium hirsutum.

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

Abstract: Field studies were conducted in 1998 and 1999 at Simcoe and Exeter, ON, to evaluate the tolerance of nine sweet corn cultivars, representing a range of genotypes, to RPA 201772 applied preemergence at 105 and 210 g ai/ha. The location × year interaction was significant for visible plant injury, plant height, and yield. All cultivars showed significant injury at Simcoe in 1999, especially at 210 g/ha. Calico Belle was the most sensitive cultivar, with RPA 201772 resulting in severe injury at Simcoe in 1999. Increased injury in 1999 was due to significant rainfall (48.5 mm) within 10 d of RPA 201772 application at Simcoe. Calico Belle also showed injury at Exeter in 1999 and at Simcoe in 1998. Plant height of all cultivars was reduced at the Simcoe location in 1999. Yield of five cultivars was also reduced at Simcoe in 1999. Sensitivity to RPA 201772 increased as application rate increased. Plant height and yield was not reduced at Exeter.

Nomenclature: RPA 201772 (proposed common name, isoxaflutole), 5-cyclopropyl-isoxazol-4-yl 2-mesyl-4-trifluoromethyl phenyl ketone; sweet corn, Zea mays L.

Additional index words: Plant height, crop injury, preemergence, benzoly isoxazole.

Abbreviations: DAT, days after treatment; OM, organic matter; PRE, preemergence.

Abstract: Purple loosestrife is an invasive, exotic perennial weed of wetlands throughout much of the United States and Canada. Once established, it forms dense colonies to the near exclusion of more desirable vegetation. Established plants are prolific seed producers. Our purpose was to investigate the germination of purple loosestrife seeds at a wide range of constant or alternating temperatures from 0 through 40 C. Purple loosestrife seeds germinate over a wide range of temperatures. We define optimum germination as not less than the maximum observed minus its confidence interval at the 0.01 level of probability. Optimum germination occurred over a considerable range of temperatures: Only 10, 15, or 20 C for 16 h alternating in each 24 h with 35 C for 8 h always supported optimum germination. Wide ranges in diurnal temperature fluctuations were conducive to maximum germination. These ranged from a maximum of 35 degrees with 0/35 C to 5 degrees with 30/35 C. No one constant temperature supported optimum germination.

Nomenclature: Purple loosestrife, Lythrum salicaria L #³ LYTSA.

Additional index words: Wetlands, seed and seedbed ecology, diurnal temperatures.

Abstract: BAY MKH 6562 [flucarbazone-sodium (proposed)], an acetolactate synthase (ALS)-inhibiting herbicide of the sulfonylaminocarbonyltriazolinone family, provides postemergence wild oat control in wheat. Whole-plant dose responses and in vitro ALS sensitivity assays were used to evaluate the magnitude and nature of cross-resistance to BAY MKH 6562 in a wild oat accession (AR1) with metabolism-based resistance to imazamethabenz, an ALS inhibitor of the imidazolinone family. An imazamethabenz-susceptible wild oat accession (AHS2), five BAY MKH 6562-resistant wild oat accessions, AN104, AN205, AN307, AN406, and ASB11, and wheat were also evaluated. AHS2 and AR1 dose responses to BAY MKH 6562 indicated a resistant/susceptible (R/S) herbicide dose required to cause 50% growth reduction (GR₅₀) ratio of 200. Inhibition of ALS from the AHS2 and AR1 wild oat by BAY MKH 6562 was similar, with a concentration of herbicide required to cause 50% inhibition of enzymatic activity (I₅₀) of 0.007 µmoles, indicating that cross-resistance was not due to an altered ALS enzyme. The GR₅₀ for BAY MKH 6562 for the AN104, AN205, AN307, AN406, and ASB11 wild oat accessions was 0.23, 0.07, 0.23, 0.22, and 0.12 kg ai/ha, respectively, and the R/S ratio to the GR₅₀ value for the AHS2 accession was 230, 70, 230, 220, and 120, respectively. Studies on ALS sensitivity to BAY MKH 6562 indicated that the I₅₀ for the AN104, AN205, AN307, AN406, and ASB11 wild oat accessions was 5.2, 0.003, 0.008, 9.8, and 0.007 µmoles, respectively, and the R/S ratio to the I₅₀ value for the AHS2 accession was 759, 0.5, 1, 1,444, and 1, respectively. Of the five wild oat accessions resistant to BAY MKH 6562, accessions AN104 and AN406 had high R/S I₅₀ ratios indicative of an altered target site and accessions AN205, AN307, and AR1 had low R/S I₅₀ ratios indicative of resistance based on metabolic degradation. Hard red spring wheat (2371) was 800-fold tolerant to BAY MKH 6562 and inhibition of ALS from wheat by BAY MKH 6562 was similar to that of ALS from the susceptible accession AHS2.

Nomenclature: BAY MKH 6562, 1H-1,2,4-triazole-carboxamide,4,5-dihydro-3-methoxy-4-methyl-5-oxo-N-[[2-(trifluoromethoxy)phenyl]sulfonyl]-sodium salt; wild oat, Avena fatua L. #³ AVEFA; wheat, Triticum aestivum L. 2371.

Additional index words: Cross-resistance, flucarbazone, metabolism.

Abbreviations: ALS, acetolactate synthase enzyme (EC 4.1.3.18); Cyt P450, cytochrome P-450 monoxygenases; DTT, dithiothreitol; FAD, flavin adenine dinucleotide; GR₅₀, herbicide dose required to cause 50% growth reduction of test plants; I₅₀, concentration of herbicide required to cause 50% inhibition of enzymatic activity; R/S, resistant/susceptible; TPP, thiamine pyrophosphate.

Abstract: Experiments examining burcucumber management in glufosinate-resistant (GR) and imidazolinone-resistant (IMI) corn were conducted in 1997 and 1998 in southeastern Pennsylvania. GR corn was planted in 38- and 76-cm rows, and postemergence (POST) treatments of glufosinate and glufosinate plus atrazine were applied to corn at the V4 or V5 growth stage. In a second study, IMI corn was planted in 76-cm rows, and 15 preemergence (PRE) and POST herbicide programs were evaluated. Herbicide treatments included RPA-201772, CGA 152005, simazine, imazethapyr plus imazapyr, imazamox, chlorimuron plus thifensulfuron, nicosulfuron plus rimsulfuron plus atrazine, CGA 152005 plus primisulfuron, and combinations with atrazine. Burcucumber germinated throughout the growing season, with greatest emergence occurring in early June, gradually decreasing to minimal emergence by mid-July. Glufosinate alone controlled burcucumber 79 to 90% 7 weeks after planting (WAP) regardless of application timing or row spacing. By 10 to 13 WAP, control was 82% or less due to lack of residual control and new burcucumber emergence. Row spacing had little effect on burcucumber emergence or control and appears to have little impact on burcucumber management in corn. In general, PRE herbicide programs were less effective than POST programs, although PRE treatments containing atrazine equaled some POST herbicides. POST-applied chlorimuron plus thifensulfuron, nicosulfuron plus rimsulfuron plus atrazine, and CGA 152005 plus primisulfuron controlled burcucumber greater than 80 and 90% in 1997 and 1998, respectively. Imazethapyr plus imazapyr and imazamox applied POST controlled burcucumber 66% 10 WAP. Adding atrazine to POST herbicide programs did not increase control, with the exception of imazethapyr plus imazapyr.

Nomenclature: Atrazine; chlorimuron; glufosinate; imazamox; imazapyr; imazethapyr; RPA-201772 (proposed name, isoxaflutole), [5-cyclopropyl-4-(2-methyl-sulphonyl-4-trifluoromethyl-benzoyl)isoxozole]; nicosulfuron; primisulfuron; CGA 152005 (proposed name, prosulfuron), {1-(4-methoxy-6-methyl-triazin-2-yl)-3-[2-(3,3,3,-trifluoropropyl)-phenyl-sulfonyl]urea}, rimsulfuron; thifensulfuron; burcucumber, Sicyos angulatus L. #³ SIYAN; corn, Zea mays L.

Additional index words: Cultural control, herbicide-resistant crops, weed emergence.

Abbreviations: EPOST, early postemergence; GR, glufosinate resistant; HRC, herbicide-resistant crops; IMI, imidazolinone resistant; MPOST, midpostemergence; POST, postemergence; PRE, preemergence; WAP, weeks after planting.

Abstract: A greenhouse study was conducted to evaluate the efficacy of imazethapyr at 35 and 53 g ai/ha applied preplant incorporated (PPI) or postemergence (POST) under various soil moisture regimes (13, 19, 25, and 50%) on barnyardgrass and red rice. Response of barnyardgrass and red rice to imazethapyr PPI was affected by soil moisture. With imazethapyr PPI, control of barnyardgrass was reduced at 50% soil moisture compared with other soil moisture regimes, and height of barnyardgrass increased as soil moisture increased from 19 to 50% 2 weeks after treatment (WAT). Barnyardgrass control declined and plant dry weight increased with the increase of soil moisture from 19 to 50% at 3 WAT. Imazethapyr PPI activity on red rice was reduced at 50% compared with other soil moisture regimes, as reflected by decreased control ratings as well as increased plant height and dry weight. Imazethapyr activity on barnyardgrass and red rice was increased at 50% soil moisture when applied POST compared with PPI. Imazethapyr POST activity on barnyardgrass and red rice was generally not affected by the soil moisture regimes or application rates. The results suggested that high soil moisture conditions reduced imazethapyr PPI efficacy on barnyardgrass and red rice. Imazethapyr POST activity seems unaffected by soil moisture conditions and thus may be used to control barnyardgrass and red rice if wet soil conditions are a concern.

Nomenclature: Imazethapyr; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; red rice, Oryza sativa L. # ORYSA; Sesbania exaltata (Raf.) Rydb. Ex A. W. Hill # SEBEX.

Additional index words: Imidazolinone herbicides, rice.

Abbreviations: POST, postemergence; PPI, preplant incorporated; WAT, weeks after treatment.

Abstract: Field studies were conducted at two locations in North Carolina in 1998 and in 1999 to evaluate weed control and peanut response following diclosulam at 27 g ai/ha preemergence (PRE) or flumioxazin at 87 g ai/ha preemergence (PRE) alone and in systems with postemergence (POST) commercial standards. All plots received a preplant incorporated (PPI) treatment of metolachlor at 1,400 g ai/ha. Metolachlor PPI plus diclosulam or flumioxazin PRE controlled common lambsquarters, common ragweed, entireleaf morningglory, large crabgrass, and yellow nutsedge as well as or better than metolachlor PPI followed by (fb) acifluorfen plus bentazon POST or paraquat plus bentazon early postemergence fb acifluorfen plus bentazon POST. Metolachlor PPI plus diclosulam PRE or flumioxazin PRE controlled ivyleaf morningglory as well as metolachlor PPI fb acifluorfen plus bentazon POST. Metolachlor PPI plus flumioxazin PRE controlled common lambsquarters better than metolachlor PPI plus diclosulam PRE while diclosulam PRE controlled common ragweed better. There was no difference in common lambsquarters control between flumioxazin and diclosulam PRE when POST herbicides were used. There was only one difference in peanut yield and net returns between metolachlor PPI fb either diclosulam or flumioxazin PRE when POST herbicides were used.

Nomenclature: Acifluorfen; bentazon; diclosulam; flumioxazin; metolachlor; paraquat; 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; large crabgrass, Digitaria sanguinalis L. Scop. # DIGSA; yellow nutsedge, Cyperus esculentus L. # CYPES; peanut, Arachis hypogaea L., ‘NC 7’, ‘NC 10C’.

Additional index words: Economic analysis, acifluorfen, bentazon, paraquat.

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

Abstract: BAY MKH 6561, a sulfonylaminocarbonyl-triazolinone herbicide for postemergence control of annual grasses and selected broadleaf weeds in wheat, was evaluated for weed control and rotational crop (barley, pea, lentil, and mustard) injury in the Pacific Northwest. BAY MKH 6561 was applied postemergence in winter wheat at 22, 45, and 90 g ai/ha during fall 1997 and spring 1998 near Moscow, ID, Pendleton, OR, and Wilcox, WA, to determine its effect on barley, pea, lentil, and mustard planted during spring 1999. At Pendleton, BAY MKH 6561 reduced barley height 6% and grain yield 11%, when applied in the spring at 90 g/ha, and visibly injured mustard 4 to 19% when applied at 45 or 90 g/ha. All BAY MKH 6561 treatments reduced mustard seed yield 47 to 54% at Moscow and 38 to 48% at Wilcox. Pea and lentil seed yields were not affected by herbicide treatments at all locations, whereas barley was not affected at Moscow and Wilcox. In growth chamber soil bioassay experiments, fall-applied BAY MKH 6561 dissipated 10 to 48% faster at Moscow compared to Pendleton, and the predicted half-life ranged from about 68 (Moscow) to 79 d (Pendleton). Dissipation of spring-applied BAY MKH 6561 at 45 and 90 g/ha was 17 to 21% slower at Moscow than Wilcox, and the predicted half-life ranged from 60 (Wilcox) to 69 d (Moscow).

Nomenclature: BAY MKH 6561, methyl 2-({[(4-methyl-5-oxo-3-propoxy-4,5-dihydro-1H-1,2,4-triazol-1- l)carbonyl]amino}sulfonyl)benzoate sodium salt; barley, Hordeum vulgare L. ‘Baronesse’; lentil, Lens culinaris Medic. ‘Pardina’; mustard, Sinapsis alba L. ‘Tilney’; pea, Pisum sativum L. ‘Columbia’; winter wheat, Triticum aestivum L. ‘Cashup’, ‘Madsen’, ‘Stephens’.

Additional index words: Corn root bioassay, dissipation, MON 37500, pH, precipitation, soil temperature, soil residues, yield.

Abbreviations: DAT, days after treatment; OM, organic matter; PNW, Pacific Northwest; POST, postemergence; PPI, preplant incorporated.

Abstract: Field studies were conducted with a biocontrol agent, Pseudomonas syringae pv. tagetis, to determine the optimal application parameters for controlling woollyleaf bursage, a pernicious perennial weed on the Texas Southern High Plains. Parameters investigated were bacterial concentration, time, season, and frequency of application. Pseudomonas syringae pv. tagetis concentration ranging from 10⁴ to 10⁸ colony forming units (CFU)/ml produced similar incidence of disease on woollyleaf bursage. Weekly, biweekly, and triweekly applications were found to be equally effective. Optimal time for application of P. syringae pv. tagetis was at midday. A single application in April, May, or June resulted in higher incidence of disease for 5 wk than the noninoculated plots, whereas single applications in July and August were not consistently different from the noninoculated plots. Weed density was negatively correlated with disease incidence for April, July, and August applications, particularly when correlations were based on disease incidence from 1 to 4 wk prior to weed density measurement. Weed densities during 1997 were lower at the end of the year when bacteria applications were made in April, May, or June, as opposed to July or August, or plots were not inoculated. In 1998, weed density was lower when bacteria applications were made in April as opposed to May or June. These investigations indicate that P. syringae pv. tagetis does infect woollyleaf bursage on the Texas southern High Plains.

Nomenclature: Woollyleaf bursage; Ambrosia grayi (A. Nels.) Shinners #³ AMBGR; Pseudomonas syringae pv. tagetis; biological control.

Additional index words: Biological control agent, biopesticide.

Abbreviations: AT, application time; B, bacteria; CFU, colony forming units; EP, evaluation period; IOD, incidence of disease.

Abstract: Several herbicides were evaluated as seed-applied treatments to determine the feasibility of controlling cheat by applying herbicide directly onto the cheat seeds during the wheat harvesting process and returning the treated seeds to the field. Seed-applied trifluralin reduced cheat emergence 80% in exploratory evaluations. In herbicide-seed mixing time and spray volume experiments, short mixing times were adequate, and spray volumes from 113 to 227 ml/kg seeds did not affect results. Herbicides applied with a sprayer-equipped auger reduced cheat emergence >90% and were as effective as herbicides applied with a rotary drum seed-treater. Increasing spray volume increased the efficacy of auger-applied treatments. Adjuvants did not improve the efficacy of seed-applied trifluralin.

Nomenclature: Trifluralin; cheat, Bromus secalinus L. #³ BROSE; wheat, Triticum aestivum L.

Additional index words: Seed treatments, grain harvesting.

Abstract: Metham has been reported as an acceptable weed control alternative to methyl bromide. However, modified application equipment is required to allow its effective use in crops that are grown on polyethylene-covered seedbeds. A power tiller was modified using commonly available materials to apply metham in a 61-cm band and shape seedbeds for laying a black polyethylene tarp. Additional modification allowed the implement to be used in strip tillage and conventional tillage systems. Metham applied using this modified power tiller effectively controlled many species of weeds, including yellow nutsedge, in transplanted watermelon.

Nomenclature: Metham; yellow nutsedge, Cyperus esculentus L. CYPES; watermelon, Citrullus lanatus (Thunb.) Mansf.

Additional index words: Alternatives to methyl bromide, fumigation.

Abbreviations: PPI, preplant incorporated; PRE, preemergence; PTO, power take-off.