Abstract: Studies were conducted in 1996 and 1997 to determine the effect of irrigation systems used to produce transplants on subsequent tolerance of banana and bell pepper (Capsicum annuum) transplants to field-applied herbicides. The irrigation systems were overhead (OH), ebb and flood (EF), and float (F). At 2 and 4 wk, banana and bell pepper injury was greatest from clomazone (1.1 kg/ha) treatments. Banana and bell pepper yield were not influenced by herbicide treatment. Although crop injury was greater in 1997, there was no herbicide or irrigation system interaction with year. OH and EF irrigated banana pepper and OH irrigated bell pepper produced the greatest total yield over two harvests, whereas F irrigated pepper yielded the least. F irrigated bell pepper plants had reduced early total yield and fancy fruits relative to other irrigation treatments. F irrigated plants yielded 32 and 22% less than OH irrigated plants in banana and bell pepper, respectively. Stand counts at 3 wk after planting (WAP) show that, unlike OH and EF treatments, F treatments lost 240 to 330 plants/ha. Differences in stand among treatments were greater in 1997 than 1996. Based on our study, the OH irrigated system appears to be the best system for producing bell pepper transplants with the greatest total yield. With banana pepper, both OH and EF irrigated systems appear to produce banana pepper transplants with the greatest total yield. Also, pepper transplant tolerance to herbicides is not affected by the irrigation system used to produce transplants.

Nomenclature: Clomazone, 2-[(2-chlorophenyl)methyl]-4,4-dimethyl-3-isoxazolidinone; napropamide, N,N-diethyl-2-(1-napthalenyloxy)propanamide; trifluralin, 2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine; pepper, Capsicum annuum L.

Additional index words: Overhead irrigation, float irrigation, ebb and flow irrigation, bell pepper, banana pepper, herbicide tolerance.

Abbreviations: DAP, days after planting; EC, emulsifiable concentrate; EF, ebb and flood; F, float; ME, microencapsulated; OH, overhead; PPI, preplant incorporated; PRE, premergence; WAP, weeks after planting.

Abstract: Combinations of 0 to 1,120 g ae/ha 2,4-D plus 0 to 42 g ai/ha metsulfuron were evaluated in both field and greenhouse experiments. Addition of metsulfuron to 2,4-D increased Virginia buttonweed (Diodia virginiana) fresh weight reduction in the greenhouse compared with 2,4-D alone, but reduction in fresh weight was not different from 32 g/ha or more of metsulfuron applied alone. In field experiments 5 wk after treatment (WAT), combinations of metsulfuron and 2,4-D did not control Virginia buttonweed greater than 32 g/ha or more of metsulfuron alone. No synergism for the combinations was observed. Field experiments conducted from 1991 to 1993 evaluated three-way combinations of herbicides for Virginia buttonweed control. Treatments included: 2,4-D plus mecoprop plus dicamba (five herbicide premixes), 2,4-D plus dichlorprop plus dicamba, 2,4-D plus MCPA plus dichlorprop, mecoprop plus MCPA plus dichlorprop, or 2,4-D plus mecoprop plus dichlorprop. Combinations containing at least 688 g/ha 2,4-D provided the most consistent Virginia buttonweed control 2 WAT. By 7 WAT, control was no more than 60% for any treatment. A separate experiment evaluated the effects of repeated applications of two- or three-way herbicide mixtures applied at least 5 wk apart when ground cover regrowth was 25%. Treatments included: 2,4-D plus dichlorprop plus dicamba ester, 2,4-D plus mecoprop plus dicamba amine, 2,4-D plus dichlorprop amine, or 2,4-D plus dichlorprop ester. Ground cover 1 yr following application of sequential treatments was 35% or less compared to 65% in the nontreated control. Following 2 yr of herbicide application, ground cover in the treated plots was 28% or less.

Nomenclature: 2,4-D, (2,4-dichlorophenoxy)acetic acid; dicamba, 3,6-dichloro-2-methoxybenzoic acid; dichlorprop, (±)-2-(2,4-dichlorophenoxy)propanoic acid; MCPA, (4-chloro-2-methylphenoxy)acetic acid; mecoprop, (±)-2-(4-chloro-2-methylphenoxy)propanoic acid; metsulfuron, 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]benzoic acid; Virginia buttonweed, Diodia virginiana (L.) #³ DIQVI.

Additional index words: 2,4-D, dicamba, dichlorprop, mecoprop, MCPA, metsulfuron, DIQVI.

Abbreviations: DMA, dimethylamine; IOE, isooctyl ester; WAT, weeks after treatment.

Abstract: Tropical soda apple (TSA) was evaluated for response to 28 herbicide treatments. Treatments containing picloram or triclopyr controlled eight-leaf, 16-leaf, and 1-yr-old TSA greater than 90% 8 wk after treatment (WAT). Control of 1-yr-old TSA did not increase 8 WAT when triclopyr was mixed in diesel fuel rather than water. In greenhouse additive interference experiments, populations of 0, 1, 2, 4, 8, 16, 32, and 64 TSA plants/700 cm² of tall fescue had no effect on tall fescue height. TSA height was affected by TSA population, and intraspecific TSA competition was expressed as etiolation at densities greater than 4 plants/700 cm². Averaged over five periods of competition, predicted yield losses of tall fescue were 14, 16, 29, and 31% and 1, 11, 19, and 23% for 8, 16, 32, and 64 TSA plants/700 cm², respectively, for each experiment. Differences in tall fescue dry matter response between experiments were attributed to ambient temperature. Dry matter per individual TSA plant decreased from 1.7 to 0.3 g as TSA density increased from 1 to 64 plants/700 cm². Percent canopy coverage of TSA relative to an area of 700-cm² surface increased proportionally as tall fescue coverage decreased. After 10 wk of competition, TSA monopolized the canopy with coverage of 92 and 94%; tall fescue coverage was limited to only 7 and 5% in experiments I and II, respectively.

Nomenclature: Picloram, 4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid; triclopyr, [(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid; tropical soda apple, Solanum viarum Dunal #³ SOLVI; tall fescue, Festuca arundinacea Schreb. # FESAR ‘Kentucky 31.’

Additional index words: Additive competitive design, chemical control, herbicides, weed density, Solanum khasianum C. B. Clarke var. chatterjeeanum Sengupta, SOLVI.

Abbreviations: TSA, tropical soda apple; WAT, weeks after treatment; WATP, weeks after transplanting.

Abstract: Seeds of giant foxtail (Setaria faberi, 4,000 seeds/m²) or velvetleaf (Abutilon theophrasti, 3,000 seeds/m²) were added to the seed bank to determine the effect of increases in weed density on herbicide efficacy in corn (Zea mays). A herbicide program consisting of SAN 582 applied preemergence followed by a postemergence application of dicamba plus atrazine was evaluated at four levels (0.0, 0.3, 0.7 and 1.0 times the label rates). At a site with low initial weed densities, the addition of velvetleaf or giant foxtail seed to the seed bank did not influence herbicide efficacy at the 1.0× rate at 9 wk after planting (WAP). Giant foxtail densities were greater 9 WAP in augmented areas than in the native seed bank plots at both the 0.3× and 0.7× rates, whereas with velvetleaf, higher densities in augmented plots were seen only at the 0.3× rate. In areas with high native weed densities, addition of seed of either species resulted in an increase in final weed densities at all herbicide rates.

Nomenclature: Atrazine, 6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine; dicamba, potassium salt of 3,6-dichloro-2-methoxybenzoic acid; SAN 582 (proposed name, dimethenamid), 2-chloro-N-(2,4 dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl)acetamide; giant foxtail, Setaria faberi Herm. #³ SETFA; velvetleaf, Abutilon theophrasti Medic. # ABUTH; corn, Zea mays L.

Additional index words: Weed seed bank, ABUTH, SETFA.

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

Abstract: Kochia (Kochia scoparia) control dropped from about 90% to less than 20% after three consecutive annual applications of acetolactate synthase (ALS)-inhibiting herbicides in several northeastern South Dakota fields. Field experiments were conducted to evaluate control of kochia resistant to ALS-inhibiting herbicides using combinations of herbicides applied postemergence (POST) in wheat (Triticum aestivum) and using herbicides applied preemergence (PRE), POST, and PRE plus POST in soybean (Glycine max). Thifensulfuron plus tribenuron did not control kochia in wheat (> 600 kochia plants/m² at harvest) and wheat yield was similar to yield of the untreated control. Dicamba plus 2,4-D (in 1996) and bromoxynil plus MCPA (in 1996 and 1997) controlled kochia and increased yields by 15% or more. Kochia was sparse (less than 1 plant/m²) in soybean plots, but grass weeds were prevalent. PRE plus POST or POST herbicide combinations that included ALS-inhibiting herbicides controlled grasses, and soybean yields were as much as 20% greater than yields with combinations that did not contain ALS-inhibiting herbicides. Adding ALS-inhibiting herbicides to wheat herbicide combinations decreased profitability because treatment costs increased while yields did not. In contrast, adding ALS-inhibiting herbicides to soybean treatments increased profitability due to better grass control, resulting in increased yield and better return.

Nomenclature: Bromoxynil, 3,5-dibromo-4-hydroxybenzonitrile; 2,4-D, (2,4-dichlorophenoxy)acetic acid; dicamba, 3,6-dichloro-2-methoxybenzoic acid; MCPA, (4-chloro-2-methylphenoxy) acetic acid; thifensulfuron, methyl 3-[[[[(4-methoxy-6-methyl-1,3,5,-triazin-2-yl)amino]carbonyl]amino]sulfonyl]-2-thiophenecarboxylic acid; tribenuron, 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)methylamino]bonyl] amino]sulfonyl]benzoic acid; kochia, Kochia scoparia (L.) Schrad. #³ KCHSC; soybean, Glycine max (L.) Merr.; wheat, Triticum aestivum L.

Additional index words: Acifluorfen, ALS inhibitor resistance, ammonium sulfate, bentazon, bromoxynil, sulfonylurea herbicides, 2,4-D, dicamba, imazethapyr, lactofen, MCPA, metribuzin, pendimethalin, thifensulfuron, tribenuron, KCHSC.

Abbreviations: ALS, acetolactate synthase (EC4.1.3.18); COC, crop oil concentrate; DAT, days after treatment; NIS, nonionic surfactant; OM, organic matter; POST, postemergence; PRE preemergence.

Abstract: Field experiments were conducted in the Mediterranean conditions of the Ebro Valley, Spain during 1995 to 1996 and 1996 to 1997 to determine the effects of imazamethabenz and PP-604 on selected durum wheat Triticum turgidum var. durum cultivars grown under irrigation. Herbicides were applied at their recommended rates of 600 g ai/ha for imazamethabenz and 375 g ai/ha for PP-604 and at twice these rates. Herbicide treatment reduced the average wheat height in three of four trials. Wheat treated with imazamethabenz was almost 2 cm shorter than wheat treated with PP-604 and almost 3 cm shorter than untreated control plants. However, durum wheat yields were not significantly reduced by treatment with imazamethabenz or PP-604 in any of the four trials, and no visible plant injury was observed. These results differ from reported yield reductions under Mediterranean dryland conditions, suggesting that durum wheat can be affected by imazamethabenz and PP-604 but irrigation enhances recovery from herbicide injury.

Nomenclature: Imazamethabenz, (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1-H-imidazol-2-yl]-4(and 5)-methylbenzoic acid (3:2); PP-604, 2-[1-ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethyl-phenyl)cyclohex-2-enone; durum wheat, Triticum turgidum L. var. durum.

Additional index words: Herbicide rates, irrigation.

Abstract: Herbicides registered for lima bean (Phaseolus lunatus L.) do not consistently control many troublesome weeds. Some herbicides registered for soybean (Glycine max) will control these weeds, but tolerance to lima bean is not known. Two field and two greenhouse studies were conducted to evaluate recently registered soybean herbicides for lima bean tolerance. Field studies were conducted in Delaware from 1996 to 1998, and in North Carolina during 1997 and 1998. The first field study evaluated the preemergence (PRE) herbicides cloransulam at 0.01, 0.02, 0.03, and 0.04 kg ai/ha; flumetsulam at 0.04, 0.05, 0.06, and 0.07 plus metolachlor at 1.3, 1.6, 1.8, and 2.1 kg ai/ha; sulfentrazone at 0.1, 0.15, 0.2, and 0.25 kg ai/ha; lactofen at 0.2 and 0.25 kg ai/ha; and the commercial standard treatment of imazethapyr plus metolachlor at 0.05 and 1.7 kg ai/ha, respectively. Lima bean injury 5 to 8 wk after emergence was lowest for imazethapyr plus metolachlor (standard treatment) and all four rates of cloransulam. Crop injury with flumetsulam plus metolachlor ranged from 0 to 18% and sulfentrazone ranged from 3 to 75% depending on location and rate. Lactofen treatments caused unacceptable lima bean injury. Yield in plots treated with cloransulam were consistently greater than in the plots treated with other herbicides. The second field study examined the postemergence (POST) herbicides cloransulam (0.013 or 0.02 kg ai/ha), bentazon (1.1 kg ai/ha), imazethapyr (0.035 or 0.053 kg ai/ha), and imazamox (0.018 or 0.036 kg ai/ha), applied when the crop was at the first trifoliolate stage. Cloransulam caused 0 to 13% crop injury and imazamox caused 3 to 25% injury depending on rate and location. In greenhouse studies, no differences were observed among eight common processing lima bean cultivars in tolerance to sulfentrazone applied PRE or to cloransulam, imazamox, imazethapyr, or bentazon applied POST.

Nomenclature: Bentazon, 3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide; cloransulam, 3-chloro-2-[[(5-ethoxy-7-fluoro[1,2,4]triazolo[1,5-c]pyrimidine-2yl)sulfonyl]amino]benzoic acid; flumetsulam, N-(2,6-difluorophenyl)-5-methyl[1,2,4]triazolo[1,5-α]pyrimidine-2-sulfonamide; imazamox, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-(methoxymethyl)-3-pyridinecarboxylic acid; imazethapyr, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid; lactofen, (±)-2-ethoxy-1-methyl-2-oxoethyl-5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate; metolachlor, 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide; sulfentrazone, N-[2,4-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl]phenyl]methanesulfonamide; lima bean, Phaseolus lunatus L., ‘M-15’, ‘F1072’, ‘M-408’, ‘Packers’, ‘Concentrated Fordhook’, ‘8-78’, ‘Eastland’; soybean, Glycine max (L.) Merr.

Additional index words: Crop tolerance; varietal sensitivity.

Abbreviations: COC, crop oil concentrate; NIS, nonionic surfactant; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.

Abstract: Field studies were conducted to assess weed control and potato (Solanum tuberosum) tolerance to ethalfluralin. Ethalfluralin applied preemergence (PRE) alone at 1.05 kg ai/ha generally did not control weeds adequately. However, ethalfluralin at 1.05 kg/ha combined with either metribuzin at 0.28 kg ai/ha or rimsulfuron at 0.018 kg ai/ha controlled common lambsquarters (Chenopodium album), redroot pigweed (Amaranthus retroflexus), and green foxtail (Setaria viridis) ≥ 98%, which was similar to control observed with several currently registered herbicide mixtures. Volunteer oat (Avena sativa) control with either ethalfluralin at 1.05 kg/ha plus EPTC at 3.4 kg ai/ha or ethalfluralin plus metribuzin was equal to registered two-way mixtures. Ethalfluralin plus metribuzin did not adequately control hairy nightshade (Solanum sarrachoides), but ethalfluralin mixtures with either rimsulfuron or EPTC controlled hairy nightshade equal to or better than the registered two-way mixtures evaluated. A sequential application of ethalfluralin PRE followed by rimsulfuron or rimsulfuron plus metribuzin postemergence (POST) did not improve hairy nightshade control compared to ethalfluralin plus rimsulfuron applied PRE. Potato tolerance to herbicide treatments applied PRE or POST to potato was evaluated in weed-free studies. Ethalfluralin alone or with metribuzin was compared to mixtures of metribuzin with either pendimethalin or EPTC. Initial visual injury with ethalfluralin PRE was ≤ 4% both years. In 1996, initial injury with ethalfluralin POST was ≤ 4% and U.S. No. 1 and total tuber yields were not affected by herbicide treatment or application timing. However in 1997, initial injury from POST ethalfluralin at 1.05 or 2.1 kg/ha was 2 or 8% and increased to 9 or 17%, respectively, at potato row closure. Averaged over all herbicide treatments, POST applications reduced U.S. No. 1 and total tuber yield 7% relative to PRE applications in 1997.

Nomenclature: EPTC, S-ethyl dipropyl carbamothioate; ethalfluralin, N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl)benzenamine; metribuzin, 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one; pendimethalin, N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine; rimsulfuron, N-[[(4,6-dimethoxy-2-pyrimidinyl)amino] carbonyl]-3-(ethylsulfonyl)-2-pyridinesulfonamide; common lambsquarters, Chenopodium album L. #³ CHEAL; green foxtail, Setaria viridis (L.) Beauv. # SETVI; hairy nightshade, Solanum sarrachoides Sendter # SOLSA; redroot pigweed, Amaranthus retroflexus L. # AMARE; volunteer oat, Avena sativa L. # AVESA; potato, Solanum tuberosum L. ‘Russet Burbank.’

Additional index words: Injury, tolerance, AMARE, AVESA, CHEAL, SETVI, SOLSA.

Abbreviations: PNW, Pacific Northwest; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.

Abstract: Field studies were conducted in 1997 and 1998 to evaluate weed control and soybean (Glycine max) yield with cloransulam and diclosulam. Cloransulam at 35 g/ha applied preplant incorporated (PPI) and preemergence (PRE) controlled at least 91% of hyssop spurge (Euphorbia hyssopifolia) and prickly sida (Sida spinosa) and at least 82% of entireleaf morningglory (Ipomoea hederacea var. integriuscula) and pitted morningglory (Ipomoea lacunosa) at 7 wk after planting. Control of these species with cloransulam was not affected by method of soil application. Control of prickly sida with cloransulam PPI or PRE was better than with cloransulam postemergence (POST) at 18 g/ha. Soybean yields were similar with cloransulam PPI (2,880 kg/ha) or PRE (3,110 kg/ha) and were comparable to imazaquin PRE at 140 g/ha (3,080 kg/ha). Weed control and soybean yields with cloransulam POST were similar to that with chlorimuron POST at 11 g/ha. SAN 582 plus cloransulam PRE followed by cloransulam POST provided the highest soybean yield (3,450 kg/ha). Diclosulam PPI or PRE provided similar levels of control of hyssop spurge, Ipomoea morningglories, and prickly sida. Overall, control of these species with diclosulam PPI or PRE was similar to that obtained with sulfentrazone plus chlorimuron PRE. Soybean yields (≥ 3,290 kg/ha) were similar regardless of method of diclosulam application, and yields were equivalent to that of sulfentrazone plus chlorimuron PRE (3,270 kg/ha).

Nomenclature: Chlorimuron, ethyl 2-[[[[4-chloro-6-methoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]benzoate; cloransulam, 3-chloro-2-[[(5-ethoxy-7-fluoro[1,2,4]triazolo[1,5-c]pyrimidin-2yl)sulfonyl]amino]benzoic acid, methyl ester; diclosulam, N-(2,6-dichlorophenyl)-5-ethoxy-7-fluoro[1,2,4]triazolo-[1,5-c]pyrimidine-2-sulfonamide; SAN 582 (proposed common name, dimethenamid), 2-chloro-N-[(1-methyl-2-methoxy)ethyl]-N-(2,4-dimethyl-thien-3-yl)acetamide; imazaquin, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imadazol-2-yl]-3-quinolinecarboxylic acid; sulfentrazone, N-[2,4-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl]-phenyl]methanesulfonamide; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray #³ IPOHG; hyssop spurge, Euphorbia hyssopifolia L. # EPHHS; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; soybean, Glycine max (L.) Merr. ‘DP 3588.’

Additional index words: Metolachlor, SAN 582, EPHHS, IPOHG, IPOLA, PANRA, SIDSP.

Abbreviations: fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; WAP, weeks after planting.

Abstract: Dose–response curves for acetochlor with and without timely rotary hoeing (two passes) were derived for corn (Zea mays) fields over 2 yr. The fields were dominated by green foxtail (Setaria viridis), which constituted 73 to 86% of the weed vegetation, but also contained minor populations of common lambsquarters (Chenopodium album), Pennsylvania smartweed (Polygonum pensylvanicum), and redroot pigweed (Amaranthus retroflexus). In the absence of herbicide, rotary hoeing achieved about 50% weed control. In the absence of rotary hoeing, weed control averaged > 90% at the full label rate of acetochlor (3 kg ai/ha on clay loam soil). With two timely rotary hoeings, however, this same level of control was achieved with only 1 kg/ha acetochlor. Given the suite of weed species present in these experiments, timely rotary hoeing substituted for 67% of the label rate of acetochlor. Timeliness of rotary hoeing operations also provided consistency of results from one year to the next.

Nomenclature: Acetochlor, 2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide; common lambsquarters, Chenopodium album L. #³ CHEAL; green foxtail, Setaria viridis (L.) Beauv. # SETVI; Pennsylvania smartweed, Polygonum pensylvanicum (L.) # POLPY; redroot pigweed, Amaranthus retroflexus L.; corn, Zea mays L.

Additional index words: Integrated weed management, interrow cultivation, preemergence herbicide, seedling emergence, timeliness.

Abstract: A 2-yr study was conducted near Mead, NE, to determine the interaction of six corn (Zea mays) hybrids having different heights and leaf angles and four herbicide rates on velvetleaf (Abutilon theophrasti) and green foxtail (Setaria viridis) biomass rating and seed production. Corn hybrid grain yields averaged over herbicide rates differed by up to 1,100 kg/ha in 1993 and 3,000 kg/ha in 1994, yet similar grain yield reductions occurred for all hybrids as herbicide rate decreased. Corn hybrids differed in suppression of weed growth and seed production, but suppression differences among hybrids were not consistent across years. Plots with the very tall, erect-leaf hybrid had 7.4 velvetleaf plants/m², whereas other hybrids had 8.6 to 10.1 plants/m². Plots with the very tall, erect-leaf hybrid also produced the lowest quantity of velvetleaf seeds of 23,100 seeds/m² versus 25,100 to 30,700 seeds/m² for plots with other hybrids. Erect-leaf hybrids suppressed weeds more effectively than horizontal-leaf hybrids. Corn hybrids had less effect on early- Fand late-season weed densities and biomass ratings and on seed production than herbicide application. Selection among current corn hybrids as a tool in integrated weed management will have a small or inconsistent influence on weed suppression.

Nomenclature: Alachlor, 2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide; atrazine, 6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine; green foxtail, Setaria viridis #³ SETVI; velvetleaf, Abutilon theophrasti Medik. # ABUTH; corn, Zea mays L.

Additional index words: Grain yield, herbicide, integrated weed control, reduced input, weed seed production, weed competition, ABUTH, SETVI.

Abbreviations: GDD, growing degree days; IFS, Illinois Foundation Seed.

Abstract: Experiments were conducted to investigate the possibility that rhizobacterial nodulation in legumes influences parasitic attack by broomrape. Small broomrape (Orobanche minor), which is commonly associated with swellings of the host root, was studied on red clover (Trifolium pratense) in the presence or absence of Rhizobium leguminosarum bv. trifolii inoculum and was compared to Egyptian broomrape (Orobanche aegyptiaca), which is not associated with host root swellings. Small broomrape showed greater percent seed germination and formed a greater number of attachments on red clover inoculated with rhizobacteria in comparison with noninoculated plants. In contrast, inoculum did not appear to enhance Egyptian broomrape seed germination or the number of its attachments on the host roots compared to noninoculated controls. In aseptic culture, the addition of Rhizobium increased the success of small broomrape in parasitizing clover but was not essential for parasitization. No rhizobacteria were detected in cultures derived from tubercles under septic or aseptic conditions. Morphological observations of small broomrape attachments on red clover suggest that parasitic attachments were not situated over the bacterial nodules but may involve parasite-induced protrusion of host plant root cortex. These results indicate that although rhizobacterial nodulation is not required for parasitization, the presence of nodules facilitates small broomrape germination and attachment to red clover.

Nomenclature: Egyptian broomrape, Orobanche aegyptiaca Pers. #³ ORAAE; small broomrape, Orobanche minor Sm. # ORAMI; red clover, Trifolium pratense L. # TRFPR; inoculum culture, Rhizobium leguminosarum bv. trifolii.

Additional index words: Parasitic weeds, nodulation, rhizobacteria, ORAAE, ORAMI.

Abbreviations: DAT, days after transplanting; GFFP, glass fiber filter paper; PE, polyethylene; YMB, yeast–mannitol broth.

Abstract: A field study was conducted in 1992 and 1993 to identify the spray volume and droplet size combinations to optimize control of common cocklebur (Xanthium strumarium) from acifluorfen by maximizing target deposition. In many instances, acifluorfen controlled common cocklebur better using either small (250 µm) or large (450 µm) spray droplets when applied at the lower carrier volumes of either 56 or 112 L/ha. When sprays were applied at 169 L/ha, there was little difference in control between droplet sizes. Deposition of acifluorfen was determined in 1993. Stepwise regression indicated that acifluorfen deposition amount is less important than environmental conditions for common cocklebur control. Relative humidity was the most significant variable for determining common cocklebur control with acifluorfen.

Nomenclature: Acifluorfen, 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid; common cocklebur, Xanthium strumarium L. #³ XANST.

Additional index words: Acifluorfen, deposition, efficacy, XANST.

Abbreviations: VMD, volume median diameter; WAT, weeks after treatment.

Abstract: A field study was conducted to determine the combined effects of row spacing, plant density, and herbicides on weed management and dry bean (Phaseolus vulgaris) yield. In weed-free dry bean, a reduction in row spacing from 69 to 23 cm increased yield by 19% and an increase in density from 20 to 50 plants/m² increased yield by 17%. In the presence of weeds, narrow rows and high plant densities increased dry bean yield, but without herbicides, yields remained low. However, when combined with herbicides, narrow-row and high-density production practices resulted in better weed control and higher dry bean yield than that attained in a wide-row and low-density production system. Herbicide combinations, often at reduced rates, controlled weeds as well or better than the full rate of any individual herbicide. Ethalfluralin applied preplant incorporated followed by reduced rates of imazethapyr or bentazon postemergence (POST) consistently controlled weeds. Imazamox exhibited the potential to provide a total POST weed control option in dry bean production. Information gained in this study will be used to develop improved weed management programs appropriate for either wide- or narrow-row dry bean production systems.

Nomenclature: Bentazon, 3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2- dioxide; ethalfluralin, N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl)benzenamine; imazamox, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-(methoxymethyl)-3-pyridinecarboxylic acid; imazethapyr, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid; small red dry bean, Phaseolus vulgaris L. ‘Ember.’

Additional index words: Integrated weed management, plant density, row spacing, ECHCG, POLCO, POLSC, SETVI, SOLSA.

Abbreviations: PAR, photosynthetically active radiation; POST, postemergence; PPI, preplant incorporated.

Abstract: The economic threshold is a concept strongly embedded within the weed management literature. There are some theoretical concerns with applying a static approach such as the economic threshold to weed management decision making. An improvement is to adopt a population management approach where the intertemporal effects of decisions are taken into account. The focus should be on managing weed populations through time rather than minimizing the yield effect of weeds in a single season or year. Rather than viewing weeds as an annual production problem, the weed seed bank can be considered a renewable resource stock, and the management goal is to deplete this resource stock through time. The principles of natural resource economics illustrate that including the intertemporal effects of weed control will, for a given size of a seed bank, result in a greater level of weed control and a higher economic benefit than if control decisions were based solely on the current period effects. A dynamic economic model was developed of an extensive Australian spring wheat (Triticum aestivum) cropping system to test these principles using wild oat (Avena fatua and A. ludoviciana) as an example. The model was solved for a 20-yr time horizon for a population management approach and the traditional static economic threshold. The economic benefits from a population management approach were significantly greater than those generated by the economic threshold, and the final seed bank was considerably lower. This result suggests that a paradigm shift from thresholds to longer term population management is warranted.

Nomenclature: Diclofop-methyl, (±)-2-[4-(2,4-dichlorophenoxy)phenoxy]propanoic acid; flamprop-methyl, N-benzoyl-N-(3-chloro-4-fluorophenyl)-dl-alanine; glyphosate, N-(phosphonomethyl)glycine; wild oat, Avena fatua L. AVEFA, winter wild oat Avena ludoviciana Dur. AVELU; wheat Triticum aestivum L.

Additional index words: Dynamic programming, economic optimum thresholds, optimum dose rate, economics, net present value, modeling, integrated weed management, rigid ryegrass, annual ryegrass, Lolium rigidum.

Abbreviations: DP, dynamic programming; EOT, economic optimum threshold; ET, economic threshold; IWM, integrated weed management; NPV, net present value; ODR, optimum dose rate.

Abstract: Experiments were conducted in subirrigated and upland Colorado pastures to compare herbicides applied alone in fall to the same herbicides preceded by one, two, or three mowings. Picloram controlled Canada thistle (Cirsium arvense) well at both sites, and in general, mowing did not improve its performance. Picloram at 560 g ai/ha and picloram plus 2,4-D at 280 plus 1,120 g ai/ha were the lowest rates that eliminated Canada thistle. Mowing did not improve chlorsulfuron performance at either site, but chlorsulfuron eliminated Canada thistle at the subirrigated site. Dicamba controlled 97% of Canada thistle at the subirrigated site, and mowing did not improve its performance; two or three mowings before spraying dicamba at the upland site improved performance, but 37% remained uncontrolled. Control from the reduced rate and the two lowest recommended rates of clopyralid plus 2,4-D was improved by two or three prior mowings at the subirrigated site, but only the highest rate benefited from two or three mowings at the upland site. Mowing alone three times per year for 2 yr controlled 85% of Canada thistle at the subirrigated site, but failed to control it at the upland site. Variability in results between experiments likely was due to a high water table at the subirrigated site, which may have restricted Canada thistle root growth and possibly made it easier to control. Inconsistent results prohibit concluding that mowing before spraying will consistently improve Canada thistle control, and such a treatment combination should not be commonly recommended.

Nomenclature: Clopyralid, 3,6-dichloro-2-pyridinecarboxylic acid; chlorsulfuron, 2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide; dicamba, 3,6-dichloro-2-methoxybenzoic acid; picloram, 4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid; 2,4-D, (2,4-dichlorophenoxy)acetic acid; Canada thistle, Cirsium arvense (L.) Scop. #³ CIRAR.

Additional index words: Integrated management, noncrop weed management, CIRAR.

Abstract: Field studies were conducted in 1996 and 1997 to determine postemergence control of purple (Cyperus rotundus) and yellow nutsedge (Cyperus esculentus) by single and sequential applications of bentazon, halosulfuron, and sulfentrazone; sequential applications of MSMA; and single applications of imazaquin and imazaquin plus MSMA. Sequential applications of halosulfuron at 70 g ai/ha controlled purple nutsedge more effectively at 10 wk after initial application (WAI) than all other herbicides. Single applications of imazaquin (0.56 kg ai/ha) or imazaquin plus monosodium salt of methylarsonic acid (MSMA, 2.24 kg ai/ha) controlled purple nutsedge adequately 6 WAI (78 and 90%, respectively) but not 18 WAI. Single applications of either halosulfuron (70 g/ha) or imazaquin plus MSMA or sequential applications of either bentazon (1.12 kg ai/ha), MSMA (2.8 kg/ha), or halosulfuron controlled yellow nutsedge greater than 80% by the end of the season in 1996 when nutsedge was in bermudagrass (Cynodon dactylon L.). However, in absence of bermudagrass in 1997, only sulfentrazone or the halosulfuron sequential treatments controlled yellow nutsedge 13 WAI. In 1996, single and sequential applications of halosulfuron reduced viability of purple nutsedge tubers to 33 and 30%, respectively, compared to 84% in the nontreated control. However, herbicide treatments did not reduce tuber viability in 1997. Sulfentrazone (0.28 kg ai/ha) plus MSMA (2.24 kg/ha) and sequential MSMA applications reduced viability of yellow nutsedge tubers to 6 and 31%, respectively, in 1997.

Nomenclature: Bentazon, 3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide; halosulfuron, methyl 5-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonylami-nosulfonyl]-3-chloro-1-methyl-1-H-pyrazole-4-carboxylate; imazaquin, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid; MSMA, monosodium salt of methylarsonic acid; sulfentrazone, N-[2,4-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl] phenyl] methanesulfonamide; purple nutsedge, Cyperus rotundus L. #³ CYPRO; yellow nutsedge, Cyperus esculentus L. # CYPES; bermudagrass, Cynodon dactylon (L.) Pers. #CYNDA.

Additional index words: Tuber viability, weed management, CYNDA, CYPES, CYPRO.

Abbreviations: fb, followed by; MSMA, monosodium salt of methylarsonic acid; NIS, nonionic surfactant; POST, postemergence; WAI, weeks after initial treatment; WP, wettable powder.

Abstract: A survey conducted across agricultural ecoregions of Saskatchewan in 1996 revealed that wild oat (Avena fatua) populations resistant to acetyl-CoA carboxylase (ACCase) inhibitors were present in approximately 10% of Saskatchewan fields (2.4 million ha). In the Aspen Parkland and Boreal Transition ecoregions, this increased to 17%. The objective of this study was to determine if agronomic practices promoted or delayed resistance and to assess producer awareness of herbicide resistance. Weed resistance and management questionnaire data from the 1996 resistance survey and management questionnaire data from the 1995 Saskatchewan weed survey were submitted to multiway frequency analysis. The frequency of occurrence of herbicide-resistant wild oat was related directly to ACCase inhibitor use. Resistance to cyclohexanedione (CHD) herbicides was not related to CHD use but to frequency of ACCase inhibitor use (i.e., CHD aryloxyphenoxypropanoate [AOPP]), suggesting that the pressure imposed by AOPPs contributed to the selection of CHD resistance in wild oat. ACCase inhibitor use was more extensive in the Aspen Parkland and Boreal Transition ecoregions than in the Mixed and Moist Mixed Grassland ecoregions. Crop rotations were not conducive to rotation of herbicides with different sites of action. Frequency of ACCase inhibitor use increased with frequency of annual crops, in spite of the inclusion of cereal and dicot crops in the rotation. Producers utilizing conservation tillage practices in the Grassland ecoregions used proportionally more ACCase inhibitors than those using conventional tillage practices. This increase in ACCase use in conservation tillage systems did not result in an increased incidence of wild oat populations resistant to ACCase inhibitors. Producers reporting troublesome wild oat populations tended to have proportionally more ACCase-resistant wild oat. Producers who reported practicing weed sanitation were less likely to have resistant wild oat than those who were less careful. Increased awareness and implementation of management practices that will reduce the dependency on ACCase herbicides are required to better enable producers to prevent, delay, or manage herbicide-resistant wild oat populations.

Nomenclature: Wild oat, Avena fatua L. #³ AVEFA.

Additional index words: Weed survey, multiway frequency analysis, aryloxyphenoxypropanoate, cyclohexanedione, management of herbicide resistance.

Abbreviations: ACCase, acetyl-CoA carboxylase; AOPP, aryloxyphenoxypropanoate; CHD, cyclohexanedione.

Abstract: The effect of nicosulfuron application timing on wild-proso millet (Panicum miliaceum) control and sweet corn (Zea mays) yield was evaluated in the field during 1991, 1992, and 1993. Sweet corn yields were equal to hand weeded controls when nicosulfuron was applied to wild-proso millet shorter than 9 cm, but the best (> 95%) wild-proso millet control occurred when nicosulfuron was applied to wild-proso millet plants between 11 and 19 cm tall. However, nicosulfuron controlled wild-proso millet 90 to 95%, 13 wk after planting, when nicosulfuron was applied to plants 8 to 10 cm tall. Nicosulfuron applications made to wild-proso millet plants less than 8 cm were made early in the season and failed to control subsequent wild-proso millet flushes. Additionally, nicosulfuron failed to control completely wild-proso millet plants larger than 20 cm. Consequently, nicosulfuron applied to wild-proso millet plants shorter than 8 cm or taller than 20 cm resulted in a rapid decline in wild-proso millet control 13 wk after planting. Nicosulfuron applied following 6.7 kg ai/ha EPTC plus 2.2 kg ai/ha cyanazine PPI in 1991, could be applied to wild-proso millet 25 cm tall without subsequent losses in wild-proso millet control or sweet corn yield. Wild-proso millet control was 93% and sweet corn yields were equal to hand-weeded controls when nicosulfuron was applied to wild-proso millet 4 cm tall and followed by one cultivation 14 d after application.

Nomenclature: Cyanazine, 2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile; EPTC, S-ethyl dipropyl carbamothioate; nicosulfuron, 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3-pyridinecarboxamide; wild-proso millet, Panicum miliaceum L. #³ PANMI; sweet corn, Zea mays L.

Additional index words: Cultivation, PANMI, yield loss.

Abbreviations: DAA, days after application; OEM, oil emulsifier concentrate; PDIR, directed postemergence; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; UAN, urea ammonium nitrate; WAP, weeks after planting.

Abstract: Field experiments were conducted in 1996 and 1997 to evaluate barnyardgrass (Echinochloa crus-galli) control, rice (Oryza sativa) yield, and grain quality with cyhalofop-butyl applied early postemergence (EPOST) or late postemergence (LPOST) in drained or flooded plots at rates of 0.15 to 0.4 kg ai/ha and standard treatments of molinate or propanil. Control with cyhalofop-butyl at 0.15 and 0.2 kg/ha applied in drained plots was greater compared to propanil and generally increased when treatments were applied EPOST to plots reflooded 2 d after treatment. Barnyardgrass control with cyhalofop-butyl at 0.15 and 0.2 kg/ha applied in flooded plots was similar to or better than the control obtained with molinate. Rice yields generally reflected differences in barnyardgrass control and were greatest with cyhalofop-butyl applied EPOST in drained plots. The 0.4 kg/ha rate of cyhalofop-butyl resulted in rice foliar injury and significant reductions in grain yield. Grain qualitative characteristics (total milling yield, grain vitreosity, grain length, and grain length to width ratio) were better with cyhalofop-butyl applied EPOST in drained plots compared with propanil or molinate.

Nomenclature: Cyhalofop-butyl; molinate; propanil; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; rice, Oryza sativa L. ‘Ispaniki A’.

Additional index words: Weed management, ECHCG.

Abbreviations: DAT, days after treatment; DBH, days before harvest; EPOST, early postemergence; LPOST, late postemergence; POST, postemergence.

Abstract: A field study was conducted to determine the effect of increasing seed rates of spring wheat (Triticum aestivum) on redstem filaree (Erodium cicutarium) biomass and seed production and on wheat yield in a zero-tillage cropping system. Wheat was sown at 50, 100, 150, 200, and 300 kg/ha in an experiment four consecutive years to determine annual and accumulated effects over time. Redstem filaree was most competitive with wheat when it emerged before or with wheat and when rainfall was plentiful during May and June. Redstem filaree biomass and seed production were markedly inhibited by drought conditions. An increase in wheat seed rate from 50 to 300 kg/ha reduced redstem filaree biomass and seed production by 53 to 95% over the years. There was little yield benefit to increasing the seed rate of weed-free wheat above 50 kg/ha. However, in the presence of redstem filaree, an increase in wheat seed rate from 50 to 300 kg/ha resulted in wheat yield being increased by 56 to 498%. Over four consecutive years, an increase in wheat seed rate from 50 to 300 kg/ha reduced redstem filaree in the soil seedbank by 79%. Higher seed rates of wheat can be an effective component of an improved program for redstem filaree management in conservation tillage cropping systems.

Nomenclature: Redstem filaree, Erodium cicutarium (L.) L'Her. ex Ait. #³ EROCI; spring wheat, Triticum aestivum L. ‘Neepawa’.

Additional index words: Competition, soil seedbank, weed seed yield, wheat plant density, wheat yield, EROCI.

Abbreviations: PAR, photosynthetically active radiation.

Abstract: Reports of resistance to grass-selective herbicides, including johnsongrass (Sorghum halepense) resistant to fluazifop-P, have become quite common. Experiments were conducted to determine if fluazifop-P resistance could be transferred from johnsongrass to crop sorghum (Sorghum bicolor) and to identify the heritability of resistance in the progeny. A population of male sterile, fluazifop-P–sensitive sorghum, AKS-82, was interplanted with fluazifop-P–resistant johnsongrass and progeny treated with 0.105 kg ai/ha fluazifop-P postemergence (POST). Surviving seedlings were backcrossed to fluazifop-P–resistant johnsongrass. Viable plants from this successful cross were then testcrossed to another sensitive sorghum, TX622. These testcross progeny were then screened for herbicide resistance by again applying fluazifop-P POST at 0.105 kg /ha. Chi-square analysis revealed that resistance to fluazifop-P was inherited by a single, dominant gene. Natural hybridization of johnsongrass and sorghum is possible, and transfer of herbicide resistance between species can occur.

Nomenclature: Fluazifop-P; johnsongrass, Sorghum halepense (L.) Pers. #³ SORHA; grain sorghum, Sorghum bicolor (L.) Moench ‘AKS-82’, ‘TX622’.

Additional index words: Hybridization, outcrossing, SORHA.

Abbreviations: ACCase, acetyl coenzyme-A carboxylase (EC 6.4.1.2); AOPP, aryloxyphenoxypropionate; CHD, cyclohexanedione; POST, postemergence.

Abstract: Field studies were conducted in 1996 and 1997 to evaluate response of eight peanut cultivars to diclosulam applied preplant incorporated at 36 g ai/ha in a weed-free environment. Peanut cultivars evaluated included ‘NC 12C’, ‘NC 7’, ‘VAC 92R’, ‘NC-V 11’, ‘NC 10C’, ‘AT VC 1’,‘NC 9’, and the experimental breeding line N90010E. Visible injury 3 wk after planting was less than 5% regardless of cultivar. No injury was observed at 21 d after planting. Diclosulam did not influence the incidence of early leaf spot, late leaf spot, southern stem rot, cylindrocladium black rot, or tomato spotted wilt virus. Diclosulam did not affect percentage of extra large kernels, sound mature kernels, other kernels, and yield.

Nomenclature: Diclosulam; peanut, Arachis hypogaea L. NC 12C, NC 7, VAC 92R, NC-V 11, NC 10C, AT VC 1, NC 9, N90010E.

Additional index words: Disease interaction, cylindrocladium black rot, Cylindrocladium crotalariae (Loos) Bell et Sobers, early leaf spot, Cercospora arachidicola Hori, late leaf spot, Cercosporidium personatum (Berk. et Curt.), southern stem rot, Sclerotium rolfsii Sacc., tomato spotted wilt virus, grade parameters, extra large kernels, sound mature kernels, sound splits, total kernels, other kernels, fancy pods.

Abbreviations: CBR, cylindrocladium black rot; DAP, days after planting; ELK, extra large kernels; PPI, preplant incorporated; SMK, sound mature kernels; SS, sound splits; TSMK, total sound mature kernels; TSWV, tomato spotted wilt virus; WAP, weeks after planting.

Abstract: The effect of seeding depth on emergence of red rice (Oryza sativa) ecotypes from Arkansas (AR), Louisiana (LA), and Mississippi (MS) was determined under dry-seeded rice production in clay and silt loam soils in Arkansas. By 21 d after planting (DAP), all red rice ecotypes had emerged from planting depths of 1.3, 2.5, 5.0, and 7.5 cm in both clay and silt loam soils. In silt loam soil, seedling emergence from 2.5 cm 7 DAP tended to be greater than from 1.3 cm in an early (normal temperature) planting. Also in this situation, the LA ecotype emerged more vigorously than the other ecotypes at all seeding depths and emerged from 7.5 cm at levels 1.5 times those of the other ecotypes at the same depth. In the clay soil, seedling emergence from 7.5 cm at 21 DAP was greater for the LA and MS ecotypes than for the AR ecotype in an early planting, but these differences were not observed for a late (elevated temperature) planting. Seedling emergence was earlier and greater in silt loam than in clay. The LA ecotype generally produced the greatest aboveground dry matter, especially at the early planting. The MS ecotype averaged 30% less dry matter production than the AR ecotype for the late planting in both soils. The ability of the LA and MS ecotypes to emerge from greater depths than the AR ecotype under certain soil and temperature conditions suggests that they could be more difficult to control with cultural practices used in dry-seeded rice culture.

Nomenclature: Red rice, Oryza sativa L. #³ ORYSA; rice, Oryza sativa L. ‘Alan’.

Additional index words: Germination, red rice emergence depth, soil texture.

Abbreviations: AGDM, aboveground dry matter; AR, Arkansas ecotype; DAP, days after planting; LA, Louisiana ecotype; MS, Mississippi ecotype.

Abstract: Field studies were conducted in 19-cm-row soybean during 1997 and 1998 to evaluate the rate and timing of glyphosate applications applied alone at 0.42 and 0.63 kg ae/ha and with other herbicides to glyphosate-resistant soybean in terms of weed control, soybean yield, and net return. Weed species included barnyardgrass, hemp sesbania, pitted morningglory, and prickly sida. Among glyphosate-alone weed control programs, sequential applications generally provided the highest and most consistent control of all species evaluated (above 90% for broadleaf species). Glyphosate applied in combination with selective postemergence (POST) herbicides or following soil-applied herbicides controlled most species comparable to sequential glyphosate applications. Most herbicide programs, except for single glyphosate applications, were comparable to sequential glyphosate applications in terms of soybean yield and net return and ranged from 2,221 to 2,827 kg/ha and $410.28 to $549.60/ha. Depending on the year, either one or two glyphosate applications were needed for adequate weed control in programs with a soil-applied herbicide. Glyphosate rate affected neither weed control, yield, nor net return. Depending on a producer's management style and weed spectrum, weed control programs with glyphosate alone, in combination with another POST herbicide, or following soil-applied herbicides are all viable options in drilled glyphosate-resistant soybean.

Nomenclature: Glyphosate; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; hemp sesbania, Sesbania exaltata (Raf.) Cory. # SEBEX; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; soybean, Glycine max (L.) Merr. ‘Delta King 5961 RR’.

Additional index words: Glyphosate economics, Echinochloa crus-galli, Ipomoea lacunosa, Sesbania exaltata, Sida spinosa, Glycine max, ECHCG, IPOLA, SEBEX, SIDSP.

Abbreviations: NIS, nonionic surfactant; POST, postemergence.

Abstract: To manage jointed goatgrass (Aegilops cylindrica), growers need an action threshold decision aid to assist them in deciding when to rotate to a spring crop instead of growing winter wheat (Triticum aestivum). A study was conducted in Washington from 1992 to 1995 to predict winter wheat yield loss based on a jointed goatgrass population in the previous year's winter wheat crop. To describe the relationship between jointed goatgrass density in year 1 and the resulting winter wheat yield loss in year 2, data were fitted to a rectangular hyperbolic model. First year jointed goatgrass densities in winter wheat of 1 to 5 plants/m² led to a second year winter wheat yield loss of 3 to 30%. Yield loss was greater in a dry year than in a normal to wet year. To initiate an action threshold for jointed goatgrass successfully, growers need to incorporate data from this study with their knowledge of yield potential, price dockage of the subsequent winter wheat crop, and profitability of alternative spring crop rotations.

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

Additional index words: Decision aid.

Abstract: Diagnosing herbicide-resistant weeds as a first step in resistance management and monitoring their nature, distribution, and abundance demands efficient and effective screening tests. This review summarizes and recommends appropriate seed sampling techniques, protocols for screening weeds for resistance to herbicides of different sites of action, interpretation of results, and information given to the grower. Elements common to all screening procedures are reviewed. Choosing appropriate discriminating doses to distinguish between resistant and susceptible weed biotypes is the most important factor in achieving accurate and consistent results. Interpretation of results is also critical because resistant weeds may comprise a small portion of the population in suspected accessions or biotypes.

Additional index words: Bioassay, discriminating dose, seed sampling, site of action, surveys.

Abbreviations: ACCase, acetyl-CoA carboxylase (EC 6.4.1.2); ALS, acetolactate synthase (EC 4.1.3.18); AOPP, aryloxyphenoxy propionate; CHD, cyclohexanedione; DAT, days after treatment; EPSP synthase, 5-enolpyruvylshikimate-3-phosphate synthase (EC 2.5.1.19); KARI, ketol-acid reductoisomerase (EC 1.1.1.86); POST, postemergence; PRE, preemergence; R, resistant; S, susceptible.