Greenhouse experiments were conducted to determine whether multiple applications of glyphosate and time of glyphosate application with regard to the crop's growth stage had a significant effect on the growth and development of glyphosate-resistant canola. Glyphosate was applied as single applications at the two-, four-, or six-leaf stage of canola; as sequential double applications at the two- and four-, two- and six-, and four- and six-leaf stages of canola; and as a triple application at all three stages. Of the plant growth parameters measured, single applications of glyphosate resulted in significant reductions to stem weight and shoot weight compared with nontreated plants, and multiple applications of glyphosate caused significant reductions to leaf area, leaf weight, stem weight, and shoot weight. Single applications of glyphosate were less injurious to glyphosate-resistant canola compared with multiple applications, and canola growth parameter reductions were greatest after earlier glyphosate applications.

Nomenclature: Glyphosate, canola, Brassica napus L.

Additional index words: Crop injury, herbicide-resistant crop, leaf stage, multiple application.

Abbreviations: EPSPS, 5-enolpyruvylshikimate-3-phosphate synthase; RH, relative humidity.

A field experiment was conducted near Davis, CA, during the 2003 and 2004 summer growing seasons to compare weed control, yield, and fruit quality in different irrigation and tillage systems in processing tomato. Trial design was a subplots with the main plots as subsurface drip irrigation or furrow irrigation, subplots were standard tillage or conservation tillage, and sub-subplots were herbicide or no herbicide. The hypothesis was that subsurface drip irrigation could limit surface soil wetting and thus inhibit germination and growth of weeds equal to or better than standard tillage and/or herbicides. In both 2003 and 2004, weed densities in the subsurface drip irrigation treatments were over 98% lower than the levels in furrow irrigation treatments. In addition, weed densities were lower in the subsurface drip–conservation till–no herbicide treatment than in any of the furrow irrigation treatments, including the furrow irrigation–standard tillage–herbicide treatments. The time required for a hand-hoeing crew to remove weeds was 5 to 13 times greater in furrow irrigation treatments compared to subsurface drip irrigation treatments. Weed biomass on beds at tomato harvest was 10 to 14 times greater in the furrow systems as compared to the subsurface drip irrigation systems. These results demonstrate the effectiveness of subsurface drip irrigation in controlling weed germination and growth, compared to tillage or herbicide applications. Tomato yield was higher in the subsurface drip irrigation treatment compared to furrow irrigation in 2004. Herbicide treatment increased yield in 2004, but only in the furrow irrigation treatment in 2003. Fruit brix level was not related to treatment in 2003, but was lower in the subsurface drip irrigation plots in 2004. These results indicate that subsurface drip irrigation can reduce weed competition in conservation tillage systems, without requiring herbicide applications.

Nomenclature: Tomato, Lycopersicum esculentum Mill.

Additional index words: Arid regions, cropping systems, fertigation, hand weeding.

Red rice is a major weed of rice in the southern U.S. and can intercross with rice. Knowledge of the plant phenotypes from such crosses would be valuable for identification and management of these plants. Male-sterile long-grain tropical japonicas ‘Kaybonnet-1789’ and ‘Cypress-1819’ were crossed with two awned and two awnless U.S. red rice types. F₁ plants produced pubescent leaves, red pericarp, and medium-grain seeds. Crosses involving awned LA3 and TX4 red rice produced F₁ plants with reddish-purple basal leaf sheaths and usually flowered within the same time periods as the parents, whereas those involving awnless StgS red rice had green basal leaf sheaths, flowered much later than either parent, and produced awnless F₁ and F₂ offspring. Crosses involving awned red rice produced F₁ plants with long awns and F₂ plants with awns ranging in length from zero to that of red rice parents. F₁ plants were taller than either parent and produced intermediate culm angles similar to red rice, whereas F₂ plants had culms ranging from erect (like rice) to more open than red rice. Thus, true F₁ hybrids from crosses between pure breeding (homozygous) rice and red rice can be positively identified by a combination of traits including pubescent leaves, medium-grain seeds with red pericarps, open plant types, and heights greater than the red rice parent. F₁ hybrids may be awned or awnless, have purple or green stems, or have normal or delayed heading. F₂ plants have a broad combination of phenotypic traits found in both parents and F₁ hybrids.

Nomenclature: Red rice, Oryza sativa L. #³ ORYSA, ‘LA3’, ‘Stuttgart strawhull’, ‘TX4’; rice, Oryza sativa L., ‘KBNT-1789’, ‘CPRS-1819’.

Additional index words: Ecotype, biotype, gene flow, gene segregation, hybrid, outcrossing, phenotypic traits, rice, red rice, weedy rice.

Abbreviations: IMI, imidazolinone; MS, male sterile; PCR, polymerase chain reaction; QTL, quantitative trait loci.

Volunteer potato is a perennial weed that is difficult to control in crop rotations. It was our objective to build a small, low-cost robot capable of detecting volunteer potato plants in a cornfield and thus demonstrate the potential for automatic control of this weed. We used an electric toy truck as the basis for our robot. We developed a fast row-recognition algorithm based on the Hough transform and implemented it using a webcam. We developed an algorithm that detects the presence of a potato plant based on a combination of size, shape, and color of the green elements in an image and implemented it using a second webcam. The robot was able to detect potatoes while navigating autonomously through experimental and commercial cornfields. In a first experiment, 319 out of 324 images were correctly classified (98.5%) as showing, or not showing, a potato plant. In a second experiment, 126 out of 141 images were correctly classified (89.4%). Detection of a potato plant resulted in an acoustic signal, but future robots may be fitted with weed control equipment, or they may use a global positioning system to map the presence of weed plants so that regular equipment can be used for control.

Nomenclature: Corn, Zea mays L, Potato, Solanum tuberosum L.

Additional index words: Autonomous navigation, autonomous weeding, glyphosate, machine-vision, site-specific weed control.

Abbreviations: DIPlib, Delft image-processing library; DSP, digital signal processor; GPS, global positioning system; JPEG, Joint Photographic Experts Group; NiMh, nickle metal hydride; PC, personal computer.

Weed management is a major production issue facing otebo bean growers in Ontario. Field trials were conducted at six Ontario locations during a 2-yr period (2003 and 2004) to evaluate the tolerance of otebo bean to the preplant incorporated (PPI) application of EPTC at 4,400 and 8,800 g ai/ha, trifluralin at 1,155 and 2,310 g ai/ha, dimethenamid at 1,250 and 2,500 g ai/ha, S-metolachlor at 1,600 and 3,200 g ai/ha, and imazethapyr at 75 and 150 g ai/ha. EPTC, trifluralin, dimethenamid, and S-metolachlor applied PPI resulted in minimal (less than 5%) visual injury and with exception of the low rate of dimethenamid causing a 16% reduction in shoot dry weight and the high rate causing an 8% plant height reduction had no adverse effect on plant height, shoot dry weight, seed moisture content, and yield. Imazethapyr applied PPI caused up to 7% visual injury and reduced plant height, shoot dry weight, and yield 8, 18, and 12% at 75 g/ha and 19, 38, and 27% at 150 g/ ha, respectively. Seed moisture content was also reduced by 0.4% with both rates. Based on these results, otebo bean is not tolerant of imazethapyr applied PPI at rates as low as 75 g/ha, the proposed use rate. EPTC, trifluralin, dimethenamid, and S-metolachlor applied PPI have a 2× rate crop safety margin for use in otebo bean weed management.

Nomenclature: Dimethenamid; EPTC; imazethapyr; S-metolachlor; trifluralin; otebo bean, Phaseolus vulgaris L. ‘Hime’.

Additional index words: Sensitivity, visual injury, tolerance, shoot dry weight.

Abbreviations: 1×, the recommended maximum use rate; 2×, twice the maximum recommended use rate; BCMV, bean common mosaic virus; DAE, days after emergence; OM, organic matter; PPI, preplant incorporated.

Field studies were conducted in 2001 and 2002 in the Black Sea Region of northern Turkey to determine the critical period for weed control (CPWC) in corn and the effects of weed interference on corn height. Treatments of increasing duration of weed interference and weed-free period were imposed at weekly intervals from 0 to 12 wk after crop emergence (WAE). The CPWC was determined with the use of 2.5, 5, and 10% acceptable yield loss levels by fitting logistic and Gompertz equations to relative yield data. With 5% yield loss level, the CPWC was 5 wk, starting at 0.2 WAE and ending at 5.2 WAE, which corresponded to the one- to five-leaf stage of corn. The CPWC increased to 8.9 wk, starting at 0 WAE and ending at 8.9 WAE, at the 2.5% yield loss level. At 10% yield loss level, the CPWC decreased to 1.7 wk, starting at 2.1 WAE and ending at 3.8 WAE.

Nomenclature: Corn, Zea mays L.

Additional index words: Maize, weed competition, weed interference.

Abbreviations: AYL, acceptable yield loss level; CLS, corn leaf stage; CPWC, critical period for weed control; DAE, days after emergence; WAE, weeks after emergence.

A field experiment was conducted in 1996 and 1997 to determine snap bean tolerance to halosulfuron based on crop injury, height, and yield. Halosulfuron was applied preemergence (PRE), postemergence (POST), and sequentially PRE followed by (fb) POST at 35, 53, and 70 g ai/ha, respectively. For comparison, a hand-weeded check was included. When data were averaged across years and halosulfuron rates, halosulfuron PRE, POST, and PRE fb POST provided similar yellow nutsedge control (74 to 82%) at snap bean harvest. Halosulfuron PRE resulted in 4% snap bean injury at harvest. Similarly, halosulfuron PRE fb POST resulted in 5% injury, while halosulfuron POST caused the most damage at 8%. Snap bean height at harvest was reduced 14% with halosulfuron POST compared to the weed-free check, with only 5 and 6% reduction caused by halosulfuron PRE and PRE fb POST, respectively. Halosulfuron POST reduced yield 39% compared to the weed-free check, while the PRE and PRE fb POST application timings produced yield similar to the check. When averaged across years and halosulfuron application timings, an increase in halosulfuron rate had no effect on yellow nutsedge control or snap bean yield. A linear trend was found for snap bean injury and plant height at harvest with snap bean injury increasing with an increase in halosulfuron rate while snap bean plant height decreased with an increase in halosulfuron rate. Application of halosulfuron PRE is the safest means to control yellow nutsedge in snap bean in North Carolina.

Nomenclature: halosulfuron; yellow nutsedge, Cyperus esculentus L. #³ CYPES; snap bean, Phaseolus vulgaris L. ‘Strike’.

Additional index words: crop injury, plant height, yield.

Abbreviations: fb, followed by; PRE, preemergence; POST, postemergence; WAP, wks after planting.

A host-specific fungus Colletotrichum truncatum strain 00-3B1 (Ct) was mixed with herbicides to improve the control of scentless chamomile, a noxious weed in western Canada. The compatibility of Ct conidia (spores) with herbicides was evaluated in vitro, and varying effects were observed with different products on spore germination. Clodinafop, glufosinate, MCPA, and 2,4-D ester were relatively benign and delayed the germination slightly, whereas dicamba, imazethapyr, metribuzin, and 2,4-D amine were noticeably more inhibitive. Bromoxynil, glyphosate, sethoxydim, and Merge® (spray adjuvant) were most inhibitive, showing >50% inhibition after 24 h. To determine potential synergy, Ct was applied at 7 × 10⁶ spores/ml in tank mixtures with selected herbicides at 1× and 0.1× registered rates under greenhouse conditions. Combining Ct with MCPA, 2,4-D ester, clopyralid, or metribuzin at 1× rate resulted in synergistic or additive interaction on scentless chamomile, increasing weed control significantly when compared to Ct or herbicides applied alone. Similar applications of Ct with imazethapyr, 2,4-D amine, dicamba, or glyphosate were antagonistic. Treatments with Ct plus 1× metribuzin killed scentless chamomile completely, whereas neither Ct nor the herbicide alone caused plant death, suggesting the value of this tank mixture.

Nomenclature: Bromoxynil; clodinafop; clopyralid; dicamba; 2,4-D; glufosinate; glyphosate; imazethapyr; MCPA; metribuzin; sethoxydim; scentless chamomile, Matricaria perforata Mérat, #³ MATIN; causal agent of anthracnose, Colletotrichum truncatum (Schwein.) Andrus & W.D. Moore.

Additional index words: Biocontrol, bioherbicide, synergy.

Abbreviations: Ct, Colletotrichum truncatum strain 00-3B1 (from scentless chamomile).

Field studies were conducted at Fayetteville, Arkansas, to determine whether 47 Palmer amaranth accessions from different areas of the southern United States varied in response to postemergence applications of the registered rates of the isopropylamine salt of glyphosate (840 g ae/ha), fomesafen (420 g ai/ha), and pyrithiobac (70 g ai/ha). Glyphosate controlled all Palmer amaranth accessions at least 99% 21 d after treatment (DAT). Palmer amaranth control with fomesafen was equivalent for all accessions and at least 96% 21 DAT. Percent dry weight reductions were at least 92 and 94% for glyphosate and fomesafen, respectively. Palmer amaranth control with pyrithiobac was variable and ranged from 20 to 94% 21 DAT, but differences could not be attributed to accession origin. Herbicides with alternate modes of action from pyrithiobac should be utilized for Palmer amaranth control in regions where pyrithiobac has been used continuously.

Nomenclature: Fomesafen, glyphosate, pyrithiobac, Palmer amaranth, Amaranthus palmeri (S.) Wats. #³ AMAPA.

Additional index words: Accession, dry weight reductions, ecotype, herbicide response variability.

Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); DAE, days after emergence; DAT, days after treatment.

Field experiments were conducted to evaluate the effect of five spray-nozzle types and three drift-control adjuvants (DCA) on glyphosate spray drift. The extended-range (XR) flat-fan nozzle at 280 kPa was used as the standard comparison. DCAs were evaluated for drift reduction with the use of the XR and air-induction (AI) nozzles. Wind speed ranged from 1.3 to 9.4 m/s (3 to 21 mph). Lethal drift (D_L) and injury drift (D_I) were determined by downwind visual observation of grain sorghum response. Drift distances were measured from the spray swath edge. The Turbo FloodJet and AI nozzles reduced D_L distance by 34%. All four drift-reducing (DR) nozzles reduced D_I distance by 22 to 32%. Reducing the pressure of the XR flat-fan nozzle from 280 to 140 kPa did not reduce D_L or D_I distance. When applied through AI nozzles, each DCA increased droplet volume diameter, one DCA reduced D_I distance and none reduced D_L distance when applied through XR tips. The DCAs did not affect D_L or D_I distance.

Nomenclature: Glyphosate; grain sorghum, Sorghum bicolor (L.) ‘Topaz’.

Additional index words: Drift-control adjuvant, flat-fan nozzle, flood nozzle.

Abbreviations: AI, air induction; AMS, ammonium sulfate; DAP, days after planting; DAT, days after treatment; DCA, drift-control adjuvant; DG, preorifice flat fan; D_I, injury drift; D_L, lethal drift; DR, Combo-Jet; GR, glyphosate resistant; HRC, herbicide-resistant crops; TD, TurboDrop; TF, Turbo FloodJet; TT, Turbo TeeJet; VMD, volume median diameter; XR, extended range.

Research was conducted to evaluate root uptake, translocation, and metabolism of ¹⁴C-sulfentrazone alone or in a mixture with clomazone in solution in flue-cured tobacco transplants. Uptake and translocation of sulfentrazone was rapid and was not affected by the addition of clomazone. Fifty-nine and 65% of the ¹⁴C absorbed by the plant was translocated to the leaves within 24 h with sulfentrazone alone and in the clomazone plus sulfentrazone mixture, respectively. Differences in plant metabolism were observed between sulfentrazone alone and sulfentrazone plus clomazone. After 3 h, 66% of the ¹⁴C recovered from the leaves was metabolized when sulfentrazone was applied alone, compared to 91% when sulfentrazone was applied with clomazone. The difference could indicate that metabolism of sulfentrazone by tobacco transplants was enhanced by the presence of clomazone.

Nomenclature: Clomazone, sulfentrazone, flue-cured tobacco, Nicotiana tabacum L. ‘NC 71’.

Additional index words: Enhanced metabolism, safening, tolerance.

Abbreviations: HAT, hours after treatment; LSS, liquid scintillation spectrometry; PPI, preplant incorporated treatment; PRE-T, pre-emergence soil surface treatment.

Greenhouse studies were conducted to determine the response of velvetleaf, common cocklebur, and ivyleaf morningglory to mesotrione and atrazine applied PRE, and to characterize the nature of any interaction between mesotrione and atrazine. Sensitivity to mesotrione was as follows: velvetleaf > common cocklebur > ivyleaf morningglory. Sensitivity to atrazine was as follows: ivyleaf morningglory > common cocklebur > velvetleaf. Combinations of mesotrione and atrazine resulted in at least an additive interaction. The activity of mesotrione and atrazine applied in combination was generally additive for control of velvetleaf and ivyleaf morningglory but was synergistic for several rate combinations.

Nomenclature: Atrazine, mesotrione, common cocklebur, Xanthium strumarium L. #³ XANST, ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE, velvetleaf, Abutilon theophrasti Medicus # ABUTH.

Additional index words: Synergism, additive, herbicide interaction.

Abbreviations: DAT, days after treatment; GR₅₀, rate causing 50% growth reduction; HPPD, 4-hydroxyphenylpyruvate dioxygenase; LDR, Logistic Dose Response equation.

Field trials were conducted in 2002 and 2003 at seven sites to determine the optimum rates of mesotrione and atrazine applied PRE for minimal crop injury and control of common lambsquarters, velvetleaf, Pennsylvania smartweed, common ragweed, giant ragweed, ivyleaf morningglory, and common cocklebur. All rates of each herbicide resulted in greater than 95% control of triazine-susceptible common lambsquarters. Mesotrione at 105 g ai/ha resulted in greater than 90% control of triazine-resistant common lambsquarters, velvetleaf, and Pennsylvania smartweed. Control of common ragweed was 90% or greater from mesotrione at 158 g/ha in combination with atrazine at 280 g/ha or greater. In addition, mesotrione at 210 g/ha combined with any rate of atrazine provided at least 92% control of common ragweed. Combinations of mesotrione and atrazine only suppressed, and did not effectively control, giant ragweed, common cocklebur, and ivyleaf morningglory.

Nomenclature: Atrazine, mesotrione, s-metolachlor, common cocklebur, Xanthium strumarium L. #³ XANST, common lambsquarters, Chenopodium album L. # CHEAL, common ragweed, Ambrosia artemisiifolia L. # AMBEL, giant ragweed, Ambrosia trifida L. # AMBTR, ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE, Pennsylvania smartweed, Polygonum pensylvanicum L. # POLPY, velvetleaf, Abutilon theophrasti Medicus # ABUTH, corn, Zea mays L.

Additional index words: Herbicide combination.

Abbreviations: ALS, acetolactase synthase; DAT, days after treatment; HPPD, 4-hydroxyphenylpyruvate dioxygenase; TR, triazine-resistant.

Information on jointed goatgrass caryopsis development is currently lacking in published literature. It is hoped that through a better understanding of jointed goatgrass caryopsis ontogeny more effective weed-management strategies will be developed. Greenhouse experiments were initiated in fall 2002 and 2003 and completed the following spring seasons. Jointed goatgrass plants were started from spikelets, vernalized for 8 wk at 4 C, and grown in a greenhouse. Treatments were the number of days after anthesis (DAA) that a spike was allowed to remain on the plant before harvesting and ranged from 2 to 34 DAA, in increments of 1 (2002) or 2 (2003) d. Individual spikes were divided at harvest into three sections: top, middle, and bottom, disarticulated from the rachis, placed into a germinator, and germination recorded each day. Goatgrass spikelets germinated as early as 2 DAA, although spikelets harvested <7 DAA had <3% germination for all spike sections and were extremely variable, especially for the middle and bottom sections. Time to germination was similar for all sections of the spike. Maximum average germination of the top section was 72% compared with 86% for the bottom and middle sections. Our data suggest that factors other than developmental rate (i.e., dormancy) may affect germination in sections of the spike. A second year of the experiment was conducted for validation. Model validation suggested that although trends were similar in both years, variation in germination response might be too great for accurate, predictive model construction. The early germination shown in this research demonstrates that control measures must be implemented earlier than previously prescribed to prevent jointed goatgrass reproduction.

Nomenclature: Jointed goatgrass, Aegilops cylindrica Host #³ AEGCY.

Additional index words: Anthesis, germination, maturity.

Abbreviations: NID, normally identically distributed; PPFD, photosynthetic photon flux density.

Field experiments were conducted to determine the effects of application timings and various herbicides on newly established ‘Coastal’ bermudagrass in 2001, 2002, and 2003. The experimental design was a split plot with three replications. Main plots consisted of three herbicide application timings of 1, 14, and 28 d after planting (DAP), and the subplots were 16 herbicide treatments. The hormone herbicides (picloram at 0.19 kg ae/ha fluroxypyr at 0.19 kg ae/ha, picloram at 0.08 kg/ha 2,4-D amine at 0.28 kg ae/ha, picloram at 0.15 kg/ha 2,4-D amine at 0.56 kg/ha, 2,4-D amine at 2.2 kg/ha, 2,4-D amine at 1.2 kg/ha dicamba at 0.42 kg ae/ha, and 2,4-D ester at 2.3 kg ae/ha) applied 1 DAP controlled large crabgrass 55 to 85%, did not injure Coastal bermudagrass sprigs, and aided establishment resulting in 22 to 27% ground cover in 2001 and 25 to 42% ground cover in 2002. Imazapic at 0.02, 0.035, and 0.05 kg ai/ha applied 1 and 14 DAP injured Coastal bermudagrass 5 to 45% across years, yet these plots had 20 to 54% ground cover compared with only 3 to 7% ground cover in the nontreated area in 2001, 2002, and 2003. The reduced rate of glyphosate (0.21 kg ae/ha) injured Coastal bermudagrass less than 8% and controlled large crabgrass 86 to 90% when applied 14 DAP, resulting in 43, 25, and 18% ground cover in 2001, 2002, and 2003, respectively. Trifloxysulfuron at 0.02 kg ai/ha applied 1 and 14 DAP did not injure Coastal bermudagrass sprigs, controlled junglerice 90%, and resulted in 73 and 52% ground cover, respectively. Coastal bermudagrass establishment was greatly increased when weeds were controlled.

Nomenclature: 2,4-D amine, 2,4-D ester, dicamba, fluroxypyr, glyphosate, imazapic, picloram, trifloxysulfuron, bermudagrass, Cynodon dactylon (L.) Pers. ‘Coastal’, junglerice, Echinochloa colona (L.) Link #³ ECHCO, large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA.

Additional index words: Bermudagrass sprigs, establishment, injury, phytotoxicity.

Abbreviations: ai, active ingredient; ae, acid equivalent; DAT, days after treatment; NIS, nonionic surfactant.

An organic herbicide carrier could help reduce misapplication and environmental pollution associated with spray application of herbicides. Pellets prepared from landscape leaves that were dried, ground, and pelletized were evaluated as a preemergence herbicide carrier for container-grown ornamental plants. Isoxaben, pendimethalin, and prodiamine at rates of 1.12, 2.25, and 2.25 kg ai/ha, respectively, with either water or landscape leaf-waste pellets as a carrier were applied to chrysanthemum ‘Lisa’, spirea ‘Neon Flash’, and wintercreeper ‘Coloratus’. Common groundsel, common purslane, and giant foxtail were seeded following herbicide application. Leaf-waste pellets as a carrier produced equivalent efficacy and phytotoxicity ratings to conventional spray application of pendimethalin and prodiamine on both chrysanthemum and wintercreeper. The leaf-waste pellets were not an effective carrier for the application of isoxaben alone. The pellets had inconsistent effects on spirea phytotoxicity and growth.

Nomenclature: Isoxaben, pendimethalin, prodiamine, common groundsel, Senecio vulgaris L. #³ SENVU, common purslane, Portulaca oleracea L. # POROL, giant foxtail, Setaria faberi Herrm. # SETFA, chrysanthemum, Dendranthema × grandiflorum (Ramat.) Kitam. ‘Lisa’, spirea, Spiraea japonica L.f. ‘Neon Flash’, wintercreeper, Euonymus fortunei (Turcz.) Hand.-Mazz. ‘Coloratus’.

Abbreviations: DAT, days after treatment.

A seedling bioassay was developed for the rapid diagnosis of resistance to clethodim and fluazifop-P in johnsongrass. The assay was based on differences in the coleoptile length of susceptible (S) and resistant (R) seedlings exposed to clethodim and fluazifop-P in petri dishes for 5 d. Bioassay concentrations of 0.09 mg/L clethodim and 0.18 mg/L fluazifop-P were chosen as discriminant based on rate responses of each biotype to increasing herbicide dose. At 5 d after treatment (DAT), the amounts of clethodim required to reduce coleoptile length by 50% (GR₅₀) for the R and S seedlings were 462.5 and 24.8 mg/L, respectively, resulting in an R:S ratio of 18.7. The fluazifop GR₅₀ values for the R and S seedlings were 618.7 and 17.5 mg/L, respectively, resulting in a R:S ratio of 35.4.

Nomenclature: Clethodim, fluazifop-P, johnsongrass, Sorghum halepense (L.) Pers. #³SORHA.

Additional index words: ACCase inhibitors, herbicide resistance.

Abbreviations: ACCase, acetyl coenzyme-A carboxylase; AOPP, aryloxyphenoxypropionate; CHD, cyclohexanedione.

A study was conducted to evaluate weed control with imazethapyr applied at different timings or a combination of timings with or without an early POST application of bensulfuron, bentazon plus aciflurofen, bispyribac, carfentrazone, halosulfuron, propanil plus molinate, or triclopyr in drill-seeded imidazolinone-resistant rice. Control of barnyardgrass, red rice, and alligatorweed was insufficient with imazethapyr at 87 g/ha PRE or at 53 g/ha late POST alone. Imazethapyr at 87 g/ha PRE followed by imazethapyr at 53 g/ha late POST controlled red rice 86% or greater but did not control hemp sesbania. The imazethapyr PRE followed by late POST combination was also weak on barnyardgrass and alligatorweed early in the season. The addition of an early POST application of the other herbicides to the imazethapyr combination improved overall weed control, especially hemp sesbania control. Among the early POST herbicides, bispyribac, carfentrazone, or propanil plus molinate were more effective in helping improve the overall weed control, resulting in better rice grain yield.

Nomenclature: Aciflurofen, bensulfuron, bentazon, carfentrazone, bispyribac, halosulfuron, imazethapyr, molinate, propanil, triclopyr, alligatorweed, Alternanthera philoxeroides (Mart.) Griseb. #³ ALRPH, barnyardgrass, Echinochloa crus-galli (L.) Beauv. # ECHCG, hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A.W.Hill # SEBEX, red rice, Oryza sativa L. # ORYSA, rice, Oryza sativa L., imidazolinone-resistant ‘93 AS-3510’ and ‘CL 121’.

Additional index words: ALS, acetolactate synthase, Clearfield rice.

Abbreviations: ALS, acetolactate synthase; DAT, days after LPOST treatment; EPOST, early postemergence; fb, followed by; IR, imidazolinone-resistant; LPOST, late postemergence; LSU, Louisiana State University.

Texas panicum is considered to be the most troublesome weed of field corn in the Southeast. Field trials were conducted in Georgia in 2003 and 2004 to compare pendimethalin, nicosulfuron, foramsulfuron, and glyphosate for Texas panicum control in irrigated field corn and to determine which herbicide provided the greatest economic returns. Pendimethalin applied early POST (EPOST), 10 to 12 d after planting (DAP), controlled Texas panicum less than 35% late in the season and resulted in reduced corn yield and net returns in 2004. Glyphosate applied sequentially POST at 21 to 24 DAP and again late POST (LPOST) at 35 to 38 DAP controlled Texas panicum 82 to 94% late in the season compared with 43 to 80% control by nicosulfuron and foramsulfuron applied POST. Texas panicum control, corn yield, and net returns were similar with glyphosate applied POST and LPOST at 0.53 or 1.1 kg ai/ha. Glyphosate applied POST and LPOST was more effective than glyphosate POST, but net returns were greater only in 2004.

Nomenclature: Atrazine, foramsulfuron, nicosulfuron, pendimethalin, potassium salt of glyphosate, Texas panicum, Panicum texanum L. #³ PANTE, corn, Zea mays L. ‘DeKalb 67-60RR’.

Additional index words: Economics, herbicide-resistant crops, postemergence.

Abbreviations: AMS, ammonium sulfate; COC, crop oil concentrate; GR, glyphosate resistant; MSO, methylated seed oil.

Field research was conducted at Columbia and Novelty, MO, to determine the impact of winter-annual weed management systems on corn and soybean grain yields, winter-annual weed control, and soybean cyst nematode (SCN) egg population densities over the crop production cycle. Corn grain yield was not affected by winter-annual weed management systems. Soybean grain yield was not affected by winter weed management systems in 2001, but at Columbia in 2002 winter rye and Italian ryegrass reduced soybean grain yield 62 and 64%, respectively. Fall-applied simazine tribenuron in corn and chlorimuron sulfentrazone in soybean controlled winter-annual weeds greater than 99%. Fall-overseeded winter rye and Italian ryegrass in corn and overseeded Italian ryegrass in soybean controlled winter weeds 66 to 86%. In the soybean studies, race 4 SCN population densities increased (P  =  0.08) in the nontreated control and remained stable (P  =  0.55) with fall-applied chlorimuron sulfentrazone from fall 2001 to spring 2002 while SCN population densities were reduced (P  =  0.06) with spring-applied chlorimuron sulfentrazone from fall 2002 to spring 2003. In the corn studies, none of the winter-annual weed management strategies reduced (P > 0.22) race 2 SCN population densities except winter rye from fall 2001 to spring 2002 (P  =  0.05). This research indicates that control of weed species considered to be weak alternative hosts for SCN affected SCN population densities some instances when race 4 SCN population densities were high in a continuous soybean production system or race 2 SCN population densities were low in a 2-yr corn production system.

Nomenclature: Chlorimuron, sulfentrazone, simazine, tribenuron, common chickweed, Stellaria media (L.) Vill. #³ STEME, field pennycress, Thlaspi arvense L. # THLAR, henbit, Lamium amplexicaule L. # LAMAM, soybean cyst nematode, Heterodera glycines Ichinohe, corn, Zea mays L. ‘Asgrow RX740 RR’, Italian ryegrass, Lolium multiflorum L. ‘Marshall’, soybean, Glycine max (L.) Merr. ‘DK 38-52’, winter rye, Secale cereale L. ‘Forage Master’.

Additional index words: Weed–nematode interaction, integrated pest management.

Abbreviations: COC, crop oil concentrate.

Woody plant herbicide screening techniques were evaluated to expedite the screening process and decrease amounts of herbicide active ingredient required. Rapid greenhouse screening of woody plant seedlings was performed in less than 6 months, and rapid seed screening was performed in less than 20 days. A traditional field screen, requiring 10 months from application to final evaluation, was performed for comparison and regression modeling purposes. Imazapyr and triclopyr were used as test chemicals and linear regressions were generated to predict traditional field screen results from rapid screens. Significant regressions were produced that predicted field responses of loblolly pine, sweetgum, and yellow-poplar with the use of both herbicides and either rapid screening technique. This indicated that rapid screening techniques could determine herbicide efficacy and/or species spectrum in much less time with significantly less herbicide. Rapid greenhouse screens of triclopyr produced more statistically significant regressions than those using imazapyr. Rapid seed screens could estimate species spectrum within 5 days after treatment. These results indicate that rapid greenhouse screen and rapid seed screen techniques can provide woody plant herbicide developers initial efficacy and spectrum of control data in a cost- and-time effective manner.

Nomenclature: imazapyr, triclopyr, green ash, Fraxinus pennsylvanica Marsh, loblolly pine, Pinus taeda L, sweetgum, Liquidambar styraciflua L. #³ LIQST, yellow-poplar, Liriodendron tulipfera L. # LIRTU.

Additional index words: Rapid greenhouse screen, rapid seed screen.

Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); DAT, days after treatment; WAT, weeks after treatment; YAT, year after treatment; % C Ht, percent control of height; % Nec, percent leaf necrosis; % Mort, percent mortality; P, P value for test of significance; R², coefficient of determination; CV, coefficient of variation; µE/m²/s, microEinstein per square meter per second.

Johnsongrass control in fallowed sugarcane fields was evaluated with glyphosate and the graminicides quizalofop, fluazifop, and clethodim applied in soybean compared with nonsoybean tillage and glyphosate programs. Glyphosate was applied to glyphosate-resistant soybean as a single early postemergence (EPOST) treatment around 30 d after planting (DAP) at rates of 840, 1,120, or 2,240 g ai/ha; as sequential treatments EPOST and late postemergence (LPOST) around 60 DAP at 560 followed by (fb) 560 or 1,120 fb 1,120 g/ha; or as a single LPOST treatment at 2,240 g/ha. Quizalofop at 77 g ai/ha, fluazifop at 420 g ai/ha, and clethodim at 280 g ai/ha were also evaluated as single EPOST treatments. In 1996 johnsongrass control 7 d after EPOST treatment (DAT) was at least 90% for glyphosate treatments but control was 73 to 77% for the graminicides. In 1997 johnsongrass control 7 DAT was at least 82% for all herbicide treatments. Excellent johnsongrass control approximately 50 DAT was achieved both years with all the glyphosate and graminicide treatments. In the nonsoybean fallow weed control programs where plots were tilled twice or three times fb one or two glyphosate applications, complete control of johnsongrass was obtained both years. In 1996 when glyphosate was applied EPOST or EPOST fb LPOST, soybean yields were equivalent and averaged 3.3 times that of the single LPOST glyphosate application. Soybean yields where the graminicides were used and where glyphosate was applied as a single LPOST treatment were no greater than the nontreated control. Economic analysis on the basis of soybean yield data and variable costs of herbicides, seed, field application, seedbed preparation, tillage, labor, fuel, repairs, and custom harvest expense in 1996 showed a positive net return only for glyphosate applied EPOST at 840 g/ha ($99.82/ha) or 1,120 g/ha ($46.94/ha) and for glyphosate applied at 560 g/ha EPOST fb LPOST ($10.41/ha). Although showing a negative net return, glyphosate applied EPOST at 2,240 g/ha ($−8.32/ha) or EPOST fb LPOST at 1,120 g/ha ($−50.97/ha), the loss was less than that for nonsoybean fallow tillage and glyphosate programs ($−155.70/ha and $−157.78/ha). In 1997, when soybean was not harvested because of environmental conditions, variable costs exceeded those of the nonsoybean programs, indicating that planting soybean strictly as a cover crop would not be economically advantageous. Sugarcane growth and yield the year following the fallow programs was not negatively affected by production of soybean regardless of herbicide program.

Nomenclature: Clethodim, fluazifop, glyphosate, quizalofop, soybean, Glycine max (L.) Merr. ‘Hartz 4102 RR’, sugarcane, Saccharum interspecific hybrids ‘CP 70-321’.

Additional index words: Graminicides, net return, perennial weed control, tillage, variable costs, weed control programs.

A replacement series study was conducted to describe the aggressivity between cucumber, smooth pigweed, and livid amaranth. Cucumber was three times more competitive than smooth pigweed or livid amaranth, under the conditions of this study. However, there was equal competition and no antagonism between smooth pigweed and livid amaranth. Where cucumbers were planted in mixture with either of the two weeds, the relative yield total values were approximately 10 to 20% higher than the monocultures. Cucumber was a superior competitor when grown in mixture with smooth pigweed or livid amaranth, and the following aggressivity hierarchy exists: cucumber > livid amaranth  =  smooth pigweed. Results from the additive field study indicated that amaranth dry weights were significantly affected by smooth pigweed and livid amaranth density. Dry weight of amaranth was decreased by 48% at Gainesville and 25% at Live Oak, at 18 plants/m². Despite differences between the Gainesville and Live Oak results, the dry weight data were similar for both smooth pigweed and livid amaranth at each location.

Nomenclature: livid amaranth, Amaranthus lividus L. #³ AMALI, smooth pigweed, Amaranthus hybridus L. # AMACH, cucumber, Cucumis sativus L.

Additional index words: Weed competition, additive study, replacement study.

Abbreviations: RY, relative yield; RYT, relative yield total; AG, aggressivity; DAT, days after transplanting.

Experiments were conducted to study the effect of application rate, growth stage, and tank-mixing azimsulfuron or bentazon on the activity of cyhalofop, clefoxydim, and penoxsulam against two morphologically distinct Echinochloa species from rice fields in Greece. Mixtures of penoxsulam with MCPA were also evaluated. Cyhalofop (300 to 600 g ai/ha) applied at the three- to four-leaf growth stage provided 62 to 85% control of early watergrass but 41 to 83% control of late watergrass averaged over mixture treatments. Control ranged from 37 to 80% for early watergrass and from 35 to 78% for late watergrass when cyhalofop was applied at the five- to six-leaf growth stage averaged over mixture treatments. Mixtures of cyhalofop with azimsulfuron or bentazon reduced efficacy on both species irrespective of growth stage or cyhalofop application rate compared with cyhalofop alone. Clefoxydim (100 to 250 g ai/ha) applied alone at the three- to four-leaf growth stage provided 98 to 100% control of early watergrass and 91 to 100% control of late watergrass; when clefoxydim was applied alone at the five- to six-leaf growth stage the control obtained was 91 to 100% for early watergrass and 79 to 100% for late watergrass. Mixtures of clefoxydim with azimsulfuron or bentazon reduced efficacy on late watergrass at the early growth stage and on both species at the late growth stage. Penoxsulam (20 to 40 g ai/ha) applied alone provided 94 to 100% control of both species at both growth stages. Mixtures of MCPA with penoxsulam reduced efficacy on late watergrass at the early growth stage and on both species at the late growth stage. Mixtures of penoxsulam with azimsulfuron or bentazon reduced efficacy only on late watergrass at the late growth stage.

Nomenclature: Azimsulfuron, bentazon, clefoxydim (BAS 625H), cyhalofop, penoxsulam (DE-638), early watergrass, Echinochloa oryzoides (Ard.) Fritsch. #³ ECHOR, late watergrass, Echinochloa phyllopogon (Stapf.) Koss. # ECHPH.

Additional index words: Antagonism, herbicide interactions, mixtures.

Abbreviations: DAT, days after treatment.

The objectives of this research were to evaluate herbicide safeners and water repellents for their efficacy in reducing injury caused by isoxaflutole to corn at four application timings (PRE, spike, two-leaf, and four-leaf), and to evaluate the retention of the combinations of isoxaflutole, herbicide safeners, and water-repellent adjuvants. The safeners R-29148 and furilazole decreased injury from isoxaflutole when applied PRE. Corn injury increased from POST applications at the two-leaf and four-leaf stage of isoxaflutole mixed with safeners compared with isoxaflutole alone. The safeners may have acted as adjuvants to increase isoxaflutole absorption. The water-repellent adjuvants did not reduce injury when applied POST with isoxaflutole. However, the combination of safener plus the water repellent DC 1-6184 reduced corn injury from POST applications of isoxaflutole. The water repellent DC 1-6184 reduced spray retention of spray solutions containing isoxaflutole or isoxaflutole plus safener.

Nomenclature: Furilazole, isoxaflutole, mesotrione, R-29148, corn, Zea mays L. ‘Dekalb 44–46’.

Additional index words: Adjuvants, protectants.

Abbreviations: DAT, d after treatment.

Biotypes of smallflower umbrella sedge and ricefield bulrush resistant to acetolactate synthase (ALS)-inhibiting herbicides have been reported in several rice areas of the world. Here, we present results of a study conducted on whole plants of seven smallflower umbrella sedge and four ricefield bulrush biotypes collected in Italian, Spanish, and Californian rice fields to evaluate cross-resistance to ALS herbicides in these important weeds of temperate rice. The following herbicides were tested: bensulfuron-methyl, halosulfuron, cinosulfuron, imazamox, and bispyribac-sodium. The smallflower umbrella sedge and ricefield bulrush biotypes studied exhibited different cross-resistance patterns, some of which have not been previously reported. The Italian smallflower umbrella sedge biotype was cross-resistant to bensulfuron-methyl, cinosulfuron, imazamox, and bispyribac-sodium, but was susceptible to halosulfuron. One smallflower umbrella sedge biotype from California was also resistant to bensulfuron-methyl, imazamox, and bispyribac-sodium, but had a lower level of resistance to halosulfuron. In contrast, the second smallflower umbrella sedge biotype from California was strongly resistant to halosulfuron and was also resistant to bensulfuron-methyl and bispyribac-sodium, but moderately resistant to imazamox. The Spanish smallflower biotype was resistant to the sulfonylurea herbicides bensulfuron-methyl and halosulfuron. Different responses were observed in ricefield bulrush. The Italian biotype was resistant to the sulfonylureas only, whereas the biotype from California exhibited broad cross-resistance to all the ALS herbicides tested. Knowledge on cross-resistance is needed to formulate herbicide use and weed management strategies for delaying the evolution of resistance to ALS herbicides in rice systems.

Nomenclature: Bensulfuron-methyl, halosulfuron, cinosulfuron, imazamox, bispyribac-sodium, smallflower umbrella sedge, Cyperus difformis L. #³ CYPDI, ricefield bulrush, Schoenoplectus mucronatus (L.) Palla (syn. Scirpus mucronatus L.) # SCMPU.

Additional index words: ALS herbicides, herbicide resistance, cross-resistance, weed management, temperate rice, rice production systems.

Abbreviations: SU, sulfonylureas; IMI, imidazolinones; TP, triazolopyrimidines; PB, pyrimidinylbenzoates; SCT, sulfonylaminocarbonyltriazolinones; FW, fresh weight; GR₅₀, herbicide dose necessary to cause 50% growth reduction; I₅₀, herbicide dose necessary to cause 50% inhibition; LD₅₀, herbicide dose necessary to cause 50% mortality; R, resistant; RI, resistance index; S, susceptible.

Response of creeping bentgrass, annual bluegrass, and Kentucky bluegrass to foliar, soil, or foliar plus soil applications of bispyribac-sodium was evaluated in greenhouse studies. Soil-alone and foliar plus soil applications of bispyribac-sodium at 148 or 296 g ai/ha resulted in greater injury and shoot dry weight reduction of all species 28 d after treatment (DAT) compared to foliar-alone treatments. Creeping bentgrass was less injured than annual or Kentucky bluegrass regardless of application placement. Further studies evaluated foliar and root absorption and translocation of ¹⁴C-bispyribac-sodium in creeping bentgrass, annual bluegrass, Kentucky bluegrass, and roughtstalk bluegrass. Foliar absorption into creeping bentgrass was less than that of other species at most harvest timings from 4 to 72 h after treatment. Annual and roughstalk bluegrass translocated greater amounts of foliar-absorbed ¹⁴C to the crown and shoots compared to creeping bentgrass. Annual and roughstalk bluegrass accumulated approximately 47% more ¹⁴C per dry weight of plant tissue than creeping bentgrass and 74% more than Kentucky bluegrass after 72 h in nutrient solution containing ¹⁴C-bispyribac-sodium. Annual and roughstalk bluegrass translocated approximately 80% of root-absorbed ¹⁴C to shoots, whereas creeping bentgrass and Kentucky bluegrass translocated slightly less (66% of absorbed for both species). These studies suggest that bispyribac-sodium is readily absorbed by roots and translocated to shoots which may contribute to its total activity within a plant. In addition, creeping bentgrass displayed lower amounts of foliar and root absorption and subsequent translocation than annual and roughstalk bluegrass which may contribute to greater bispyribac-sodium tolerance displayed by creeping bentgrass.

Nomenclature: Bispyribac-sodium, annual bluegrass, Poa annua L. #³ POAAN, creeping bentgrass, Agrostis stolonifera L. ‘L-93’ #AGSST, roughstalk bluegrass, Poa trivialis L. ‘Winterplay’ #POATR, Kentucky bluegrass, Poa pratensis L. ‘Baron’ #POAPR.

Additional index words: Herbicide placement, site of uptake.

Abbreviations: ALS, acetolactate synthase (EC 2.2.1.6); HAT hours after treatment; LSS, liquid scintillation spectroscopy; WAT, weeks after treatment.

Sulfentrazone was applied POST at 13, 26, or 53 g ai/ha alone or in combination with metribuzin at 280 or 420 g ai/ha in field trials conducted with ‘Russet Burbank’ potatoes in 2002 to 2004. Sulfentrazone alone provided less than 84% redroot pigweed, common lambsquarters, and kochia control, although control usually improved to 90% or greater when metribuzin was included. Hairy nightshade control reached 90% only when the highest rates of both herbicides were applied in combination. Sulfentrazone alone did not provide any volunteer oat control, whereas control was 85% when the highest metribuzin rate was included. Potato crop injury, consisting of chlorosis, interveinal blackening of the leaves, eventual necrosis, leaf malformation, and plant stunting, increased as the sulfentrazone rate increased. In contrast, injury decreased as metribuzin rate increased from 0 to 420 g/ha, when averaged across sulfentrazone rates. Reduction in injury levels and increased weed control translated to improved tuber yields as metribuzin rate increased. However, when sulfentrazone was combined with the highest metribuzin rate, potato injury was still relatively high at 26 and 18% at 1 and 4 wk after treatment, and acceptance of sulfentrazone applied POST with metribuzin by potato growers is unlikely.

Nomenclature: Metribuzin, sulfentrazone, common lambsquarters, Chenopodium album L. #³ CHEAL, kochia, Kochia scoparia (L.) Shrad. # KCHSC, redroot pigweed, Amaranthus retroflexus L. # AMARE, hairy nightshade, Solanum sarrachoides Sendtn # SOLSA, volunteer oat, Avena sativa L. # AVESA, potato, Solanum tuberosum L. ‘Russet Burbank’.

Additional index words: Herbicide interaction, potato crop response, safening effect.

Abbreviations: WAT, weeks after treatment.

Blessed thistle is an important medicinal crop in Europe and recently has become more significant in North America. A limiting factor in blessed thistle production is weed interference. Field experiments were conducted near Plovdiv, Bulgaria, to study the effect of selected herbicides on weed control, crop productivity, and crop quality. Seed yields of blessed thistle were increased with metribuzin alone at 0.5 kg ai/ha, pendimethalin alone 1.32 kg ai/ha, pendimethalin at 1.32 kg ai/ha plus metribuzin at 0.5 kg ai/ha, trifluralin at 0.84 kg ai/ha plus linuron at 1.0 kg ai/ha, and in the hand-weeded control compared to the nonweeded control (nontreated check). Pendimethalin and metribuzin were safe both alone and in combination for weed control in blessed thistle. Bentazon at 0.96 kg ai/ha inhibited blessed thistle development and reduced seed yields compared to the untreated check. Generally, weed control increased the content of silymarin and decreased the amount of seed oil. Overall, seeds contained 0.26 to 0.36% taxifolin, 0.69 to 0.99% silydianin plus silycristin, 1.31 to 1.78% silybin, and 0.27 to 0.39 % isosilybin.

Nomenclature: Bentazon, linuron, metribuzin, pendimethalin, trifluralin, blessed thistle, Silybum marianum (L.) Gaertn. ‘Silmar’ #³ SLYMA.

Additional index words: Medicinal plants, seed oil, seed yield, silymarin, taxifolin, silydianin, silycristin, silybin, isosilybin.

Field trials were conducted to evaluate weed control and soybean tolerance with co-application of pyraflufen-ethyl and glyphosate. Pyraflufen-ethyl applied at 11, 23, or 45 g ai/ha in combination with glyphosate did not affect control of barnyardgrass, browntop millet, redroot pigweed, sicklepod, or smellmelon compared to glyphosate alone or co-applied with chlorimuron. Initial benefit (7 DAT) to pitted morningglory control with pyraflufen-ethyl plus glyphosate compared to glyphosate alone or co-applied with chlorimuron was not observed 28 DAT. Hemp sesbania control was increased by pyraflufen-ethyl at 45 g/ha plus glyphosate and glyphosate plus chlorimuron relative to glyphosate applied alone. Pyraflufen-ethyl plus glyphosate resulted in significant visual soybean injury, and a reduction in soybean yield was observed with pyraflufen-ethyl at 45 g/ha relative to glyphosate applied alone or in combination with chlorimuron. Results from a weed-free study confirmed crop injury and yield reduction potential with pyraflufen-ethyl plus glyphosate. Overall results suggest no benefit with respect to weed control or crop tolerance to pyraflufen-ethyl inclusion in a glyphosate-resistant soybean weed control program over that observed with currently registered co-application of glyphosate and chlorimuron.

Nomenclature: Chlorimuron, glyphosate, pyraflufen-ethyl, barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG, browntop millet, Brachiaria ramosa (L.) Stapf. # PANRA, hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill # SEBEX, pitted morningglory, Ipomoea lacunosa L. # IPOLA, redroot pigweed, Amaranthus retroflexus L. # AMARE, sicklepod, Senna obtusifolia L. # SENOB, smellmelon, Cucumis melo L. var. dudaim Naud. # CUMMD, soybean, Glycine max (L.) Merr.

Additional index words: Co-application, crop response, crop tolerance, postemergence.

Abbreviations: lf, leaf; PDS, post-directed spray; PPO, protoporphyrinogen oxidase.

Turf managers traditionally avoid seeding cool-season turfgrass in spring due to summer annual weed interference and poor growing conditions for cool-season grasses. Siduron is the most accepted herbicide for weed control in spring-seeded tall fescue, but it has low residual activity and does not control many weeds other than crabgrass. Isoxaflutole, mesotrione, and quinclorac were evaluated as alternatives to siduron. Single applications of these herbicides controlled crabgrass equivalent to or better than siduron. Sequential applications of isoxaflutole, mesotrione, or quinclorac effectively controlled smooth crabgrass without injuring tall fescue. Isoxaflutole and mesotrione controlled broadleaf plantain, henbit, and yellow woodsorrel; quinclorac marginally controlled henbit; and siduron did not control broadleaf weeds. Turfgrass cover 9 wk after seeding was dependent on environment and equivalent between treatments except at a location with predominately broadleaf weeds where siduron treatments resulted in less cover due to weed infestation. Sequential applications of isoxaflutole, mesotrione, and quinclorac provide an effective, safe option for chemical weed control during establishment of cool-season turfgrass.

Nomenclature: Isoxaflutole, mesotrione, quinclorac, siduron, broadleaf plantain, Plantago major L. #³ PLAMA, henbit, Lamium amplexicaule L. # LAMAM, smooth crabgrass, Digitaria ischaemum Schreb.ex Muhl. # DIGIS, yellow woodsorrel, Oxalis stricta L. # OXAST ‘Midnight’, tall fescue, Festuca arundinacea Schreb. ‘Crossfire II’.

Additional index words: Cool-season turfgrass, turfgrass establishment, turfgrass injury.

Abbreviations: EPOST, early postemergence; fb, followed by; GRF, Glade Road Research Facility, Blacksburg, VA; LPOST, late postemergence; TRC, Turfgrass Research Center, Blacksburg, VA; WAIT, weeks after initial treatment; WAP, weeks after planting.

Control of glyphosate-resistant (GR) horseweed in no-till cotton has become a serious challenge for midsouth producers. Control of GR horseweed prior to no-till cotton planting (burndown) was examined with glufosinate applied at a standard rate (0.47 kg ai/ha) 30, 21, and 14 d before planting (DBP) and at 0.35 and 0.58 kg ai/ha 14 DBP. Glufosinate at 0.47 kg ai/ha was also tank-mixed with 2,4-D, dicamba, or flumioxazin 30 DBP, and with diuron, pendimethalin, prometryn, or glyphosate at 14 DBP. Glufosinate applied at the standard rate 21 or 30 DBP did not control GR horseweed (<55%), but did provide better control (85%) when applied 14 DBP. The high rate of glufosinate (0.58 kg ai/ha) applied 14 DBP controlled GR horseweed. Tank mixtures of glufosinate with dicamba or 2,4-D at 30 DBP controlled GR horseweed. Tank mixtures of glufosinate with either prometryn or diuron provided initial burndown and residual weed control. Tank mixtures of glufosinate pendimethalin or flumioxazin did not increase control of existing horseweed, but did provide residual control 56 days after application.

Nomenclature: Horseweed, Conyza canadensis (L.) Cronq. #³ ERICA, cotton, Gossypium hirsutum L. ‘FiberMax 966’.

Additional index words: Burndown, herbicide application timing.

Abbreviations: DAA, days after application.

Weed control in organic vegetable production systems is challenging and accounts for a large portion of production costs. Six methods to prepare a stale seedbed were compared on certified and transitional organic land in Salinas, CA, in 2004. Weed control operations occurred on raised beds 2 to 3 d before planting baby spinach or a simulated vegetable planting. A flamer and an herbicide application of 10% v/v of a clove oil mixture (45% v/v clove oil) at 280 L/ha (iteration 1) or 15% v/v of a clove oil mixture (45% clove oil) at 467 L/ha (iterations 2 and 3) were used to control weeds without disturbing the soil. Top knives on a sled, a rolling cultivator, and a rotary hoe were used to control weeds while tilling the bed top. A bed shaper–rototiller combination was also used, which tilled the entire bed. Broadleaf weed control was 36% with clove oil, 63% with the rotary hoe, and significantly higher (87 to 100% control) with the remaining treatments in iteration 1. Broadleaf weed control was consistently lower (72 to 86% control) with the flamer than all other treatments (95 to 100% control) in iterations 2 and 3. The difference between sites can probably be attributed to differences in weed size. The flamer and the clove oil herbicide had the lowest number of weeds emerging with the crop following stale seedbed formation. The most expensive technique was clove oil at $1,372/ha. The estimated cost of forming the stale seedbed with the remaining weed management tools ranged from $10 to $43/ha.

Nomenclature: Spinach, Spinacia oleracea L. #³ SPQOL.

Additional index words: Flaming, cultivation, weed emergence, irrigation, stale seedbeds, vegetables.

Abbreviations: USDA-ARS, U.S. Department of Agriculture–Agricultural Research Service.

During dry weather, preplant irrigation of raised beds followed by shallow tillage to create a smooth planting bed is necessary to establish a good lettuce stand. Depletion of germinable weed seeds in the top 5 cm of soil by the sequence of preplant irrigation, followed 7 to 14 d later by shallow tillage to prepare a seedbed, reduces weed density in the subsequent crop. Preplant irrigation and tillage reduces weed density and, when used together with preplant herbicide, provides effective weed control in the cropping season. Preplant and in-crop weed densities resulting from furrow or sprinkler preplant irrigation, followed by shallow tillage and lettuce planting 7 or 14 d later, were compared with the no preplant irrigation control. During the 14-d preplant period, up to 127 weeds/m² emerged and were removed by shallow tillage before crop planting. Preplant irrigation and shallow tillage reduced in-crop weed density by up to 77% and reduced hand-weeding and crop-thinning time by up to 50% compared with the no preplant irrigation and no herbicide control. Delaying tillage for 14 d following preplant irrigation provided sufficient time for adequate heat unit accumulation (>120 growing degree days, base 10 C), allowing for many weeds to germinate and be killed by shallow tillage. However, 7 d between preplant irrigation and tillage resulted in less heat unit accumulation (<50 growing degree days, base 10 C) and less weed germination before tillage. Preplant irrigation together with pronamide at either 0.67 or 1.34 kg ai/ha reduced weed density compared with the no preplant irrigation. Effective use of preplant irrigation and preplant weed removal may increase the consistency of weed control with lower pronamide rates. Preplant irrigation followed by shallow tillage is an effective cultural practice to control in-crop weeds for conventional lettuce production.

Nomenclature: Pronamide, burning nettle, Urtica urens L. #³ URTUR, henbit, Laminum amplexicaule L. # LAMAM.

Additional index words: Cultural weed control, furrow-irrigation, preplant weed removal, sprinkler-irrigation, vegetables.

Abbreviations: df, degree-of-freedom; GDD, growing degree-days.

Fifty-five soybean cyst nematode (SCN)–infested production fields across Indiana were surveyed in March 2004 to assess broadleaf winter weed prevalence. The most frequently occurring weeds were common chickweed (87%), speedwell (83%), buttercup (58%), and henbit (53%). Henbit and wild garlic were present at the highest average densities, both occurring at greater than 50 plants/m². Based on relative abundance indices, common chickweed and henbit were the most prevalent winter weeds in this survey. As a composite, winter weed hosts of SCN were found in 93% of fields and occurred at an average density of 151 plants/m². No correlation existed between weed density and SCN egg counts. Frequency, uniformity, density, and diversity indices for individual weed species were generally higher in the southern region of Indiana than in the north. Thus, the region of highest risk for SCN reproduction and population increase on winter weeds in Indiana appears to be in the southern part of the state.

Nomenclature: Buttercup, Ranunculus spp, common chickweed, Stellaria media (L.) Vill. #³STEME, henbit, Lamium amplexicaule L. # LAMAM, speedwell, Veronica spp, wild garlic, Allium vineale L. # ALLVI, soybean cyst nematode, Heterodera glycines Ichinohe.

Additional index words: Crop rotation, integrated pest management, purple deadnettle, soil temperature, winter annual weeds.

Abbreviations: GPS, Global Positioning System; GR, glyphosate-resistant.