Managing glyphosate-resistant (GR) horseweed in no-till cotton continues to be a serious challenge for midsouthern producers. Field studies were conducted in 2008 and 2009 to evaluate spring burndown applications of saflufenacil on GR horseweed prior to planting cotton. Saflufenacil controlled GR horseweed at least 94% up to 7 d before planting (DBP) without causing significant cotton injury. Saflufenacil applied at 7 or 14 DBP controlled GR horseweed while still providing residual control until planting. Moreover, saflufenacil, on silt loam soil evaluated in this study, showed no more injury than dicamba applied 7 or more DBP. Results indicated that saflufenacil is an option in cotton for controlling GR horseweed much closer to cotton planting than 42 DBP (current saflufenacil label). At 25 g ha⁻¹, which is the standard labeled rate in cotton, saflufenacil provided > 90% control of GR horseweed. Saflufenacil as a GR horseweed burndown, could replace the current dicamba standard every other year to reduce the probability of horseweed developing resistance to dicamba or salflufenacil.

Nomenclature: Horseweed, Conyza canadensis (L.) Cronq. ERICA; cotton, Gossypium hirsutum L. Phytogen 485WRF

Research was conducted for 2 yr at Marianna, AR, to determine whether the fall-planted cover crops rye, wheat, turnip, and a blend of brown and white mustard (Caliente) would aid weed management programs in conservation-tilled, enhanced, glyphosate-resistant cotton. Wheat and rye easily were established both years and turnip and mustard blend stands were better in the second year. The cover crops alone were more suppressive of Palmer amaranth, pitted morningglory, and goosegrass in 2007 than in 2008. Rye was generally superior to wheat in suppressing the three evaluated weeds. Once herbicides were applied, there were seldom differences among cover crops for a particular herbicide program as a result of the highly efficacious herbicide programs. Cotton yields were not affected by wheat, rye, or the mustard blend, but yields were lowest in plots that followed turnip both years, possibly because of allelopathy. Integration of cover crops, especially cereals, into conservation-tilled, glyphosate-resistant cotton aided early-season weed management and could reduce the selection of glyphosate for herbicide resistance.

Nomenclature: Goosegrass, Eleusine indica (L.) Gaertn. ELEIN; Palmer amaranth, Amaranthus palmeri S. Wats AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; brown mustard, Brassica juncea (L.) Czern.; cotton, Gossypium hirsutum L; rye, Secale cereale L.; turnip, Brassica rapa L., wheat, Triticum aestivum L.; white mustard, Sinapis alba L

Velvetleaf is one of the most significant and fastest spreading alien weeds in Europe, and it is a difficult weed to control in conventional sugarbeet. Laboratory experiments were carried out in 2007 and 2008 and field experiments were carried out in 2006, 2007, and 2008 with the aim of finding effective herbicide combinations and optimum timing of control. Herbicides containing the active ingredients phenmedipham, desmedipham, ethofumesate, clopyralid, and triflusulfuron were all tested at different timings. Phenmedipham desmedipham ethofumesate gave 87% velvetleaf control in pot experiments when applied at the growth stages of velvetleaf cotyledons and one true leaf, but only 27 to 42% control in field trials. Triflusulfuron gave 76% control in pot experiments and 83 to 88% control in field experiments. The timing of the first and second herbicide applications was very important: the first application of herbicides must be at the cotyledon stage of velvetleaf. A 1-wk delay in first application reduced herbicide efficacy by 8%. A 5-d period between the first and second treatments gave 93% control, while a 10-d period between the first and second treatments gave only 77% control. Sugarbeet yield decreased by 60 to 86% due to competition with velvetleaf when a standard herbicide combination (phenmedipham desmedipham ethofumesate) was used, and the velvetleaf produced between 6,700 and 14,800 seeds m⁻². Inclusion of triflusulfuron in the herbicide treatment significantly reduced velvetleaf seed production to between 200 and 4,700 seeds m⁻². In most cases, inclusion of triflusulfuron increased sugarbeet yield. Better velvetleaf control occurred in years when the sugarbeet canopy developed early and the index of leaf area of sugarbeet was higher.

Nomenclature: Clopyralid; desmedipham; ethofumesate; phenmedipham; triflusulfuron; velvetleaf, Abutilon theophrasti Medik.; sugarbeet, Beta vulgaris ssp. vulgaris var. altissima L

Field studies were conducted in 2007 and 2008 at seven sites in Ohio, Indiana, and Illinois to determine the effect of PRE herbicide and POST application timing on weed control and yield of glyphosate-resistant corn. Levels of PRE herbicide included none; low—atrazine; medium—atrazine and metolachlor; and high—atrazine, mesotrione, and metolachlor. Glyphosate was applied POST when corn was 30 cm tall, or 1 or 2 wk later. Common lambsquarters, giant foxtail, and giant ragweed infested at least six of the seven sites, and other weed species occurred at two to three sites. Control of weeds at the time of POST application ranged from 48 to 91%, 58 to 99%, and 87 to 100% for the low, medium, and high levels of PRE herbicide, respectively, averaged over POST application timing. Control of giant foxtail and redroot pigweed decreased by about 20% between the second and third POST timing, averaged over PRE herbicide, but control of other weeds was similar among timings. Late-season control of common ragweed, velvetleaf, common lambsquarters, and Pennsylvania smartweed exceeded 90%, regardless of PRE herbicide or POST timing. Control of redroot pigweed, ivyleaf morningglory, and giant ragweed was as low as 74, 67, and 83%, respectively, but the high level of PRE herbicide resulted in 90 to 97% control of these weeds. An interaction between PRE herbicide and POST timing for late-season control of giant foxtail, tall waterhemp, and yellow nutsedge reflected the more effective control among POST timings from the higher levels of PRE herbicide. The overall trend in this study was for more effective weed control in PRE/POST herbicide programs with more comprehensive PRE herbicides that have substantial activity on both grass and broadleaf weeds. Highest yield occurred where the PRE treatment consisted of a two- or three-way combination of herbicides applied at 50% of the recommended rate or higher. Yield was reduced at all POST timings with atrazine alone or in the absence of PRE herbicide.

Nomenclature: Atrazine; glyphosate; mesotrione; metolachlor; common lambsquarters, Chenopodium album L. CHEAL; common ragweed, Ambrosia artemisiifolia L. AMBEL; giant foxtail, Setaria faberi Herrm. SETFA; giant ragweed, Ambrosia trifida L. AMBTR; ivyleaf morningglory, Ipomoea hederacea Jacq. IPOHE; Pennsylvania smartweed, Polygonum pensylvanicum L. POLPY; redroot pigweed, Amaranthus retroflexus L. AMARE; common waterhemp, Amaranthus rudis Sauer AMATA; velvetleaf, Abutilon theophrasti Medicus ABUTH; yellow nutsedge, Cyperus esculentus L. CYPES; corn, Zea mays L. ZEAMX

Research was conducted in 2007 and 2008 to evaluate weed-control options in an imazethapyr-resistant rice production system. Raised beds were formed, and imidazolinone-resistant hybrid rice ‘CL 730’ was drill-seeded on beds. Five herbicide programs applied up to the four- to six-leaf stage of rice were evaluated with and without additional “as-needed” herbicide at later stages. All the herbicide combinations and as-needed herbicides tested in this research were labeled for rice, and only minor transient injury (< 5%) was initially observed. Weeds emerged throughout the growing season, and as-needed herbicides were applied after the four- to six-leaf stage of rice to control these late-emerging weeds and weeds not effectively controlled with earlier applications, primarily Palmer amaranth. Most of the Palmer amaranth at this site was insensitive to imazethapyr (possibly acetolactate synthase resistant). Therefore, application of as-needed herbicides with different modes of action, such as 2,4-D, were used to improve Palmer amaranth control. Rice yields were often numerically higher in plots that received additional herbicide after the six-leaf stage of rice, but yields were not significantly improved.

Nomenclature: Imazethapyr; 2,4-D; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; rice, Oryza sativa L. ‘CL 730’ ORYSA

The widespread evolution of resistance in rigid ryegrass populations to the highly effective, in-crop, selective herbicides used within southern Australian grain-crop production systems has severely diminished the available herbicide resource. A new PRE grass-selective herbicide, pyroxasulfone, may offer Australian grain producers a new option for rigid ryegrass control in wheat crops. The efficacy and level of selectivity of rigid ryegrass control with pyroxasulfone was investigated for a range of annual crop species in potted-plant, dose–response studies. In comparison with other currently available PRE herbicides, pyroxasulfone provided effective control of both resistant and susceptible rigid ryegrass populations. Additionally, control of these populations was achieved at rates that had little or no effect on the growth and survival of wheat. This crop was also the most tolerant of cereal species, with triticale, barley, and oat being more injured at higher pyroxasulfone rates than wheat was. In general though, pulse-crop species were found to be more tolerant of high pyroxasulfone rates than cereal-crop species. There were subtle effects of soil type on the efficacy of pyroxasulfone, where higher rates were required to achieve effective control on soils with higher clay or organic matter contents. The ability of pyroxasulfone to selectively control resistant and susceptible rigid ryegrass populations as identified in these studies clearly indicate the potential for widespread use and success of this herbicide in Australian cropping systems.

Nomenclature: Pyroxasulfone (proposed common name), 3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)pyrazol-4-ylmethylsulfonyl]-4,5-dihydro-5,5-dimethyl-1,2-oxazole (formerly KIH-485, now BAY-191); rigid ryegrass, Lolium rigidum Gaudin LOLRI; common barley, Hordeum vulgare L. HORVX; oat, Avena sativa L. AVESA; triticale, ×Triticosecale rimpaui Wittm. TTLSS; common wheat, Triticum aestivum L. TRZAX

Research was conducted over 2 yr to evaluate soybean response to harvest aid herbicide treatments paraquat at 0.28 kg ai ha⁻¹, paraquat with carfentrazone at 0.014 kg ai ha⁻¹, and sodium chlorate at 6.72 kg ai ha⁻¹. Indeterminate and determinate soybean cultivars were treated when moisture of seed collected from the uppermost four nodes of plants averaged 60, 50, 40, 30, and 20% (± 2%). For each soybean cultivar, the harvest aid treatment by application timing interaction was not significant, and data for harvest aid treatments were averaged. Application of harvest aid at 60% average seed moisture reduced yield for the maturity group (MG) IV indeterminate cultivar 15.4% compared with the nontreated; 100-seed weight was reduced 12.4%. Yield and seed weight were not negatively affected when harvest aid was applied at 50% average seed moisture and soybean was harvested 14 and 15 d before the nontreated control. Although planting date in the 2 yr for the indeterminate cultivar differed by 26 d, number of days from planting to harvest aid application at 50% average seed moisture was 112 and 116 d. For MG V and MG VI determinate cultivars, application of harvest aid at 60% average seed moisture reduced yield compared with the nontreated control 22 and 18.1%, respectively, and at 50% average seed moisture 15.6 and 4%, respectively; seed weight reductions of 8.9 to 33.3% accompanied the yield reductions of the two cultivars. Reduction in soybean yield and seed weight was not observed when harvest aid was applied at 40% average seed moisture, and harvest for the 2 yr was 8 and 9 d earlier for the MG V cultivar and 10 and 14 d earlier for the MG VI cultivar.

Nomenclature: Carfentrazone; paraquat; sodium chlorate; soybean, Glycine max L. Pers. ‘Asgrow 4403 RR’, ‘Asgrow 5903 RR’, ‘Asgrow 6202 RR’

We conducted a series of field experiments to determine the role of several factors that might contribute to the inconsistent control of common lambsquarters with glyphosate. Experiments in 2006 and 2007 determined common lambsquarters response to glyphosate under a wide range of measured environmental conditions. Glyphosate was applied at 0.84 kg ae ha⁻¹ plus 3.8 kg ha⁻¹ ammonium sulfate (AMS) to 10-cm-tall plants on 18 dates in each year and to 20-cm-tall plants on 18 dates in 2007. Control was less for six application dates relative to control for 48 other dates. Poor control was attributed to rainfall on one of these six dates, but for the other five dates, regression analysis did not identify any significant relationships between environmental conditions (relative humidity, temperature at time of treatment, or minimum and maximum temperature pre- and posttreatment) and control, even though a wide range of conditions occurred. To determine the effects of plant growth stage on control, glyphosate was applied at 0.1 to 3.2 kg ha⁻¹ plus 3.8 kg ha⁻¹ AMS to 10- and 20-cm-tall plants at four sites. The glyphosate ED₅₀ value (the effective dose that reduced shoot mass by 50% relative to nontreated plants) was 1.9 to 3.0 times greater for 20- than 10-cm-tall plants in three site-years, but was not affected by plant height in one site-year. We also conducted experiments to determine the effect of rainfall on glyphosate efficacy. Across years, common lambsquarters control increased from 44 to 75% as the interval between glyphosate application (0.84 kg ha⁻¹ 3.8 kg ha⁻¹ AMS) and simulated rainfall increased from 0.5 to 4.0 h, respectively. Our results did not identify environmental conditions that explained reduced glyphosate efficacy in all cases, but they suggest that rainfall after application and plant height can be important factors contributing to the inconsistent control of common lambsquarters.

Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L. CHEAL

Field studies were conducted in Wyoming and Nebraska in 2007 through 2009 to evaluate winter wheat response to aminocyclopyrachlor. Aminocyclopyrachlor was applied at rates between 15 and 120 g ai ha⁻¹ 6, 4, and 2 mo before winter wheat planting (MBP). Redroot pigweed control was 90% with aminocyclopyrachlor rates of 111 and 50 g ha⁻¹ when applied 4 or 2 MBP. Aminocyclopyrachlor at 37 g ha⁻¹ controlled Russian thistle 90% when applied 6 MBP. At Sidney, NE, winter wheat yield loss was > 10% at all aminocyclopyrachlor rates when applied 2 or 4 MBP, and at all rates > 15 g ha⁻¹ when applied 6 MBP. At Lingle, WY, > 40% winter wheat yield loss was observed at all rates when averaged over application timings. Although the maturing wheat plants looked normal, few seed were produced in the aminocyclopyrachlor treatments, and therefore preharvest wheat injury ratings of only 5% corresponded to yield losses ranging from 23 to 90%, depending on location. The high potential for winter wheat crop injury will almost certainly preclude the use of aminocyclopyrachlor in the fallow period immediately preceding winter wheat.

Nomenclature: Aminocyclopyrachlor; redroot pigweed, Amaranthus retroflexus L., AMARE; Russian thistle, Salsola tragus L. SASKR; winter wheat, Triticum aestivum L

Few herbicides are available that will selectively control annual bluegrass in a polyculture of bermudagrass overseeded with perennial ryegrass. Research was conducted to evaluate multifaceted annual bluegrass control programs in overseeded bermudagrass. Treatments included various combinations of four herbicides: foramsulfuron applied 2 wk prior to overseeding (WPO); ethofumesate and bispyribac-sodium (bispyribac) applied 12 or 12 followed by (fb) 15 wk after overseeding (WAO); and prodiamine applied 15 WAO to provide continued PRE annual bluegrass control. Foramsulfuron at 0.03 kg ha⁻¹ applied 2 WPO controlled annual bluegrass 63% 28 WAO. Foramsulfuron fb ethofumesate or bispyribac applied 12 or 12 fb 15 WAO improved control to 91% or greater. Ethofumesate or bispyribac applied with prodiamine at 1.1 kg ha⁻¹ at 15 WAO did not improve annual bluegrass control compared with ethofumesate or bispyribac treatments alone according to pairwise contrasts. Only bispyribac-containing treatments induced unacceptable perennial ryegrass injury. Bispyribac applied with prodiamine reduced perennial ryegrass cover greater than bispyribac alone according to pairwise contrast. These data indicate that ethofumesate or bispyribac applied sequentially 12 and 15 WPO can effectively control annual bluegrass in bermudagrass turf overseeded with perennial ryegrass.

Nomenclature: Bispyribac, ethofumesate, foramsulfuron, prodiamine; annual bluegrass, Poa annua L.; bermudagrass, Cynodon dactylon (L.) Pers., ‘Riviera’; hybrid bermudagrass, Cynodon dacylon (L.) Pers. X C. transvaalensis Burtt-Davy, ‘Tifway’; perennial ryegrass (Lolium perenne L.) LOLPE ‘Palmer IV’

Seashore paspalum is used on golf courses in warm temperate regions, but prolific growth and seedhead development may reduce turfgrass quality. Field experiments were conducted to investigate efficacy of flazasulfuron and trinexapac-ethyl on seashore paspalum seedhead suppression, clipping reduction, and canopy height. Flazasulfuron applied from 4.5 to 27 g ai ha⁻¹ increased clipping reductions from the untreated by 22 to 75% and seedhead suppression from the untreated by 16 to 86% at 2 to 4 wk after treatment. Trinexapac-ethyl applied alone at 96 g ai ha⁻¹ provided erratic levels of seedhead suppression from the untreated, but reduced clippings by approximately 50 to 75% from nontreated by 2 to 4 wk after treatment. On several dates, trinexapac-ethyl enhanced clipping reductions and seedhead suppression from flazasulfuron compared to flazasulfuron alone. Trinexapac-ethyl exacerbated seashore paspalum injury from high flazasulfuron rates (18 to 27 g ha⁻¹) but injury never exceeded 23%. Trinexapac-ethyl reduced seashore paspalum height by 50% in unmowed areas at 16 wk. Flazasulfuron at 16 or 27 g ha⁻¹ with trinexapac-ethyl provided consistent seedhead suppression and clipping reductions ranging from approximately 70 to 95% of nontreated. These tank-mixtures have promising implications for use in seashore paspalum golf course fairways.

Nomenclature: Flazasulfuron; trinexapac-ethyl; seashore paspalum, Paspalum vaginatum Sw., ‘Sea Isle 1’, ‘Sea Isle Supreme’

Goatsrue response to eight herbicide treatments was evaluated in greenhouse and field trials. Herbicides tested on goatsrue grown from seed in the greenhouse included 2,4-D amine, dicamba, chlorsulfuron, picloram, imazapyr, imazamox, aminopyralid, and triclopyr. Each herbicide was applied at rates of 0.125×, 0.25×, 0.5×, 1.0×, and 2.0×, where X is equal to the labeled rate. Goatsrue was most sensitive to the acetolactate synthase inhibitors chlorsulfuron and imazapyr, with 50% inhibition values of 0.07× (3.7g ai ha⁻¹) and 0.16× (90 g ai ha⁻¹) respectively. Goatsrue did not respond to increasing 2,4-D and imazamox rates. Herbicides evaluated in the greenhouse were also tested at two field sites (Smithfield and Amalga, UT), except imazamox, which was replaced by metsulfuron. Field studies gave some varying results, but overall showed that chlorsulfuron, metsulfuron, aminopyralid, and picloram gave at least 93% control at Smithfield, and 89% control at Amalga 24 mo after treatment (MAT). Treatments of chlorsulfuron, metsulfuron, aminopyralid, and picloram were also effective at increasing perennial grass cover at Smithfield 24 MAT. All treatments at Smithfield decreased seedling goatsrue cover, whereas only aminopyralid and picloram decreased seedling cover at Amlaga 11 MAT.

Nomenclature: 2,4-D amine; dicamba; chlorsulfuron; picloram; imazapyr; imazamox; aminopyralid; triclopyr; metsulfuron; goatsrue, Galega officinalis L

Experiments were initiated during 2003 and 2004 to evaluate application placement equipment for plant growth regulator (PGR) applications along bahiagrass roadsides. Recently designed equipment combine low-volume application and pesticide placement technology. Application placement equipment conceal the image of a traditional spray application. Evaluated application placement equipment included a wet-blade mower (Burch Wet Blade) and rotary-wick applicator (Weedbug™) compared with a traditional broadcast spray. Wet-blade mowers are designed to mow and simultaneously apply a pesticide solution to a cut stem or leaf in a single pass, whereas rotary-wick applicators are designed to wick a solution onto foliage. Evaluated PGRs included imazapic (9, 35, or 53 g ha⁻¹) and sulfometuron-methyl (26 g ha⁻¹). Bahiagrass injury varied with application placement equipment and was greater with rotary-wick applications in 2003, compared with foliar broadcast applications and the wet-blade mower. Bahiagrass seedhead suppression ranged from 31 to 60% with application placement equipment in July 2003 compared with 93% for a broadcast spray. In 2004, rotary wick- or broadcast-applied PGRs provided excellent (> 90%) seedhead suppression. Although application placement equipment may have advantages to broadcast-spray applications, evaluated equipment did not enhance bahiagrass suppression along roadsides in North Carolina compared with a foliar broadcast spray. Additional research is needed to determine if this type of application may provide consistent results with other species and compounds.

Nomenclature: Imazapic; sulfometuron-methyl; bahiagrass, Paspalum notatum (Flueggé), ‘Pensacola’

Triticale is a low input crop, produced in North America primarily for silage for animal feed. Currently, seed growers have few herbicide options for producing certified seed. There is anecdotal evidence that triticale tolerates many of the same herbicides as wheat. In 2004 and 2005, the tolerance of three spring triticale varieties (AC Alta, AC Ultima, and Pronghorn) was tested with four herbicides registered for wheat: florasulam MCPA ester, clodinafop-propargyl, thifensulfuron-methyl/tribenuron-methyl, and sulfosulfuron-methyl 2,4-D ester. Herbicides were applied at the label rate (1×) for wheat and twice (2×) that rate. Crop injury, plant height, biomass, and seed yields were quantified. Neither florasulam MCPA ester, clodinafop-propargyl, nor thifensulfuron-methyl/tribenuron-methyl at 1× or 2× use rates significantly injured triticale. Sulfosulfuron-methyl 2,4-D ester reduced triticale height at the 1× and 2× rates, as well as reduced biomass and yield at the 2× rate. Florasulam MCPA ester, clodinafop-propargyl, and thifensulfuron-methyl/tribenuron-methyl do not cause significant crop injury and can be used for weed control in spring triticale, but sulfosulfuron-methyl 2,4-D ester is not recommended for use in triticale.

Nomenclature: Clodinafop-propargyl; 2,4-D ester; florasulam; MCPA ester; sulfosulfuron-methyl; thifensulfuron-methyl/tribenuron-methyl; triticale, ×Triticosecale Wittmack ‘AC Alta’, ‘AC Ultima’, ‘Pronghorn’; wheat, Triticum spp

Methyl bromide has been a key fumigant for broad-spectrum weed control in polyethylene-mulched bell pepper. However, the ozone-depleting nature of methyl bromide has led to its scheduled phaseout from U.S. agriculture. Thus, an effective alternative to methyl bromide is needed. Field trials were conducted in 2007 and 2009 to evaluate the crop response and weed control efficacy of allyl isothiocyanate (ITC) in polyethylene-mulched bell pepper. The experiment included various combinations of two mulch types (low density polyethylene [LDPE] and virtually impermeable film [VIF] mulch) and six rates of allyl isothiocyanate (0, 15, 75, 150, 750, 1,500 kg ha⁻¹). Additionally, a standard treatment of methyl bromide/chloropicrin (67 ∶ 33%) at 390 kg ha⁻¹ under LDPE mulch was included for comparison. Bell pepper injury was < 3% in all treatments, except 11% injury at 1,500 kg ha⁻¹ allyl isothiocyanate under VIF mulch at 2 wk after transplanting (WATP). VIF mulch did not provide additional weed control and marketable pepper yield over LDPE mulch. Allyl isothiocyanate at 932 (± 127) kg ha⁻¹ controlled yellow nutsedge (90%), Palmer amaranth (97%), and large crabgrass (92%) through 6 WATP and maintained the marketable yield equivalent to methyl bromide treatment. This research demonstrates that allyl ITC under an LDPE mulch can serve as a potential alternative to methyl bromide for weed control in polyethylene-mulched bell pepper.

Nomenclature: Allyl isothiocyanate; methyl bromide; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; yellow nutsedge, Cyperus esculentus L. CYPES; bell pepper, Capsicum annuum L. ‘Heritage’

Field experiments were conducted in Auburn, AL in 2008 and 2009 to assess new aryloxyphenoxypropionate (AOPP) herbicides applied alone and tank-mixed with triclopyr for Tifway bermudagrass control in Zorro zoysiagrass. Treatments included three sequential applications of clodinafop (0.07 kg ai ha⁻¹); triclopyr (1.12 kg ae ha⁻¹); clodinafop triclopyr (0.07 1.12 kg ha⁻¹); fenoxaprop (0.10 kg ai ha⁻¹); fenoxaprop triclopyr (0.10 1.12 kg ha⁻¹); metamifop (0.40 kg ai ha⁻¹); and metamifop triclopyr (0.40 1.12 kg ha⁻¹). Clodinafop, fenoxaprop, and metamifop applied alone controlled Tifway bermudagrass 32 to 65% when rated 3 wk after the final application; however, the addition of triclopyr to these AOPP herbicides increased bermudagrass control to ≥ 89%. All AOPP herbicides applied alone caused unacceptable injury to Zorro zoysiagrass (20 to 42%) 3 wk after the final application. Clodinafop resulted in the greatest zoysiagrass injury (42%), whereas metamifop caused moderate injury (20%). Zorro zoysiagrass exhibited less injury (< 3%) and greater turf coverage (≥ 95%) when AOPP herbicides were tank-mixed with triclopyr. Of the three AOPP herbicides evaluated in this study, only fenoxaprop is currently labeled for use on turfgrass. However, the nonlabeled herbicides (clodinafop and metamifop) provided bermudagrass control and zoysiagrass safety equal to the commercial standard (fenoxaprop) 3 wk after the final application when tank-mixed with triclopyr. Where zoysiagrass is contaminated with bermudagrass, turf managers will likely have to make applications of AOPP herbicides tank-mixed with triclopyr over multiple years to control bermudagrass as it will continue to regrow from deep rhizomes.

Nomenclature: Clodinafop; fenoxaprop; metamifop; triclopyr; hybrid bermudagrass, Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy, ‘Tifway’; zoysiagrass or Manilagrass, Zoysia matrella (L.) Merr., ‘Zorro’

Continuous planting of lettuce from December to September each year in the Salinas Valley of California requires preparation of raised fallow beds ready for planting. Application of soil residual herbicides during winter fallow periods controls weeds but must be used with caution because germinating lettuce seedlings are very sensitive to herbicide soil residues. Three herbicides were applied to fallow beds at about 90, 60, and 30 d before lettuce was seeded. Herbicides tested were flumioxazin at 71, 105, and 211 g ai ha⁻¹, two formulations of oxyfluorfen each at 280 and 560 g ha⁻¹, and carfentrazone at 36 g ha⁻¹. Herbicide injury to lettuce was assessed by visual estimates, crop stand, and number and weight of marketable lettuce heads. The 71 g ha⁻¹ rate of flumioxazin, both oxyfluorfen formulations, and carfentrazone did not injure seeded lettuce or reduce the number or weight of lettuce heads. Flumioxazin at 211 g ha⁻¹ injured lettuce, reducing the number of marketable heads, and should not be used within 90 d of lettuce planting.

Nomenclature: Carfentrazone; flumioxazin; oxyfluorfen; lettuce, Lactuca sativa L

Field trials were established in 2005 and continued in 2006 to evaluate a conventional broadcast herbicide sprayer compared to a variable spray (sensor-activated) weed-sensing sprayer (WSS). The computer-based Herbicide Application Decision Support System (WebHADSS™) was used to determine a portion of the herbicides applied (based on herbicide efficacy and economics). Weed control, herbicide usage, crop yield, and net returns were compared across treatments. The broadcast applications were usually the most effective at controlling weeds. A PPI herbicide did not always improve weed control compared to treatments in which no PPI herbicide was applied. Variable treatments used less herbicide than the broadcast system in both years. Cotton lint yields in broadcast applications were similar to the weed-free check in both years of the study. Variable treatments often provided equivalent net returns (gross yield revenue less weed control cost) to the broadcast treatments. Although herbicide savings were observed in the variable treatments when compared to a broadcast system, a reduction in weed control was observed, indicating the need for future improvements of this system. A site-specific weed management program used in conjunction with WebHADSS™ may have potential in cotton production systems in the Texas Southern High Plains where weed densities are low.

Nomenclature: Cotton, Gossypium hirsutum L

The utility of solaria (1 by 1-m plastic sheets) to predict densities of a few weed species in summer crops has been demonstrated previously, but needed further research to be adopted by farmers and advisors. We tested the method to detect important weeds in Argentina and Minnesota, and determined the minimum number of solaria required to predict the presence of emerged weed seedlings in the forthcoming growing season. Three experiments were performed in Buenos Aires Province, Argentina, and one in Minnesota. Solaria were placed in fields with different previous crops and soil management: no tillage (two fields) and conventional tillage (two fields). Preceding crops were corn (one field), wheat (one field), and double-cropped wheat/soybean (two fields). After weeds were enumerated, solaria were removed, sunflower (one field) and soybean (three fields) were planted, and weeds later assessed in each crop. Results indicate that one solarium per 1.9 ha can detect common lambsquarters with 95% confidence within the next summer crop. For other species, one solarium per 4.2, 1.2, 1.0, and 1.8 to 2.7 ha (depending upon field site) for large crabgrass, prostrate knotweed, wild buckwheat, and green foxtail, respectively, was required. The low cost and simplicity of assessment make this technique more suitable than that of soil seed-bank samples to predict weed emergence. The number of solaria required to forecast weed infestation levels confidently is sufficiently low that their use may be justified, especially in small fields of high-value crops.

Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; green foxtail, Setaria viridis (L.) Beauv. SETVI; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; prostrate knotweed, Polygonum aviculare L. POLAV; wild buckwheat, Polygonum convolvulus L. POLCO; corn, Zea mays L.; soybean, Glycine max (L.) Merr.; sunflower, Helianthus annus L.; wheat, Triticum aestivum L

Direct-seeding of cover crops is often promoted to reduce potential soil loss during the winter, enhance soil fertility, and reduce energy use and equipment traffic on fields. The impact of direct-seeding of cover crops on wild-proso millet seedling emergence in subsequent crops is unknown. In this study, a pulse–chase experiment determined the effect of five fall soil management strategies, two spring primary tillage levels, and two herbicide programs on wild-proso millet emergence in a subsequent crop of snap beans. Wild-proso millet seeds were sown following sweet corn harvest in two commercial production fields to simulate seed rain at a density of 500 and 1,000 seeds m⁻² in the fall of 2004 and 2005, respectively. The experimental design was a split–split plot. Five fall treatments were applied to main plots and included direct drilling of cover crops, conventionally tilled and drilled cover crops, a winter fallow treatment, and two additional treatments that were direct-drilled and conventionally tilled in the fall but that were not seeded with cover crops to separate the effects of tillage and cover crops on wild-proso millet emergence. Main plots were split in the spring and snap beans planted without primary tillage or conventionally planted after the soil was tilled. Tillage and cover crop treatments applied in the fall influenced emergence in the spring but with slightly different outcomes at the two sites. Direct drilling without a cover crop produced more wild-proso millet seedlings in snap beans than the winter fallow plot; tillage before cover crop planting in the fall produced recruitment levels less than or equal to densities in the winter fallow plots, with one exception. At one site, cover crops increased emergence compared to plots without cover crops. Spring tillage did not alter the affect of the five fall management treatments on wild-proso millet emergence. Direct-seeding of cover crops should be done with equipment or methods that minimize soil disturbance to prevent movement of wild-proso millet seeds into protected and favorable zones of emergence in the soil.

Nomenclature: Wild-proso millet, Panicum miliaceum L.; snap beans, Phaseolus vulgaris L. ‘OR91G’ and ‘Medinah’

The need for sustainable agricultural-production systems has generated demand for effective, nonsynthetic, alternative weed-control strategies. For some vegetable crops there are few herbicide options available, and there is little prospect of new herbicides being registered for vegetable crops. Brassicaceae seed meal, a residue product of the seed oil extraction process, can provide a resource for supplemental nutrients, disease control, and weed suppression. The objective of this study was to evaluate the effect of different Brassicaceae seed meals and application rates on the emergence of wild oat, Italian ryegrass, prickly lettuce, and redroot pigweed, which are some of the major weeds in vegetable production systems. White mustard seed, Indian mustard seed, and rapeseed meals were used with (intact) or without a functional myrosinase enzyme (denatured). Intact white mustard seed meals applied at a rate of 2000 kg ha⁻¹ significantly reduced weed seedling emergence and weed dry biomass compared with intact rapeseed-meal–amended treatments. Indian mustard showed significantly better herbicidal efficacy on the grassy weeds than did white mustard, which was most effective in controlling broadleaf weeds. In all instances, a 1000 kg ha⁻¹ application rate of either Indian mustard or white mustard exhibited greater herbicidal effect than did the 2000 kg ha⁻¹ application rate of rapeseed meal. These results demonstrate that all glucosinolates are not equal in herbicidal effects. The herbicidal effects of the mustard seed meal could offer vegetable growers a new option for weed control, particularly in organic production systems. In practice, it would seem feasible to treat soils with a blend of Indian mustard and white mustard seed meals so that both grass and broadleaf weeds could be effectively controlled.

Nomenclature: Indian mustard, Brassica juncea (L.) Czern ‘Pacific Gold’; rapeseed, Brassica napus L. ‘Dwarf Essex’; white mustard, Sinapis alba L. ‘IdaGold’; Italian ryegrass, Lolium perenne L. spp. multiflorum (Lam.) Husnot; prickly lettuce, Lactuca serriola L.; redroot pigweed, Amaranthus retroflexus L.; wild oat, Avena fatua L

The sharp decline in the area of lupin grown in Australia is partly attributed to the failure to control herbicide-resistant weeds in narrow-leaf lupin crops grown with the conventional 25-cm-wide row spacing. Growing lupin with wider row spacing allows for interrow weed control by nonselective herbicides using a sprayshield or physical methods. During 2003 to 2006, two experiments conducted at five sites evaluated the efficacy of interrow weed control techniques in narrow-leaf lupin crops grown in 55- to 65-cm-wide rows within the Western Australia wheatbelt. Interrow herbicides were applied POST using sprayshields, intrarow herbicides were banded on lupin rows at seeding, and interrow weeds were mowed using a garden mower. The main weed species at each site was rigid ryegrass, blue lupin, or wild radish. Paraquat plus diquat applied on the interrow of the lupin crop with sprayshields controlled up to 100% of weeds between rows, leading to increases in lupin grain yield in most of the sites. Glyphosate alone, a mixture of glyphosate plus metribuzin, and glyphosate followed by paraquat plus diquat also controlled interrow weeds, but did not increase lupin grain yield at any site. Thus, paraquat plus diquat is a better choice for interrow weed control in wide row lupin than glyphosate. Mowing did not improve weed control, but mowing followed by paraquat plus diquat increased lupin grain yield at one site. Regression models predicted that there was a strong relationship between weed biomass and lupin grain yield.

Nomenclature: Diquat; glyphosate; paraquat; propyzamide(3,5-dichloro-N-(1,1-dimethyl-2-propynyl)benzamide); blue lupin, Lupinus cosentinii Guss; rigid ryegrass, Lolium rigidum Gaud. LOLRI; wild radish, Raphanus raphanistrum L. RAPRA; narrow-leaf lupin, Lupinus angustifolius L

We studied the emergence phenology of large and smooth crabgrass in lawn and bare soil environments and identified ornamental plants as phenological indicators that predict the progress of emergence. From 2002 to 2004, we monitored emergence of large and smooth crabgrass in field plots to estimate the dates of first emergence, and 25, 50 and 80% emergence. Each year, we monitored 74 taxa of ornamental plants to determine dates of first and full bloom. We compiled dates of weed emergence and ornamental blooming to create a biological calendar of phenological events for each year, ordered by average cumulative degree days (DD) (January 1 start date, 10 C base temperature). Ornamental plant flowering events that occurred in a regular sequence before crabgrass emergence events were identified as the phenological indicators. We also evaluated DD and rule-based models for predicting crabgrass emergence and optimum time of PRE herbicide application. In general, smooth crabgrass reached each emergence stage earlier than large crabgrass. Differences in emergence between environments were not consistent over years for the two species. There was no consistent pattern in parameters for DD models predicting emergence events for either crabgrass species or environment. For published DD models, the deviation between observed and predicted emergence events ranged from 0 to > 60 d. Published rule-based predictions, though accurate in some cases, were sometimes difficult to implement. The order of ornamental plant blooming and crabgrass emergence events was generally consistent over years (R²  =  0.977). The biological calendar provided useful crabgrass emergence predictions using real-time field-based indicators of sequential biological events that can help managers plan and optimize management strategies.

Nomenclature: Large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; smooth crabgrass, Digitaria ischaemum (Schreb.) Schreb. ex Muhl. DIGIS

Common cocklebur is a new weed in irrigated maize grown for forage in the hot, dry region of northwest Pakistan. We conducted experiments in the Khyber Pakhtunkhwa Province, Peshawar, Pakistan, during 2006 and 2007 to evaluate the interaction of common cocklebur density and maize density on biomass, leaf area index (LAI), and plant height of forage maize. Seven common cocklebur densities (0, 2, 4, 6, 8, 10, and 12 plants m⁻²) in maize planted at four densities (5, 7.5, 10, and 12.5 plants m⁻²) were evaluated. An ANOVA for both years revealed significant main effects and interactions for all variables. Regression of measured variables against common cocklebur density showed that maize biomass declined linearly as common cocklebur density increased from 0 to 12 plants m⁻², with an increasing rate of decline for high maize densities and low maize densities. Combined data for all maize densities revealed that the relationship between maize biomass and common cocklebur biomass fit a linear function, with 1.28 to 1.35 kg ha⁻¹ loss in maize biomass for each kilogram per hectare increase in common cocklebur biomass from about 1,500 to 3,200 kg ha⁻¹. Above 8 to 10 common cocklebur plants m⁻², weed biomass declined, presumably due to intraspecific competition. An increase in common cocklebur density decreased maize LAI about 0.15 to 0.3 units for each additional common cocklebur plant per square meter in 2006, and 0.11 to 0.24 units in 2007. Common cocklebur LAI increased in a linear fashion as density of the weed increased. Results suggest that the effect of common cocklebur interference on maize biomass was associated with a change in allocation of resources, resulting in increased crop height growth at the expense of a reduction in LAI and presumably potential light interception by the crop as common cocklebur density increased.

Nomenclature: Common cocklebur, Xanthium strumarium L. XANST; maize, Zea mays L

With increasing incidence of glyphosate-resistant weeds worldwide, greater farmer awareness of the importance of glyphosate stewardship and proactive glyphosate-resistance management is needed. A Web-based decision-support tool ( http://www.weedtool.com) comprising 10 questions has been developed primarily for farmers in western Canada to assess the relative risk of selection for glyphosate-resistant weeds on a field-by-field basis. We describe the rationale for the questions and how a response to a particular question influences the risk rating. Practices with the greatest risk weighting in western Canadian cropping systems are lack of crop-rotation diversity (growing mainly oilseeds) and a high frequency of glyphosate-resistant crops in the rotation. Three case scenarios are outlined—low, moderate, and high risk of glyphosate-resistance evolution. Based on the overall risk rating, three best-management practices are recommended to reduce the risk of glyphosate resistance in weeds.

Nomenclature: Glyphosate

The replication of experiments over multiple environments such as locations and years is a common practice in field research. A major reason for the practice is to estimate the effects of treatments over a variety of environments. Environments are frequently classed as random effects in the model for statistical analysis, while treatments are almost always classed as fixed effects. Where environments are random and treatments are fixed, it is not always necessary to include all possible interactions between treatments and environments as random effects in the model. The rationale for decisions about the inclusion or exclusion of fixed by random effects in a mixed model is presented. Where the effects of treatments over broad populations of environments are to be estimated, it is often most appropriate to include only those fixed by random effects that reference experimental units.

A survey of 109 fields was conducted across western Canada in spring 2007 to determine the extent of ALS-inhibitor and dicamba (synthetic auxin) resistance in kochia. Weed seedlings were collected from fields in three provinces of western Canada and transplanted into the greenhouse. Seeds were harvested from selfed plants, and the F₁ progeny were screened for resistance to the ALS-inhibitor mixture thifensulfuron–tribenuron or dicamba. All kochia populations were susceptible to dicamba. ALS inhibitor–resistant kochia was found in 85% of the fields surveyed in western Canada: 80 of 95 fields in Alberta, six of seven fields in Saskatchewan, and all seven fields in Manitoba. For the 93 ALS inhibitor–resistant populations, the mean frequency (±SE) of parental plants classified as resistant was 61 ± 3%. Most of the resistant populations (87%) were heterogeneous and contained both resistant and susceptible individuals. ALS sequence data (Pro₁₉₇ and Asp₃₇₆ mutations) and genotyping data (Trp₅₇₄ mutation) obtained for 87 kochia parental (i.e., field-collected) plants confirmed the presence of all three target-site mutations as well as two mutational combinations (Pro₁₉₇ Trp₅₇₄, Asp₃₇₆ Trp₅₇₄) in resistant individuals.

Nomenclature: Dicamba; thifensulfuron; tribenuron; kochia, Kochia scoparia (L.) Schrad. KCHSC, synonym: Bassia scoparia (L.) A.J. Scott