Success of postemergence weed management often depends upon application timing and weed seedling size. To develop a predictive tool for estimating green foxtail development and optimizing timing of management operations, seedling growth was monitored in fields for two years, as well as in a single greenhouse experiment, and compared with elapsed thermal time (growing degree days, GDD, base 10 C). The relationship between seedling height (mm) and GDD was similar both years and could be described by the following equation: Height = (-0.27 + 0.033 * GDD)2. A comparable equation described seedling growth in a greenhouse. Leaf number was linearly related to GDD. Green foxtail in corn was controlled with nicosulfuron applied at seven intervals between 100 and 450 GDD after corn planting in 1993 and 1994. In 1993 corn yield losses due to green foxtail interference were least when nicosulfuron was applied 200 to 300 GDD after planting, at which time green foxtail height was 50 to 100 mm. In 1994 corn yield losses were minimized if nicosulfuron was applied any time before 300 GDD.

Five broadleaf crops, alfalfa, peanut, soybean, tobacco, and tomato, were tested for their susceptibility to three broomrape species, branched, Egyptian and crenate, in the greenhouse. All five crop species were parasitized by one or more broomrape species. Peanut plants were most susceptible and soybean plants were least susceptible to parasitism by broomrape. Egyptian and branched broomrapes had a wider host range affecting plants in both the Solanaceae and Fabaceae. Crenate broomrape mainly infected plants belonging to Fabaceae, except for the few attachments to tomato and tobacco. Apparently, this is the first report on parasitism of peanut plants by branched broomrape and that of peanut and alfalfa plants by crenate broomrape. Parasitism of soybean plants by any of the broomrape species also was observed for the first time in these experiments. These results indicate that broomrapes, although not a major problem on any of the crops in the United States, could parasitize several major broadleaf crops should the parasite become established.

Field trials were conducted in no-till field corn in northern Missouri to compare weed control and crop response of metolachlor plus atrazine applied under five preplant herbicide management practices. The practices consisted of (1) applying the entire dose of metolachlor plus atrazine 15, 30, or 45 d early preplant (EPP), (2) applying a split application of an EPP (67%) followed by (fb) a PRE (33%), (3) applying the entire dose PRE, (4) applying metolachlor PRE fb dicamba early post (EPOST), or (5) applying atrazine alone EPOST. Weed control at 7 wk after planting was more variable with EPP treatments than with EPP fb PRE or PRE treatments. Giant foxtail and fall panicum control was greatest with treatments that included metolachlor PRE. Velvetleaf and common cocklebur control was greatest with atrazine or dicamba EPOST and was generally unacceptable (< 80%) with any soil-applied herbicide treatment. Common lambsquarters control was greater than 90% with all treatments that included metolachlor, atrazine, or dicamba, regardless of timing. Corn yields were slightly higher with EPP fb PRE and PRE fb EPOST dicamba than with EPP alone. The results suggest that herbicide applications made nearer to the date of planting provide less variable weed control and corn yield than treatments made more than 15 d EPP.

Field research was conducted at three locations in Mississippi to evaluate CGA-277476 tank mixtures with four broadleaf herbicides for possible improvement of broadleaf weed control. Tank mixtures in this research were typically additive, although some instances of antagonism were noted. Control of morningglory (Ipomoea) species and hemp sesbania (Sesbania exaltata) was not consistently improved by the addition of acifluorfen, chlorimuron, fomesafen, or imazaquin to 59 or 79 g ai/ha CGA-277476. However, when a large population of weeds was present, the addition of acifluorfen, chlorimuron, or fomesafen to 59 or 79 g/ha CGA-277476 improved control over CGA-277476 alone. Prickly sida (Sida spinosa) was not controlled more than 68% with any treatment in this study; however, horse purslane (Trianthema portulacastrum) was controlled at least 90% with either 79 g/ha CGA-277476 alone or tank-mixed with acifluorfen, fomesafen, chlorimuron, or imazaquin. The addition of CGA-277476 to acifluorfen or fomesafen did not improve control over acifluorfen or fomesafen alone on any of the weeds evaluated; however, the addition of CGA-277476 to imazaquin improved hemp sesbania control over imazaquin alone. Tank mixtures did not result in yields greater than CGA-277476 alone in areas with moderate weed pressure, whereas in areas with severe weed pressure, tank mixtures improved soybean (Glycine max) yield over CGA-277476 alone.

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

Greenhouse and outdoor container experiments were conducted to determine garden spurge and large crabgrass emergence when seeds were placed either on top of or below three different mulch materials [pine bark (PB), hardwood (HW), or pine straw (PS)] applied at five depths (0, 1.3, 2.5, 5.1, and 10.2 cm). To elucidate mulch characteristics that contributed to weed control, photosynthetic active radiation (PAR) was recorded underneath each mulch layer, moisture retention was monitored for 24 h following irrigation, and particle size was determined using standard soil sieves. HW reduced PAR (97%) more than did PB (90%) or PS (92%) at 1.3 cm, but few or no differences were noted between mulches at greater mulch depths. HW also contained the highest percentage of small particles and consequently retained more water (29%), than PB (14%) or PS (22%) 24 h following a simulated irrigation event. Emergence of large crabgrass and garden spurge was consistently greater when seeds were placed on top of the mulch, compared to seeds placed below. Emergence of both species also tended to respond to increasing depth in a quadratic manner, indicating that once a critical level of mulch was applied (2.5 to 5 cm), further reductions in weed emergence would not be observed, at least over the short term (12 wk). PB and PS tended to provide a greater reduction in emergence of both species compared to HW. This research also indicates that larger particle materials such as PB or PS would be advantageous because of their ability to suppress weed emergence regardless of seed position.

Double-crop soybean after winter wheat is a component of many cropping systems across eastern and central Kansas. Until recently, control of Palmer amaranth and common waterhemp has been both easy and economical with the use of sequential applications of glyphosate in glyphosate-resistant soybean. Many populations of Palmer amaranth and common waterhemp have become resistant to glyphosate. During 2015 and 2016, a total of five field experiments were conducted near Manhattan, Hutchinson, and Ottawa, KS, to assess various non-glyphosate herbicide programs at three different application timings for the control of Palmer amaranth and waterhemp in double-crop soybean after winter wheat. Spring-POST treatments of pyroxasulfone (119 g ai ha–1) and pendimethalin (1065 g ai ha–1) were applied to winter wheat to evaluate residual control of Palmer amaranth and waterhemp. Less than 40% control of Palmer amaranth and waterhemp was observed in both treatments 2 wk after planting (WAP) double-crop soybean. Preharvest treatments of 2,4-D (561 g ae ha–1) and flumioxazin (107 g ai ha–1) were also applied to the winter wheat to assess control of emerged Palmer amaranth and waterhemp. 2,4-D resulted in highly variable Palmer amaranth and waterhemp control, whereas flumioxazin resulted in control similar to PRE treatments that contained paraquat (841 g ai ha–1) plus residual herbicide(s). Excellent control of both species was observed 2 WAP with a PRE paraquat application; however, reduced control of Palmer amaranth and waterhemp was noted 8 WAP due to subsequent emergence. Results indicate that Palmer amaranth and waterhemp control was 85% or greater 8 WAP for PRE treatments that included a combination of paraquat plus residual herbicide(s). PRE treatments that did not include both paraquat and residual herbicide(s) did not provide acceptable control.

Field trials were conducted in 2009 and 2010 near Paterson, WA and Ontario, OR to evaluate weed control and potato tolerance to PRE-applied pyroxasulfone, saflufenacil, and KSU12800 herbicides. Pyroxasulfone at 0.09 to 0.15 kg ai ha−1 and saflufenacil at 0.05 to 0.07 kg ai ha−1 applied PRE alone or in tank mixes with several currently labeled herbicides did not injure potatoes at either site in both years. KSU12800 at 0.15 kg ai ha−1 injured potatoes from 18 to 26% for a period of about 4 wk after emergence at Ontario both years. In addition, KSU12800 at 0.29 and 0.45 kg ha−1 injured potatoes from 17 to 38% at 17 d after treatment (DAT) at Paterson in 2009. Pyroxasulfone at 0.15 kg ha−1 controlled barnyardgrass, hairy nightshade, and redroot pigweed 96% or greater, but control of common lambsquarters was variable. Saflufenacil at 0.07 kg ha−1 provided greater than 93% control of common lambsquarters, hairy nightshade, and redroot pigweed at both sites in 2010. KSU12800 at 0.15 kg ha−1 controlled common lambsquarters, hairy nightshade, and redroot pigweed 99% or more at Ontario, but only 87 to 93% at Paterson in 2010. These herbicides did not reduce yield of U.S. no. 1 tubers or total tuber yields compared to standard labeled herbicide treatments when weed control was adequate.

Dry pea improves corn yield and tolerance to weed interference compared with soybean, spring wheat, or canola as preceding crops. To understand this synergy between dry pea and corn, growth and nutrient concentration of corn were examined following dry pea or soybean in sequence. Each corn plot was split into weed-free and weed-infested subplots, with foxtail millet established at one density to provide uniform weed interference. Compared with soybean, dry pea improved corn grain yield 10% in weed-free conditions and corn tolerance to weed interference more than twofold. Dry pea synergy to corn in weed-free conditions was not related to differences in corn development, height, or nutrient status of corn seedlings. When foxtail millet was present, dry pea increased corn height and rate of development late in the growing season compared with soybean. Improved corn tolerance to weed interference was not related to seedling emergence or growth of foxtail millet, as these parameters did not vary with preceding crop. Other biological factors must be involved in dry pea synergy to corn.

Smooth barley is an annual weed species that is infesting crops and pastures in South Australia. Complicating control options is the presence of herbicide-resistant biotypes. A field trial was conducted to identify alternative herbicides for the management of acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicide-resistant smooth barley in field pea. Preplant (PP) soil applications of pyroxasulfone; prosulfocarb plus S-metolachlor; dimethenamid-P; propyzamide; trifluralin alone or with triallate or with diuron; or imazamox applied POST were evaluated for their effectiveness and crop safety. Propyzamide, pyroxasulfone, or imazamox applied POST provided a high level of smooth barley control, did not cause any crop injury, and increased field pea grain or forage yield compared with the nontreated. Furthermore, propyzamide or pyroxasulfone reduced panicle density and seed production in smooth barley, whereas the effectiveness of POST imazamox varied over the two seasons. Dimethenamid-P reduced the impact of smooth barley on field pea yield, but cause stunting, and was less effective than propyzamide, pyroxasulfone, and imazamox in reducing smooth barley seed production. Negative relationship between field pea yield and smooth barley panicle density indicated that smooth barley is highly competitive in field pea crops and can cause large yield losses. The results of this investigation suggest that propyzamide or pyroxasulfone applied PP and imazamox applied POST could be used effectively in the field for the management of ACCase-inhibiting herbicide-resistant smooth barley in South Australia.

Widespread occurrence of herbicide-resistant weeds and more variable weather conditions across the United States has made weed control in many crops more challenging. Preemergence (PRE) herbicides with soil residual activity have resurged as the foundation for early season weed control in many crops. Field experiments were conducted in Janesville and Lancaster, Wisconsin, in 2021 and 2022 (4 site-years) to evaluate the weed control efficacy of solo (single site of action [SOA]) and premix (two or more SOAs) PRE herbicides in conventional tillage corn. Treatments consisted of 18 PRE herbicides plus a nontreated check. At the Janesville-2021 site, S-metolachlor + bicyclopyrone + mesotrione, atrazine + S-metolachlor + bicyclopyrone + mesotrione, and clopyralid + acetochlor + mesotrione provided >72% giant ragweed control. At the Janesville-2022 site, none of the PRE herbicides evaluated provided >70% giant ragweed control due to the high giant ragweed density and the lack of timely rainfall. At the Lancaster-2021 site, atrazine, dicamba, and flumetsulam + clopyralid provided <45% waterhemp control, but the remaining treatments provided >90% control. At the Lancaster-2022 site, the efficacy of some PRE herbicides was reduced due to the high waterhemp density; however, most herbicides provided >75% control. At the Lancaster-2021 and Lancaster-2022 sites, only dicamba and S-metolachlor did not provide >75% common lambsquarters control. Group 15 PRE herbicides provided >75% control of giant foxtail. Across weed species, PRE herbicides with two (78%) and three (81%) SOAs provided greater weed control than PRE herbicides with a single SOA (68%), indicating that at least two SOA herbicides applied PRE result in better early season weed control. The efficacy of the PRE herbicide treatments evaluated herein varied according to the soil seedbank weed community composition and environmental conditions (i.e., rainfall following application), but the premixes were a more reliable option to improve early season weed control in conventional tillage corn.

Studies were conducted in 2003 and 2004 over seven environments evaluating rice root growth inhibition (RGI) and foliar injury from penoxsulam at 30 and 60 g ai/ha and bispyribac-sodium at 30 g ai/ha applied to four- to five-leaf rice at three flood timings, 1, 7, and 14 d after herbicide treatment (DAT), for five rice cultivars, ‘Bengal’, ‘Cypress’, ‘Wells’, ‘Cocodrie’, and ‘XP712’. Flooding at 1 and 7 DAT resulted in greater RGI compared with flood at 14 DAT when evaluated 1 wk after flood (WAF). By 2 WAF, RGI was greater with flooding at 1 DAT compared with flooding at 7 DAT for cultivars Bengal, Cypress, and Wells. Analyzing flood timing 1 DAT, bispyribac-sodium reduced root growth of Bengal and Cypress compared with penoxsulam at 30 g/ha at 1 week after treatment (WAT). At 2 WAT, RGI for Cocodrie was higher following penoxsulam at 60 g/ha when compared with bispyribac-sodium. By 3 WAT, RGI was higher following penoxsulam at 60 g/ha when compared with penoxsulam at 30 g/ha for Cocodrie and greater than bispyribac-sodium and penoxsulam at 30 g/ha for Cypress. Foliar injury following penoxsulam at both rates was less than injury following bispyribac-sodium for all cultivars except XP712 at 1 WAT. XP712 resulted in < 5% RGI and < 6% foliar injury at each evaluation. Rice grain yield was not affected by herbicide treatment for any cultivar compared with the standard treatment of propanil plus quinclorac.

Dissipation of imidazolinone herbicides imazaquin and imazethapyr under no-till field conditions was not affected by straw mulch level (1,300, 3,600, or 5,900 kg/ha) in either of 2 yr of field data. Half-lives averaged 7 d for imazaquin and 8 d for imazethapyr. Chlorimuron half-lives averaged 5 d. Imazaquin and imazethapyr residues did not injure corn (Zea mays) the growing season following application. Injury from chlorimuron to corn planted the next year was greatest where applications were made to the highest straw level, reducing corn yield 6%. In laboratory experiments, uniformly cut wheat (Triticum aestivum) straw placed over sand intercepted all three herbicides equally. Herbicide interception was 16, 43, 69, and 89% for straw levels of 840, 1,680, 3,360, and 6,720 kg/ha, respectively. In the laboratory, simulated rainfall removed more imazaquin and imazethapyr from straw than chlorimuron, and approximately 10% of the applied imazaquin or imazethapyr and 20% of the applied chlorimuron remained on the straw after application of 1.0 cm of water. Imazaquin and imazethapyr dissipated 59 and 20%, respectively, during a 7-d incubation period in the greenhouse. Imazaquin dissipation was equal between sand and straw, whereas imazethapyr dissipation was primarily from sand. Chlorimuron did not dissipate from either straw or sand. This indicated that chlorimuron, a sulfonylurea, was more stable than either imidazolinone under these conditions.

Glyphosate was applied to pepper as single or sequential applications to assess the consequences of drift or other accidental exposures. Foliar injury increased and plant vigor declined with increased rates of glyphosate and were exacerbated by a second application. Single applications at flowering (stage 1) were more damaging than single applications after fruit set (stage 2). Decline in marketable yield with increased glyphosate rate was greater with stage 1 applications, except in spring 1987 when marketable yields with single applications of glyphosate at stage 1 or stage 2 were statistically similar. Sequential applications resulted in the lowest marketable yields. Total yields declined with increased glyphosate rate and decline was more pronounced with sequential applications than with single applications. Total yield was affected to a greater extent when glyphosate was applied at stage 1 than at stage 2. Yield was more sensitive to two successive exposures than to single applications. Mean fruit weight was reduced by glyphosate in two of the four experiments.

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.

This greenhouse experiment examined the response of homozygous susceptible and acetolactate synthase (ALS) inhibitor–resistant plants from six Canadian kochia accessions with the Pro197 or Trp574 mutation to six alternative herbicides of different sites of action. The null hypothesis was ALS-inhibitor–resistant and –susceptible plants from within and across accessions would respond similarly to herbicides of different sites of action. This hypothesis was accepted for all accessions except that of MBK2 with the Trp574 mutation. Resistant plants of that accession were 80, 60, and 50% more sensitive than susceptible plants to pyrasulfotole, mesotrione (hydroxyphenylpyruvate dioxygenase [HPPD] inhibitors), and carfentrazone (protoporphyrinogen oxidase [PPO] inhibitor), respectively. However, no differential dose response between resistant and susceptible plants of this kochia accession to bromoxynil, fluroxypyr, or glyphosate was observed. A previous study had found marked differences in growth and development between resistant and susceptible plants of this accession, but not of the other accessions examined in this experiment. Negative cross-resistance exhibited by resistant plants of accession MBK2 to PPO and HPPD inhibitors in this experiment may be a pleiotropic effect related to the Trp574 mutation.

Pluchea lanceolata (DC.) C. B. Clarke # PLULA is an aggressive, pernicious, rhizomatous evergreen weed in the Asteraceae. In other literature, P. lanceolata Oliv. & Hiern has also been mentioned (Anonymous 1992, pp. 731 and 1147). With heavy root branches and dense subterranean parts, P. lanceolata is a common weed of sandy and saline tracts of the dry plains of the northwestern parts of India (Dakshini and Sabina 1981; Inderjit 1993; Rice 1995). It also occurs in North Africa, Afghanistan, and Pakistan (Nasir and Ali 1972; Oliver 1885). In India, it occurs both in cultivated and uncultivated areas. It causes considerable damage to winter and summer season crops. The control measures through conventional methods such as deep plowing, burning of aboveground parts, and herbicides are found to be unsuccessful. This rapidly spreading perennial weed apparently cannot be used for forage because of its disagreeable bitter taste (Anonymous 1976). Allelopathy has been reported as a probable cause of P. lanceolata interference (Inderjit and Dakshini 1990, 1992b, 1994a, 1994b, 1996a, 1996b; Inderjit et al. 1996).

Tillage is used in sugarcane to control weeds, eliminate ruts caused by harvest, destroy residue from the previous crop, and incorporate fertilizer. The effect of weed control and tillage programs on sugarcane growth and yield and on economics was evaluated over two growing seasons. In the first study, weeds were effectively controlled with a March application of hexazinone at 0.59 kg ai/ha plus diuron at 2.10 kg ai/ha either banded or broadcast. When tillage of row shoulders and middles in March was eliminated, soil temperature in the sugarcane drill early in the season was equal to that where March tillage was performed. Sugarcane early and late season stalk population and sugarcane and sugar yield were each equivalent for the full season tillage (tillage of row shoulders and middles in March and in May) and the no-till programs. Elimination of a single tillage operation reduced cost $16.28/ha, and herbicide applied as a band rather than broadcast reduced cost $30.49/ ha. For the no-till program, with herbicide banded in March, net return was increased $32.56/ha. In a subsequent study conducted at five locations, weed control was excellent when either pendimethalin at 2.77 kg ai/ha plus metribuzin at 1.26 kg ai/ha or hexazinone plus diuron at 0.59 kg/ha and 2.10 kg/ha was used. When the March tillage was eliminated, sugar yield was increased 8.6% (620 kg/ ha), and net return was increased $152.68/ha compared with March tillage. When the May tillage was eliminated sugar yield was increased 8% (580 kg/ha), and net return was increased $143.88/ha compared with May tillage. A reduction in tillage cost accounted for only $16.28 of the increase in net return per hectare, with the remainder due to increased yield with the elimination of the tillage operation.

Sulfonylurea-tolerant soybean (STS soybean) tolerance to imazethapyr (70 g/ha) plus thifensulfuron (4.4 g/ha) tank mixture was evaluated in 1993 and 1994 at two locations in Illinois. Thifensulfuron injury was reduced from 27% in non-STS soybean to 1% in STS soybean 14 days after treatment (DAT). STS and non-STS soybean did not differ in response to imazethapyr alone with < 6% injury 14 DAT. Injury from the tank mix was reduced from 40% in non-STS soybean to 24% in STS soybean 14 DAT. However, a synergistic interaction between the herbicides exists in STS soybean. The yield of injured soybean was not reduced in either STS or non-STS soybean. Injury to STS soybean from the tank mix was decreased by reducing the rate of imazethapyr from 70 g/ha to 52.5 or 35 g/ha. Reducing the thifensulfuron rate mixed with imazethapyr at 70 g/ha did not decrease injury in STS soybean. Control of smooth pigweed, common lambsquarters, and common cocklebur was not affected by reducing the rate of either herbicide in the tank mixture.

Field studies were conducted at Lewiston and Rocky Mount, NC, in 1996 and 1997 to evaluate weed control and peanut response to preplant incorporated (PPI) treatments of diclosulam alone and in systems with postemergence (POST) commercial standard herbicides. All plots received ethalfluralin PPI at 840 g ai/ha. In both years, ethalfluralin plus diclosulam PPI at 17 or 26 g ai/ha followed by (fb) acifluorfen plus bentazon POST, paraquat plus bentazon POST, or imazapic POST controlled common lambsquarters, ivyleaf morningglory, pitted morningglory, prickly sida, smooth pigweed, spurred anoda, and yellow nutsedge in a manner similar to or better than did the commercial standards of ethalfluralin PPI fb metolachlor preemergence (PRE) fb acifluorfen plus bentazon or ethalfluralin PPI fb acifluorfen plus bentazon POST. Yield from peanut treated with diclosulam systems that included POST herbicides was equivalent to or higher than that from peanut treated with ethalfluralin PPI fb metolachlor PRE fb acifluorfen plus bentazon POST or ethalfluralin PPI fb acifluorfen plus bentazon POST. Peanut exhibited excellent tolerance to diclosulam PPI at all rates.