Fruit trees in orchards of the mid-Atlantic region of the United States are often planted in vegetation-free rows alternating with grass alleys. Grass managed to suppress weeds but to compete minimally with fruit trees may be an alternative to herbicide and tillage. This research was conducted in the greenhouse and field to assess five different grasses that may suppress weeds without reducing yield of fruit trees. In the greenhouse with high seeding rates, red fescue competed more effectively than did chewings fescue, tall fescue, and perennial ryegrass with three weeds (damesrocket, cornflower, and chicory). However, with reduced seeding rates, similar to rates used in the field, grass competitiveness with weeds was similar between red fescue, tall fescue, and perennial ryegrass. Similar results were obtained during a 4-yr field experiment; roughstalk bluegrass competed least effectively with weeds but the other four grasses provided similar weed suppression—generally providing as much weed suppression as traditional herbicides. None of the candidate grasses significantly reduced yields of 10-yr-old apple and peach trees, although fruit size was affected by some grasses. The grass that was least suppressive of yield, roughstalk bluegrass, was the least effective in controlling weeds. Annual mowing in combination with four of the grasses tested is one option to manage the orchard floor with reduced herbicides, but fruit size may decrease.

Research was conducted in winter of 2000 and spring of 2001 to determine the extent of simazine-resistant annual bluegrass in Mississippi. Samples of annual bluegrass seed or mature plants were collected from 71 locations across the state and grown in the greenhouse. Four weeks after treatment with 22.4 kg ai/ha simazine (10× rate), samples from 31 of 71 locations (30 golf courses and one nongolf course) evaluated in the greenhouse had simazine-resistant annual bluegrass plants. Thus, 43% of the golf courses tested in the greenhouse had triazine-resistant annual bluegrass present. When natural field populations were treated with an equivalent simazine rate, simazine-resistant annual bluegrass plants were observed in 90% of the sites found to be resistant in the greenhouse screen.

Field and greenhouse experiments were conducted to evaluate postemergence (POST) soybean injury and weed control with CGA-277476 and cloransulam-methyl alone and in tank mixtures. In the field, visible soybean injury was 12 to 14% from CGA-277476 and 9 to 13% from cloransulam-methyl 7 d after treatment. Tank mixtures of either herbicide with acifluorfen or acifluorfen plus thifensulfuron were more injurious than CGA-277476 or cloransulam-methyl applied alone. Both CGA-277476 and cloransulam-methyl reduced velvetleaf dry weight 82%, and cloransulam-methyl reduced common ragweed dry weight 92%. Neither herbicide adequately controlled common lambsquarters, redroot pigweed, nor eastern black nightshade. The addition of acifluorfen to the spray solution improved common ragweed, common lambsquarters, redroot pigweed, and eastern black nightshade control with CGA-277476 and improved common lambsquarters, redroot pigweed, and eastern black nightshade control with cloransulam-methyl. Tank mixing thifensulfuron with CGA-277476 or cloransulam-methyl increased common lambsquarters and redroot pigweed control. In the greenhouse, CGA-277476 at 20 g ai/ha reduced velvetleaf dry weight 98%, and 79 g/ha was required to reduce common ragweed dry weight 93%. Cloransulam-methyl at 4.4 g ai/ha reduced velvetleaf dry weight 98% and common ragweed dry weight 94% at 8.8 g/ha. Chlorimuron reduced yellow nutsedge dry weight more than CGA-277476 or cloransulam-methyl. Antagonism of POST graminicide activity by CGA-277476 was grass species and graminicide related. CGA-277476 reduced giant foxtail control by clethodim but not by quizalofop. Cloransulam-methyl tank mixed with clethodim or quizalofop controlled giant foxtail.

Studies were conducted at the Vegetable Substation in Kibler, AR, in 1992 and 1993, in the same plots, to evaluate weed suppression by spring-seeded cover crops and to determine the effects of cover crop and imazethapyr on no-till southern pea. A plot without cover, conventionally tilled before planting southern pea, served as control. Weed control treatments, applied as subplots in each cover crop, included a weedy check, handweeded check, and half and full rates of imazethapyr (0.035 and 0.07 kg/ha) followed by sethoxydim (0.22 kg/ha). Biomass of Palmer amaranth 6 WAR without herbicides, was less in Italian ryegrass and sorghum-sudangrass residues than in oat residue and no cover crop. Over the years, Palmer amaranth density increased 333% without cover crops and 28% with cover crops. Rice flatsedge density increased four to five times in oat and sorghum-sudangrass residues but remained the same in Italian ryegrass residue. In general, Italian ryegrass residue suppressed the most weeds. Oat residue was least suppressive. Italian ryegrass and sorghum-sudangrass also reduced southern pea stand. Regardless of cover crop and year, half and full rates of imazethapyr followed by sethoxydim equally reduced density of Palmer amaranth, goosegrass, large crabgrass, southwestern cupgrass, and rice flatsedge compared with the untreated check. Residual control of Palmer amaranth by imazethapyr was higher at the full rate than the reduced rate, regardless of cover crop. Half rate of imazethapyr followed by sethoxydim controlled 94 to 100% of Palmer amaranth, rice flatsedge, large crabgrass, and southwestern cupgrass late in the season, regardless of cover crop in 1992 and 1993. Southern pea yield in untilled plots with cover crops was two to three times lower than yield in plots with preplant tillage and no cover crops mostly because of reduction in crop stand in the presence of cover crops.

Black medic is a troublesome weed in commercial strawberry fields in Florida. It emerges during crop establishment from the planting holes punched in plastic mulches that are installed on raised beds. Clopyralid is registered for posttransplant applications at 140 to 280 g ae ha−1 but growers typically report suppression, not control. An outdoor potted experiment was designed to model the black medic dose-response curve and determine the effect of plant size at application on control. Two plant sizes were selected: designated small (0.5- to 1-cm stem length) and large (3- to 6-cm stem length). Dose-response curves were generated using a log-logistic four-parameter model. At 22 d after treatment (DAT), there was a significant interaction between clopyralid rate and black medic growth stage on both epinasty (P = 0.0022) and chlorosis (P = 0.0055). The effective dosage to induce 90% (ED90) epinasty were 249.5 and 398.3 g ha−1 for the small and large growth stages, respectively. The ED90 for chlorosis was 748.2 for the small growth stage, whereas the estimated value for the large was outside the measured range. For necrosis there was no significant effect of growth stage, and the ED90 was 1,856.3 g ha−1. The aboveground dry biomass ED90 for the small growth stage was 197.3 g ha−1, and the estimated ED90 value for the large was not within the measured range. Results indicate that clopyralid adequately controls black medic when applied at maximum label rates when stems were 0.5 to 1 cm long but not when plants were larger. Poor efficacy typically observed in commercial fields is likely due to black medic plant size or lack of herbicide coverage via shielding by strawberry plants.

Rice cultivar, growth stage at application, or both may influence rice tolerance to quinclorac. Field studies were conducted to compare the response of five rice cultivars ‘Bowman’, ‘Cheniere’, ‘CL161’, ‘Cocodrie’, and ‘XL723’ to postflood quinclorac applications. Quinclorac at 0.56 kg ai ha−1 was applied 2 and 4 wk after flood (WAF). Pooled across quinclorac application timings, no differences in maturity were detected among the cultivars in 2008, but maturity of Cheniere and XL723 were delayed compared with CL161 and Cocodrie in 2007. Maturity of Cheniere and XL723 was delayed in 2007 compared with 2008. Pooled over cultivar, maturity was similar for 2 and 4 WAF applications in 2007 but was delayed for 2 WAF treatments in 2008. Regardless of year, postflood quinclorac applications reduced rough rice yield of all cultivars except Bowman. Cheniere and XL723 had lower rough rice yields compared with other cultivars in 2007; however, in 2008, rough rice yields of Cheniere, CL161, Cocodrie, and XL723 were similar, but still lower, than that of Bowman. Pooled over cultivar, postflood quinclorac reduced rough rice yields more when applied 4 WAF than at 2 WAF during both years. Our results demonstrate that Cheniere and XL723 are less tolerant than Bowman is to postflood quinclorac applications and that all evaluated cultivars are more susceptible to quinclorac applied at later developmental stages. Consequently, if circumstances necessitate a postflood quinclorac application, the herbicide should be applied no later than panicle initiation and should not be applied to Cheniere or XL723.

In the southeastern United States many farmers double-crop winter wheat with soybean or cotton. However, there is little information about residual injury of herbicides used in wheat to these rotational crops. Experiments were conducted from 2007 to 2008 and 2008 to 2009 in soft red winter wheat to evaluate response of rotational crops of soybean and cotton after application of various acetolactate synthase herbicides in wheat. Pyroxsulam, mesosulfuron, sulfosulfuron, propoxycarbazone, or chlorsulfuron plus metsulfuron at multiple rates were applied to wheat approximately 110 to 120 d before planting rotational crops. Soils were Tift loamy sand at Ty Ty, GA and Faceville sandy loam at Plains, GA. After wheat harvest, soybean (‘Pioneer 97M50’) and cotton (‘DP 0949 B2RF’) were strip-tillage planted and evaluated for injury, stand density, height over time, and yields. For both locations, wheat was tolerant to all herbicide treatments with little to no visible injury 7 to 90 d after application. Pyroxsulam injury was less than sulfosulfuron or mesosulfuron. At recommended use rates, wheat injury was transient with no effect on yield. Double-crop soybean for both locations had no differences in stand establishment for any herbicide treatments. There was significant carryover injury to soybean and cotton for sulfosulfuron applied to wheat for the Faceville sandy loam. There was no effect of herbicide treatment on cotton stand. There was little to no difference in residual activity on rotational crops between pyroxsulam and other wheat herbicides when labeled rates were applied. This is significant as pyroxsulam is used to control Italian ryegrass and wild radish in this region.

Two populations of Palmer amaranth suspected of being resistant to glyphosate have been reported since 2007 in pecan orchards in Doña Ana County, New Mexico. The objectives of the study were to confirm and evaluate the level of resistance, to evaluate the effectiveness of alternative herbicide mechanisms of action, and to compare the cost of effective alternative herbicides for weed management in pecan orchards. Greenhouse experiments indicated that the resistant populations were able to survive glyphosate at 736 g ae ha−1. Compared with a susceptible (S) population, one of the resistant (R) populations had sevenfold resistance to glyphosate. POST application of 12 herbicides, with five different mechanisms of action, all provided at least 88% control of both R and S populations when applied at their recommended field rates. PRE application of trifluralin and metolachlor also provided more than 99% control of R and S populations. The results of field studies indicated that the financial benefit of season-long weed management with glyphosate, in pecan orchards, was comparable with some of the tested alternative herbicides.

Glyphosate-resistant (GR) Palmer amaranth is a problematic, annual broadleaf weed in soybean production fields in Nebraska and many other states in the United States. Soybean resistant to 2,4-D, glyphosate, and glufosinate (Enlist E3TM) has been developed and was first grown commercially in 2019. The objectives of this research were to evaluate the effect of herbicide programs applied PRE, PRE followed by (fb) late-POST (LPOST), and early-POST (EPOST) fb LPOST on GR Palmer amaranth control, density, and biomass reduction, soybean injury, and yield. Field experiments were conducted near Carleton, NE, in 2018, and 2019 in a grower’s field infested with GR Palmer amaranth in 2,4-D–, glyphosate-, and glufosinate-resistant soybean. Sulfentrazone + cloransulam-methyl, imazethapyr + saflufenacil + pyroxasulfone, and chlorimuron ethyl + flumioxazin + metribuzin applied PRE provided 84% to 97% control of GR Palmer amaranth compared with the nontreated control 14 d after PRE. Averaged across herbicide programs, PRE fb 2,4-D and/or glufosinate, and sequential application of 2,4-D or glufosinate applied EPOST fb LPOST resulted in 92% and 88% control of GR Palmer amaranth, respectively, compared with 62% control with PRE-only programs 14 d after LPOST. Reductions in Palmer amaranth biomass followed the same trend; however, Palmer amaranth density was reduced 98% in EPOST fb LPOST programs compared with 91% reduction in PRE fb LPOST and 76% reduction in PRE-only programs. PRE fb LPOST and EPOST fb LPOST programs resulted in an average soybean yield of 4,478 and 4,706 kg ha−1, respectively, compared with 3,043 kg ha−1 in PRE-only programs. Herbicide programs evaluated in this study resulted in no soybean injury. The results of this research illustrate that herbicide programs are available for the management of GR Palmer amaranth in 2,4-D–, glyphosate-, and glufosinate-resistant soybean.

A field study was conducted at Vezaiciai branch of the Lithuanian Institute of Agriculture from 1998 to 2000 to determine weed emergence dynamics in potato and to estimate the effect of different intervals of weed crop competition on potato tuber yield if regular interrow cultivation was applied. Treatments varying in intervals of weed-free conditions and competition were laid out in a randomized complete block design with six replications. The greatest emergence of annual broadleaf such as common lambsquarters and other weeds (62 to 86% of the season total) in the crop was observed in the period from potato planting until flowering. Emergence of winter annuals such as field violet and scentless mayweed was greatest in the period from the 20-cm potato plant height until harvesting. The 20-cm potato height was the most important stage affecting potato yield loss due to weed competition. Potato yield losses due to weed competition were minimized when weeds were removed before the potatoes reached 20 cm or kept clean from this point forward. The results indicated that the critical weed-free period, when weed competition was detrimental to yield, started from planting and lasted until 25 d after flowering.

Based on field surveys and evaluations in the greenhouse, two fungal pathogens, Bipolaris sacchari and Drechslera gigantea, were identified as promising biological control agents for cogongrass. In greenhouse trials, the application of spore suspensions of these fungi containing 105 spores/ ml in a 1% aqueous gelatin solution to cogongrass plants and their incubation in a dew chamber for 24 h resulted in disease symptoms that ranged from discrete lesions to complete blighting of leaves. Disease severity (DS), based on a rating scale for southern corn leaf blight with 50% as the maximum DS rating, ranged from 42 to 49%. In greenhouse experiments, the application of spores formulated in an oil emulsion composed of 4% horticultural oil, 10% light mineral oil, and 86% water resulted in higher levels of foliar blight with no dew exposure or shorter periods of dew exposure (4, 8, or 12 h) as compared with the application of spores formulated in 1% gelatin. Field trials demonstrated that under natural conditions, the application of a spore and an oil emulsion mixture containing 105 spores/ml of either fungus could cause foliar injury from disease and phytotoxic damage from the oil emulsion. Depending on the application rate (100 or 200 ml/plot), the level of foliar injury ranged from 40 to 86% (based on a field assessment scale of 0 to 100% foliar injury) with B. sacchari as the test fungus. However, with D. gigantea as the test fungus, foliar injury ranged from 9 to 70% depending on the application volume and the oil concentration used. Although B. sacchari and D. gigantea were capable of causing foliar blight on cogongrass, the regenerative ability of the rhizomes allowed cogongrass to recover from the damage caused by these fungi. However, the level of injury caused by these fungi is sufficient to support their use as components for integrated management of cogongrass.

Clomazone was evaluated preplant incorporated (PPI) or post-transplant (PT) for weed control in sweet potatoes. No crop injury by clomazone was detected. Clomazone controlled (≥90%). broadleaf signalgrass, large crabgrass, barnyardgrass, and prickly sida at all rates and methods of application (MOA). Common cocklebur was controlled (≥93%) by clomazone at 1.1 kg ai ha-1 applied PT or at 3.4 kg ai ha-1 PPI in 1988 and at all rates and MOA in 1989. Clomazone did not control carpetweed.

Catchweed bedstraw, common hempnettle, wild buckwheat, and wild oat are serious competitors to arable crops in many parts of the world where cutting implements may be used to control weeds. After cutting, regrowth may become a problem. In greenhouse experiments, weed species were cut at different stages of development (wild oat had two or three leaves, and the dicot weed species were 10 or 15 cm high) and at different heights aboveground (5 and 8 cm). Three weeks after sowing, biomass was measured and compared with that of uncut plants. Cutting height had a significant effect on the regrowth of all species. Common hempnettle was the most sensitive to cutting height followed by wild oat, wild buckwheat, and catchweed bedstraw. Increasing cutting height from 5 to 8 cm above the soil surface increased biomass production by 100 to 400% for all species. Cutting catchweed bedstraw at 8 cm resulted in larger biomass production than that of uncut plants (about 30%). For this species, weed control by cutting once in the growing season, 8 cm aboveground, may result in increased weed biomass production when compared with no cutting. The stage of development when the plants were cut did not have a significant effect on the regrowth ability of any of the species, probably because the two growth stages were relatively close in time.

Russian thistle is a severe problem in fields after crop harvest in the Pacific Northwest (PNW) and is controlled either by tillage or broadcast applications of various herbicides. A study was conducted in Washington in 2000 and 2001 at four sites to compare the efficacy of two herbicide treatments applied with a light-activated, sensor-controlled (LASC) sprayer and a conventional broadcast sprayer for postharvest Russian thistle control. Additionally, simple economic comparisons, excluding fixed costs, were made among herbicide treatments and application methods. Both herbicide applicators controlled Russian thistle similarly within each herbicide treatment. Weed control was unacceptable (≤ 75%) when glyphosate plus 2,4-D was applied with either applicator. In contrast, Russian thistle control was > 90% with paraquat plus diuron regardless of applicator. The overall reduction in chemical use was 42% with the LASC compared with the broadcast applicator when averaged over the four sites. Herbicide and surfactant cost savings, using 2007 prices for the LASC compared with the broadcast applicator, ranged from $6.68/ha to $18.21/ha with the paraquat plus diuron treatment and averaged $13.27/ha less for the four sites. The use of the LASC for postharvest Russian thistle control can reduce growers' input costs, increase growers' profits, and improve environmental quality by reducing the amount and area of a restricted-use chemical.

Experiments were conducted in 1996 and 1997 in water-seeded and drill-seeded production systems to determine rice response to clomazone applied at rates ranging from 0.28 to 2.2 kg ai/ha on silt loam and silty clay soils. Clomazone-induced bleaching of rice seedlings was 15% or less when clomazone was applied at 0.28 or 0.56 kg/ha. Increasing the rate of clomazone increased bleaching in most experiments. Clomazone at 0.84 kg/ha or higher delayed seed head emergence in five of eight experiments. Clomazone at lower rates did not delay seed head emergence. Although clomazone at 0.28 and 0.56 kg/ha did not reduce grain yield, clomazone at 0.84 and 1.1 kg/ha reduced grain yield in one experiment while clomazone at 1.7 and 2.2 kg/ha reduced yield in two experiments. The influence of soil type and seeding method on rice's tolerance to the microencapsulated formulation of clomazone could not be demonstrated in these experiments. Clomazone was more injurious in drill-seeded production than in water-seeded production.

The sedge genus Kyllinga consists of 40 to 45 species distributed in tropical, subtropical, and warm temperate regions around the world (KUkenthal 1936; Tucker 1987). This genus of low rhizomatous perennials or cespitose annuals is classified in the large cosmopolitan family Cyperaceae. Many Kyllinga species are considered weedy (Holm et al. 1979; Tucker 1987), while Kyllinga nervosa Steudel is considered an important forage plant in Africa (McNaughton 1985).

Fenoxaprop, fluazifop/fluazifop-P, haloxyfop, and quizalofop at 0.14 kg ai ha−1 and sethoxydim at 0.28 kg ai ha−1 were applied broadcast over-the-top in spray volumes of 94 and 374 L ha−1, each at 138 and 345 kPa, to control johnsongrass in soybeans over a 5-yr period. The two spray volumes provided equal control, but control was better when treatments were applied at 345 kPa than at 138 kPa. There were no significant interactions among herbicides, spray volumes, or spray pressures. Most of the spray was deposited on the upper surface of the plant canopy. Less than 10% of the herbicide spray applied penetrated into the canopy onto water-sensitive spray cards located 10, 20, 30, or 40 cm above the ground.

Growth chamber experiments were conducted in the fall of 2006 and spring of 2007 to determine winter wheat, flixweed, and henbit response to POST treatments of saflufenacil at 13, 25, and 50 g ai ha−1 applied alone and in combinations with bentazon at 560 g ai ha−1 or 2,4-D amine at 533 g ae ha−1 and nonionic surfactant (NIS) at 0.25% v/v. Mixtures of saflufenacil and 2,4-D amine were also applied without NIS. Necrosis was observed on wheat leaves within 1 d after treatment (DAT) and peaked at 5 to 7 DAT. Saflufenacil at 13, 25, or 50 g ai ha−1 applied alone or in combination with 533 g ae ha−1 of 2,4-D amine plus NIS caused 19 to 38% (alone) and 24 to 40% (in combination) wheat foliar necrosis, respectively. Foliar necrosis of wheat was 14% or less when saflufenacil, at any rate, was mixed with bentazon or 2,4-D amine without NIS. Combinations of saflufenacil at any of the rates tested plus bentazon and NIS did not reduce wheat dry weight. Saflufenacil plus 2,4-D amine without adjuvant resulted in similar wheat dry weights as 2,4-D amine. Saflufenacil plus 2,4-D amine without NIS provided 99% control of flixweed at 21 DAT, but henbit control ranged from 81 to 88%. In comparison, saflufenacil at 50 g ha−1 mixed with bentazon and NIS controlled flixweed at 92% and henbit at 63% at 21 DAT. This research indicates saflufenacil has potential for POST use in winter wheat to control winter annual broadleaf weeds when tank-mixed with 2,4-D amine without NIS, but additional research is needed to discover ways to improve crop safety without reducing weed control.

A survey of seven production fields in Indiana, Illinois, and Ohio was conducted to assess henbit and purple deadnettle growth and soybean cyst nematode (SCN) development and reproduction on these weeds. Autumn and spring growth of purple deadnettle and henbit was influenced by location within each state. In general, winter annual weeds were larger in size and reached maturity earlier in the spring at the southern sample sites than those in the north. All growth stages of SCN were found to be associated with henbit and purple deadnettle at both autumn and spring sample timings. SCN juveniles were generally found infecting roots at highest abundance in the spring. SCN cyst and egg production also were widespread and occurred to a much higher degree during the autumn than the spring developmental period. The results of this survey indicate that management tactics designed to minimize the potential for SCN reproduction on winter annual weeds would probably be most effective if conducted in the autumn, when the majority of SCN reproduction occurred. However, spring populations of winter annual weeds that harbor SCN juveniles might facilitate additional SCN reproduction and population increase if the weeds are not controlled in a timely manner prior to planting.

Carinata is a new biofuel crop that was recently introduced in the southeastern USA as a winter crop. This crop is competitive after canopy closure, but there is a need for weed control options at earlier growth stages. Field experiments were conducted from 2014 to 2016 to determine the safety of several PRE and POST herbicides in carinata. Pendimethalin at 1080 g ai ha−1 applied preplant incorporated (PPI) and PRE caused no carinata injury, or plant density and yield reductions. S-metolachlor was also safe at 694, 1070, 1390, and 2780 g ai ha−1 applied at PRE, 3 d after planting (DAP) and at the 2- to 6-leaf stage. Flumioxazin at 72 g ai ha−1 applied PRE was highly injurious on carinata preventing its establishment. Among the POST herbicides evaluated, clopyralid at 210 g ae ha1 and clethodim at 136 g ai ha−1 caused minor injury to carinata but did not reduce yield compared to the nontreated control. Acifluorfen at 420 g ai ha−1, bentazon at 840 g ai ha−1, and carfentrazone at 18 g ai ha−1 applied POST to carinata caused 75 to 100% injury. Under stressful conditions (i.e. high summer temperatures) all POST herbicides caused more injury than under more favorable conditions for growth in Florida (i.e. winter). The present study identified pendimethalin, S-metolachlor, clopyralid and clethodim as potential herbicides for weed control in carinata, and flumioxazin, acifluorfen, bentazon, and carfentrazone as herbicides that can be used to control volunteer carinata plants in rotational crops.