Chlorimuron and imazethapyr applied with nonionic surfactant, crop oil concentrate, or organosilicone-based adjuvant were evaluated for purple nutsedge control in the field. Additional experiments compared chlorimuron and imazethapyr control of purple nutsedge when applied with crop oil concentrate at two growth stages. Chlorimuron controlled purple nutsedge better than did imazethapyr in most experiments. Chlorimuron performed better when applied with crop oil concentrate than with nonionic surfactant or organosilicone-based adjuvant. Imazethapyr control with the organosilicone-based adjuvant or crop oil concentrate was similar and greater than imazethapyr with nonionic surfactant. Control was greater when herbicides were applied to 2- to 6-cm tall purple nutsedge compared with plants 8 to 10 cm tall in two of three trials.

Understanding the biology of tropical soda apple (TSA) is necessary to develop effective control strategies. Tropical soda apple seedling emergence, growth, and regeneration from roots were evaluated. Plant growth (height, leaf number, flowering) was monitored over 110 d in a greenhouse experiment. Emerged seedlings required 83 d to reach a height of 40 cm and 108 d to flower. Total nonstructural carbohydrate concentrations in TSA root and stem fractions, monitored monthly for 1 yr, were highest in December (35%-root, 18%-stem). Seedling emergence as affected by planting depth (0, 1, 2, 4, 8 cm) and regeneration from root segments (7.5, 15 cm long) placed on the soil surface and 5 and 10 cm deep were studied in separate greenhouse experiments. Seedling emergence was lowest (P < 0.05) for seed placed on the soil surface (6.9%) and at a depth of 8 cm (19.4%) with the highest level of TSA emergence predicted at 63% for seed planted 3.6 cm deep. Regeneration from roots was higher (P < 0.05) for the 15-cm root segments than for the 7.5-cm segments while depth of root segment placement did not affect regeneration. Weed control strategies should involve cultural and chemical practices that affect both roots and seeds.

Field trials were conducted in 2000 and 2001 in New Jersey to evaluate quinclorac and siduron for large crabgrass control in summer-seeded creeping bentgrass (‘L-93’). Bentgrass was surface seeded on June 30 and June 26 in 2000 and 2001, respectively. Treatments consisted of preemergence (PRE) applications of siduron at 3.4, 5.0, and 6.7 kg ai/ha and PRE and postemergence (POST) applications of quinclorac at 0.4, 0.6, 0.8, and 1.7 kg ai/ha. POST applications were timed to a crabgrass growth stage of three leaves to one tiller. All POST quinclorac applications included methylated seed oil at 1% (v/v). Percent crabgrass cover in untreated plots at 30 d after planting (DAP) averaged 10 and 50% in 2000 and 2001, respectively. All PRE treatments, with the exception of quinclorac applied at 0.4 kg/ha in 2001, reduced crabgrass cover by 80% or more at 30 DAP. Crabgrass control decreased in late August when siduron and quinclorac were applied at the lower rates in 2001. PRE quinclorac applications at the rate of 0.6 kg/ha or higher in 2000 or 1.7 kg/ha in 2001 caused significant thinning of the bentgrass stand at 30 DAP. All POST quinclorac treatments provided excellent crabgrass control in 2000, but the 0.8-kg/ha or higher rate was required to reduce crabgrass infestation levels by at least 80% in 2001. All POST quinclorac applications caused significant chlorosis to the creeping bentgrass in both years. However, significant thinning of the bentgrass stand was not evident, with the exception of 1.7 kg/ha, in 2001. These studies suggest that PRE applications of siduron should be used for the highest level of creeping bentgrass safety in summer restoration projects. The use of quinclorac should be limited to POST applications to control escaped crabgrass once the newly emerging creeping bentgrass has become well established.

Full-season johnsongrass competition reduced sugar yields by 53 and 44% in ‘CP 70–321’ and ‘CP 72–370’ sugarcane, respectively, primarily by reducing sugarcane stalk populations. Stalk population and height and sugar yields of both cultivars were optimized when asulam was applied at 3.7 kg ai/ha during April and early May. Asulam at 3.4 kg/ha, applied a second time 8 weeks later, generally increased johnsongrass control but did not increase sugar yields over one early application. By delaying the application, the potential for sugarcane injury from asulam applied once or twice increased in both cultivars. Injury appeared to be related to the stage of sugarcane growth and temperature and moisture stress at application time with asulam phytotoxicity being more pronounced in CP 72–370. Populations of johnsongrass stems in the year after treatment reflected the degree of johnsongrass control by asulam and the competitiveness of the crop in the previous year.

Fatoua villosa (mulberry weed) is a new and invasive weed of container nurseries and landscapes in the southeastern United States. Studies were conducted to determine the effects of light, planting depth, mulch depth, and temperature on mulberry weed seed germination and seedling emergence. Light stimulated mulberry weed seed germination, with less than 5% of seeds germinating in the dark compared with 48 to 60% germinating in the light. In all emergence studies, the highest number of seedlings emerged when seeds were placed on the soil surface, with emergence decreasing as planting or mulch depth increased. Planting depths of ≥ 1.8 cm or mulch depths of ≥ 3.7 cm reduced mulberry weed emergence by ≥ 90%. These data suggest that mulch would control mulberry weed effectively. To study the effects of temperature on germination, two seed batches collected locally in October 1998 and August 1999 were used. Maximum germination of seeds collected in 1998 occurred at 25 C, with germination decreasing at higher temperatures and no germination at lower than 15 C or over 40 C. For seeds collected in 1999, maximum germination occurred from 19 to 29 C, with germination decreasing with temperatures above 29 C or below 19 C. At temperatures of 15 and 42 C germination, percentages were 71 and 11%, respectively. Seedlings germinated at 15 C developed slowly but otherwise appeared normal. For both seed lots, seedlings were stunted and chlorotic at ≥ 38 C. That mulberry weed seed germinated over a wide range of temperatures suggests its potential to emerge throughout most of spring, summer, and autumn in the southeastern United States.

Preemergence herbicides were applied at recommended and three times the recommended rates during 1995, 1996, and 1997 to eight established zoysiagrass (Zoysia spp.) cultivars. Oxadiazon was the only herbicide that did not significantly reduce the quality of any zoysiagrass cultivar. The zoysiagrass cultivars had intermediate tolerance to prodiamine and pendimethalin, while oryzalin, dithiopyr, and benefin plus oryzalin caused the highest injury. ‘Emerald’ and ‘Meyer’ cultivars were least affected by herbicide application. ‘Diamond,’ ‘El Toro,’ ‘Cavalier,’ and ‘Crowne’ showed moderate injury, while ‘Royal' and ‘Palisades’ had the greatest injury. When the performance of zoysiagrass cultivars was averaged across herbicides, turf quality in May was best for Meyer, El Toro, and Crowne. The quality of the majority of cultivars except for Royal improved during the summer and was similar to that of Meyer by late August both years.

Two field studies, a seeded study and a golf course study, were conducted to compare competition among creeping bentgrass, annual bluegrass, and roughstalk bluegrass when subjected to common weed control practices and foliar applications of iron and magnesium. A research site was selected for the seeded study and divided into 10 whole plots receiving irrigation at either 50 or 100% evapotranspiration deficit. Each whole plot was further divided into subplots receiving one of seven treatments: bensulide, ethofumesate, trinexapac-ethyl, foliar Mg, foliar Fe, foliar Mg plus foliar Fe, and control. The site was seeded to a mixture of creeping bentgrass, annual bluegrass, and roughstalk bluegrass in September 1995, and treatments began in March 1996. Annual bluegrass was reduced 29% in plots treated with foliar Fe and 65% in plots treated with foliar Fe plus foliar Mg. Roughstalk bluegrass was significantly reduced in seeded plots treated with foliar iron (50%), plant growth regulator (75%), and foliar iron plus foliar magnesium (100%). Annual bluegrass and roughstalk bluegrass proportions were not affected by irrigation regime. In a second study, the most effective treatment, foliar magnesium plus foliar iron, was tested on a working golf course fairway and on a practice putting green beginning April 1997 and ending November 1997. Treatments on the golf course fairway and practice putting green were ineffective due to the established, perennial nature of the annual bluegrass biotypes on these sites. Further research is required to improve the efficacy of nutritional treatments on these perennials.

Spring tillage is a component of an integrated weed management strategy for control of early emerging glyphosate-resistant weeds such as common ragweed; however, the effect of tillage on common ragweed emergence pattern is unknown. The objectives of this study were to evaluate whether spring tillage during emergence would influence the emergence pattern or stimulate additional emergence of common ragweed and to characterize common ragweed emergence in southeast Nebraska. A field experiment was conducted for three years (2014 to 2016) in Gage County, Nebraska in a field naturally infested with glyphosate-resistant common ragweed. Treatments consisted of a no-tillage control and three spring tillage timings. The Soil Temperature and Moisture Model (STM2) software was used to estimate soil temperature and moisture at a 2-cm depth. The Weibull function was fit to total common ragweed emergence (%) with day of year (DOY), thermal time, and hydrothermal time as independent variables. Tillage treatments and year had no effect on total common ragweed emergence (P=0.88 and 0.35, respectively) and time to 10, 25, 50, 75, and 90% emergence (P=0.31). However, emergence pattern was affected by year (P=<0.001) with 50% total emergence reached on May 5 in 2014, April 20 in 2015, and April 2 in 2016 and 90% total emergence reached on May 12, 2014, May 8, 2015, and April 30, 2016. According to the corrected information-theoretic model comparison criterion (AICc), the Weibull function with thermal time and base temperature of 3 C best explained the emergence pattern over three years. This study concludes that spring tillage does not stimulate additional emergence; therefore, after the majority of the common ragweed has emerged and before the crop has been planted, tillage could be used as an effective component of an integrated glyphosate-resistant common ragweed management program in Nebraska.

Cleavers species (false cleavers and catchweed bedstraw) are among the top 10 most abundant weeds across the prairie region of western Canada, and are increasing in relative abundance at the fastest rate since the 1970s. In 2008, two false cleavers populations from Tisdale and Choiceland, Saskatchewan, were suspected of acetolactate synthase (ALS) –inhibitor resistance. Dose-response experiments were conducted with the use of imazethapyr and florasulam, both ALS inhibitors, as well as fluroxypyr, a synthetic auxin. Additionally, a 1,954–base-pair region of the ALS gene including sites known to confer ALS resistance were sequenced. Both populations were highly resistant to imazethapyr (resistance factors greater than 100), one population (Tisdale) was highly resistant to florasulam (Choiceland population susceptible, although a second, larger screening of 200 individuals indicated low frequency [2%] florasulam resistance), and both populations were susceptible to fluroxypyr. All sequenced Tisdale individuals screened with imazethapyr posessed the Trp574Leu mutation. In contrast, three point mutations were found for Choiceland individuals sequenced: Ser653Asn, Trp574Leu, and Asp376Glu. These ALS target-site mutations have not been documented previously in this species.

Poor annual bluegrass control was reported in golf course roughs following treatment with prodiamine (1120 gaiha−1) and glyphosate (840 gaeha−1) during hybrid bermudagrass dormancy. Research was conducted to determine if this annual bluegrass phenotype was resistant to both prodiamine and glyphosate and to determine the efficacy of herbicide mixtures for controlling this phenotype in the field. In PRE or POST dose-response experiments, 9 to 31 times more prodiamine or glyphosate was needed to control (or reduce dry biomass of) this resistant phenotype by 50% compared to an herbicide-susceptible phenotype. Moreover, glyphosate-susceptible plants accumulated 50% more shikimic acid (898 mgkg−1) 6 d after treatment than those resistant to glyphosate (394 mgkg−1). October (fall) applications of herbicide mixtures containing trifloxysulfuron, simazine, S-metolachlor, or mesotrione controlled this resistant annual bluegrass phenotype 84 to 98% in April (spring), with no differences detected among treatments. Our findings document the second instance of annual bluegrass evolving multiple resistance in a managed turfgrass system. However, several herbicide mixtures can be used to effectively manage this resistant phenotype.

Research conducted in the field identified 14 injury criteria associated with dicamba (Clarity® diglycolamine salt) applied at 0.6 to 280 g ae ha–1 (1/1,000 to 1/2 of 560 g ha–1 use rate) to indeterminate soybean at V3/V4 or R1/R2. For each criterion, injury was rated using a scale of 0=no injury, 1=slight, 2=slight to moderate, 3=moderate, 4=moderate to severe, and 5=severe. Greatest crop injury 15 d after treatment (DAT) was observed for dicamba rates of 0.6 to 4.4 g ha–1 for upper canopy pale leaf margins (3.8 to 4.2) at V3/V4 and for terminal leaf cupping (4.1 to 5.0) at R1/R2, and for rates of 0.6 to 8.8 g ha–1 for upper canopy leaf cupping (3.8 to 4.8) and upper canopy leaf surface crinkling (3.4 to 4.4) at V3/V4. Injury 15 DAT was equivalent to the nontreated control for dicamba rates as high as 4.4 g ha–1 for lower stem base swelling at V3/V4 and for upper canopy leaf rollover/inversion and terminal leaf necrosis at R1/R2; for rates as high as 8.8 g ha–1 for leaf petiole base swelling and stem epinasty at R1/R2, and lower stem base lesions/cracking (V3/V4 and R1/R2 average); and for rates as high as 17.5 g ha–1 for lower leaf soil contact at V3/V4 and leaf petiole droop at R1/R2. The response to increasing dicamba rate observed for the injury criteria was in contrast to the steady increase in visual injury and plant height reduction rated as 0 to 100%. The moderate to severe upper canopy leaf cupping, pale leaf margins, and leaf surface crinkling, and terminal leaf cupping 15 DAT with dicamba at 0.6 to 4.4 g ha–1 corresponded to soybean yield loss of 1% to 9% for application at V3/V4 and 2% to 17% at R1/R2.

The nonnative biotype of common reed has invaded wetlands in many states including Nebraska, especially along the Platte River from Wyoming to the eastern edge of Nebraska. Therefore, three studies (disking followed by herbicide, mowing followed by herbicide, and herbicide followed by mechanical treatment) were conducted for 3 yr (2008 to 2010) at three locations in Nebraska. The objective was to evaluate common reed control along the Platte River using an integrated management approach based on herbicides (glyphosate or imazapyr), mowing, and disking, either applied alone or in combination. The level of weed control was determined by visual rating, percent flowering, and stem density. On the basis of visual rating, disking and mowing used alone provided common reed control for only a few months. However, the control was significantly prolonged (e.g., at least three seasons) when disking and mowing were combined with herbicide applications. Disking followed by herbicide and mowing followed by herbicide significantly reduced flowering and plant densities (P = 0.0001) compared to the untreated check. These results suggest that a combination of weed control methods has potential to control common reed.

Field experiments were conducted to determine suitable application timings and rates of MON 37500 for downy brome control in winter wheat. MON 37500 applied preemergence (PRE) or in fall postemergence (POST) provided better control of downy brome than when applied spring POST. MON 37500 at rates ranging from 19 to 33 g ai/ha applied PRE or fall POST controlled downy brome >85%. MON 37500 applied spring POST at 60 g/ha only suppressed growth of downy brome. Winter wheat was not visibly injured and maturity was not delayed by MON 37500 applied up to 60 g/ha at any of the application timings. Winter wheat yield responded positively to all MON 37500 treatments but PRE or fall POST applications usually resulted in greater yields than spring POST applications. Wheat yields progressively increased with increasing rates of MON 37500 up to 30–40 g/ha, above which yields tended to plateau or, in two instances, decline slightly. MON 37500 is an important new herbicide that should enable growers to better manage downy brome in winter wheat production systems.

Dry peas (pea) usually require early and effective weed management for optimum yields. However, it is not always possible to control all weeds with a single herbicide application. In experiments at Lacombe and Lethbridge, Alberta, Canada, we determined the relative importance of controlling redstem filaree or wild oat, or both species. Bentazon, sethoxydim, or a imazethapyr/imazamox mixture was applied to control redstem filaree, wild oat, or both weeds, respectively. None of the herbicides caused visually detectable crop injury. Time of weed removal effects on pea yield were inconsistent. In addition, applying half or full herbicide rates did not usually influence weed biomass, pea yield, or pea seed weight. Averaged across all variables except herbicide, pea yield losses due to competition from redstem filaree, wild oat, or both species averaged 31, 47, or 53%, respectively. When redstem filaree and wild oat were controlled with imazethapyr/imazamox, pea yields were the same as weed-free check plots in three of four location-years (89% of weed-free yields for all four location-years). Optimal pea yields in weed communities with redstem filaree and wild oat as dominant species were more dependent upon selecting an herbicide that controlled both species than a specific time of weed removal or herbicide rate.

Water use by weeds is one type of loss that contributes to the cost of weeds to agriculture. Water use efficiency provides a mechanism by which water use by weeds can be estimated. Uncontrolled weed growth could result in estimated irrigation costs exceeding $50.00/ha. Weeds like barnyardgrass at threshold densities in irrigated crops like sugarbeet or tomato are estimated to increase production costs by about $20.00/ha depending on water cost.

Field studies were conducted from 1998 to 2000 in Beltsville, MD, to evaluate the effects of preemergence (PRE) applications of BAY FOE 5043 + metribuzin, s-metolachlor, and diclofop on crop injury, yield, and control of diclofop-tolerant Italian ryegrass in winter wheat. No injury was observed in 1999. In 2000, minor stunting of wheat plants was observed where high rates of BAY FOE 5043 + metribuzin and s-metolachlor were utilized. Wheat plants outgrew the stunting and grain yields were not affected. High rates of BAY FOE 5043 + metribuzin and s-metolachlor provided equally effective Italian ryegrass control in 1999, averaging 85% or greater in June. In 2000, all rates of BAY FOE 5043 + metribuzin provided 93% or greater Italian ryegrass control, whereas s-metolachlor at 0.43 kg/ha or greater provided 85% Italian ryegrass control or greater when evaluated in June. In 1999, wheat yields from plots treated with BAY FOE 5043 + metribuzin, or s-metolachlor at 0.43, 0.56, or 0.84 kg/ha, were higher than from the nontreated control. In 2000, all wheat yields from plots treated with BAY FOE 5043 + metribuzin and s-metolachlor were higher than from the nontreated control.

A survey of 146 fields was conducted to investigate herbicide performance in winter wheat-producing areas of southwestern Nebraska during August and September of 1986. Only 55% of the fields received an excellent rating for weed control and stubble quality; one third rated as unacceptable. Weed control after wheat harvest was improved by planting ‘Bounty 310’, ‘Siouxland’, ‘Vona’, and ‘Centura’ winter wheat cultivars rather than ‘Mustang’, ‘Hawk’, ‘Pioneer 2656’, and ‘Wings'. Fertilizing winter wheat in the fall, planting wheat at the optimum date, high wheat stem density, using a winter wheat-corn-fallow rotation, not spraying herbicides after wheat harvest on days that it rained or air temperature exceeded 35 C, and spraying weeds when they were small also improved weed control in wheat stubble. Nine months after wheat harvest, fields treated with atrazine before July 16 had more volunteer wheat than fields treated later.

Research was conducted to determine the effects of tillage on fluometuron and norflurazon loss in runoff when applied preemergence in cotton. Cumulative water loss and norflurazon and fluometuron concentrations in runoff were not affected by tillage systems. In 1992, the no-till system had less sediment loss in runoff than the conventional tillage system. Tillage systems did not affect sediment loss in 1993. The highest amount of total fluometuron loss occurred with the conventional tillage system in 1992, whereas the reduced tillage system had the lowest amount in 1993. There were no differences in cumulative norflurazon loss between tillage systems in 1992, and as with fluometuron loss, norflurazon loss in runoff was less with the reduced tillage system in 1993. This research indicates that, while conservation tillage may reduce sediment loss, it may not necessarily be the best management tool for decreasing the loss of herbicides in runoff.

Rapid germination and root growth have been identified as important plant characteristics for establishment in arid environments. This study evaluates germination, radicle elongation, and root growth rates of two annual grasses, two forage species, and yellow starthistle. Yellow starthistle germination, radicle elongation, and root growth were faster than those of medusahead and hedgehog dogtailgrass. Subterranean clover possessed rapid seedling growth characteristics similar to those of yellow starthistle, whereas Palestine orchardgrass was most delayed.

Experiments were conducted in 2008, 2009, and 2010 to determine the influence of water source as carrier and other agrochemicals on glyphosate efficacy and physicochemical compatibility. Glyphosate efficacy was not affected by most water sources, when compared with deionized water, although response was not consistent across all weed species, including cereal rye, common lambsquarters, common ragweed, goosegrass, Italian ryegrass, large crabgrass, Palmer amaranth, tall morningglory, and wheat. Control by glyphosate was not negatively affected when coapplied with cloransulam-methyl, dicamba, flumioxazin, pyrithiobac-sodium, thifensulfuron-methyl plus tribenuron-methyl, trifloxysulfuron-sodium, and 2,4-D but was affected by acifluorfen and glufosinate. Calcium, manganese, and zinc solutions consistently reduced weed control by glyphosate, whereas boron seldom affected efficacy. Compared with deionized water, Italian ryegrass control was affected by water sources when applied at seedling and jointing stages more so than at tillering and heading growth stages. Calcium, manganese, and zinc reduced control regardless of growth stage. Precipitates were not produced when glyphosate was applied with the water sources or fertilizer solutions. However, transient precipitates developed when glyphosate was coapplied with cloransulam-methyl, flumioxazin, thifensulfuron-methyl plus tribenuron-methyl, and trifloxysulfuron-sodium but not when coapplied with acifluorfen, dicamba, glufosinate, pyrithiobac-sodium, and 2,4-D. Solution pH ranged from 4.11 to 5.60 after glyphosate was added, regardless of solution pH before glyphosate addition.