Caucasian old world bluestem (OWB), seeded for conservation and forage production, has escaped into rangelands in the southern and central Great Plains. Glyphosate, imazapic, imazapyr, imazethapyr, and sulfometuron methyl herbicides were applied at the four- to five-leaf stage and again 8 wk later in 2003 and 2005 to control Caucasian OWB. Glyphosate at 1.14 kg ai/ha at each application was the only treatment that reduced frequency and tiller density of Caucasian OWB, and also controlled over 80% of growth, at 6 wk after the first treatment (WAT) both years. After the first autumn frost, plots treated with glyphosate and imazapyr at 0.28 kg ai/ha at each application had lower frequency and much greater suppression of Caucasian OWB growth than plots treated with other herbicides. Tiller densities and seedhead densities were also less in plots treated with glyphosate and imazapyr compared to other herbicides and the nontreated control. Biomass at the end of the season was near zero for plots treated with glyphosate and imazapyr in 2003, and 26 to 46% of the nontreated control biomass in 2005. Frequency of Caucasian OWB the year following treatment was less than 5% for both glyphosate and imazapyr. Broadcast application of glyphosate and imazapyr also controlled remnant native vegetation in plots, thus different application methods, such as ropewick application, may be useful to avoid native grass injury.

Experiments were conducted in 2004 and 2005 in Virginia to evaluate KIH-485 for shattercane control. KIH-485 was applied to glyphosate-resistant corn at three rates (166, 209, and 250 g ai/ha) and two timings (preemergence [PRE] and postemergence [POST]) and compared to standard rates of S-metolachlor, acetochlor, and pendimethalin. PRE treatments were applied alone, while POST treatments were combined with 1,121 g ai/ha of glyphosate. A single POST application of glyphosate, a nontreated weedy control (WC), and a weed-free control (WFC) were also evaluated. In 2004, at 1 mo after planting (MAP), shattercane was controlled 73, 86, and 93% with the three PRE treatments of KIH-485 compared to only 50, 49, and 48% control with S-metolachlor, acetochlor, and pendimethalin, respectively. Similar levels of shattercane control were also observed with these treatments at 1 MAP in 2005. In both years at 4 MAP, KIH-485 combined with glyphosate applied POST controlled shattercane 96% or greater. However, when glyphosate was combined with S-metolachlor, acetochlor, or pendimethalin, shattercane control was less than 88% in either year. Corn yields with POST applications of KIH-485 plus glyphosate were equivalent to yield from the WFC and greater than yield from any PRE treatment. Early-season shattercane control was promising with KIH-485; however, season-long control only occurred when KIH-485 was applied POST in combination with glyphosate.

Rattail fescue, a winter annual grass weed, has been increasing in Pacific Northwest (PNW) dryland cereal producing areas. Although rattail fescue is not a new weed species in the PNW, its incidence is expanding rapidly in circumstances where soil disturbances are minimized such as in direct seed systems. Options for effective rattail fescue control in winter wheat cropping systems have not been adequately investigated and need to be developed. Rattail fescue control with herbicide treatments was investigated in imidazolinone-resistant winter wheat using imazamox and other herbicides. Across multiple sites and two growing seasons, crop injury from herbicide treatments was minor to negligible with some exceptions. Treatments containing imazamox or mesosulfuron produced minor, transient winter wheat crop injury at some locations in some years. With the exception of flufenacet applied preemergence (PRE), control of rattail fescue in wheat was variable with single herbicide applications, but improved with sequential herbicide treatments. Rattail fescue biomass was greatly reduced by several treatments especially those containing flufenacet or from sequential herbicide application. Crop yield varied among sites due to growing season precipitation, and in some cases from rattail fescue control or herbicide related crop injury.

In previous research, summer annual weeds were successfully controlled in no-till corn with between-row mowing systems that consisted of soil-residual preemergence herbicides banded over corn rows followed by mowing weeds close to the soil surface one or two times later during the growing season. The objective of this research was to determine whether between-row mowing systems could successfully control both winter annual and summer annual weeds as well as broadcast herbicides perform in no-till corn. In two of three years in Missouri, between-row mowing systems controlled and reduced both winter annual and summer annual weed cover and prevented weeds from reducing corn yields. Corn yields for the following no-till weed management systems equaled the weed-free check: winter annual weed control with between-row mowing plus preplant, banded, postemergence-applied glyphosate at 1.1 kg ae/ha and later summer annual weed control with postplant, banded, preemergence-applied atrazine plus S-metolachlor at 2.2 plus 1.8 kg ai/ha followed by between-row mowing. Winter annual weeds growing between rows were controlled with one mowing, and later summer annual weeds were controlled with either one late or “middle” mowing or two mowings (i.e., early and late). Total herbicide use was reduced 50% (i.e., 25 and 25%, respectively) in no-till corn. Commercially acceptable corn stands were needed for between-row mowing systems to adequately control weeds. In one of three years when corn stands were half of those of the other two years, broadcast herbicides performed better than between-row mowing systems in no-till corn.

Annual ryegrass has been proposed as a cover crop in the corn–soybean cropping systems of the U.S. Midwest because of its low seed cost, rapid establishment, contribution to soil quality, weed suppressive abilities, and susceptibility to common broad-spectrum herbicides. However, cover crops can reduce the subsequent main crop yield by creating unfavorable germination and emergence conditions, harboring pests, and if not controlled, competing with the main crop. This study, conducted in Illinois, Oregon, and Tennessee, investigated the efficacy of glyphosate for annual ryegrass winter cover crop removal. Glyphosate at 415, 830, and 1,660 g ae/ha was applied to annual ryegrass at late tiller, second node, boot, and early flowering stages. Annual ryegrass control was consistently maximized with the highest glyphosate rate applied at the boot or early flower stage. Annual ryegrass biomass was generally the lowest with the highest rate of glyphosate applied at the earlier stages. Overall, no single application timing at any glyphosate rate provided complete control or biomass reduction of the annual ryegrass cover crop. A sequential herbicide program or a glyphosate plus a graminicide tank-mix probably will be needed for adequate annual ryegrass stand removal.

Research was conducted to evaluate the residual effect of burning and mechanical removal of sugarcane crop residue on weed control and sugarcane growth and yield. In one study, crop residue was removed in December or January within 3 wk after sugarcane harvest. Mechanical removal of residue from the row top and placement in the row middle using a Sunco Trash Tiger® was compared with burning and a no removal control. Superimposed on each residue removal treatment was tillage of row sides and middles in March and in May and a no-tillage program. Tillage efficiency in March when sugarcane was emerging from the winter dormant period was not negatively affected when residue was removed mechanically. Crop residue on the soil surface did not completely suppress winter weed emergence and growth. Based on sugarcane and sugar yield averaged across locations and tillage programs, mechanical removal of residue was as effective as burning. Sugar yield was reduced 7.9% when residue was not removed from the row top compared with burning or mechanical removal. In another study, crop residue of sugarcane harvested in early December was burned or removed mechanically from the row top 4 d after harvest and also mechanically in January, February, or March. Crop residue ground cover of 79% in March on the row top where residue was not removed provided some suppression of winter weeds. Sugarcane shoot population in April was reduced 16.1% when residue removal was delayed until March compared with December. Averaged across tillage and no-tillage treatments in March, sugarcane yield did not differ when residue was removed by burning in December compared with mechanical removal in December or January. Delaying mechanical removal of residue until February or March compared with residue removal in December decreased sugar yield an average of 13.1%.

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.

Diclosulam is generally applied either PPI or PRE to peanut to control certain broadleaf weeds and suppress sedges. Research was conducted to determine efficacy and peanut response to POST applications of diclosulam at 9, 13, 18, and 27 g ai/ha. Efficacy of diclosulam was affected by application rate and environment. Common ragweed control ranged from 60 to 100%, entireleaf morningglory control from 56 to 100%, marestail control from 78 to 85%, and nodding spurge from 50 to 97%. Smooth pigweed and common lambsquarters were both controlled less than 35%. Diclosulam controlled yellow nutsedge and eclipta less than 70 and 80%, respectively. In separate experiments, diclosulam and imazapic controlled dogfennel more effectively than acifluorfen, bentazon, imazethapyr, lactofen, paraquat, or 2,4-DB. Visual estimates of peanut injury were 15% or less for all rates during both years. Peanut yield ranged from 3,340 to 3,730 kg/ha in 2002 and 5,230 to 5,820 kg/ha in 2003. Foliar injury and peanut pod yield were influenced by diclosulam rate, although no clear relation was evident. Cultivar and diclosulam rate did not interact with respect to visual injury or pod yield.

Reducing herbicide rates can reduce production costs and the potential for carryover injury in subsequent crops, but may also compromise residual weed control. When used at the highest recommended rates (0.35 kg ai/ha), fomesafen may cause carryover injury on sweet corn. One of the most valuable attributes of fomesafen use in snap and dry beans is control of common ragweed. Field experiments were conducted in 1999, 2000, and 2002 to investigate both the residual ragweed control from fomesafen at 0.09, 0.18, and 0.36 kg ai/ha and the potential for a second application to extend the duration of residual control, while reducing the total amount applied per season. Results were significantly affected by weather conditions. In a very wet year (2000), with the greatest ragweed pressure, a single application of fomesafen at 0.20 kg/ha was predicted to provide at least 90% control of ragweed throughout snap and dry bean seasons. In the driest year (1999), 0.09 kg ai/ha provided greater than 90% control for the same period. Regardless of whether a single or double application was made, the total amount of fomesafen required per season was less than the manufacturer's recommended rate. Compared with making a single application, two low-rate applications did not reduce the total fomesafen rate required per season. To help insure at least 90% control of ragweed throughout the snap and dry bean seasons a grower should apply 0.20 kg ai/ha early in the season. Lower rates may be used, but in wet seasons, a second application may be needed to prevent yield loss or interference of ragweed with mechanical harvesting.

Experiments were conducted at the Upper Coastal Plain Research Station near Rocky Mount and at the Peanut Belt Research Station near Lewiston-Woodville in 2002 and 2003. Peanut injury was minimal (< 5%) with all soil-applied programs. S-Metolachlor PRE alone or in mixture with sulfentrazone, diclosulam, or flumioxazin controlled annual grasses similarly (66 to 87%). The addition of imazapic plus 2,4-DB POST increased annual grass control (> 93%). Sulfentrazone or diclosulam in mixture with S-metolachlor were the best PRE options, with 94% and 92% control of yellow and purple nutsedge, respectively, with flumioxazin being least effective at 70%. Diclosulam and flumioxazin in mixture with S-metolachlor were the best PRE options, with 99% and 93%, respectively for common ragweed control, whereas sulfentrazone was the least effective at 65%. S-Metolachlor in mixture with sulfentrazone, diclosulam, or flumioxazin PRE were similar (87 to 90%) for common lambsquarters control. S-Metolachlor in mixture with sulfentrazone, diclosulam, or flumioxazin provided similar levels of entireleaf, ivyleaf, pitted, and tall morningglory control (87, 86, and 87%, respectively) and better than S-metolachlor alone at 64%. Flumioxazin in mixture with S-metolachlor was the best PRE option for control of Palmer amaranth at 96%, whereas diclosulam with S-metolachlor was the best PRE option for control of eclipta at 100%. The prepackaged mixture of acifluorfen and bentazon plus 2,4-DB POST and imazapic plus 2,4-DB POST were similar for all morningglory species (> 96%) and Palmer amaranth control (93 and 97%, respectively). Peanut treated with S-metolachlor plus diclosulam PRE numerically yielded the highest at 3,210 kg/ha, but were statistically equivalent to S-metolachlor plus flumioxazin PRE at 3,040 kg/ha. Peanut treated with imazapic plus 2,4-DB POST yielded the most at 3,400 kg/ha, while peanut treated with a prepackaged mixture of acifluorfen and bentazon plus 2,4-DB POST yielded less (3,070 kg/ha).

Field research was conducted in southern New Mexico to determine the effect of halosulfuron rate, timing of application, and adjuvant on purple nutsedge suppression and chile pepper injury under cultivated conditions. POST-directed treatments of 36 or 53 g ai/ha were applied 2 or 4 wk after thinning direct-seeded chile pepper. Herbicide treatments included a nonionic surfactant or methylated seed oil plus ammonium sulfate plus polyacrylamide polymer. Herbicide rate, adjuvant, and timing of the application had little effect on overall nutsedge suppression; however, herbicide treatment proved to be an important component for managing purple nutsedge in this experiment. Yields were higher with halosulfuron treatment compared with the weedy control. Whereas halosulfuron treatment with 53 g/ha increased chile yield relative to the weedy control, injury and yield results comparing 36 and 53 g/ha rates consistently suggested that halosulfuron should be applied at rates ≤ 36 g/ha in a single application to avoid possible injury. Halosulfuron treatment combined with cultivation and effective crop rotation may reduce the impact of purple nutsedge interference in chile pepper.

Field experiments were conducted at five sites in Nebraska in 2000 and 2001 to determine the effect of planting depth and isoxaflutole rate on the response of an isoxaflutole-sensitive corn hybrid, ‘Pioneer 33-G’ across variable environments. Corn was planted at depths of 2.5 and 5.0 cm, and isoxaflutole was applied PRE at the recommended (1×) and twice the recommended (2×) rate. The effects of planting depth and herbicide rate on injury varied considerably across site–years. When injury was evident, it was generally greater at the high rate of isoxaflutole (2×) and at the shallow planting depth (2.5 cm). In most site–years, corn recovered from early season injury, and yields were not reduced, except at Scottsbluff, NE, and North Platte, NE, where soils were lower in organic matter and higher in pH. Isoxaflutole rates should be carefully selected for soils with low organic matter and high pH.

A field study was conducted at two sites in southwestern Ontario, Canada, from 2002 to 2005 to assess the cumulative effects of different weed management strategies applied to the same plots over time in a corn–soybean rotation. These strategies included a POST broad-spectrum herbicide applied at recommended or reduced rates and use of a computer decision aid to select the POST herbicide having the greatest net return (economic threshold approach) based on weed populations before treatment or seed-bank estimates. Four years after study initiation, increased weed populations were observed only in the nontreated control. The reduced rate and economic threshold approaches did not lead to increased weed seed banks compared with the recommended rate of a broad-spectrum herbicide. Reductions in herbicide rate were more effective than the use of economic thresholds for reducing the risk of environmental impact in corn and soybeans. Weed populations in this study were generally above threshold levels, and herbicides selected by the computer decision aid tended to be older, less-expensive herbicides with high use rates. Recommendations by the computer decision aid were generally more effective and more profitable when based on weed populations before treatment than when based on seed-bank estimates.

Field studies were conducted from 2000 to 2002 to determine whether glyphosate applied during periods of low temperature (< 10 C) provides effective control of garlic mustard without injury to nontarget native herbs. A 1% glyphosate solution was applied on three dates between November and March in 2000 to 2001 and 2001 to 2002, when average daily temperatures ranged from −4.2 to 7 C. Glyphosate reduced the population density of prereproductive springtime garlic mustard infestations, regardless of application timing. During the primary bolting period (April to June), mortality of garlic mustard rosettes in sprayed plots was 87 to 94%, whereas mortality in nontreated plots was 12% in the first year and 41% in the second. Nontarget native herbaceous species were not injured by the cold-weather herbicide applications and exhibited higher springtime densities than in the nontreated plots. By targeting garlic mustard rosettes during the part of the year when most other plant species are dormant, managers can selectively control garlic mustard without damage to native herbs and, thereby, increase forest restoration success.

Livestock poisoning can occur on short-grass prairies when locoweeds are actively growing in spring before warm-season grasses begin growth. White locoweed grows in early spring, completes flowering and seed production by early summer, and goes dormant. Perennial cool-season grasses may provide competition to suppress locoweed or reduce its reestablishment following control. Furthermore, these grasses may provide alternative palatable forage to livestock early in the spring. The objective of this study was to suppress white locoweed reinvasion by seeding cool-season grasses at two mixed-grass and two short-grass prairie sites. White locoweed and associated species were controlled with glyphosate (1.1 kg ai/ha) and picloram (0.38 kg ae/ha) in 3 by 15 m plots. The plots were seeded to ‘CDII’ crested wheatgrass, ‘Vavilov’ Siberian wheatgrass, ‘Luna’ pubescent wheatgrass, ‘Bozoisky’ Russian wildrye, smooth brome, ‘NewHy’ wheatgrass, sideoats grama, and ‘Immigrant’ forage kochia. In addition, a native grass plot, treated with picloram to control locoweed without harming the native grasses, and a nontreated control plot, were established in each replication. Establishment of crested wheatgrass, Siberian wheatgrass, and Russian wildrye averaged 60% over all sites. The other treatments had establishment rates < 30% and were considered unsuccessful. Forage production of Russian wildrye was 2,962 kg/ha, Siberian wheatgrass was 2,736 kg/ha, and crested wheatgrass was 2,339 kg/ha, compared with 1,051 kg/ha for the nontreated control. Mortality of locoweed seedlings was greatest in the pubescent wheatgrass seeding. All seeded species suppressed reestablishment of indigenous locoweed plants.

Field and greenhouse studies were conducted in 2000 and 2001 in Mississippi to determine the most effective POST herbicide programs for control of Texasweed in glyphosate-resistant soybean. In the field, Texasweed plants recovered from most POST herbicide treatments, and plant death rarely occurred. A sequential application of 1,100 g ae/ha glyphosate followed by 840 g/ha glyphosate was the only treatment that controlled at least 90% of Texasweed 4 wk after treatment. Texasweed control ranged from 80 to 87% for lower rates of glyphosate applied once or twice and 390 g ai/ha fomesafen. The addition of fomesafen or other herbicides to glyphosate did not improve control compared with glyphosate alone. In the greenhouse, glyphosate at 560 g/ha controlled 93 and 90% of one- and two-leaf plants, respectively, but at least 1,400 g/ha was required to obtain 90% control of four-leaf plants. Fomesafen at 260 g/ha controlled 93 to 99% of one- to four-leaf Texasweed plants in the greenhouse.

The dissipation of trifloxysulfuron in solution has not been evaluated. The objectives of this study were to evaluate the effect of spray carrier pH (pH values of 5, 7, and 9) on dissipation of trifloxysulfuron during a 21-d period and to evaluate the resulting effects on efficacy on Palmer amaranth. ANOVA of half-life values indicated that hydrolysis occurred more rapidly under acidic spray carrier pH with no differences between neutral and alkaline pH levels. Trifloxysulfuron solutions that were applied to Palmer amaranth significantly decreased dry weights compared with nontreated at all pH levels and time intervals. These results indicated that trifloxysulfuron dissipation was most rapid when the spray tank pH was more acidic, but trifloxysulfuron efficacy was not adversely affected by chemical degradation on Palmer amaranth. Data suggest that pesticide applicators may reduce trifloxysulfuron degradation in spray tanks by using neutral or alkaline spray carriers.

Greenhouse research was conducted to evaluate the effects of POST-applied clopyralid and clopyralid plus additives (surfactants and herbicides) on eight processing spinach varieties for leaf injury and yield. Results demonstrate that when applied alone, clopyralid caused mild injury in the form of slight to moderate leaf malformations and crinkling in all tested spinach varieties. Leaf injury increased significantly 10, 20, and 35 days after treatment (DAT) when additives were mixed with clopyralid compared with when clopyralid was applied alone. Applications of clopyralid + phenmedipham increased leaf injury over clopyralid applied alone and all other clopyralid + additive treatments. Within varieties, spinach yields recorded 35 DAT were generally not reduced with any clopyralid + additive treatment, except when phenmedipham was added to the mixture. The leaf injury associated with clopyralid in this study, though consistent across varieties, generally appears to be cosmetic and may not be detrimental to spinach yields or to the quality of spinach harvested for canning or freezing.

Studies were initiated to evaluate absorption, translocation, and distribution of 14C-quinclorac in propanil- and quinclorac-resistant (R-BYG) and -susceptible (S-BYG) barnyardgrass. No differential absorption of 14C-quinclorac was observed between R-BYG and S-BYG, but more 14C remained in the treated leaf of S-BYG (57% of total absorbed) compared with the R-BYG leaf (34% of total absorbed) at 72 h after treatment (HAT). After 12 HAT, 20 and 15% of the amount absorbed had been translocated basipetally by R-BYG and S-BYG, respectively. At 72 HAT, 27 and 17% of the total absorbed 14C had been translocated acropetally by R-BYG and S-BYG, respectively. The levels of 14C above the treated leaf continued to increase throughout the duration of the experiment in R-BYG while levels of 14C above the treated leaf in S-BYG remained relatively constant. Seven percent more of the total absorbed 14C was exuded from roots of R-BYG than S-BYG at 72 HAT. Although differential translocation was observed between R-BYG and S-BYG, it is unclear whether this difference is a cause of quinclorac resistance or an effect of some other physiological process. Further research is needed to determine if differential translocation is due to metabolism or other physiological factors.