Downy brome is one of the leading plant pests in winter wheat and no-till spring wheat in many areas of the country. It has recently been studied in North Dakota where it is emerging as a serious crop competitor. Downy brome plants produced up to 60 tillers and more than 7,500 seeds when no control measures were used and densities were less than 2 plants m−2. Experiments focusing on herbicide-application timing identified differences in downy brome control and the grain yield of spring wheat. Regardless of fall or spring application timing, glyphosate applied PRE to wheat completely controlled downy brome in 2007. In 2008, control was not achieved with the earliest glyphosate-application timings because of late-emerging plants. When comparing fall and spring application timings of other herbicides, imazapic provided at least 79% control at each timing and location, resulting in the highest imazamox-resistant spring wheat yield. In general, herbicides performed better when applied in fall than they did when applied in spring. When herbicides were applied POST, imazamox provided the greatest downy brome control and usually caused the largest numerical reduction in downy brome biomass, seed, and stem number. If downy brome was left untreated, regression analysis predicted approximately 2,000 stems m−2 could result in total yield loss of spring wheat.

We conducted a greenhouse study to evaluate the differential response of Palmer amaranth to glyphosate and mesotrione and to quantify the level of tolerance to mesotrione in recalcitrant (difficult-to-control) accessions and their offspring. Seeds were collected from 174 crop fields (corn, cotton, and soybean) across Arkansas between 2008 and 2016. Palmer amaranth seedlings (7 to 10 cm tall) were treated with glyphosate at 840 g ae ha–1 or mesotrione at 105 g ha–1. Overall, 47% of the accessions (172) were resistant to glyphosate with 68% survivors. Almost 35% of accessions were highly resistant, with 90% survivors. The majority of survivors from glyphosate application incurred between 31% and 60% injury. Mesotrione killed 66% of the accessions (174); the remaining accessions had survivors with injury ranging from 61% to 90%. Accessions with the least response to mesotrione were selected to determine tolerance level. Dose–response assays were conducted with four recalcitrant populations and their F1 progeny. The average effective doses (ED50) for the parent accessions and F1 progeny of survivors were 21.5 g ha–1 and 27.5 g ha–1, respectively. The recalcitrant parent populations were three- to five-fold more tolerant to mesotrione than the known susceptible population, as were the F1 progeny.

Common purslane is a widely distributed summer annual weed. It can reproduce vegetatively from stem cuttings by forming adventitious roots from the cut end of the stem. Apart from large stem cuttings, it is unclear whether purslane cuttings of various plant tissues differ in their ability to reproduce asexually. The objective of the study was to determine the survival and asexual reproductive capacity of purslane cuttings. A greenhouse study evaluated three cuttings from two stem locations and a leaf from one stem location for their survival and new leaf growth after 21 d. Cuttings included a stem node with either leaves attached or removed and a stem internode, all from proximal and distal stem locations relative to the root crown, and a leaf from a proximal stem node. Stem node cuttings had ≥ 70% survival, whereas internodes had 0% survival. Nodes with leaves attached further increased survival by > 20%. The location of the cutting on the main stem did not affect survival. Only noded cuttings produced new leaves, and cuttings with leaves attached produced the most new leaves. For purslane to vegetatively reproduce, nodes on stem cuttings are required, and the presence of leaves on the cutting improves the survival and new leaf growth of cuttings. Therefore, mechanical methods of weed control that chop and spread purslane leaves and stems might not be effective and could ultimately increase weed populations.

Seed of three weed species collected from the grain bins of combines while standing hard red winter wheat was harvested germinated better than hand-harvested seed. Combine-harvested curly dock seed germinated from 4 to 24% more than hand-harvested seed. Curly dock seed harvested with a commercial-type combine germinated better than those harvested with a small-plot combine. Harvesting slimleaf lambsquarters and Venice mallow seed with a commercial-type combine also enhanced germination compared to hand-harvested seed.

Palmer amaranth has a long history of evolving resistance to herbicides to the point at which it has become a significant obstacle to row crop production. A survey of Palmer amaranth escapes in dicamba-resistant cotton and soybean fields in Tennessee was conducted in fall 2021 with the objective of determining whether poor control was due to environmental phenomena or the development of dicamba resistance. A greenhouse dicamba dose-response screen was conducted on 15 Tennessee accessions. Three accessions were identified with a relative resistance factor between 1.85 and 2.49, and one accession from Lauderdale County was found with a relative resistance factor of 14.25. The Lauderdale County 1 accession developed a higher dicamba resistance level than all others evaluated and can no longer be effectively controlled using dicamba. The history of Palmer amaranth escaping dicamba in the Lauderdale County 1 location from 2019 to 2021 in the field and in preliminary greenhouse screens would suggest that the dicamba resistance has passed between generations. This research documents the first findings of Palmer amaranth control failures in cotton and soybean fields due to the evolution of dicamba resistance.

Postemergence spring applications of picloram and picloram plus 2,4-D frequently reduced mature height and peduncle length of hard red winter wheat in field experiments. Yield reductions were more severe from picloram applied alone to the first joint growth stage than late tillering stage wheat. In two of six experiments picloram plus 2,4-D reduced yield more than picloram alone. Yields of four wheat cultivars were reduced by picloram and picloram plus 2,4-D at one of two locations. At the second location only the yield of ‘Chisholm’ and ‘Rohm and Haas Seed 7837’ were reduced by those herbicides.

Field trials were conducted in the spring of 2007 and 2008 to investigate the critical period of interference between American black nightshade and triploid watermelon. To determine the critical period, the maximum period of competition and minimum weed-free period were examined. American black nightshade (2 plants m−2) was established into watermelon plots at watermelon transplanting and removed at 0, 1, 2, 3, 4, and 5 wk after transplanting to determine the maximum period of competition. American black nightshade (2 plants m−2) was established into watermelon plots at 0, 1, 2, 3, 4, and 5 wk after transplanting and remained until watermelon harvest to determine the minimum weed-free period. To avoid yield loss from exceeding 10% of a crop grown weed-free, the maximum period of competition and minimum weed-free period were found to be 3.9 and 3.6 weeks after transplanting, respectively. Therefore, if American black nightshade is controlled at any time during the critical period of 3.6 to 3.9 wk after transplanting, yield loss should not exceed 10% of a crop grown weed-free.

Annual bluegrass is one of the most difficult-to-control weeds in creeping bentgrass putting greens. Field trials were conducted in 2003 and 2005 to evaluate bispyribac-sodium for annual bluegrass management in creeping bentgrass greens maintained at a 3 mm mowing height. Bispyribac-sodium applied weekly at 12 or 24 g ai/ha controlled annual bluegrass 86% 12 wk after initial treatment (WAIT). In 2003, bispyribac-sodium applied at 12 and 24 g/ha/wk injured creeping bentgrass approximately 15 and 50% by 4 WAIT, respectively. However, injury was transient and was not evident by 12 WAIT. In 2005, the 12 and 24 g/ha/wk injured creeping bentgrass 15 and 85% by 8 WAIT, respectively, and was still evident throughout the trial. Putting green quality was reduced when compared to nontreated creeping bentgrass by the same treatments. The removal of annual bluegrass caused soil exposure until creeping bentgrass grew over the bare areas, contributing to decreased quality evaluations. Management of annual bluegrass in creeping bentgrass putting greens is possible with bispyribac-sodium. However, these results indicate bispyribac-sodium can cause excessive injury when applied to creeping bentgrass mowed at 3 mm.

In the field, eight barley (Hordeum vulgare L.) cultivars tolerated postemergence applications of AC 222,293 [a mixture of methyl 6 and 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl) m- and p-toluate] at 0.4 to 1.4 kg/ha. AC 222,293 at 0.4 kg ai/ha applied at the 1.5- to 2-leaf stage controlled wild oats (Avena fatua L. # AVEFA) 96%, whereas 0.7 kg/ha applied at the 3.5- to 4-leaf stage controlled wild oats only 93%. Sugarbeets (Beta vulgaris L.) but not alfalfa (Medicago sativa L.), corn (Zea mays L.), pinto beans (Phaseolus vulgaris L.), or sunflower (Helianthus annus L.), were injured when planted 6 to 8 months after fall applications of AC 222,293 at 0.4 to 1.1 kg/ha.

Glufosinate at 2.2 kg ai/ha injured rice transformed with the BAR gene more when applied to one- to two-leaf (23 to 26%) than to three- to four-leaf (13 to 19%) plants. Visible injury was least when applications were made at boot stage (3 to 14%). However, applications at boot stage caused an average grain yield reduction of 16%. Most treatments did not influence rice plant height. Among single applications (0.3, 0.4, 0.6, 0.8, and 1.1 kg/ha), 1.1 kg/ha glufosinate at three- to four-leaf stage of red rice resulted in greater control (91%) than at panicle initiation (74%) or at boot stage (77%). Injury to red rice was two to 11 times greater than the injury to BAR-transformed rice depending on glufosinate rate and application timing.

Desiccants are currently used to improve lentil dry-down prior to harvest. Applying desiccants at growth stages prior to maturity may result in reduced crop yield and quality, and leave unacceptable herbicide residues in seeds. There is little information on whether various herbicides applied alone or as a tank-mix with glyphosate have an effect on glyphosate residues in harvested seed. Field trials were conducted at Saskatoon and Scott, Saskatchewan, Canada, from 2012 to 2014 to determine whether additional desiccants applied alone or tank mixed with glyphosate improve crop desiccation and reduce the potential for unacceptable glyphosate residue in seed. Glufosinate and diquat tank mixed with glyphosate were the most consistent desiccants, providing optimal crop dry-down and a general reduction in glyphosate seed residues without adverse effects on seed yield and weight. Saflufenacil provided good crop desiccation without yield loss, but failed to reduce glyphosate seed residues consistently. Pyraflufen-ethyl and flumioxazin applied alone or tank mixed with glyphosate were found to be inferior options for growers as they exhibited slow and incomplete crop desiccation, and did not decrease glyphosate seed residues. Based on results from this study, growers should apply glufosinate or diquat with preharvest glyphosate to maximize crop and weed desiccation, and minimize glyphosate seed residues.

Glyphosate application to the rapid-response (RR) biotype of glyphosate-resistant (GR) giant ragweed ensues in loss of foliage via rapid tissue death, thereby reducing glyphosate translocation. Experiments were performed to determine if this GR response, in contrast to a non-rapid response (NRR) GR biotype, results in antagonism of the selective herbicides atrazine, cloransulam, dicamba, lactofen, and topramezone. Application of glyphosate at 1,680 g ae ha–1 in the greenhouse resulted in antagonism between all five selective herbicides for the RR biotype, whereas glyphosate applied at 420 g ha–1 was antagonistic only for cloransulam. Application of selective herbicides 2 d prior to glyphosate treatment avoided the antagonism observed in the RR biotype. In the field, glyphosate mixtures with dicamba and topramezone were antagonistic on the RR biotype across both 2015 and 2016 field seasons. Thus, the RR effectively reduces glyphosate efficacy but also has potential to diminish the activity of glyphosate mixtures with selective herbicides, and the degree of antagonism between these mixtures escalates at increasing glyphosate rates.

Morningglories are summer annual or perennial dicots, and are troublesome weeds in sugarcane cultivated in northern India. If not controlled, they may compete with sugarcane, interfere in the harvest operation, and reduce yields. Managing morningglories in sugarcane continues to be a serious challenge for sugarcane growers. Field experiments were conducted during the 3-yr period from 2007 to 2009 to evaluate herbicides applied PRE and POST for control of morningglories in sugarcane. The herbicides applied PRE included diuron, metribuzin, and atrazine at 1.6, 1.4, and 1.0 kg ai ha−1, respectively, applied alone or followed by 2,4-D amine salt (0.58 or 1.16 kg ae ha−1) or 2,4-D sodium salt (0.8 or 1.6 kg ae ha−1) applied POST. Herbicides applied PRE controlled morningglories ≤ 87% at 15 d after treatment (DAT); however, control reduced to ≤ 56% at 90 DAT. Control improved when herbicides applied PRE were followed by POST application of 2,4-D amine or sodium salt. For example, diuron applied PRE followed by 2,4-D amine salt applied POST at any rate provided 100% control of morningglories at 15 and 30 DAT. At 90 d after POST application, control ranged from 68 to 82% with the PRE followed by POST herbicides, compared to 0% control when metribuzin or atrazine were applied PRE alone. The density and biomass of morningglories was also reduced to zero in treatments that included 2,4-D amine salt. The number of millable canes, cane height, and single cane weight was superior in PRE followed by POST herbicide treatments compared to herbicides applied PRE alone. Maximum cane yield was recorded for the treatments that included 2,4-D amine or sodium salt compared to only PRE treatments, and it was usually comparable with the nontreated weed-free control. It is concluded that a combination of PRE and POST herbicides were effective for control of morningglories; however, more research is required to evaluate other herbicides and their tank mix partners for control of morningglories in sugarcane.

Asia minor bluegrass (AmB) is a major weed impacting rapeseed production in Dongting Lake District, China. Growth chamber experiments were conducted to determine the influence of environmental factors on germination and emergence of AmB. The optimum constant temperature for germination was around 20 C. Seeds showed germination percentages above 60% under 22/15 and 24/19 C day/night temperature regimes. Seeds could germinate in the dark, but light exposure significantly enhanced the germination percentage. More than 50% of seeds germinated over a pH range between 4 and 10. Seeds were highly sensitive to osmotic stress, and germination was completely inhibited at an osmotic potential of −0.4 MPa, indicating that it was favored by a moist environment. Increasing salinity reduced germination of AmB seeds from 58% at 0 mM to 13% at 80 mM NaCl. The highest seedling emergence (62%) was observed when seeds were placed on the soil surface, and no seedlings emerged from seeds placed at a depth of 5 cm. This work shows that the climate and soil conditions in Dongting Lake District are suitable for AmB seed germination and that no-till fields, where seeds remain on the soil surface, promote the successful establishment of the weed.

Seedlings of proso millet usually were killed by discing and rototilling in field experiments but populations were not reduced by mowing or by compressing under tractor wheels. In greenhouse experiments, recently emerged seedlings had the greatest mortality after raking and desiccation treatments but were less affected by shoot and/or root damage. In contrast, seedlings treated several weeks after emergence suffered greater mortality from shoot damage and less from desiccation. Two weedy proso millet biotypes, black and Crown, were used in the field experiments, and up to six biotypes were used in the greenhouse. Few significant differences among biotypes were found. Young (emerging) seedlings were extremely resilient to all treatments.

Field experiments were conducted in 1986 and 1987 to determine the efficacy of various herbicides applied in the spring or fall for redvine population reductions. Spring applications of dicamba and picloram reduced redvine populations 4 mo after application. These treatments also reduced soybean density. A sequential spring followed by fall application of dicamba reduced redvine stem counts 32 to 45% the following year. Spring or spring followed by fall applications of clopyralid and hexazinone were not effective in reducing redvine populations. A fall application of clopyralid, dicamba, Dowco 433, glyphosate, or imazapyr reduced redvine regrowth 78 to 97% the following year. Dicamba at 2.2 kg ae ha-1, 3.4 kg ae ha-1 glyphosate, and 0.28 kg ai ha-1 imazapyr increased soybean yield the following year because of reduced redvine competition and lack of herbicide injury. Redvine populations were unaffected by fall applications of fosamine, hexazinone, and picloram, or clomazone applied in the spring or in the fall followed by a sequential spring application. A sequential spring followed by fall treatment of 1.1 + 1.1 kg ha-1 dicamba or 0.14 + 0.14 kg ae ha-1 clopyralid reduced trumpetcreeper population 49 to 58% the following year.

A 2-yr field study was conducted in Blackville, SC, to assess the potential for using small-grain cover crops and glyphosate as a means of reducing or eliminating the need for atrazine in irrigated Southeastern corn production. Oats, rye, and wheat were no-till, drill seeded each fall and subsequently desiccated in early spring before corn planting. A bareground conventional tilled treatment also was included. Within each cover crop system, the herbicides evaluated included (1) no herbicide; (2) 1.68 kg ai/ha atrazine plus 1.08 kg ai/ha S-metolachlor at corn planting followed by 0.84 kg ae/ha glyphosate; or (3) two applications of 0.84 kg/ha glyphosate alone, applied sequentially. All systems were compared with conventional tillage without a cover crop with 1.68 kg/ha atrazine plus 1.08 kg/ha S-metolachlor at planting followed by 1.12 kg/ha atrazine. Biomass of rye, oats, and wheat at dessication was 497, 369, and 340 g/m2, respectively. All cover crops delayed early-season corn growth. Detrimental effects on early-season corn growth from the oats cover crop were still apparent 7 wk after emergence (WAE), with corn height and biomass reduced 8 and 19%, respectively. Weed biomass in nontreated plots was reduced 84, 68, and 21% by oats, rye, and wheat, respectively, 3 WAE. Oats were more inhibitory of corn and weed growth than rye, although rye produced greater surface residue, indicating possible allelopathy affects. In the presence and absence of each cover crop, atrazine plus S-metolachlor followed by glyphosate or sequential glyphosate applications alone were effective in providing season-long control of pitted morningglory, entireleaf morningglory, Palmer amaranth, Florida pusley, large crabgrass, and common bermudagrass. Corn yields and gross profit margins in sequential glyphosate–treated plots were equivalent or superior to the standard atrazine-based program, which indicates that effective and economical alternatives to atrazine are available.

This paper describes the application of a relatively new remote sensing tool, airborne video imagery, for distinguishing weed and brush species on rangelands. Plant species studied were false broomweed, spiny aster, and Chinese tamarisk. A multispectral video system that acquired color-infrared (CIR) composite imagery and its simultaneously synchronized three-band [near-infrared (NIR), red, and yellow-green] narrowband images was used for the false broomweed and spiny aster experiments. A conventional color camcorder video system was used to study Chinese tamarisk. False broomweed and spiny aster could be detected on CIR composite and NIR narrowband imagery, while Chinese tamarisk could be distinguished on conventional color imagery. Quantitative data obtained from digitized video images of the three species showed that their digital values were statistically different (P = 0.05) from those of associated vegetation and soil. Computer analyses of video images showed that populations of the three species could be quantified from associated vegetation. This technique permits area estimates of false broomweed, spiny aster, and Chinese tamarisk populations on rangeland and wildland areas.

Annual bluegrass and roughstalk bluegrass are turfgrasses, but they can also be two of the most serious weed problems in highly maintained turfgrass. Ethofumesate has been used to control annual bluegrass; however, the results have been erratic, and ethofumesate is not widely utilized for annual bluegrass control in turfgrass. The objective of this research was to characterize the response of annual, roughstalk, and Kentucky bluegrasses and creeping bentgrass to a range of ethofumesate rates. Single applications of ethofumesate from 3.4 to 20.2 kg ai/ha were made to all four species during May of 1999 to 2001. All four species were injured from rates of ≥6.7 kg/ha. Roughstalk bluegrass was most injured by a single ethofumesate application. Percent roughstalk bluegrass control increased linearly with rate, and greater than 85% control was observed for rates of ≥16.8 kg/ha. In contrast, annual bluegrass showed almost no control, with rates ≤10.2 kg/ha, and the highest rate tested, 20.2 kg/ha, controlled only 47 to 62% of the annual bluegrass. Kentucky bluegrass was the least sensitive bluegrass species, with a maximum control of 3 to 15% from 20.2 kg/ha of ethofumesate. Creeping bentgrass was the least sensitive of the species tested, with low levels of control regardless of rate. During 3 yr of testing, maximum control of bentgrass from any rate was 4%. Single, high-rate applications of ethofumesate hold promise to control roughstalk bluegrass in creeping bentgrass turf. Sixteen Kentucky bluegrass cultivars used for low-cut athletic fields were evaluated for their tolerance to sequential ethofumesate applications during 1999 and 2002. The cultivars showed significant differences in ethofumesate tolerance, with ‘Moonlight’ and ‘America’ never showing any injury to sequential ethofumesate applications, while ‘Northstar’ and ‘Total Eclipse’ were severely injured.

Barnyardgrass and morningglory control POST with glufosinate at 840 g a.i./ha 28 d after treatment was 79 to 85% and 83 to 90%, respectively, when no more than 35 d elapsed between initial spring soil tillage and herbicide application. For the same rate of glufosinate, prickly sida and hemp sesbania were controlled 68 and 92%, respectively. Comparable barnyardgrass control was obtained with glufosinate at 560 and 840 g/ha, which was greater than at 420 g/ha. Hemp sesbania control was similar for all rates of glufosinate. In comparison, paraquat at 1050 g a.i./ha controlled 40 to 65% barnyardgrass, 44 to 75% morningglory, 41% prickly sida, and 92% hemp sesbania. With 840 g a.i./ha glyphosate and SC-0224, barnyardgrass, morningglory, prickly sida, and hemp sesbania were controlled 55 to 89%, 55 to 81%, 45 to 61%, and 56 to 68%, respectively. Soybean yield was 5.8, 7.6, 6.0, and 5.9 times greater than the nontreated check for 1050 g/ha paraquat and 840 g/ha glufosinate, glyphosate, and SC-0224, respectively.