We conducted an online survey of weed scientists in the United States and Canada to (1) identify research topics perceived to be important for advancing weed science in the next 5 to 10 years and (2) gain insight into potential gaps in current expertise and funding sources needed to address those priorities. Respondents were asked to prioritize nine broad research areas, as well as 5 to 10 subcategories within each of the broad areas. We received 475 responses, with the majority affiliated with academic institutions (55%) and working in cash crop (agronomic or horticultural) study systems (69%). Results from this survey provide valuable discussion points for policy makers, funding agencies, and academic institutions when allocating resources for weed science research. Notably, our survey reveals a strong prioritization of Cultural and Preventative Weed Management (CPWM) as well as the emerging area of Precision Weed Management and Robotics (PWMR). Although Herbicides remain a high-priority research area, continuing challenges necessitating integrated, nonchemical tactics (e.g., herbicide resistance) and emerging opportunities (e.g., robotics) are reflected in our survey results. Despite previous calls for greater understanding and application of weed biology and ecology in weed research, as well as recent calls for greater integration of social science perspectives to address weed management challenges, these areas were ranked considerably lower than those focused more directly on weed management. Our survey also identified a potential mismatch between research priorities and expertise in several areas, including CPWM, PWMR, and Weed Genomics, suggesting that these topics should be prime targets for expanded training and collaboration. Finally, our survey suggests an increasing reliance on private sector funding for research, raising concerns about our discipline’s capacity to address important research priority areas that lack clear private sector incentives for investment.

The current assays to confirm herbicide resistance can be time- and labor-intensive (dose–response) or require a skill set/technical equipment (genetic sequencing). Stakeholders could benefit from a rapid assay to confirm herbicide-resistant weeds to ensure sustainable crop production. Because protoporphyrinogen oxidase (PPO)-inhibiting herbicides rapidly interfere with chlorophyll production/integrity; we propose a new, rapid assay utilizing spectral reflectance to confirm resistance. Leaf disks were excised from two PPO-inhibiting herbicide-resistant (target-site [TSR] and non–target site [NTSR]) and herbicide-susceptible redroot pigweed (Amaranthus retroflexus L.) populations and placed into a 24-well plate containing different concentrations (0 to 10 mM) of fomesafen for 48 h. A multispectral sensor captured images from the red (668 nm), green (560 nm), blue (475 nm), and red edge (717 nm) wavebands after a 48-h incubation period. The green leaf index (GLI) was utilized to determine spectral reflectance ratios of the treated leaf disks. Clear differences of spectral reflectance were observed in the red edge waveband for all populations treated with the 10 mM concentration in the dose–response assays. Differences of spectral reflectance were observed for the NTSR population compared with the TSR and susceptible populations treated with the 10 mM concentration in the green waveband and the GLI in the dose–response assay. Leaf disks from the aforementioned A. retroflexus populations and two additional susceptible populations were subjected to a similar assay with the discriminating concentration (10 mM). Spectral reflectance was different between the PPO-inhibiting herbicide-resistant and herbicide-susceptible populations in the red, blue, and green wavebands. Spectral reflectance was not distinctive between the populations in the red edge waveband and the GLI. The results provide a basis for rapidly (∼48 h) detecting PPO-inhibiting herbicide-resistant A. retroflexus via spectral reflectance. Discrimination between TSR and NTSR populations was possible only in the dose–response assay, but the assay still has utility in distinguishing herbicide-resistant plants from herbicide-susceptible plants.

Shade avoidance alters the way plants grow, usually causing them to grow taller at the expense of placing resources into leaves, roots, seeds, and other harvestable materials. Sugar beet (Beta vulgaris L.) is a rosette-forming biennial species that has limited capacity to grow tall in the first year of growth. In the context of crop–weed competition, it is mostly unknown to what extent shade avoidance reduces yield in sugar beet relative to other effects like resource competition. To determine the extent of yield loss due to shade avoidance in a field-relevant situation, sugar beets were grown alongside Kentucky bluegrass (Poa pratensis L.) sod in a field study. Roots were separated with a steel root barrier placed into the ground between the grass and beets. Four treatments included a weed-free control (no root barrier or grass), a root barrier control (with root barrier but no grass), shade avoidance (with root barrier and grass), and full competition (with grass but no root barrier). The presence versus absence of grass was the primary driver of effects on measured sugar beet growth and yield parameters, regardless of whether a root barrier was present. Leaf number and root length were also impacted by the presence of the root barrier. These results suggest that shade avoidance is at least as important as root interactions and resource depletion in the context of early-season sugar beet yield loss due to weeds.

Vinasse, a liquid fermentation residual of bio-ethanol production that also contains solid particles in suspension, is commonly used as a soil amendment. Previous studies reported vinasse reduced seed germination and seedling establishment, suggesting herbicidal activity. Laboratory experiments were conducted to determine whether vinasse herbicidal activity is present in the liquid or solid phase, and whether it affects plants during seed early germination (i.e., imbibition), late germination (i.e., embryo growth and radicle protrusion), or seedling growth. Most of the herbicidal activity was associated with the liquid phase, and for most species, seed viability was predominantly affected after the imbibition phase. Susceptibility to vinasse was species dependent. Lettuce (Lactuca sativa L.) germination was <8% when seeds were imbibed and germinated in vinasse solutions or imbibed in water and germinated in vinasse. Conversely, imbibing lettuce seeds in vinasse solutions and germinating them in water did not change their germination in comparison with seeds imbibed and germinated in water (>80% germination). Wheat (Triticum aestivum L.) and sicklepod [Senna obtusifolia (L.) H. S. Irwin & Barneby] germination decreased 10% and 35% when seeds were imbibed and germinated in vinasse, respectively, while Palmer amaranth (Amaranthus palmeri S. Watson) and southern crabgrass [Digitaria ciliaris (Retz.) Koeler] germination decreased >90%. All evaluated species reduced radicle growth as vinasse concentration increased. Filtered liquid vinasse with reduced concentration of salt and ionic compounds inhibited radicle growth similarly to unfiltered vinasse, indicating that the herbicidal activity was not due to osmotic effects and was likely present in the organic liquid phase. Amaranthus palmeri, S. obtusifolia, and D. ciliaris increased the proportion of dormant seed more than 2-fold when they were imbibed or imbibed and germinated in vinasse solutions. Vinasse might be useful for weed management to reduce germinable weed seedbanks by increasing seedling mortality and seed dormancy either by properly timing of its application as a soil amendment or by purifying herbicidal compounds and using them directly for weed control.

Perfluidone {1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide} controlled wild Allium species when applied in the fall, winter, or early spring after the plants had emerged in bermudagrass [Cynodon dactylon (L.) Pers.] and zoysia (Zoysia spp.) turf. A single 3.4- or 4.5-kg/ha rate generally resulted in good to excellent control, but repeated treatments for 2 consecutive yr were required to obtain consistent control.

Growth and percentage survival was measured for slash pine (Pinus elliottii Engelm.), shortleaf pine (P. echinata Mill.), Virginia pine (P. virginiana Mill.), and loblolly pine (P. taeda L.) seedlings treated with: (a) 0.07 to 4.48 kg/ha 2,6-dichlorobenzonitrile (dichlobenil), (b) 0.28 to 8.96 kg/ha 1,1-dimethyl-3-(a,a,a-trifluoro-m-tolyl)urea (fluometuron), or (c) 1.12 to 8.96 kg/ha S-propyl butylethylthiocarbamate (pebulate). Herbicide toxicity to pine seedlings was in order of dichlobenil > fluometuron > pebulate. Acceptance of mild growth reduction would permit pebulate utilization in seed bed nurseries.

Napropamide [2-(a-naphthoxy) N,N-diethylpropionamide] applied to cranberry (Vaccinium macrocarpon Ait.) as a granular or wettable powder formulation at 20 kg/ha in March 1978 controlled aster (Aster subspicatus Nees) and birdsfoot trefoil (Lotus corniculatus L.) without any phytotoxicity to ‘McFarlin’ cranberry vines. Earlier application in February was ineffective, and late application in April injured the vines. Napropamide 10% granular applied at 14 kg/ha in March 1979 controlled aster 90% and birdsfoot trefoil 70%, and the 50% wettable powder formulation controlled aster 90% and birdsfoot trefoil 80%. Applications of granular napropamide at 12 kg/ha in March of 1979 or 1980 controlled both weeds 70%.

New Line Early Perfection peas (Pisum sativum L.) in the 10th-node stage were treated with a foliar broadcast application of 1 lb/A of the sodium salt of carboxyl carbon-14 labeled 4-(2-methyl-4-chlorophenoxy) butyric acid (MCPB*). Direct counting of C14 indicated that MCPB* equivalent to 8.4 ppm on the fresh weight basis was in or on the pea tissue immediately after treatment. The concentration declined rapidly for 6 days following treatment and then at a reduced rate until shelled pea harvest 5 weeks later. Translocation of C14 was studied by autoradiography. Most of the labeled material was retained at the application site. Very little was translocated to the new growth or into the pea seed. The plants retained C14 equivalent to 0.4 ppm MCPB* at the time of harvest with a concentration in the shelled peas of not more than 0.1 ppm.

Plants of curly dock (Rumex crispus L.) were subjected to soil temperatures of 10, 15, 26, and 35 C in a growth chamber. A soil temperature of 10 C was most favorable for root growth and production of large seeds. The highest yields of seeds and fruit were obtained at 26 C. Significant reductions in seed and fruit production, wt per 100 seeds, plant height, and growth rate occurred at 35 C. The total germination of mature seeds was not affected by soil temperature, but the seeds ripened at 26 and 35 C germinated faster than those from the 10 and 15 C treatments.

Weed control trials were conducted on loblolly pine (Pinus taeda L.) or slash pine (Pinus elliottii Engelm.) seedbeds at 12 locations in the southeastern United States. Good weed control was obtained from 2,4-bis-(isopropylamino)-6-(methylthio)-s-triazine (prometryne) at 2.2 and 4.5 kg/ha; N,N-dimethyl-2,2-diphenylacetamide (diphenamid) at 4.5 and 9 kg/ha; α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) at 1.1 and 2.2 kg/ha; and 2-ethylthio-4,6-bis-isopropylamino-s-triazine (GS-16068) at 2.2 and 4.5 kg/ha as preemergence applications immediately followed by irrigation. Diphenamid and trifluralin treatments were not injurious to either pine species at either rate. GS-16068 was only slightly injurious at the high rate at one location. Prometryne was injurious at two locations at the high rate and at one location at the low rate.

Heights of corn and giant foxtail (Setaria faberii Hermm.) were measured during 1963, 1964, and 1965 in east-central Illinois to establish guidelines for postemergence control of this weed in corn. With an average planting date of May 9, corn grew to a height of 6 in and foxtail 2 in by May 28. With corn growing at a daily rate of 1 in and foxtail ½ in from June 5 to 20, foxtail height was 40 to 45% that of corn.

Dicamba (3,6-dichloro-o-anisic acid) and 2,3,6-trichlorobenzoic acid (2,3,6-TBA) applied in lanolin pastes to leaves or roots of host plants growing in soil were translocated acropetally and affected witchweed (Striga lutea Lour.) plants parasitizing roots of host plants. Emerged witchweed plants exhibited characteristic epinastic responses while emergence of other witchweed plants was delayed. Broadcast foliar treatments of dicamba and 2,3,6-TBA to corn (Zea mays L.) applied before witchweed emergence generally reduced the intensity of the infestation and delayed emergence. However, injury to corn, expressed as failure of kernel development and grain yield decreases, sometimes occurred. Injury was greater when herbicide application was delayed until corn was in the early tassel stage. Dicamba was more effective than 2,3,6-TBA for witchweed control. However, no treatment gave season-long control of witchweed. Yearly variations in corn injury precluded a selection of optimum treatment dates and rates for control of witchweed by this technique.

Field trials were conducted from 1991 to 1993 in the northern cotton-producing area of Alabama to evaluate the interaction of various production inputs for pest management and cotton development, maturity, and yield. Two levels of tillage (conventional and no-till), herbicide (1.12 and 2.24 kg ai ha−1 fluometuron, preemergence, with post-directed herbicides), insecticide (0.5 and 0.85 kg ai ha−1 aldicarb, in-furrow), and fungicide (0.9 kg ai ha−1 quintozene plus ethridazole, in-furrow or 0.14 kg ai ha−1 metalaxyl, hopper-box) programs were evaluated. The inputs investigated did not interact significantly to change the overall production strategy. Prickly sida required a higher level of herbicide input than did the entireleaf/ivyleaf morningglory complex. Both species were sufficiently controlled using reduced levels of fluometuron without sacrificing yield; however, cultivation was necessary in conventional tillage treatments to maintain control. A postemergence-directed herbicide treatment was also necessary for weed control, regardless of tillage. Decreasing the levels of each input simultaneously did not interact to affect cotton stand, height, early-season thrips counts, cotton maturity, or yield. Cotton was shorter in no-till than conventional plots.

The control of roadside weeds and brush has always been a major problem of roadside construction and maintenance engineers. People charged with the responsibility of keeping our highways, county, trunk and local roads free of weeds and brush have heretofore found the control of unsightly weeds and brush a major and laborious problem and expense. For the control of many annuals such as hemp, giant ragweed, small ragweed, daisy fleabane, etc., a very thorough, systematic mowing program, coupled with the establishment of a heavy grass cover has in many instances sufficed to keep weed growth down to a minimum. However, for the control of such roadside weeds as Canada thistle, perennial sow thistle, poison ivy, etc., as well as for the control of all types of brushy growth, the mere mowing and laborious cutting of such plants has not resulted in eradication. The mowing of perennial weeds and brush is like “picking apples off a tree” — such picking does not kill the tree. Furthermore, programs of control involving brush have had to be repeated every two or three years at terrific expense to the tax payer. Laborious mowing and hand cutting is followed quickly by regrowth, which in a year or so is as bad or worse as the original stand which was removed.

Field trials conducted in the three major peppermint-producing regions of Oregon showed that repeated applications of bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] at 2.2 kg/ha controlled Canada thistle [Cirsium arvense (L.) Scop.] in peppermint (Mentha piperita L.) selectively. Repeat applications of 2.2 kg/ha controlled Canada thistle better than single applications of 3.4, 4.5, or 6.7 kg/ha. Late May or June applications were more effective than early May applications. The number of Canada thistle shoots was reduced 82% 10 months after repeat applications but had almost returned to the original number 22 months after application. Basipetal translocation of bentazon was demonstrated by observing bentazon injury symptoms on untreated Canada thistle shoots which were attached by a root to bentazon-treated shoots.

The major reserve lipid of yellow foxtail [Setaria lutescens (Weigel) Hubb.] caryopses is triacylglyceride stored in lipid bodies. Lipid bodies are heavily concentrated in the cells of the embryo axis, scutellum, and aleurone layer and are roughly spherical (average diam 0.5 μm). Percentage lipid (hot isopropanol extract) on a fresh-weight basis of mature, unimbibed seed and caryopses collected locally was about 6.4 and 11%, respectively. About 95% of the total (0.23 mg/caryopsis) was saponifiable and distributed among fatty acid classes as follows: 16:0, 5.8%; 18:0, 1.5%; 18:1, 16.2%; 18:2, 73.7%; and 18:3, 2.8%. In nondormant caryopses, saponifiable lipid content declined (18:1 and 18:2 only) about 23% during the first 6 days after imbibition in the dark at 25 C. This modest decline was preceded by the appearance of an alkaline lipase at about 24 h after the onset of imbibition. Free fatty acids accumulated during these early stages of germination and accounted for about 22% of the total saponifiable lipid remaining (0.17 mg/caryopsis) 6 days after the onset of imbibition. Lipid content and lipase activity did not change in dormant caryopses treated similarly. The delayed initiation of lipid mobilization in germinating caryopses suggests that triacylglyceride degradation is not a pivotal metabolic pathway controlling dormancy.

Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} at 2 or 4 ppmw placed 0 to 3, 8 to 11, or 15 to 18 cm deep in soil columns reduced root and shoot weights of buffelgrass [Pennisetum ciliare (L.) Link # PESCI] 30 days after emergence. Plains bristlegrass (Setaria macrostachya H.B.K.) seedling shoot weights were not reduced when 2 ppmw tebuthiuron was placed 8 to 11 cm deep or deeper. Effects of tebuthiuron at 0.13 to 0.50 ppmw on buffelgrass shoot and net tiller production were not moderated by the presence of honey mesquite (Prosopis glandulosa # PRCJG) in the pots. However, regardless of tebuthiuron dosage, average height and shoot weight of buffelgrass seedlings were greater when seedlings were grown in soil collected from beneath honey mesquite canopies compared to growth in soil from interspaces. Therefore, spatial variations in buffelgrass response to applications of tebuthiuron for control of invading shrubs may largely be attributed to soil changes induced by woody plants rather than to presence of shrubs.

Five preplant, soil-incorporated herbicides were evaluated over a 2-year period for their effect upon the growth of representative varieties of 15 common species of spring-planted annual flowers. Of these, α,α,α,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) was effective in combining freedom from plant injury with control of weeds. Only in phlox (Phlox nana compacta Nutt., var. Fireball) was growth reduced significantly over the 2-year period by this herbicide at 2 lb/A while petunia (Petunia hybrida, var. Snow Lady) was reduced in 1 of 2 years. N,N-dimethyl-2,2-diphenylacetamide (diphenamid) at 4 and 8 lb/A was effective and ethyl N,N-dipropylthiocarbamate (EPTC) at 4 lb/A was fairly effective, but both were tolerated by fewer flower species. N-(2-mercaptoethyl) benzenesulfonamide S-(O,O-diisopropyl phosphorodithioate) (bensulide) at 10 lb/A and methyl 3,4-dichlorocarbanilate (swep) at 5 lb/A were not phytotoxic to any species but were relatively ineffective in controlling the weeds present.