Wild garlic (Allium vineale L.) continues to be an important problem weed of Eastern and Southeastern United States. It is spread principally by aerial bulblets mixed with seed. The present rules and regulations used by seed laboratories to determine bulblet viability seem inadequate. This paper will discuss the use of 2,3,5–triphenyltetrazolium chloride, referred to as TZ, as an indicator of bulblet viability.

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.

Annual bluegrass (Poa annua L.) populations in turfgrass have evolved resistance to several herbicides in the United States, but there has been no confirmed resistance from an agricultural field. Recently, glyphosate failed to control a P. annua population found in a field in a soybean [Glycine max (L.) Merr.] and rice (Oryza sativa L.) rotation in Poinsett County, AR. The present study focused on determining the sensitivity of a putatively resistant accession (R1) to glyphosate compared with two susceptible accessions (S1 and S2). The experiments included a dose–response study, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene copy number and expression analysis, and assessment of mutations in EPSPS. Based on the dose–response analysis, R1 required 1,038 g ae ha−1 of glyphosate to cause 50% biomass reduction, whereas S1 and S2 only required 148.2 and 145.5 g ae ha−1, respectively. The resistance index (RI) was approximately 7-fold relative to the susceptible accessions. Real-time polymerase chain reaction data revealed at least a 15-fold increase in the EPSPS copy number in R1, along with a higher gene expression. No mutations in EPSPS were found. Gene duplication was identified as the main mechanism conferring resistance in R1. The research presented here reports the first incidence of glyphosate resistance in P. annua from an agronomic field crop situation in the United States.

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.

Dimethylarsenic acid (cacodylic acid), 2-methoxy-3,6-dichlorobenzoic acid (dicamba), 2,6-dinitro-N,N-di-n-propyl-alpha-alpha-alpha-trifluoro-p-toluidine (trifluralin), and O-(2-4-dichlorophenyl) O-methyl isopropyl-phosphoramidothioate (DMPA) were tested to determine if they could selectively control nimblewill (Muhlenbergia schreberi J. F. Gmel.) in Kentucky bluegrass (Poa pratensis L.) pasture. DMPA reduced the nimblewill population 95% during the initial year of treament, while other herbicides gave only 61 to 72% reduction. No effect on nimblewill was evident the second year after application. None of the herbicides caused severe or permanent injury to the bluegrass.

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.

I feel greatly honoured to have been invited to cross the Atlantic to address so distinguished a gathering in the weed research and control fields.

Red alder (Alnus rubra Bong.) was readily killed by growing season treatments with a 1 to 1 mixture of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in diesel oil. Except for 1-inch-diameter trees, it was resistant to dormant season treatments. Treatments applied during moderate rain were less effective than during rain-free periods.

The fast growing woody plant known as marabú, (Dichrostachys nutans), is native to Africa but it has found a favorable environment in Cuba. At present, dense stands of it, 20 feet and more in height, cover vast areas of the island, and a great deal of land has had to be abandoned on account of it. The ease with which it becomes established in turf or in neglected sugar cane lends exceptional interest to the development of methods of controlling, or, if possible of eradicating the plant.

Cover cropping is a suggested soil conservation practice widely investigated in cropping systems. Cover crops suppress weeds and often are part of an integrated weed management plan that could lead to reduced herbicide use and possibly reduce the weed seedbank. Winter brassica cover crops are popular in the eastern Washington potato (Solanum tuberosum L.) production region, but in western Washington, the production of brassica seed crops presents disease issues along with the risk of cross-pollination, which limits the use of brassica cover crops. Research for this article was conducted in two trials from 2018 to 2020 and 2019 to 2021in Mount Vernon, Washington, to identify winter cover crops compatible with regional restrictions and climatic challenges in western Washington cropping systems. Treatments including a no-cover control, eight single species (including brassicas, grasses, and legumes), and a grass–legume mixture were investigated. Cover crop and weed biomass production were measured, and percent ground cover for cover crops and weeds by species was estimated. Cover crop biomass and weed suppression varied by year due to variable environments, but annual ryegrass (Lolium multiflorum Lam.) and the mixture were most consistent in producing large amounts of biomass and reducing weed biomass and cover in all years. The variability of percent weed cover response to environment was ameliorated when weed cover was normalized within each year’s control.

Morningglories (Ipomoea spp.) are among the most troublesome weeds in cucurbits in the United States; however, little is known about Ipomoea spp. interference with horticultural crops. Two additive design field studies were conducted in 2020 at two locations in Indiana to investigate the interference of ivyleaf morningglory (Ipomoea hederacea Jacq.), entireleaf morningglory (Ipomoea hederacea Jacq. var. integriuscula A. Gray.), and pitted morningglory (Ipomoea lacunosa L.) with triploid watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai]. Immediately after watermelon was transplanted, Ipomoea spp. seedlings were transplanted into the watermelon planting holes at densities of 0 (weed-free control), 3, 6, 12, 18, and 24 plants 27 m−2. Fruit was harvested once a week for 4 wk, and each fruit was classified as marketable (≥4 kg) or non-marketable (<4 kg). At 1 wk after the final harvest, aboveground biomass samples were collected from 1 m2 per plot and oven-dried to obtain watermelon and Ipomoea spp. dry weight. Seed capsules and the number of seeds in 15 capsules were counted from the biomass sample to estimate seed production. Ipomoea spp. densities increasing from 3 to 24 plants 27 m−2 increased marketable watermelon yield loss from 58% to 99%, reduced marketable watermelon fruit number 49% to 98%, reduced individual watermelon fruit weight 17% to 45%, and reduced watermelon aboveground biomass 83% to 94%. Ipomoea spp. seed production ranged from 549 to 7,746 seeds m−2, greatly increasing the weed seedbank. Ipomoea spp. hindered harvest due to their vines wrapping around watermelon fruits. The most likely reason for watermelon yield loss was interference with light and consequently less dry matter being partitioned into fruit development due to less photosynthesis. Yield loss was attributed to fewer fruits and the weight of each fruit.

Junglerice [Echinochloa colona (L.) Link.] is the most important grass weed species in Australian summer cropping systems. Although it is mainly a spring- and summer-emerging weed species, field observations suggest that E. colona is expanding its seasonality. A common garden experiment was conducted at the University of Queensland farm to examine the effect of planting dates on phenology, growth, and fecundity of eight populations of E. colona. All populations were planted every second month from September to July in 2019 to 2020 and 2020 to 2021. Echinochloa colona took the shortest time (4 to 6 d) to emerge when planted in November or January. However, the November population took the longest number of growing degree days to exhibit panicle emergence. In both years, populations differed in height and leaf, tiller, panicle, and seed production in response to planting times. Plants produced significantly greater biomass for the November planting (123 to 147 g plant−1) followed by the January planting and then the September planting. The March planting produced the lowest biomass. In the first year, the lowest number of seeds (3,500 seeds plant−1) was produced by the March planting; however, in the second year, similar numbers of seeds were produced by the March and July plantings. In the first year, seed production (51,000 seeds plant−1) was greatest for the November planting; however, some populations also produced a similar number of seeds for the January planting. In the second year, significantly greater seed production (111,000 seeds plant−1) was observed for the January planting compared with other planting dates. The aboveground biomass and seed production of E. colona were positively correlated. This study reveals variations among E. colona populations and suggests that although greater emphasis must be placed on controlling spring- and summer-emerging plants, management practices need to be extended throughout the year to control E. colona in southeastern Australia.

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.

Basal bark treatment with triclopyr butoxyethyl ester is used to control woody invasive plants, including Brazilian peppertree (Schinus terebinthifolia Raddi). However, the ester formulation cannot be applied where standing water is present, which includes wetlands where S. terebinthifolia is found. In 2009, a low-volatile acid formulation of triclopyr was labeled for use in aquatic sites, which allows for basal bark applications when standing water is present. This formulation may have utility for controlling woody plants in standing water. However, anecdotal observations of injury to non-target plants following applications during periods of inundation have been reported. To address this, mesocosm studies were conducted to assess non-target injury through triclopyr root exudation or release from the surface of treated stems via flooding. Mesocosms contained S. terebinthifolia as the treated target, while sugarberry (Celtis laevigata Willd.), buttonbush (Cephalanthus occidentalis L.), and red maple (Acer rubrum L.) were included as non-targets. In the first study, the pathway of root exudation for non-target injury following triclopyr (34 g L−1) basal bark application was isolated with activated charcoal placed at the soil surface. In the second study, mesocosms were flooded to assess triclopyr release from the surface of treated stems and subsequent non-target injury. Defoliation of non-target species posttreatment was ≤8%, and triclopyr was detected at ≤5 µg L−1 in mesocosm wells when activated charcoal was present. Posttreatment non-target defoliation up to 92%, coupled with triclopyr concentrations in surface waters and wells as high as 4,637 µg L−1, indicated triclopyr movement as a result of flooding. Additionally, triclopyr non-target injury from soil activity independent of flooding was observed. These findings provide limited evidence of triclopyr root exudation but considerable evidence of triclopyr release during flooding following basal bark treatment and support a cautionary approach to basal bark application when standing water is present.

Castorbeans (Ricinus communis L.) are extremely tolerant of the rotary hoe. Its timely use plus cultivation gave effective weed control in castorbeans. The preemergence herbicides, used either alone or in combination, that appeared most promising for selective control of weeds in castorbeans were: 2-chloro-N,N-diallylacetamide (CDAA), dimethyl-2,3,5,6-tetrachloroterephthalic acid (DCPA), ethyl N,N-dipropylthiolcarbamate (EPTC), N-1-naphthylphthalamic acid (NPA), 2,6-dinitro-N,N-dipropyl-alpha, alpha, alpha-trifluoro-p-toluidine (trifluralin), and propyl dipropylthiolcarbamate (R-1607). The most dependable weed control practice in castorbeans was the use of preemergence herbicides in combination with rotary hoeings plus cultivation.