Southern threecornerjack (Emex australis Steinh.) produces both aerial seeds on the branches and subterranean seeds at the base of the plant crown approximately 1 to 2 cm underground. Prior research indicated that seeds buried at a depth of 1 cm have a much higher probability of germinating in the following season compared with seeds on the soil surface. The current research investigated the number of subterranean seeds produced per plant, timing of subterranean seed production, and germination requirements of subterranean seeds compared with aerial seeds. This research demonstrated that E. australis plants from multiple populations produced subterranean seeds beginning at the 4-leaf development stage, before the production of aerial seeds. Individual plants produced a maximum of 30 subterranean seeds. Germination of subterranean and aerial seeds following afterripening over the summer to autumn (December to May) fallow was similar, demonstrating that the different seed types had no differences in dormancy. Further, the subterranean seeds did not have the light requirement for germination observed in aerial seeds. Subterranean seeds had 22.2% and 24.3% germination in light and dark conditions, respectively, compared with aerial seeds, which had 26.9% germination in light conditions and 12.3% germination in the dark. Production of subterranean seeds was low, given that a mature E. australis plant may produce more than 1,100 aerial seeds, but the subterranean seeds formed earlier in plant development. Recommendations for postemergence herbicides are to spray E. australis at the 2- to 4-leaf stage of growth, yet some plants may have already produced mature subterranean seeds by this stage. Further research is required to determine the impact of subterranean seeds on population ecology.

Replacement series are used by researchers to understand how competition-related variables influence dynamics from the individual to the population and community levels, but this approach has been criticized because of inherent biases associated with plant size differences and density-dependent responses. The use of functional densities instead of demographic densities was proposed to minimize those biases. This work explored three models to determine reference densities for replacement series experiments based on (1) maximum biomass, (2) biomass at onset of diminishing returns (i.e., inflection point), and (3) nitrogen (N)-uptake equivalency. Replacement series experiments were conducted using redroot pigweed (Amaranthus hybridus L.):maize (Zea mays L.) and giant foxtail (Setaria faberi Herrm.):maize proportions of 1:0, 0.75:0.25, 0.5:0.5, 0.25:0.75, and 0:1. The monoculture density for each species was established according to the three models. Density selection criteria resulted in major differences in competitive interactions between species. The use of functional densities at which the biomass accumulation inflection point for the smaller species allowed both species to exhibit either increases or decreases in biomass production depending on competitive interactions for all interspecific mixtures. Conversely, the maximum biomass model favored the larger species, almost completely inhibiting the growth of the smaller species, which resulted in a poor characterization of competitive responses of the smaller species. The N uptake equivalency model resulted in interactions closer to the predicted neutral competition. The model based on the biomass accumulation inflection point was the most sensitive and informative across all interspecific mixtures for both species. We propose that to reduce bias associated with species size differences when determining reference densities for replacement series experiments, at least two criteria must be met: (1) the experiment sensitivity allows measuring and quantifying the competitive responses for both species in all mixtures, and (2) the balance between density and carrying capacity of the system minimizes intraspecific competition.

No-till planting organic soybean [Glycine max (L.) Merr.] into roller-crimped cereal rye (Secale cereale L.) can have several advantages over traditional tillage-based organic production. However, suboptimal cereal rye growth in fields with large populations of weeds may result in reduced weed suppression, weed–crop competition, and soybean yield loss. Ecological weed management theory suggests that integrating multiple management practices that may be weakly effective on their own can collectively provide high levels of weed suppression. In 2021 and 2022, a field experiment was conducted in central New York to evaluate the performance of three weed management tactics implemented alone and in combination in organic no-till soybean planted into both cereal rye mulch and no mulch: (1) increasing crop seeding rate, (2) interrow mowing, and (3) weed electrocution. A nontreated control treatment that did not receive any weed management and a weed-free control treatment were also included. Cereal rye was absent from two of the five fields where the experiment was repeated; however, the presence of cereal rye did not differentially affect results, and thus data were pooled across fields. All treatments that included interrow mowing reduced weed biomass by at least 60% and increased soybean yield by 14% compared with the nontreated control. The use of a high seeding rate or weed electrocution, alone or in combination, did not improve weed suppression or soybean yield relative to the nontreated control. Soybean yield across all treatments was at least 22% lower than in the weed-free control plot. Future research should explore the effects of the tactics tested on weed population and community dynamics over an extended period. Indirect effects from interrow mowing and weed electrocution should also be studied, such as the potential for improved harvestability, decreased weed seed production and viability, and the impacts on soil organisms and agroecosystem biodiversity.

Herbicides are the primary tool for controlling weeds in peanut (Arachis hypogaea L.) and are crucial to sustainable peanut production in the United States. The literature on chemical weed management in peanut in the past 53 yr (1970 to 2022) in the United States was systematically reviewed to highlight the strengths and weaknesses of different herbicides and identify current research gaps in chemical weed management. Residual weed control in peanut is achieved mainly with dimethenamid-P, ethalfluralin, pendimethalin, and S-metolachlor. More recently, the use of the protoporphyrinogen oxidase inhibitor flumioxazin and acetolactate synthase inhibitors, such as diclosulam, for residual weed control in peanut has increased considerably. Postemergence broadleaf weed control in peanut is achieved mainly with acifluorfen, bentazon, diclosulam, imazapic, lactofen, paraquat, and 2,4-DB, while the graminicides clethodim and sethoxydim are the major postemergence grass weed control herbicides in peanut. Although several herbicides are available for weed control in peanut, no single herbicide can provide season-long weed control due to limited application timing, lack of extended residual activity, variability in weed control spectrum, and rotational restrictions. Therefore, effective weed management in peanut often requires herbicide mixtures and/or sequential application of preplant-incorporated, preemergence, and/or postemergence herbicides. However, the available literature showed a substantive range in herbicide efficacy due to variations in environmental conditions and flushes of weed germination across years and locations. Despite the relatively high efficacy of herbicides, the selection of herbicide-resistant weeds is another area of increasing concern. Future research should focus on developing new strategies for preventing or delaying the development of resistance and improving herbicide efficacy within the context of climate change and emerging constraints such as water shortages, rising temperatures, and increasing CO2 concentration.

Harvest weed seed control (HWSC) is an effective technique for managing wild radish (Raphanus raphanistrum L.), a weed that retains its seed until harvest. However, earlier flowering time (leading to increased seed shedding before harvest) is a risk to HWSC effectiveness. This study investigated the effects of repeated HWSC on the evolution of R. raphanistrum flowering dates, using two methods: an adaptation of the SOMER model that included flowering genes (called SOMEF); and a mathematical calculation of the endpoints of flowering date evolution utilizing the relevant life-history equations. In weed management systems with highly effective herbicides, the additional use of HWSC predicted R. raphanistrum population extinction. Low weed numbers and rapid extinction meant that any gradual evolution in days to first flower (DFF) was insufficient to lead to HWSC evasion. In alternative management systems with less vigorous herbicide control and using HWSC, modeling predicted a maximum 2- to 3-d reduction in DFF. In contrast, mathematical calculations of the phenotypes maximizing seeds returned to the seedbank predicted an endpoint to evolution of 12-d earlier flowering, which matched field observations. However, genetic change postulated by the mathematical calculations was not hampered by a restriction to changing DFF allele frequencies. Unknown accompanying genetic changes could affect germination dates or flowering triggers.

Simulation modeling that included only flowering genes failed to predict the magnitude of an observed 12-d reduction in DFF. Differences between the 12 d observed in the field (and predicted using mathematical calculations) and the modest changes demonstrated in this field-based modeling study are postulated to be due to unaccounted evolutionary changes in R. raphanistrum.

Velvetleaf (Abutilon theophrasti Medik.) is a troublesome broadleaf weed that competes with crops for resources such as soil moisture. Water stress can affect the ability of weed species to grow and produce seeds. The objective of this study was to determine the effect of degree of water stress on the growth and fecundity of A. threophrasti using soil moisture sensors under greenhouse conditions. Abutilon threophrasti seeds collected from a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] field were grown in silty clay loam soil, and plants were maintained at 100%, 75%, 50%, and 25% soil field capacity (FC) corresponding to no, light, moderate, and high water-stress conditions, respectively. Water was added daily to pots based on soil moisture levels detected by a Meter Group 5TM sensor to maintain the desired water-stress level required by treatment. Plants maintained at 100% FC had the maximum number of leaves (28 leaves plant−1), followed by 21 and 15 leaves plant−1 at 75% and 50% FC, respectively. Abutilon threophrasti at 100% and 75% FC achieved maximum plant height (108 to 123 cm) compared with 83 cm at 50% FC. Abutilon threophrasti maintained at 75% FC had the greatest growth index (79,907 cm3) followed by 72,197 cm3 at 100% FC and 64,256 cm3 at 50% FC. Seed production was similar at 100%, 75%, and 50% FC (288 to 453 seeds plant−1) compared with 2 seeds plant−1 at 25% FC. This is because the majority of plants maintained at 25% FC did not survive more than 77 d after transplanting. Seed germination was 96% to 100% at 100%, 75%, and 50% FC compared with 20% germination at 25% FC. Abutilon threophrasti can survive ≥50% FC continuous water-stress conditions, although with reduced leaf number, plant height, and growth index compared with 75% and 100% FC.

An in-depth understanding of the germination response of troublesome weed species, such as feather fingergrass (Chloris virgata Sw.), to environmental factors (temperature, soil moisture, etc.) could play an essential role in the development of sustainable site-specific weed control programs. A laboratory experiment was conducted to understand the germination response of 10 different biotypes of C. virgata to five temperature regimes (ranging from 15/5 to 35/25 C) under a 12/12-h (light/dark) photoperiod. No consistent germination behavior was observed between biotypes, as some biotypes demonstrated high final cumulative germination (FCG) at low alternating temperature regimes (15/5 and 20/10 C) and some biotypes exhibited high FCG at a high alternating temperature regime (30/20 C). All biotypes revealed late germination initiation (T10, time taken to reach 10% germination) at the lowest temperature range (15/5 C), ranging from 171 to 173 h. However, less time was required to reach 90% germination (T90), ranging from 202 to 756 h. At higher alternating temperature regimes (30/20 and 35/25 C), all biotypes initiated germination (T10) within 40 h, and a wide range of hours was required to reach 90% germination (T90), ranging from 284 to 1,445 h. Differences in FCG of all the biotypes at all the temperature ranges showcased the differential germination nature among biotypes of C. virgata. The cool temperatures delayed germination initiation compared with warmer temperatures, even though FCGs were similar across a wide range of thermal conditions, indicating that this species will be problematic throughout the calendar year in different agronomic environments. The data from this study have direct implications on scheduling herbicide protocols, tillage timing, and planting time. Therefore, data generated from this study can aid in the development of area- and species-specific weed control protocols to achieve satisfactory control of this weed species.

Sweetpotato [Ipomoea batatas (L.) Lam.] is a staple crop that provides nutritional benefits to humans globally, but it is subject to yield loss when competing with weeds, especially during the early stage of establishment. Yield loss can vary widely based on the cultivar, production environment, weed species, and management techniques. To address this challenge, we conducted field research at the Samuel G. Meigs Horticulture Research Farm, Lafayette, IN, and at the Southwest Purdue Agricultural Center, Vincennes, IN, in 2022 to determine the effect of sweetpotato cultivar on the critical weed-free period. The experiment was a split-plot design, with weed-free interval treatments as the main plot factor and cultivar as the subplot factor. The three cultivars used were ‘Covington’, ‘Monaco’, and ‘Murasaki’. Weeds were removed by hand and allowed to establish and compete with the crop beginning at 0, 14, 21, 28, 35, or 42 d after transplanting (DAP). As the weed-free interval increased from 0 to 42 DAP, predicted total yield increased from 19 kg ha−1 to 20,540 kg ha−1 for Covington, 3 kg ha−1 to 11,407 kg ha−1 for Monaco, and 125 kg ha−1 to 13,460 kg ha−1 for Murasaki at the Lafayette location. At Vincennes, as the weed-free interval increased from 0 to 42 DAP, predicted total yield increased from 14,664 kg ha−1 to 33,905 kg ha−1 for Covington, 4,817 kg ha−1 to 18,059 kg ha−1 for Monaco, and 12,735 kg ha−1 to 21,105 kg ha−1 for Murasaki. A threshold of ≤10% total yield reduction was achieved by maintaining sweetpotatoes weed-free 24 DAP for Covington, 20 DAP for Murasaki, and 33 DAP for Monaco.

No differences in the anatomy or bud pattern development were observed between young tap and lateral roots of rush skeletonweed (Chondrilla juncea L.). Shoots and lateral roots arise from meristemic zones that originate from a continuous pericyclic ring. Incubation of excised root segments resulted in rapid development of stem buds which showed geotropic response in 24 h. The development of identifiable leaf initials occurred prior to emergence through the epidermis in 8 days.

Treatment of soil with fumigants to kill dormant weed seeds is a valuable practice but control in the surface one or two inches is often poor. This is because the fumigant vapors diffuse rapidly out of the soil into the atmosphere before building up a lethal concentration near the surface. Improved weed control has been reported by proper confinement of fumigant vapors in the soil with impervious seals. Water seals have been advocated by some workers as a satisfactory substitute for impervious covers. However, only limited experimental data are available comparing soil fumigation results with different methods of sealing the soil surface.

In a previous study Stadtherr and Widmer reported that several herbicides provided excellent weed control in field plantings of garden chrysanthemums (Chrysanthemum morifolium) The present study was undertaken (a) to compare the best herbicides of the previous study with newer materials, (b) to obtain additional data on herbicides which had been tested for one year only, and (c) to determine the effectiveness of herbicides applied in granular form.

A successful weed control program, whether it be Federal, State or County is involved with research, education and regulation.

Had laws been enacted and properly enforced in all states thirty or forty years ago to prohibit the introduction of noxious weeds the weed problems of today would not be so serious.

Spot-treatments of young cotton with 2,2–dichloropropionic acid, simulating control of clumps of perennial grass, resulting in 10 to 25% reductions in cotton stands, did not cause proportional reductions in yields of seed cotton. Increased growth of cotton plants adjacent to skips compensated for reduced stands. The treatments did not affect boll components or fiber properties of cotton.

Dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) applied at 0.37 kg/ha controlled black nightshade (Solanum nigrum L.) better than did trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 0.56 kg/ha. Dinitramine applied at 0.37 kg/ha was equal to 0.56 kg/ha of trifluralin for control of green foxtail [Setaria viridis (L.) Beauv.], yellow foxtail [Setaria glauca (L.) Beauv.], and redroot pigweed (Amaranthus retroflexus L.). Dinitramine produced more root aberrations in sugarbeets (Beta vulgaris L. ‘Mono Hy D2′) than did trifluralin when sprayed on nonexposed or exposed hypotcotyledonary tissues of seedlings. When soil surrounded most of the hypocotyls at the time of application, 0.56 kg/ha of dinitramine affected 57 to 87% of the roots, whereas the same rate of trifluralin affected 1 to 8% of the roots. When the hypocotyls were exposed at the time of application, 100% of the roots were affected by dinitramine compared to 25% of all roots treated with trifluralin. Dinitramine applied at 0.37, 0.42, and 0.56 kg/ha lowered the quality and yield of sugarbeet roots, with the highest rate significantly reducing percentage purity, percentage sucrose, and recoverable sucrose. Trifluralin did not affect these parameters.

The injurious effects of different rates of fenuron (3-peynyl-1,1-dimethylurea) on four species of brush were recorded for two years in two different types of southwestern brushlands, the Oak-chaparral and the Chihuahuan Desert Shrub. Fenuron was more injurious to fire sprouts than to mature plants of turbinella oak (Quercus turbinella Greene) in the Oak- chaparral type especially at 2 to 8 lb/A ai. The effects of fenuron on mature plants were reduced by burning, suggesting that much of the fenuron absorbed was residual in the stems, twigs, and leaves where it was destroyed by the fire. The effect of fenuron on the fire sprouts changed only slightly between six months and two years. Gibberellic acid was applied to sprouts and mature oak plants appeared to slightly reduce the injurious effects of some rates of fenuron during the first six months but no gibberellin induced differences were observed after two years. In the Chihuahuan Desert shrub type, tarbush (Flourencia cernua DC.) and whitethorn (Acacia constricta Benth.) were about equally susceptible to injury by fenuron with creosotebush (Larrea tridentata (DC.) Cov.) slightly more resistant. Summer applications just before the rainy season were most effective and 4 lb/A combined high shrub kill with greatest grass growth.

Although 8 and 16 lb/A ai killed and injured both grasses and shrubs on the oak plots, grass naturally reseeded into these plots within six months after treatment, but on the Chihuahuan Desert area grass had not recovered on the plots treated at 8 lb/A after two years. This difference in grass re-establishment was probably due to rainfall differences which would give differences in leaching of fenuron. Palatability of the grasses in the oak plots increased due to fenuron treatments, particularly on the heavily treated plots. These studies indicate that moderate rates of fenuron, applied just prior to favorable seasonal rains and repeated at several-year intervals, may be used to control turbinella oak sprouts and mature Chihuahuan Desert shrubs. However, treatments would only be economical where high forage and watershed values would result.

A number of investigators have tested 2,4–D (2,4–dichlorophenoxyacetic acid) for the control of weeds in asparagus. Several workers (1, 3, 4, 6) have suggested the use of 2,4–D at rates varying from one to three pounds acid equivalent per acre as a pre-emergence treatment after disking in the spring and again after disking at the end of the cutting season. Warren and Hernandez (5) applied 2,4–D at the rate of four pounds per acre on April 28 just after the asparagus bed was disked. The yield and appearance of the asparagus spears was not affected by the treatment. According to Ahlgren et al. (1), pre-emergence application of 2,4–D caused injury to the first emerging spears in some cases, but caused little permanent damage. These and other investigators found asparagus plants susceptible to foliage applications of 2,4–D and warned against spraying the fern.

During a 2-year study corn exhibited relatively good tolerance to flaming at a speed of 4 mph. Soybeans were more susceptible to injury by flaming at early growth stages than was corn. For weed control conventional cultivation and preemergence herbicides were superior to flaming. Damage to crop or weeds was influenced by morphology of the plant, size of plant, adjustment of equipment, number of flamings, and speed or length of exposure.

This study suggests that flame cultivation would not be very competitive in areas where preemergence herbicides and conventional cultivation give satisfactory control of weeds. Although cost of gas would be about equal to cost of herbicide, cost of flame cultivation equipment is about five times greater, and flame cultivation would require 2 to 4 more trips over the field. Flame cultivation may have more potential in the drier areas where preemergence herbicides have been less effective.