London rocket is hypothesized to be the most important overwintering host of the beet leafhopper in southern New Mexico. Knowledge of the environmental factors affecting the emergence of this plant is essential to developing a predictive model for London rocket and leafhopper populations. The temperature and moisture optima for London rocket germination and emergence were assessed using growth chamber studies. Temperatures of 5 to 35 C and soil water tension treatments of − 0.01 to − 1.5 MPa were tested. Optimal seed burial depth also was assessed. Optimal London rocket germination occurred at approximately 15 C and maximum emergence was achieved at 15 to 20 C with soil moisture tensions of − 0.01 to − 1.2 MPa. London rocket emergence occurred best at a seed burial depth of 2 mm.

Studies conducted from 1964 to 1967 on three soil types indicated that α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), dimethyl tetrachloroterephthalate (DCPA), and 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) applied preplant and incorporated with two tandem diskings in March or April prior to bedding, gave excellent control of a mixture of Amaranthus sp. and volunteer sorghum (Sorghum bicolor (L.) Moench) in cotton (Gossypium hirsutum L.) planted in early May. Cotton was not stunted and yields were not appreciably reduced. When trifluralin was applied, soil residues the next year dictated that sorghum planting be delayed until May.

We evaluated nine systems of weed control over a 3-year period for cotton (Gossypium hirsutum L.) tolerance and control of weeds on Tifton loamy sand soil. Cultivation with sweeps did not control weeds effectively, which allowed weed competition to reduce cotton yields. Five cultivations plus an annual average of 185 hr/ha hand-hoeing was required to keep cotton relatively free of weeds for 7 to 8 weeks after planting. The use of herbicides offered certain economic advantages over systems using only cultural practices in controlling weeds. A preplant application of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) reduced annual hand-hoeing requirements by 66 hr/ha. The level of weed control at harvest time increased each year in all systems that used a herbicide program, but not where only cultivation or hand-hoeing was used. The continuous use of specific weed-control systems shifted weed populations. Systems that achieved 100% control by the end of the third year included all of the following: (a) a preplanting or at planting treatment of trifluralin or EPTC (S-ethyl dipropylthiocarbamate) plus (b) a preemergence application of fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea], (c) two directed postemergence sprays with MSMA (monosodium methanearsonate), and (d) diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. Large crabgrass [Digitaria sanguinalis (L.) Scop.] and Florida pusley (Richardia scabra L.) were nearly eliminated where we used trifluralin. Systems that did not include a postemergence application of MSMA allowed common cocklebur (Xanthium pennsylvanicum Wallr.), Florida beggarweed [Desmodium tortuosum (Sw.) DC], and other weeds to emerge and remain in the crop row, reducing yield of lint cotton. Cotton yield appeared to be directly related to the level of early-season weed control. We did not detect biologically active soil residues at harvest time each year. Our weed-control systems did not affect cotton fiber length, strength, or color.

Studies were conducted to determine the relative competitive ability and productivity of an atrazine-resistant biotype (WRB1) and an atrazine-susceptible accession (WSA1) of velvetleaf from Wisconsin. Noncompetitive productivity studies conducted in the field and greenhouse during 1992 and 1993 showed that instantaneous relative growth rate, net assimilation rate, and leaf area ratio of the WRB1 biotype and WSA1 accession were similar. There were no consistent differences between the WRB1 biotype and WSA1 accession in plant height, shoot dry biomass, and leaf area over time. The WRB1 biotype and WSA1 accession did not differ in noncompetitive seed yield. A replacement series experiment conducted in the field in 1992 and 1993 showed that the WRB1 biotype and WSA1 accession did not differ in shoot dry biomass or seed yield at densities of 36, 64, and 100 plants m−2. Results suggest that resistance to atrazine has not reduced the noncompetitive productivity or the intraspecific competitive ability of the WRB1 biotype relative to the WSA1 accession. Thus, even in the absence of atrazine selection intensity, the frequency of atrazine resistance gene(s) is unlikely to decrease in the velvetleaf population from which the WRB1 biotype was selected.

A 3-yr (1982, 1983, and 1984) study was conducted to determine the relationship between tillage and six weed control treatments for soybean [Glycine max (L.) Merr. ‘Williams 79′] production on silt loam (Udollic and Mollic Ochraqualfs). Conventional tillage consisted of spring moldboard plowing and secondary tillage with a combination tool just before planting. No-tillage consisted of a foliar application of glyphosate [N-(phosphonomethyl)glycine] at the time of planting. Weed control treatments included combinations of no weed control with and without soybean plants, preemergence herbicide application only, postemergence herbicide application only, and combined preemergence and postemergence applications with and without additional handweeding. In 1982, a year of above-normal seasonal rainfall, conventional tillage had significantly greater soybean grain yields than no-tillage for all weed control treatments except the preemergence-only treatment. Yields within tillage systems and between weed control treatments in 1982 were not significantly different because adequate rainfall reduced the effect of weed competition for soil moisture. Soybean seed yields in 1983 and 1984 in no-tillage were equal to or significantly greater than those of conventional tillage. No-tillage treatments had greater soil moisture conservation and soil moisture availability resulting in less plant water stress during podfilling in periods of drought in 1983 and 1984. In all 3 yr, conventional tillage had significantly greater early weed growth than no-tillage in the treatments with and without soybean plants where no preemergence or postemergence herbicides were used. Comparing treatments with and without soybean plants indicated an average increase of 36 and 38% weed control for no-tillage and conventional tillage, respectively.

Based on chlorophyll content, hydroponically cultured soybean seedlings were 254, 66, and 13 times more tolerant to clomazone than velvetleaf, corn, and smooth pigweed, respectively. Clomazone, at concentrations that inhibited chlorophyll, did not affect fresh weight accumulations of any species except velvetleaf. However, in velvetleaf, fresh weight accumulation was only half as sensitive to clomazone as the leaf chlorophyll content. Uptake of 14C-clomazone from nutrient solution by 72 h after treatment (HAT) (pigweed > velvetleaf > soybean > corn) indicates that differential absorption cannot account for selectivity. Shoot:root ratios of 14C recovered from soybean, corn, velvetleaf, and pigweed by 72 HAT were 0.39, 0.84, 1.67, and 2.37, respectively. The limited acropetal clomazone translocation in soybean seedlings may account to a small degree for soybean tolerance to clomazone. Conversion of clomazone to more polar metabolites was rapid in all four species. There were no significant differences among species in the percentage of 14C activity recovered as clomazone from root tissue by 72 HAT. Of the 14C activity recovered from shoots of soybean, corn, pigweed, and velvetleaf seedlings by 72 HAT, 46, 59, 35, and 54%, respectively, was clomazone. Differences in clomazone uptake, distribution, and metabolism among the four species were either insignificant or poorly correlated to selectivity, and therefore cannot account for the tremendous differences in clomazone sensitivity among these species. These observations indicate, indirectly, that differences at the site of action may account for selectivity.

Greenhouse studies determined the influence of 14 adjuvants and desmedipham plus phenmedipham on velvetleaf control and sugarbeet injury by triflusulfuron. A second study determined if six adjuvants, or desmedipham plus phenmedipham, influenced 14C-triflusulfuron absorption by cotyledon or first true leaves of velvetleaf. Triflusulfuron applied twice at 4.4 g ai ha−1 (split application), alone or in combination with any adjuvant, did not reduce sugarbeet dry weight. Desmedipham plus phenmedipham applied twice at 370 g ai ha−1 (split application) reduced sugarbeet dry weight 3%. The addition of an adjuvant to desmedipham plus phenmedipham reduced sugarbeet dry weight 21 to 66% depending on the adjuvant. Sugarbeet injury was not greater when triflusulfuron was applied with any adjuvant (except urea ammonium nitrate (UAN)) plus desmedipham plus phenmedipham compared to desmedipham plus phenmedipham plus the respective adjuvant alone. Velvetleaf was most easily controlled in the cotyledon stage of growth. Velvetleaf control by triflusulfuron increased from 0 (no adjuvant) to 80% by the addition of Scoil or Sylgard 309 plus UAN. Cotyledonary leaves of velvetleaf absorbed 28% more 14C-triflusulfuron than first true leaves. Adjuvant increased 14C-triflusulfuron absorption by cotyledonary leaves from 15% (no adjuvant) to 48 to 90%. Desmedipham plus phenmedipham decreased velvetleaf control by triflusulfuron plus X-77 or X77 plus UAN compared to triflusulfuron plus the adjuvant alone. Velvetleaf control by triflusulfuron plus other adjuvants was not reduced by desmedipham plus phenmedipham. Absorption of 14C-triflusulfuron by cotyledonary and first true leaf velvetleaf decreased when desmedipham plus phenmedipham was added to triflusulfuron plus Dash, Dash plus UAN, X-77, X-77 plus UAN, and Sylgard 309 plus UAN.

Ludwigia is an important broadleaf weed of direct-seeded rice in Asia. Crop interference that relies on shading may have potential as a component of integrated weed management strategies but it requires understanding the extent to which rice can interfere with weed growth and how these weeds may respond. The growth of ludwigia was studied when grown alone and in competition with 4 and 12 rice (cv. IR72) plants. Rice interference reduced ludwigia height, number of branches, and shoot and root biomass. However, ludwigia showed the ability to reduce the effects of rice interference by increasing leaf weight ratio, increasing stem and leaf biomass in the upper half of the plant, and increasing specific stem length. At 11 wk after seeding, for example, ludwigia grown with 12 rice plants had 38% greater leaf weight ratio compared to plants grown alone. When grown with 12 rice plants, the weed had 82% of its leaf biomass in upper half of the plant compared to only 25% in weeds grown alone. The results showed that ludwigia responded to rice interference with a combination of adaptations typical of many weed species. Despite such plasticity, the control of ludwigia may be achieved by dense rice stands and increasing interference.

The effect of mowing regime on lateral spread and rhizome growth of dallisgrass and bahiagrass was determined in field studies conducted in 2003 and 2004 in North Carolina over 5 mo. Treatments were selected to simulate mowing regimes common to intensively managed common bermudagrass turfgrass and include 1.3-, 5.2-, and 7.6-cm heights at frequencies of three, two, and two times per week, respectively. A nonmowed check was included for comparison. Lateral spread of dallisgrass was reduced 38 to 47% regardless of mowing regime when compared with the nonmowed check. Rhizome fresh weight of dallisgrass was reduced 49% in 2003 and 30% in 2004 when mowed at the 7.6-cm regime after 5 mo, whereas the 5.2-cm mowing regime caused a reduction of 31%. Rhizome fresh weight of dallisgrass was most negatively affected by the 1.3-cm regime, which caused reductions of 57% in 2003 and 37% in 2004. Lateral spread of bahiagrass was more strongly affected by mowing height and frequency than dallisgrass, with reductions of 21 to 27%, 40%, and 44 to 62% when mowed at 7.6, 5.2, and 1.3-cm regimes, respectively. Rhizome fresh weight of bahiagrass was reduced 24 to 33%, 55%, and 70 to 73% when mowed at 7.6, 5.2, and 1.3 cm, respectively. Based upon these results, areas mowed at a golf course rough height (≥ 5.2 cm) may be more conducive to bahiagrass spread, whereas dallisgrass may tolerate areas mowed at a fairway height (1.3 cm). Mowing at the shorter heights examined in this study clearly reduced the potential of Paspalum spp. vegetative spread and may help to explain observed distributions of Paspalum spp. infestations in bermudagrass turfgrass.

Weeds are plants that grow along with cultural plants, both groups making up a community. The prevalence of weed species becomes adjusted to cultural management practices and often, they are not able to survive without their cultivated counterpart. In this way, some weeds become more or less domesticated plants (e.g. Bromus secalinus L.).

Sesbania [Sesbania cannabina (Retz.) Pers.] is a problematic emerging weed species in Australian cotton-farming systems. However, globally, no information is available regarding its seed germination biology, and better understanding will help in devising superior management strategies to prevent further infestations. Laboratory and glasshouse studies were conducted to evaluate the impact of various environmental factors such as light, temperature, salt, osmotic and pH stress, and burial depth on germination and emergence of two Australian biotypes of S. cannabina. Freshly harvested seeds of both biotypes possessed physical dormancy. A boiling-water scarification treatment (100±2 C) of 5-min duration was the optimum treatment to overcome this dormancy. Once dormancy was broken, the Dalby biotype exhibited a greater germination (93%) compared with the St George biotype (87%). The nondormant seeds of both biotypes showed a neutral photoblastic response to light and dark conditions, with germination marginally improved (6%) under illumination. Maximum germination of both biotypes occurred under an alternating temperature regime of 30/20 and 35/25 C and under constant temperatures of 32 or 35 C, with no germination at 8 or 11 C. Seed germination of both biotypes decreased linearly from 87% to 14% with an increase in moisture stress from 0.0 to −0.8 MPa, with no germination possible at −1.0 MPa. There was a gradual decline in germination for both biotypes when imbibed in a range of salt solutions of 25 to 250 mM, with a 50% reduction in germination occurring at 150 mM. Both biotypes germinated well under a wide range of pH values (4.0 to 10.0), with maximum germination (94%) at pH 9.0. The greatest emergence rate of the Dalby (87%) and St George (78%) biotypes was recorded at a burial depth of 1.0 cm, with no emergence at 16.0 cm. Deep tillage seems to be the best management strategy to stop S. cannabina’s emergence and further infestation of cotton (Gossypium hirsutum L.) fields. The findings of this study will be helpful to cotton agronomists in devising effective, sustainable, and efficient integrated weed management strategies for the control of S. cannabina in cotton cropping lands.

The objective of this study was to evaluate weed control, crop yields, potential soil loss, and net returns to management of an integrated weed management system in no-till corn and soybean compared to an herbicide-based strategy. The integrated weed management system reduced herbicide inputs by delayed cover crop termination, herbicide banding, and high-residue cultivation (reduced herbicide [RH]), while the other system used continuous no-tillage and herbicides to control weeds (standard herbicide [SH]). Research was conducted within the Penn State Sustainable Dairy Cropping Systems Experiment, where corn and soybean are each planted once in a 6-yr crop rotation. In this 3-yr study, weed density and biomass were often greater under RH management, but weed biomass never exceeded 19 g m–2 in corn and 21 g m–2 in soybean. Corn yield and population did not differ in any year, and net returns to management were $33.65 ha–1 higher in RH corn due to lower herbicide costs and slightly, though not significantly, higher yields. Soybean yield was lower in RH compared to SH in 2 of 3 yr, and was correlated with soybean population and cover crop residue. Net financial returns were $43.69 ha–1 higher in SH soybean compared to RH. Predicted soil loss never exceeded T (maximum allowable soil loss) for any treatment and slope combination, though soil loss was 100% greater on a 10% slope under RH management (vs. SH) due to cultivation.

Experiments were conducted in controlled environments and in the field on winter-hardy Triticum aestivum and three weed species commonly found in cereal fields in the United Kingdom to examine whether overwinter shoot growth of individual plants could be described by accumulated thermal time calculated using base temperatures derived from growth cabinets. Individuals of each species were grown in a controlled environment at constant temperatures ranging from 5 to 20 C and harvested sequentially. Base temperatures for the increase of dry weight and green area were estimated by fitting a simple linear model describing growth in response to the thermal sum. The estimated base temperatures for shoot dry matter accumulation of Alopecurus myosuroides, Stellaria media, Galium aparine, and T. aestivum were −0.8, −3.3, −1.4, and 0.2 C, respectively, and estimated base temperatures for increase in green area were 0.4, −1.7, 1.9, and 2.2 C, respectively. Each species also was grown in monoculture in the field over 2 yr at a range of sites to examine whether the base temperatures estimated from the controlled environment studies could be used to model weed and crop growth in response to thermal time in the field. The field data were described well when an expolinear function was fitted to accumulated thermal time calculated using the base temperatures derived from the controlled environment studies.

Foliar absorption of 2,4-D-C14 was rapid in both species. Cotton decarboxylated the side chain of 2,4-D several times faster than sorghum. Both species released C14O2 faster from the carboxyl than from the methylene position. Cotton slowly converted 2,4-D to a chromatographically different material in young leaves and bolls. Sorghum rapidly converted 2,4-D to a product different from 2,4-D and the 2,4-D-complex in cotton. After cotton recovered from 2,4-D-treatment, the regulator could not be detected in subsequent vegetative or reproductive growth.

Seeds of witchweed (Striga asiatica) were found in undisturbed Lakeland sand in all layers to 60 inches deep.

Knowledge of economic threshold level and growth habits of weeds in chickpea is essential to implement timely, effective, and economical weed control treatments. The effect of weed density on growth and yield performance in chickpea using dragon spurge as a test weed was investigated for 2 consecutive yr. Dragon spurge density levels of 5, 10, 15, 20, 25, 30, 35, and 40 plants m−2 were compared with weed-free plots. Each increment in densities of dragon spurge from 5 to 40 plants m−2 reduced plant height, number of fruits, seeds, and dry weight per plant. Chickpea grain yield losses varied between 1 to 63% with dragon spurge density ranging from 5 to 40 plants m−2. The seed protein content of chickpea was found to be significantly reduced above a weed density of 25 plants m−2. Maximum N, P and K uptake by dragon spurge was 1,520, 1,020, and 7,350 mg m−2, respectively. Thus, dragon spurge should be controlled at densities above 5 plants m−2 to achieve optimum chickpea yield.

Recently, several incidents of glyphosate failure on junglerice [Echinochloa colona (L.) Link] have been reported in the midsouthern United States, specifically in Mississippi and Tennessee. Research was conducted to measure the magnitude of glyphosate resistance and to determine the mechanism(s) of resistance to glyphosate in E. colona populations from Mississippi and Tennessee. ED50 (dose required to reduce plant growth by 50%) values for a resistant MSGR4 biotype, a resistant TNGR population, and a known susceptible MSGS population were 0.8, 1.62, and 0.23 kg ae ha−1 of glyphosate, respectively. The resistance index calculated from the these ED50 values indicated that the MSGR4 biotype and TNGR population were 4- and 7-fold, respectively, resistant to glyphosate relative to the MSGS population. The absorption patterns of [14C]glyphosate in the TNGR and MSGS populations were similar. However, the MSGS population translocated 13% more [14C]glyphosate out of the treated leaf compared with the TNGR population at 48 h after treatment. EPSPS gene sequence analyses of TNGR E. colona indicated no evidence of any point mutations, but several resistant biotypes, including MSGR4, possessed a single-nucleotide substitution of T for C at codon 106 position, resulting in a proline-to-serine substitution (CCA to TCA). Results from quantitative polymerase chain reaction analyses suggested that there was no amplification of the EPSPS gene in the resistant populations and biotypes. Thus, the mechanism of resistance in the MSGR population (and associated biotypes) is, in part, due to a target-site mutation at the 106 loci of the EPSPS gene, while reduced translocation of glyphosate was found to confer glyphosate resistance in the TNGR population.

The spring-tine harrow is gaining popularity for mechanical weeding. However, its weeding performance and mechanism have not been well understood. A spring-tine harrow was first tested in a controlled indoor soil bin at four different travel speeds (4, 6, 8, and 10 km h−1) with three different spring-loading settings (low, medium, and high). Then the harrow was tested in a wheat (Triticum aestivum L.) field at the same spring-loading settings at three different weeding timings (early, middle, and late) in 2019 and 2020. Soil cutting forces (draft and vertical), soil displacements (forward and lateral), soil working depth, weed control efficacy, weed density, and crop damage were measured. The results showed that the spring-loading setting had a more dominant effect on working depth and soil cutting forces than the speed. The soil displacements were more dependent on the speed compared with the spring-loading setting. Treatment effects on weeding performance indicators in the field were similar across years. Adjusting the spring-loading setting from low to high improved the weeding efficacy from 44.9% to 73.9% in 2019 and from 51.6% to 78.1% in 2020. Consequently, the final weed density was minimized at the high loading setting, with the reduction in 2020 being significant. The middle weeding timing caused the least crop damage, while reducing the final weed density by approximately one-third compared with the control (without mechanical weeding), which was the most desired outcome among the three timings tested.

When weeds were controlled in sorghum by hand-weeding or a herbicide there was no advantage or need for cultivation. Control of weeds in sorghum with preemergence herbicides was feasible, but the combination of cultivation and herbicides gave more dependable weed control than either method used alone. Preemergence applications of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) were the most effective for controlling weeds and increasing sorghum yields. In decreasing order of effectiveness were 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine), 2-chloro-N,N-diallylacetamide (CDAA) + trichlorobenzyl chloride (TCBC), and postemergence atrazine applications.

Weeds compete with crops for light, soil water, and nutrients. Nitrogen (N) is the primary limiting soil nutrient. Forecasting the effects of N on growth, development, and interplant competition requires accurate prediction of N uptake and distribution within plants. Field studies were conducted in 1999 and 2000 to determine the effects of variable N addition on monoculture corn and velvetleaf N uptake, the relationship between plant N concentration ([N]) and total biomass, the fraction of N partitioned to leaves, and predicted N uptake and leaf N content. Cumulative N uptake of both species was generally greater in 2000 than in 1999 and tended to increase with increasing N addition. Corn and velvetleaf [N] declined with increasing biomass in both years in a predictable manner. The fraction of N partitioned to corn and velvetleaf leaves varied with thermal time from emergence but was not influenced by year, N addition, or weed density. With the use of the [N]–biomass relationship to forecast N demand, cumulative corn N uptake was accurately predicted for three of four treatments in 1999 but was underpredicted in 2000. Velvetleaf N uptake was accurately predicted in all treatments in both years. Leaf N content (NL, g N m−2 leaf) was predicted by the fraction of N partitioned to leaves, predicted N uptake, and observed leaf area index for each species. Average deviations between predicted and observed corn NL were < 88 and 12% of the observed values in 1999 and 2000, respectively. Velvetleaf NL was less well predicted, with average deviations ranging from 39 to 248% of the observed values. Results of this research indicate that N uptake in corn and velvetleaf was driven primarily by biomass accumulation. Overall, the approaches outlined in this paper provide reasonable predictions of corn and velvetleaf N uptake and distribution in aboveground tissues.