Although Palmer amaranth is currently not widespread in most dry edible bean−producing states in the United States, it is widespread in western Nebraska, a major dry edible bean−producing region. There is currently a lack of research on management and biology of Palmer amaranth within dry edible bean production. The objective of this study was to quantify the impact of season-long Palmer amaranth interference on yield of dry edible bean and seed production of Palmer amaranth. A field study was conducted in Scottsbluff, NE, in 2020 and 2021. Palmer amaranth interference at densities of 0, 0.2, 0.3, 0.5, 1, and 2 plants m−1 row of dry edible bean was evaluated. Palmer amaranth interference reduced dry edible bean yield by 77% at a weed density of 2 plants m−1 row compared to the weed-free control, and a 5% yield reduction threshold was estimated to occur at a Palmer amaranth density of 0.02 plants m−1 row. Yield reduction occurred primarily through a reduction in the number of pods per plant as Palmer amaranth density increased. Palmer amaranth plants produced 91,000 to 376,000 seeds per plant depending on densities, and as many as 140,000 seeds m−2. Study results will help farmers and other stakeholders estimate Palmer amaranth interference within their fields, and may help justify the economic cost of incorporating additional Palmer amaranth management practices.

Despite being classed as an asocial species, aggregations of sea anemones can be common in abundant species. UK populations of the geographically common aggressive intertidal sea anemone Actinia equina, form clustered aggregations notwithstanding a violent nature towards neighbours and relatives. Smaller in body size, and more abundant than those found in warmer climates, little research has been undertaken to discover what factors affect body size. This study investigates whether aggregation, distance to neighbour, submergence at low tide or pH in rock pools affect body size of A. equina in their natural habitat. Populations were investigated at five sites on the Yorkshire coast during August and September 2016. A total of 562 anemones were recorded revealing that solitary anemones were significantly larger than those found in clustered aggregations. In addition, anemones found submerged in rock pools at low tide were significantly larger than those found on emergent rock, and smaller anemones were found in significantly higher pH conditions (8.5+) than larger anemones. Anemones submerged at low tide are constantly able to feed and not subject to harsh conditions such as wind exposure and temperature, hence they can achieve larger sizes. Consequently, the size of the anemones may reflect a trade-off between the benefits of aggregating in exposed environments and the costs of competition for a reduced food resource.

The rain forests of South-East Asia represent a biodiversity hotspot of terrestrial leeches, but we have only fragmentary and often anecdotal information on this component of tropical communities. To address the foraging tactics of terrestrial leeches, we studied the vertical distribution of Haemadipsa picta on foliage in a Bornean tropical rain forest. We investigated the links between leech body length and the above-ground height of their ambush positions under natural conditions and in a choice experiment performed under semi-natural conditions. We studied 167 leeches, which varied considerably with respect to body length (4–29 mm). On average, the leeches ambushed at lower heights under natural conditions than under experimental conditions (47.7 cm vs. 67.5 cm), though the heights of ambush positions overlapped considerably. Leeches that chose higher ambush positions under natural conditions consistently chose higher ambush positions in the experiment (Pearson r = 0.29). Under both natural and experimental conditions, leech body length was positively correlated with the height of ambush positions (Pearson r = 0.48); on average, a 1-mm increase in body length corresponded to a 2–3 cm higher ambush position. Our findings suggest that H. picta individuals actively choose hunting locations according to their above-ground height, shifting their ambush sites over ontogeny to higher foliage. We hypothesize that growing leeches might target different prey following ontogenetic shifts in the foraging optima, ultimately decreasing intraspecific competition.

Research was conducted during 1988 and 1989 in Georgia and Florida to determine the densitydependent effects and critical periods of wild poinsettia interference with peanut. Peanut yield loss ranged from 0 to approximately 50% over the wild poinsettia density range from 0 to 32 plants 9 m−1 peanut row. Predicted peanut yield losses across 2 yr in Georgia were 0, 4, 8, 12, 15, 26, 40, and 54% for season-long wild poinsettia interference at densities of 0, 1, 2, 3, 4, 8, 16, and 32 plants 9 m−1 of row, respectively. Across 2 yr in Florida, predicted peanut yield losses were 0, 9, 14, 22, 30, 37, and 41% for wild poinsettia densities of 0, 1, 2, 4, 8, 16, and 32 plants 9 m−1 row, respectively. Peanuts had to be maintained poinsettia free for 10 wk after peanut emergence to prevent yield loss. Wild poinsettia that interfered with peanut for more than 2 wk after peanut emergence reduced peanut yield.

Greenhouse studies were conducted to determine the effect of phosphorus (P) fertility on intra- and interspecific competition between lettuce and spiny amaranth for 4 wk after emergence. Total lettuce shoot biomass per pot and weight per plant increased 39 and 44% in response to increased P fertility, respectively. P fertility had no impact on growth of spiny amaranth. Total shoot biomass of spiny amaranth increased with increasing density from four to eight plants, however, lettuce did not. Total shoot biomass of both species increased as density increased from 4 to 16 plants. Spiny amaranth, but not lettuce, weight per plant decreased in response to intraspecific competition. Reciprocal yield analysis showed that spiny amaranth produced 2.4 times more biomass than lettuce when competing intraspecifically and four times more biomass under interspecific competition. Lettuce weight per plant was not affected. Relative yield analysis indicated that spiny amaranth was more competitive than lettuce regardless of P fertility. However, increased P fertility increased competitiveness of lettuce. Relative crowding coefficients indicated that spiny amaranth at the low density with low P fertility was 33 times more competitive than lettuce. Addition of P caused lettuce and spiny amaranth to be equally competitive at the lowest density; however, at the highest density, spiny amaranth was 4 tunes more competitive than lettuce regardless of additional P.

Research was conducted from 1982 through 1984 on a Shipps clay soil (Udic chromustert) in east-central Texas to determine the density-dependent effects and critical periods of johnsongrass [Sorghum halepense (L.) Pers. # SORHA] competition with cotton (Gossypium hirsutum L.). Two experiments were conducted each year, one to assess cotton yield response to increasing johnsongrass density and the second to establish the johnsongrass-free requirement of cotton and the johnsongrass competition period. A critical minimum density of 2 plants/9.8 m of row was observed. Full-season johnsongrass competition densities exceeding 2 plants/9.8 m of row resulted in seed cotton yield reductions each year. Yield decline was most rapid as density increased from 2 to 8 plants/9.8 m of row. Yield loss averaged 1, 4, 14, 40, 65, and 70% for johnsongrass densities of 1, 2, 4, 8, 16, and 32 plants/9.8 m of row, respectively. Percent yield loss was proportional to yield potential at johnsongrass densities of 4 and 8 plants/9.8 m of row. Three to four weeks of rhizome johnsongrass competition or 6 weeks of seedling johnsongrass competition resulted in significant yield reductions. Maintaining cotton johnsongrass free for 4 weeks did not prevent significant yield reductions.

The impact of weed density and weed distribution on irrigated corn yield was investigated in Colorado. Weed densities examined were 0,33,50, or 100% of the indigenous weed population. A series of weed distribution treatments were achieved by varying the length of the weed-free and weedy zones within the corn row while maintaining a constant weed population of 33 or 50% of the indigenous weed level. Grain yield was affected by weed density, but not by weed distribution. Each additional weed reduced corn yield 8.5 and 2.3 kg ha−1 in 1991 and 1992, respectively. When corn yields were estimated with a computer weed/corn management model, weed densities 5 to 8 wk after planting provided a better yield reduction estimate than weed densities immediately before harvest.

Experiments were conducted to determine the productivity, inter-, and intraspecific competitive ability of giant foxtail accessions resistant (PCW1) and susceptible (AC1) to acetyl-coenzyme A carboxylase (ACCase) inhibitors. Under noncompetitive conditions in the field, shoot dry biomass, plant height, and leaf area over time were similar between the PCW1 and AC1 accessions. The instantaneous relative growth rate and instantaneous net assimilation rate did not differ between the accessions; however, the instantaneous leaf area ratio was slightly greater for the AC1 accession than the PCW1 accession. The seed yield was similar between the PCW1 and AC1 accessions. Addition series experiments were conducted in the field to determine the intraspecific competitive ability of the PCW1 and AC1 accessions. Regression surface analysis of reciprocal mean shoot dry biomass and seed yield indicated that the relative competitive ability of the PCW1 and AC1 accessions was similar. Replacement series experiments were conducted in the greenhouse with or without corn to determine the interspecific competitive ability of the accessions. The relative growth rate, shoot dry biomass, and seed yield of the PCW1 and AC1 accessions were greater without than with corn competition. The relative competitive ability of the PCW1 and AC1 accessions was similar with or without corn competition based on shoot dry biomass or seed yield. These results indicated that the intra- and interspecific competitive ability of the PCW1 and AC1 giant foxtail accessions are similar and suggest that resistance to ACCase inhibitors has not reduced the relative fitness of the PCW1 accession.

Growth, seed production, and dormancy of velvetleaf in response to shading were evaluated in the field. Velvetleaf plant height, leaf number, number of branches, and plant dry weight decreased linearly with increasing shade. No differences were observed for plant height, number of leaves, or branches/plant when plants were shaded 30% or not shaded throughout the growing season. However, the 76% shade treatment reduced velvetleaf height (1984 only), leaf number, stem branches, and plant dry weight. These reductions were greater in 1984 than 1985 except for plant dry weight that decreased by 88% each year. The number of capsules and the number of seeds/plant decreased linearly with increasing shade levels, while the seed weight increased with increasing shade level. Shading also decreased seed dormancy. These results demonstrate that shade suppresses velvetleaf growth and seed production, and shortens the dormancy of seeds that are produced by these plants.

The study was conducted to determine the seasonal and diurnal water stress of soybeans [Glycine max (L.) Merr. ‘Lee 74′] grown under intraspecific competition (competition between plants of the same species) and interspecific competition (competition between plants of different species) with common cocklebur (Xanthium pensylvanicum Wallr.). Midday xylem potentials decreased as the season progressed and were lower in common cocklebur during vegetative growth of soybean and in soybean during reproductive growth. For a given species differences in xylem potential due to mode of competition were small. In the diurnal studies xylem potential for each species decreased to a minimum in the early afternoon but recovered to the original pre-dawn values at night. As the season progressed leaf xylem potential (a) decreased at a greater rate, (b) decreased sooner in the day, and (c) recovered at a slower rate. It was shown that differences in xylem potential between soybean and common cocklebur on a given day were small. Greater diffusive resistance values generally were found with soybean than with common cocklebur and with each species grown under interspecific competition.

Purple nutsedge (Cyperus rotundus L.) and yellow nutsedge (C. esculentus L.) appeared to be equally acceptable for oviposition by caged Bactra verutana Zeller, but purple nutsedge was significantly more suitable as a host: 90% of the larvae survived to maturity on purple nutsedge compared with 65% on yellow nutsedge. Responses of the plant species to both larval feeding injury and plant density were similar but purple nutsedge tended to be injured more than yellow nutsedge. At a high shoot density (nine shoots per pot), production of tubers by purple nutsedge was more adversely affected by feeding of five larvae per shoot than was production by yellow nutsedge: tuber dry weights were reduced 93 and 80% and numbers of tubers per pot were reduced 77 and 62%, respectively. Production of inflorescences was greatly reduced in both species. The effect of B. verutana on inflorescences may be more important for yellow nutsedge, which is generally considered to reproduce freely by seeds. Both species of nutsedge probably would be about equally affected by augmentation of B. verutana populations as a method of biological control.

A model of competition for light between peanut and three broadleaf weed species has been developed to run with the PNUTGRO model. The model simulates shading of the peanut canopy by reducing the total daily PAR received by the peanuts in a manner that realistically represents timing and quantity of light capture by the weeds. Data were collected in nursery plots of Florida beggarweed, sicklepod, and wild poinsettia in 1989, 1990, and 1991. These data provided the values for the critical parameters: maximum attenuation of PAR by the weed, time when the weed overtops the peanut canopy, time when maximum attenuation is reached, and the distance of influence of the weed. Florida beggarweed overtopped the peanut canopy 52 DAP, and reduced PAR reaching the peanuts 45% by 73 DAP. Sicklepod overtopped the peanut canopy 42 DAP and reached an attenuation of 41% 79 DAP. Wild poinsettia overtopped the peanut canopy 44 DAP, and had an attenuation value of 39% 85 DAP. The distances of influence were 162, 150, and 192 cm for Florida beggarweed, sicklepod, and wild poinsettia, respectively. Observed yield losses in the distance of influence were 26, 27, and 22%, respectively. The model predictions accounted for at least 90% of the yield losses observed in field studies. The model also proved capable of simulating competitive differences between morphologically and phenologically different populations of Florida beggarweed. Simulation models will play an important role in reducing the expenditure of time and resources required to document yield losses due to weeds in peanuts.

Field research was conducted from 1990 through 1992 to evaluate the effect of the fungal pathogen, Colletotrichum coccodes, on velvetleaf intra- and interspecific (with soybean) competition across a range of monoculture and 1:1 mixture densities. In pure stand, application of this velvetleaf foliar pathogen had little impact on seed yield of the weed. In these plots, velvetleaf intraspecific competition stimulated vertical growth and favored the rapid replacement of diseased leaf tissue that had prematurely senesced. In mixtures, however, C. coccodes inoculation differentially influenced the yield of both species. In two of three years, C. coccodes inoculation reduced velvetleaf seed yields by, an average, 60% compared with yields for control (uninoculated) plants. Velvetleaf suffered greater yield losses from soybean interspecific competition in the presence of C. coccodes, especially at the lower planting densities. The decline in velvetleaf yield was primarily attributed to the stunting effect of the pathogen, which allowed soybean plants to grow above the weed. Consequently, soybean yield losses within inoculated mixture plots were generally lower than for control plots, although significant increases (23%) in soybean yield were recorded only in 1992. The inoculation treatment had relatively little impact on the number of seeds produced per fruit or seed unit weight in both species regardless of whether plants were grown in monocultures or in mixtures. The finding that C. coccodes has only a limited effect on velvetleaf performance in pure stand, while having a significantly greater effect in a competitive environment with a soybean crop, has important ramifications as to the value and accuracy of initial efficacy testing that rates potential biocontrol agents based solely on their effect within pure stands of the target weed.

Research was conducted from 1983 through 1986 to compare the competitiveness of three cotton cultivars of different height with johnsongrass. Cultivars evaluated were: ‘1209-619-7’, ‘TAMCOT SP37-H’, and 'Stoneville 213’, which had an average height at maturity of 66, 122, and 168 cm, respectively. Each cultivar was grown with johnsongrass densities of 0, 4, and 6 plants/6 m of row with a 1-m row spacing. Johnsongrass biomass data confirmed that all three cultivars did compete with johnsongrass, but regression analyses using cultivar as a covariate revealed no difference in the competitiveness of the three cultivars.

Field studies were conducted to determine the influence of phosphorus (P) fertility and method of application (banded versus broadcast) on the competitive interaction of lettuce and spiny amaranth. Weed density significantly affected lettuce head weight and spiny amaranth shoot biomass after 5 wk of interference. Weed density and duration of interference had little or no effect on P content of lettuce tissue. Duration of interference did affect P concentration of spiny amaranth; however, weed density did not Spiny amaranth competition reduced lettuce yield, but P was not the limiting factor. Duration of interference and method of P application interactively affected lettuce head weight; however, only duration of interference affected spiny amaranth biomass. Seven wk of interference caused a decrease in lettuce head weight of 20, 8, and 24% when P was broadcast, banded, or not applied, respectively. Banding of P reduced the negative impact of spiny amaranth on lettuce. Although method of P application influenced the interaction between lettuce and spiny amaranth, interspecific competition between the two species probably was not due to competition for P but some other factor.

Seeds of false cleavers (Galium spurium L.) grown in mid-May germinated 12 to 14 days after planting in central Alberta. The plants flowered from early July to late August and developed fruits from mid-July to early September. Plants from the late-June sowing date developed fruits until early October unless early fall frost killed the plants. Plants from seeds sown after mid-July remained in a vegetative state until late September and did not flower. Seedlings that emerged in August and September survived a mild prairie winter and resumed growth the following spring. Under greenhouse conditions, plant height ranged from 77 to 113 cm and the number of branches at first node ranged from 6 to 14, as plant density decreased from 16 to 1 plant/pot. Shoot dry weight decreased by 50% as plant population doubled, 46 days after emergence. The number of seeds produced/plant decreased from 3500 to 175 as plant density increased from 1 to 16 plants/pot. In growth chamber studies, plant growth was greatest at 20 compared to 16 or 24C.

Two parameters of physiological competence, rate of CO2 fixation and intraspecific competitiveness, were determined for one or more atrazine-resistant isolates of the photosynthetic bacterium Rhodobacter sphaeroides. Measured over a 2-h period under optimal conditions, two of the resistant isolates fixed CO2 at a greater rate than the atrazine-susceptible, wild-type organism. In a mixed culture study, an atrazine-resistant strain was able to grow and compete successfully with the susceptible, wild-type strain for at least 14 days.

The Eurasian perennial mustard, hoary cress, Cardaria draba (Brassicaceae), is an invasive weed in western North America that can displace native plants and other desirable forage species in pastures and rangelands. This study investigated the competitive ability of 11 grasses representing nine species in the genera Festuca and Poa from either North America (NA) or Europe (EU) against hoary cress. Hoary cress was grown alone and with four different grass densities under controlled conditions with ample water and nutrient supply, typical for riparian and disturbed habitats, in which hoary cress infestations are commonly found. Of the five Festuca grasses tested, only Schedonorus phoenix (= F. arundinacea) decreased hoary cress biomass. Four of the six Poa grasses tested decreased hoary cress biomass and were ranked by decreasing competitive effects as follows: P. annua > P. compressa (EU) > P. pratensis (EU) > P. compressa (NA). The most competitive grass species also experienced higher intraspecific competition. Within both grass genera, Eurasian species were more competitive against hoary cress than their North American congeners, which suggests that hoary cress establishment may be facilitated by lower biotic resistance in the invaded range. Regardless of origin, sod-forming Poa species were competitive at low densities, while Festuca species only had significant effects at high densities if at all. Based on our results we recommend the use of Poa species for restoration of riparian and disturbed sites following the control of hoary cress infestations to restrict recolonization.

A full-season field study was conducted near College Station, TX to determine the competitive interference of Palmer amaranth on cotton development, yield, and fiber properties and to measure Palmer amaranth development as influenced by intraspecific competition. Palmer amaranth densities ranged from 0 to 10 plants/9.1 m of row. Palmer amaranth decreased cotton canopy volume by 45% at 10 wk after cotton emergence (WAE) and cotton biomass by greater than 50% at 8 WAE at the highest density. Cotton yields decreased linearly from 13 to 54% for 1 to 10 Palmer amaranth plants/9.1 m of row. Cotton lint properties were not influenced by Palmer amaranth density. Palmer amaranth volume and individual biomass were not affected by intraspecific competition at any of the densities.

Herbicides are the basis for conventional management of purple nutsedge, one of the world's most troublesome weeds. However, as concern rises over their environmental impact, farmers are being required to reduce herbicide usage. Herbicide efficacy is strongly affected by weed growth stage and density at application, and when herbicides are applied under optimal conditions, low rates can provide maximal control efficacy (CE). Therefore, this study aimed to determine the time window for control of purple nutsedge using a low rate of herbicide, based on an effective degree days (EDDs) model, at low (one tuber) and high (10 tubers) densities. Two experiments were performed under field conditions, in the summers of 2009 and 2010. Rate of 3.75 g a.i. ha−1 trifloxysulfuron was applied once on each of five individual application dates. The growth of both treated and untreated plots was evaluated by means of leaf cover area (LCA) and biomass, which were then used to establish the time window for control. Results showed differences in both growth parameters between low and high tuber densities. The high-density patches reached LCA and fresh biomass values of 1,367 g and 1.12 m2, respectively, compared to 604 g and 0.69 m2, respectively, in the lower density patches. The favorable control periods based on biomass and LCA for the lower density patches were set to later dates than those for the higher density patches, 626 EDD compared to 483 EDD for biomass, and 786 EDD compared to 502 EDD for LCA, respectively. Although differences between the biomass- and LCA-based favorable control periods were observed at both tuber densities, the computed linear relations between the two growth parameters enabled adjusting them and setting the appropriate control period.