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Publications (89)
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Southern California grasslands have largely been type-converted to dominance by exotic annual grasses, leading to displacement of many native grass and forb species. Crimson fountaingrass, Pennisetum setaceum, an exotic perennial C-4 species and a relatively new invader to California, is expanding to areas currently occupied by purple needlegrass,...
Herbicides are used in agricultural and wildland ecosystems to reduce the density of weeds and promote the growth of desirable species. Use of herbicides in agroecosystems may change composition of weed populations. In wildlands, herbicides may increase the diversity of native species. Threats to plant biodiversity caused by habitat loss and invasi...
Evolved herbicide resistance (EHR) is an important agronomic problem and consequently a food security problem, as it jeopardizes herbicide effectiveness and increases the difficulty and cost of weed management. EHR in weeds was first reported in 1970 and the number of cases has accelerated dramatically over the last two decades. Despite 40 years of...
The history of some invasive species is so complex that their origins can be difficult to determine. One example of such invasive species is the California invasive known as “wild artichoke thistle” (Cynara cardunculus var. sylvestris), found in natural and disturbed ecosystems. Wild artichoke thistle is a Mediterranean native and the progenitor of...
Invasive species researchers often ask: Why do some species invade certain habitats while others do not? Ecological theories predict that taxonomically related species may invade similar habitats, but some related species exhibit contrasting invasion patterns. Brassica nigra, Brassica tournefortii, and Hirschfeldia incana are dominant, closely rela...
Background/Question/Methods
Fountain grass (Pennisetum setaceum) is a perennial C4 African bunchgrass that is invasive outside its native range and spreading in wildlands in Hawaii and the Southwestern U.S. This species is increasing in California, but little is known about potential habitat suitability or impacts. A climate-matching model based...
1. Exotic annual plants are an increasingly important ecological issue and new, creative approaches to management are required. In desert ecosystems of the southwestern USA, the forbs Brassica tournefortii, Erodium cicutarium and Schismus spp. dominate and alter native annual communities. Hand weeding B. tournefortii is currently the most common co...
As invasive plants continue to increase worldwide, there is an increased demand to assess and categorize species for management priority. This study assessed the use of a climate-matching model to improve predictions of plant species spread. We analyzed species that had been chosen using expert opinion for designated listing as able to spread widel...
Introduction The Technology Environmental and Economic Concerns Summary—Long- and Short-Range Prospects Literature Cited
The relationship between plant community composition and invasibility has been studied extensively but seldom in the context of ecosystem restoration. Experimental riparian restoration plots differing in species composition and density were established and evaluated for susceptibility to invasion by giant reed, a common riparian invader in Californ...
Giant reed is one of the most widespread invasive species in riparian habitats in California and other coastal states of the United States. This species is thought to spread primarily asexually by flood dispersal of stem and rhizome pieces; viable seeds have not been found in the United States. Research was conducted to quantify genetic variation i...
Giant reed is an extremely aggressive riparian invader in California. Little is known about its response to nitrogen, which is often elevated in watersheds downstream from agricultural fields and wastewater treatment facilities. Two pot-experiments were conducted to quantify physiological responses of giant reed, and a co-occurring riparian species...
Background/Question/Methods
As invasive plants continue to increase worldwide, there is an increased demand to assess and categorize species for management priority. This study assessed the use of a climate-matching model to improve predictions of plant species spread. We analyzed species that had been chosen using expert opinion for designated li...
Modern weed science combines basic and applied sciences in the study of weeds, typically defined as plants that are objectionable or interfere with the activities or welfare of humans. Although weeds have been associated with human activity since the beginning of crop cultivation, the history of weed science parallels the history of modern day agri...
Weed science is a diverse field that relies upon many fundamental disciplines to generate theories and empirical information about weedy plants. This information is used to develop and improve technology designed to manage weeds. Weed management includes three components— prevention, eradication, and control of weeds or undesirable plants—as well a...
Feral rye is an agricultural and ruderal weed of the western United States. We investigated how it has phenotypically diverged from its cultivated ancestor, domesticated cereal rye, and across its range since the introduction of its progenitor. Vegetative growth, flowering phenology, and reproductive characters of feral populations from across a 13...
Abutilon theophrasti is one of the worst agricultural weeds in North America, yet it has not reached that status in California in the 80 yr since it was first reported. The research reported here examined the distribution and modeled climatic requirements of A. theophrasti to determine whether it is likely to spread more widely in the state. Herbar...
Invasive species are known for their ability to form monocultures that exclude native species, yet intraspecific interactions
among invasives have not been well studied. Cynara cardunculus (L.) is an invasive perennial thistle that establishes high-density populations in coastal California grasslands. We examined
the natural distribution of C.cardu...
Arundo donax L. (Poaceae) is an aggressive invader in California’s riparian habitats. Field experiments were conducted to examine invader
and site attributes important in early invasion. One hundred A.donax rhizomes were planted along five transects into each of three southern California riparian habitats. Pre-planting rhizome
weight was recorded,...
Weeds exist as a category of vegetation because of the human ability to select desirable traits from among various members of the plant kingdom. Just as some plants are valued for their uses or beauty, others are reviled for their apparent lack of these characteristics. Weeds are recognized worldwide as an important type of undesirable, economic pe...
Prevention, Eradication, and ControlWeed Management in AgroecosystemsManagement of Invasive Plants in Natural EcosystemsMethods and Tools to Control Weeds and Invasive PlantsSummary
The classic reference on weeds and invasive plants has been revised and updated. The Third Edition of this authoritative reference provides an in-depth understanding of how weeds and invasive plants develop and interact in the environment so you can manage and control them more effectively. The guide includes an introduction to weeds and invasive p...
Cycles of Land Use, Expansion, and Intensification for ProductionApproaches for Pest and Weed ManagementNovel EcosystemsNovel Weed/Invasive Plant Management SystemsValue Systems in Agricultural and Natural Ecosystem ManagementSummary
Ecological PrinciplesManagement PrinciplesSocial PrinciplesSummary
NeighborsInterferenceModifiers of InterferenceMethods to Study Interference (Competition)Intensity and Importance of CompetitionCompetition ThresholdsMechanisms of CompetitionOther Types of Interference than CompetitionNegative Interference in Addition to CompetitionPositive InterferenceSummary
Herbicides as Commercial ProductsChemical Properties of Herbicides that Affect UseHerbicide ClassificationHerbicide Symptoms and SelectivityHerbicide ApplicationFate of Herbicides in EnvironmentSummary
Half TitleTitleCopyrightContentsPrefaceBurdock by Charles Goodrich
Principles of Plant DemographyDynamics of Weed and Invasive Plant SeedRecruitment: Germination and EstablishmentSummary
Plant Invasions over Large Geographical AreasLocal InvasionsFactors That Influence InvasibilityInvasibility and Exotic Plant InvasivenessSummary
The success of weed management based on ecological principles and weed biology will depend on a better understanding of the effect of environment on lift history strategies, growth, and competition of weeds; and crops, and particularly upon the ability to predict weed and crop phenology, This paper reviews the importance of phenotypic plasticity to...
Pennisetum clandestinum Hochst ex Chiov. (kikuyugrass) is a C4 grass that has become an invasive weed in temperate climates. We examined ecophysiological mechanisms that have allowed it to become a successful weed in these locations by comparing P. clandestinum and two other common turigrass species, Festuca arundinacea Schreb. (tall fescue cv. Moj...
Dispersal of offspring is a critical step in the spread of invasive species, yet dispersal patterns are seldom well studied,
inhibiting effective management and ecological understanding of invasions. Dispersal patterns can be affected by characteristics
of the parent plant and by climatic or site characteristics, including community vegetation stru...
The effect of growth temperature on biomass production and photosynthesis of nearly-isonuclear triazine-resistant and -susceptible Senecio vulgaris L. bio-types was investigated. Plants were grown in growth chambers with day/night temperatures of 13/8, 20/15 and 30/25°C, and were harvested 35, 42, 49 and 56d after planting (DAP). The S biotype prod...
Arundo donax L. is a rhizomatous perennial, asexually reproducing species that has invaded riparian habitats throughout Mediterranean
climate zones. This research evaluated ramet demography of A. donax in two California riparian communities that differed in nitrogen availability. Quadrats were established along 100 m transects
at each site and orie...
The identities of two novel perennial nutsedge biotypes collected near Bakersfield, CA, were assessed using isozyme and random-amplified polymorphic deoxyribonucleic acid markers in conjunction with morphological analysis. The two biotypes, designated as CK (Cyperus rotundus cv. ‘Kempeni’) and CR (Cyperus esculentus cv. ‘Robusta’), morphologically...
Invasibility of experimental riparian communities by Arundo donax
Quinn, Lauren and Jodie Holt Department of Botany and Plant Sciences, University of California, Riverside <lquinn@citrus.ucr.edu>
As invasive plants enter new areas, they necessarily interact with resident plant communities. Several researchers have found a link between the function...
Arundo donax L. (giant reed) is an invasive perennial plant that has spread widely in riparian areas in California, where it has altered wildlife habitats, created a fire hazard, compromised water conservation efforts, and affected flood control. Currently, physical removal is the primary means of controlling this weed, which is ineffective because...
■ Abstract Contributions from the field of population biology hold promise for understanding and managing invasiveness; invasive species also offer excellent oppor- tunities to study basic processes in population biology. Life history studies and demo- graphic models may be valuable for examining the introduction of invasive species and identifying...
Experiments were conducted to test several methods for estimating low temperature thresholds for seed germination. Temperature
responses of nine weeds common in annual agroecosystems were assessed in temperature gradient experiments. Species included
summer annuals (Amaranthus albus, A. palmeri, Digitaria sanguinalis, Echinochloa crus‐galli, Portul...
Abutilon theophrasti is one of the worst agricultural weeds in North America, yet it has not reached that status in California in the 80 yr since it was first reported. The research reported here examined the distribution and modeled climatic requirements of A. theophrasti to determine whether it is likely to spread more widely in the state. Herbar...
Minutes of the WSSA Board of Directors Meeting Orlando, Florida July 28 and 29, 1996 - Volume 45 Issue 2 - Jodie S. Holt
We examined the relationship between temperature and emergence of yellow nutsedge tubers to generate predictive models for the arid southwestern United States. Field experiments were conducted in California and Arizona to obtain phenological and temperature data needed to generate degree-day models. The effect of air temperature on emergence was te...
Experiments were conducted to examine the effects of low soil moisture on yellow nutsedge emergence in relation to thermal and chronological time and test the ability of thermal models generated previously to predict emergence under water stress. Unsprouted tubers from California and Arizona were planted in pots, buried at field sites in California...
Minutes of the WSSA Board of Directors Meeting Thursday, February 8, 1996, Norfolk, VA - Volume 44 Issue 4 - Jodie S. Holt
Experiments were conducted to establish low temperature thresholds for initiation of bud sprouting in dormant vegetative propagules of johnsongrass, purple nutsedge, and yellow nutsedge, and seed germination in cotton. Weed propagule sprouting and cotton seed germination responses to temperature were determined in a series of experiments conducted...
Photographic techniques and the point-frame transect method were used to study areal growth of kikuyugrass grown in the field without competition in 1990 and 1991. The effect of cutting height on plant extension was also examined in 1991. There were no differences in sward area between eight selections planted in 1990, except on the first measureme...
Light regulates many facets of plant growth and development through the effects of quantity of total energy and of photons, spectral quality, duration, and photoperiod. Numerous techniques and types of equipment are available for quantifying light in plant canopies. The effect of total quantity of light on weed and crop productivity has been descri...
Using starch gel electrophoresis, we examined the genetic variability of kikuyugrass collected from three golf course sites within its geographical range in California. These experiments were conducted to determine the method of spread of kikuyugrass in areas where it is considered invasive. Samples from roughs and fairways of each of these locatio...
Genetic variation of morphological and phenological characters of yellow nutsedge ( Cyperus esculentus L.) from California was investigated and compared with isozyme data from the same populations. The importance of collection location, individual genotype, and isozyme genotype to phenotypic characteristics was evaluated. Analyses were conducted on...
Concerns in the public and agricultural sectors about the impacts of agricultural practices have led many weed scientists to refocus research efforts toward development of alternative strategies of weed management. To develop methods of weed management that will supplement or replace herbicides, the impacts of agricultural practices on weeds must b...
At least 57 weed species, including both dicots and monocots, have been reported to have biotypes selected for resistance to the triazine herbicides. In addition, at least 47 species have been reported to have biotypes resistant to one or more of 14 other herbicides or herbicide families. These herbicides include the aryloxyphenoxypropionics, bipyr...
Herbicide Resistance in Weeds and Crops – Caseley J. C. , Cussans G. W. , and Atkin R. K. , editors. 1991. Butterworth-Heinemann Ltd., Oxford. 513 p. illus., Hardcover, ISBN: 0-7506-1101-4, $95.00. - Volume 6 Issue 2 - Jodie S. Holt
Growth characteristics and competitive relationships of cotton and three perennial weeds (johnsongrass, purple nutsedge, and yellow nutsedge) were investigated at the USDA Cotton Research Station in Shafter, CA. In growth analysis experiments, yellow nutsedge and johnsongrass had highest values for height, biomass, leaf area production, growth rate...
Weed scientists are trained broadly in agronomy, botany, chemistry, soils, and other agricultural disciplines. The study of weeds, rather than the techniques used or the questions asked, unifies weed scientists around a common focus. It is often difficult for weed scientists to identify closely with any one scientific discipline, since the techniqu...
Herbicide Resistance Workshop: Weed Science Society of America Montreal, Canada February 5, 1990 - Volume 5 Issue 1 - Jodie S. Holt
Wild oat and wheat were synchronized in their development and were shown to be equally
competitive in southern California studies. Competition effects of wild oat were most
evident in wheat after the stem elongation stage.
Isonuclear triazine-susceptible and triazine-resistant Senecio vulgaris L. biotypes were developed by making reciprocal crosses between susceptible and resistant biotypes to obtain F(1) hybrids and backcrossing the hybrids to the appropriate pollen parent. The electrophoretic isozyme patterns of the enzyme aconitase obtained from leaf extracts of t...
Herbicide-resistant weed species have become widespread in recent years. Fifty-five weed species, including 40 dicots and 15 grasses, are known to have biotypes resistant to the triazine herbicides. One or more resistant species have arisen in 31 states of the United States, four provinces of Canada, 18 countries in Europe, and Israel, Japan, Austr...
Herbicide Resistance: Proceedings of a Symposium of the Weed Science Society of America February 8, 1989, Dallas, Texas - Volume 4 Issue 1 - Jodie S. Holt
Natural selection for a particular trait incurs an initial cost to the organism in terms of fitness, or its ability to survive and reproduce. In weeds selected for herbicide resistance, this generalization holds true for biotypes possessing the maternally inherited trait of triazine resistance. This mutation has a detrimental effect on photosynthes...
Competitive interactions of wheat and wild oats in relation to variations in plant density of both species were investigated in field studies under irrigation and added fertilizer. Competition studies included comparisons by both additive and replacement series. The additive series was used to study plant responses to competition under fixed densit...
The relationship of triazine resistance to decreased plant productivity was investigated in Senecio vulgaris L. F(1) reciprocal hybrids were developed from pure-breeding susceptible (S) and resistant (R) lines. The four biotypes (S, S x R, R, R x S) were compared in terms of atrazine response, electron transport, carbon fixation, and biomass produc...
(1) Triazine-susceptible and resistant biotypes of Senecio vulgaris, collected from the same field in Salinas, California, were compared to determine whether reduced productivity and competitiveness accompany the trait of triazine resistance in biotypes with identical environmental histories. Characteristics of growth, resource allocation, developm...
Genetic diversity within and among populations of yellow nutsedge ( Cyperus esculentus L. # CYPES) was analyzed to evaluate and quantify the genetic consequences of the reported predominance of asexually-produced tubers as colonizing agents. Ten populations were examined using starch gel electrophoresis for allozyme analysis. Four populations of pu...
A study was conducted to investigate the physiological responses of greenhouse-produced Oxalis corniculata seeds to light, temperature, moist heat treatment, aging, and season of production. Fresh seeds exhibited over 90% germination and required low levels of light (5 ,umol m-2 s-1, 400-700 nm) to germinate. Seeds germinated over a broad, yet seas...
A study was conducted to investigate the physiological responses of greenhouse-produced Oxalis corniculata seeds to light, temperature, moist heat treatment, aging, and season of production. Fresh seeds exhibited over 90% germination and required low levels of light (5 μmol m⁻² s⁻¹, 400–700 nm) to germinate. Seeds germinated over a broad, yet seaso...
The importance of seeds in the reproduction and maintenance of yellow nutsedge ( Cyperus esculentus L. # CYPES) populations was evaluated. Isozyme analysis using starch gel electrophoresis was performed on 20 individuals of each of 10 widely separate populations in California. Genetic variation among individuals served as an indicator of the relati...
Anatomical and physiological characteristics of leaves of triazinesusceptible and -resistant biotypes of common groundsel (Senecio vulgaris L.) were studied in order to explain the differences in light-saturated photosynthetic rates previously reported. Leaves were of uniform leaf plastochron index from greenhouse-grown plants. Susceptible plants h...
Field studies were established in 1974 and 1975 at various locations in San Diego County, CA, to evaluate several herbicides for the control of chamise ( Adenostoma fasciculatum H.&A.) and redshank chamise ( Adenostoma sparsifolium Torr.). Herbicide effects on vegetation were reevaluated in 1982. Plots originally treated with 2.2 or 4.5 kg ae/ha of...
Photosynthetic oxygen evolution in response to flashing light was studied in triazine-susceptible and triazine-resistant biotypes of Senecio vulgaris L. Studies were conducted to determine if the modification of the herbicide-binding site which confers s-triazine resistance also affects the oxygen-evolving system. Oxygen evolution was measured usin...
Comparative growth, development, and resource allocation of triazine - susceptible and triazine - resistant biotypes of common groundsel ( Senecio vulgaris L.), grown under two light regimes, were studied over a 7 - week period. Dry-matter production, height, number of leaves, and leaf area of the susceptible biotype were greater than those of the...
Studies were conducted to determine a physiological basis for competitive differences between Senecio vulgaris L. biotypes which are either resistant or susceptible to triazine herbicides. Net carbon fixation of intact leaves of mature plants was higher at all light intensities in the susceptible biotype than in the resistant biotype. Quantum yield...
Introduction Brassica tournefortii (Sahara mustard) is an exotic annual mustard currently spreading in southwestern deserts, including the Mojave. B. tournefortii, or Sahara mustard, is one of only a few exotic plants able to spread rapidly and dominate desert ecosystems. It first appeared in the Coachella Valley in 1927 (Sanders and Minnich 2000),...
