Showing papers on "Allelopathy published in 1996"

Utilization of Allelopathy for Weed Management in Agroecosystems

Abstract: Biorational alternatives are gaining increased attention for weed control because of concerns related to pesticide usage and dwindling numbers of labeled products, particularly for minor-use crops. Allelopathy offers potential for biorational weed control through the production and release of allelochemics from leaves, flowers, seeds, stems, and roots of living or decomposing plant materials. Under appropriate conditions, allelochemics may be released in quantities suppressive to developing weed seedlings. Allelochemics often exhibit selectivity, similar to synthetic herbicides. Two main approaches have been investigated for allelopathic weed suppression. One is use of living rotational crops or mulches that interfere with the growth of surrounding weeds [e.g., tall red fescue, Festuca arundinacea Schreb.; creeping red fescue, F. rubra L. subsp. commutata; asparagus, Asparagus officinalis L. var. altilis); sorghum, Sorghum bicolor (L.) Moench; alfalfa, Medicago saliva L.; black mustard, Brassica nigra (L.) Koch; and oat, Avena saliva L.]. Attempts to select germplasm with enhanced suppressive ability have been limited. The second is use of cover crop residues or living mulches to suppress weed growth for variable lengths of time (e.g., winter rye, Secale cereale L.; winter wheat, Triticum aestivum L.; and sorghum). Cover crop residues may selectively provide weed suppression through their physical presence on the soil surface and by release of allelochemics or microbially altered allelochemics. The ability to understand the physiological basis for allelopathy in a crop plant may allow the weed scientist or ecologist to work closely with molecular biologists or traditional plant breeders to selectively enhance the traits responsible for weed suppression.

Plant phenolics in allelopathy

Abstract: Phenolics are one of the many secondary metabolites implicated in allelopathy To establish that allelopathy functions in a natural ecosystem, the allelopathic bioassay must be ecologically realistic so that responses of appropriate bioassay species are determined at relevant concentrations It is important to isolate, identify, and characterize phenolic compounds from the soil However, since it is essentially impossible to simulate exact field conditions, experiments must be designed with conditions resembling those found in natural systems It is argued that allelopathic potential of phenolics can be appreciated only when we have a good understanding of 1) species responses to phenolic allelochemicals, 2) methods for extraction and isolation of phenolic allelochemicals, and 3) how abiotic and biotic factors affect phenolic toxicity

Interactions Involving Allelopathy in Cropping Systems

Abstract: Allelopathic inhibition typically results from the combined action of a group of allelochemicals which, collectively, interfere with several physiological processes. The objectives of this paper are to summarize research that illustrates the joint action of allelochemicals, and to provide evidence that both the amount and detrimental action of these compounds depends on the extent of associated abiotic and biotic stresses. Allelopathy is strongly coupled with other stresses of the crop environment, including insects and disease, temperature extremes, nutrient and moisture variables, radiation, and herbicides. These stress conditions often enhance allelochemical production, thus increasing the potential for allelopathic interference. In the paradigm of interactions, the data indicate that crops are more sensitive to allelopathy when moisture, temperature, or nutrient conditions are less than optimal. For example, the inhibition threshold concentration for ferulic acid to affect seedling growth was reduced with even minor moisture stress (ψ = - 0.15 MPa) or a growth temperature at the higher end of the normal range for a species. Under greenhouse conditions, additive inhibition resulted from the joint action of ferulic acid with low levels of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], atrazine [6-chloro-N-ethyl-N'(1-methylethyl)-1,3,5-triazine-2,4-diamine], or trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoro-methyl)benzenamine]. Interactions of multiple stresses in crop environments will determine the relative impact of allelopathy. Allelopathystress interactions also have implications for herbicide and residue management strategies, crop rotations, biological control measures, and tillage practices that can contribute to a more sustainable agriculture.

Allelopathy in Forage Crop Systems

Abstract: Secondary plant metabolites and their degradation products are important in all agroecosystems including those with forage crops. Allelopathy affects cropping systems and interseeding of one species into established sods of another. Autotoxicity and heterotoxicity are types of allelopathy. Alfalfa (Medicago saliva L.) has been investigated as both an autotoxic and heterotoxic species. Reestablishment of alfalfa immediately after alfalfa has usually resulted in poor stands due to autotoxicity, and several other forage species also exhibit autotoxicity. Many forage species have shown heterotoxicity, both between forage species and weed species. Several investigators have identified various allelochemicals and/or families of allelochemicals as being responsible for allelopathic reactions. Identifying such chemicals would aid in developing resistant forage cultivars and in maintaining a productive and profitable crop. Crop rotation, cover-crop management, interplanting, double cropping, no-till planting, and nonrotational cropping systems are involved with allelopathic effects. Some alfalfa cultivars possess some resistance to these allelochemicals. Therefore, a breeding program could provide resistant germplasms. Various forage grasses and some weed species have demonstrated allelopathic effects on alfalfa, and alfalfa has allelopathic effects on some weed species. This alone may provide an insight for herbicide studies in alfalfa production.

Distinguishing Resource Competition and Chemical Interference: Overcoming the Methodological Impasse

Abstract: Understanding allelopathy may hold the key to new weed management strategies. However, the difficulty of distinguishing chemical interference from competition has hindered studies of allelopathy in natural and cultivated plant communities. Experimental rigor has increased, but has yet to provide unambiguous proof of allelopathy. The complexities of allelopathic interactions, as illustrated by ongoing investigations in the Florida scrub, make it unlikely that clear examples will be forthcoming. While conclusive proof of chemical interference may not be attainable, the challenge of obtaining strong supportive evidence remains. Progress is needed in bioassay methods that distinguish allelopathy from other interference mechanisms. Phytotoxic effects are density-dependent in a manner inconsistent with resource competition, suggesting that allelopathy can be distinguished by characteristic growth responses across planting densities. In monoculture, greater phytotoxicity at low plant densities causes deviations from expected yield-density relationships. In mixed culture, the target-neighbor method, in which differing densities of a neighbor species are planted around a target plant, has been used to study phytotoxic effects. In the presence of an applied phytotoxin, increased growth of sensitive target plants as the density of insensitive neighbors increases is inconsistent with a hypothesis of resource competition and provides compelling, though not conclusive, evidence for chemical interference. Once evidence of allelopathy is obtained from plant growth studies, supportive analytical data must be obtained from analyses of toxin concentrations and flux rates in the soil and rhizosphere. The use of adsorbent materials originally applied to the analysis of organic pollutants should allow the measurement of allelochemical flux rates in addition to static concentrations.

Allelopathy in the Management of Plant-Parasitic Nematodes

Abstract: There are numerous reports of nematicidal chemicals in crude plant homogenates, leachates, and decomposing residues. These compounds are usually assumed to be secondary metabolites, which serve as chemical defenses against disease and parasites. When such compounds are released into the rhizosphere, they are known as allelochemicals. The possibility exists to exploit allelochemicals for nematode control, and there have been many attempts to use this approach either by rotation, intercropping, or green manure treatments. Results have met with mixed success. Proof of allelochemical activity in field situations is difficult to obtain, but it is evident that some rotation crops are significantly better at reducing nematode populations than others. Rotations with non-host plants may simply deny the nematode population an adequate food source for reproduction (passive suppression), whereas allelopathic crops kill nematodes by the production of toxic compounds (active suppression). Progress toward sustainable agriculture should benefit from studies on allelopathic nematode control. However, grower acceptance of new plant-rotation strategies are based on economic and logistical considerations as well as efficacy. A potential practical application of allelopathic nematode control that involves using rapeseed as a green manure crop to reduce populations of Xiphinema americanum sensu lato in temperate orchards is presented. Key words: allelopathy, amendment, Brassica, glucosinolate, green manure, isothiocyanate, management, nematode, rapeseed, rotation, thioglucosidase, Xiphinema.

Effect of saponins on the growth and activity of rhizosphere bacteria

Abstract: Saponins are a group of steroid or triterpenoid glycosides and related chemicals (sapogenins: non-glycosylated) found in roots, shoots, seeds, and flowers of many plant species. Saponins are of agronomic interest because of allelopathic interference with plant growth (Oleszek and Jurzysta, 1987; Waller et al., 1993). Saponins can be released into the soil by secretion from roots and/or leaching from living or decaying plant material (Mishustin and Naumova, 1955; Oleszek and Jurzysta, 1987). Conservation management practices designed to maintain plant residues on the soil surface such as the use of cover crops and reduced tillage are rapidly being adopted by growers; thus the impact of these compounds and other natural products on crop productivity and soil and rhizosphere microbial ecology warrants study.

Response of Insect Herbivores to Multiple Allelochemicals Under Different Thermal Regimes

Abstract: Temperature and food quality are well known to constrain the growth of insect herbivores, but less is known about how these factors may interact. We examined the effects of three tomato allelochemicals (chlorogenic acid, rutin, and tomatine) and two thermal regimes (210: 10?C and 26?: 15?C, representing spring and summer respectively) on three insect herbivores: a Solanaceae specialist, Manduca sexta, and the polyphagous Hel- icoverpa zea and Spodoptera exigua. The alkaloid tomatine slowed development of the polyphagous H. zea, but the two phenolics had little effect. Development of the polyphagous S. exigua was faster with tomatine at the cool thermal regime, and slower with the two phenolics together at the warm thermal regime. All three of the tomato allelochemicals slowed development of the specialist M. sexta. Values of approximate digestibility (or assimilation efficiency) for the two polyphagous species spanned a range twice that of the Solanaceae specialist, increasing when allelo- chemicals were added to diet. Our techniques permitted us to separate pre- and post-ingestive effects of allelochemicals on mass gained, but we found complex interaction of allelo- chemicals and of temperature and allelochemicals. The effects of an allelochemical on larval performance often depended on the combi- nation of other allelochemicals in the diet. But the allelochemicals did not always have a negative effect, and multiple allelochemicals did not always have a more negative effect than a single allelochemical. Interaction between thermal regime and the allelochemicals was also common. For example, whether rutin had a negative, neutral, or positive effect on relative growth rate of S. exigua depended on thermal regime and presence or absence of chlorogenic acid. Often the negative effect of an allelochemical was greater at the warm regime than at the cool regime, but not consistently so. Another experiment showed that thermal regime did not affect allelochemical concen- tration in the diets. Over time (7 d), only tomatine concentration declined. Therefore, the interactive effects of thermal regime and allelochemicals on the insect herbivores were not an artifact of the experimental procedures. Overall, the results indicated that insect performance is not a simple function of tem- perature and food quality because interactions occur between these factors. They also suggest that the array of chemical defenses exhibited by a particular plant species may be shaped in part by temperature altering the efficacy of allelochemicals.

Allelopathic Influence of Germinating Seeds and Seedlings of Cover Crops on Weed Species

Abstract: Bioassays using binary mixtures that included a cover crop with known allelopathic potential and a weed species were employed to determine the importance of allelopathy compared to resource competition as interference mechanisms. Responses of weed species germinated with cover crops in a petri dish were measured. Interference between weed and cover crop seedlings was determined in a greenhouse experiment using the additive design, which included partitions to reduce above- and below-ground competition and used capillary mat subirrigation to control moisture and fertilizer availability. Germinating sorghum reduced radicle length of weeds, whereas germinating rye tended to increase weed radicle length. Methods limited above-ground competition, so likely interference mechanisms were below-ground competition and allelopathy. Germination with a cover crop had little effect on germination and shoot length of weeds. Increased density of rye but not of sorghum reduced growth of barnyardgrass seedlings. Reduced number of barnyardgrass leaves in the presence of rye was likely due to allelopathy. Suppression of barnyardgrass dry weight attributed to allelopathic interference by rye was successfully separated and compared to the combined effects of competition and allelopathy.

Experiments on bioassay sensitivity in the study of allelopathy

Abstract: The purpose of these experiments was to study the effects of various experimental procedures and conditions on bioassay sensitivity in allelopathic studies. The following factors were considered: bioassay methods, choice of test species, the effect of osmotic potential on germination and growth of the test species, growth in dark or in light and the effect of concentrating the extracts in vacuo. Extracts from rape and rye were used in the studies to act as allelopathic agents. Ryegrass appeared as the most sensitive test species when grown horizontally on quartz sand, while radish was the most sensitive test species when grown on filter paper in transparent boxes at a 45° angle. Root length was the most sensitive growth variable measured. Percent germination appeared a more sensitive measure than the speed of germination index, "S", when germinated seeds were counted after one and two days for radish and ryegrass, respectively. A rise in the osmotic potential affected germination more than root length, and radish appeared more sensitive to a rise in osmotic potential than ryegrass. A confounding of germination and root length inhibition may therefore, give misleading results.

Enzymatic oxidation products of allelochemicals as a basis for resistance against insects: effects on the corn leafhopper Dalbulus maidis.

Abstract: Oxidation products of com allelochemicals generated by peroxidases or tyrosinases were tested in 10% sucrose solutions for effects on the corn leafhopper Dalbulus maidis. Some reduction in feeding was noted with hydrogen peroxide (a cofactor for peroxidase). Significant reduction in feeding was noted with chlorogenic acid, ferulic acid, p-coumaric acid, and 6-methoxybenzoxazolinone (MBOA), but not rutin at 400 ppm in solution. Oxidation products of these compounds all caused significantly less feeding by the leafhoppers compared to the original compound. Oxidation products generated by peroxidase from ferulic acid and 6-methoxybenzoxazolinone caused significant mortality to the leafhoppers within 5 days. Thus, provided conditions are such that oxidizing enzymes and allelochemicals can interact due to damage by insects, resistance may be significantly enhanced by the oxidized products as opposed to the effects of the allelochemicals alone.

Use of a comparative approach to identify allelopathic potential and relationship between allelopathy bioassays and “competition” experiments for ten grassland and plant species

Abstract: Various allelopathy bioassays were used to evaluate the allelopathic potential of 10 grassland forage species against a common test (phytometer) species,Carduus nutans L. Aqueous extracts did not influenceC. nutans germination, although radicle elongation was often severely inhibited.C. nutans was strongly affected by shoot, but not root, leachates. Decomposing ground tissue had mixed effects, and often stimulated shoot production ofC. nutans. Calculation ofR2 (coefficient of determination) values between these results, and the results of previous experiments investigating the effects of the same 10 species onC. nutans emergence and development in field plots and glasshouse competition experiments frequently revealed strong, statistically significant relationships. Our results therefore provide correlative evidence for the importance of allelopathy in field conditions.

Gracilaria conferta and its epiphytes: 3. Allelopathic inhibition of the red seaweed byUlva cf.lactuca

Abstract: In a previous study (Svirski et al., 1993), it was found that growth inhibition ofGracilaria spp., when cultured in the presence ofUlva cf.lactuca, was not due to shading or nutrient depletion, but seemed to be caused by competition for inorganic carbon or some type of allelopathy. In the present study, we attempted to differentiate between these two possible influences by (1) growing the two algae in biculture under various conditions, but keeping inorganic carbon levels constant and measuring net photosynthesis, respiration and growth rates, and by (2) measuring growth rates ofGracilaria spp. in the presence of extracts derived from media previously used to growUlva cf.lactuca.

Endophytic bacteria of red clover as agents of allelopathic clover-maize syndromes

Abstract: The early growth effects of red clover endophytic bacteria on maize seedlings were examined in greenhouse trials. We found that endophytic bacteria from preceding clover ( Trifolium pratense L.) crops can be causal agents of the inhibitory allelopathic ‘clover-maize syndrome’. The effect was shown to be both direct (as in imbibition studies with bacterial suspensions of individual isolates) and indirect (as in leachate studies). Imbibition or watering with the crude leachate (leachate plus microorganisms) as opposed to filtered leachate (leachate minus microorganisms) derived from soil in which clover had been growing, prompted a reduction in the rate of emergence and growth of maize seedlings ( Zea mays L.) but not germination percentage. It is concluded that the inhibitory allelopathic response in clover-maize sequences is a side-effect of the competition between bacteria for the same ecological niche which usually results in temporary growth retardation.

Allelopathic effects on germination and seedling growth of clovers by endophyte-free and -infected tall fescue

Abstract: Reports of allelopathy by tall fescue (Festuca arundinacea Schreb.) on Trifolium species are inconsistent. Many tall fescue plants are infected with a fungal endophyte (Acremonium coenophialum Morgan-Jones & Gams), which may account for some of the inconsistencies. My objective was to investigate the allelopathic effect of extracts of endophyte-free (TF-E) and -infected (TF+E) tall fescue seeds on the seed germination and seedling growth (shoot, root, and root-hair length and root-hair density) of five Trifolium species (ball clover, T. nigrescens Viv.; crimson clover, T. incarnatum L.; red clover, T. pratense L.; subterranean clover, T. subterraneum L.; and white clover, T. repens L.). Extracts were prepared by passing 50 g of seed through a pulverizing mill, soaking the milled seed in 500 mL of deionized water, filtering, and sterilizing the solution. Differences among allelopathic effects for seed germination were attributed to legume species. Although the presenee of fungal endophyte had no effect on seed germination, germination of ball, crimson, and red clover seed was significantly reduced in extracts of tall fescue seed. Differences among allelopathic effects for shoot and root lengths were attributed to legume species. Seedling shoot length was significantly increased and root length was significantly decreased for clover seedlings grown in tall fescue extracts. Differences among allelopathic effects for root-hair length and density were attributed to species and substrate (TF - E vs. TF + E) differences. There was a 34% reduction in root-hair length and a 45% reduction in root-hair density for clover seedlings grown in seed extracts compared with seedlings grown in water. Seed germination and seedling shoot and root lengths inadequately expressed the subtle allelopathic effects of the fungal endophyte. Micromorphological characters, such as root hairs, may be more sensitive in detecting allelonathic effects.

Determination of allelopathic potential of a weed Pluchea lanceolata through a multifaceted approach

Abstract: The allelopathic potential of soils from four sites infested with the weed Pluchea lanceolate (DC.) C.B. Clarke (Asteraceae) was investigated. All sites had similar precipitation, similar crops, and weeds in addition to P. lanceolata. The objectives of this study were threefold: first, variations in the allelopathic effects of P. lanceolata infested soils on growth of three crops; second, soil phenolic content as a result of P. lanceolata infestation; and third, if the chemical characteristics and mycoflora of soils and biotic characteristics of P. lanceolata are responsible for the differences in allelopathic potential. Allelopathic effects of P. lanceolata infested soils were assessed on seedling growth of onion, cucumber, and turnip. Qualitative variation in the soil phenolic content from the four P. lanceolata infested sites was observed. No significant differences in soil mycoflora, soil nutrients, and P. lanceolata biotic characteristics were observed. Growth experiments showed mat crops demonstrate...

Factors influencing the allelopathic activity of the planktonic cyanobacterium Trichormus doliolum

Abstract: An axenic culture of Trichormus doliolum Bharadwaja, Komarek et Anagnostidis (Nostocales, Cyanophyta) showed growth inhibition of several axenic cyanobacteria and chlorophytes. Allelopathic activity was observed in both phosphorus-limited and -replete chemostat cultures. Phosphorus limitation led to a change in the composition of the released organic compounds and to increased allelopathic activity of the exudate. Allelopathic activity of exudates of the phosphorus-limited and -replete chemostat was confined to the same high-performance liquid chromatography fraction, indicating that the allelopathic compounds released may be similar if not identical. The exudates inhibited photosynthetic oxygen production and enhanced chlorophyll fluorescence in other cyanobacteria. Growth-inhibiting effects showed a linear dose dependency, indicating that even small concentrations of allelopathic compounds influenced the growth of other cyanobacteria and algae. A biomass of Trichormus doliolum 20 times less tha...

Novel anthelmintic compounds and molluscicides from medicinal plants.

Abstract: This review assesses the role that can be played by allelochemicals (bioactive secondary compounds) from medicinal and other plants in the control of human helminthic diseases. In the search for new anthelmintics among plant allelochemicals, 3 practical issues have considerable significance. They are the range and capacity of anthelmintic bioassays utilised in preclinical studies in vitro on plant extracts, the phenomenon of coexistent allelochemicals with overlapping activity spectra within single plants, and the problem of non-specific cytotoxins among plant allelochemicals. These topics are discussed in the context of the present absence of any clinically useful plant anthelmintics. In the search for new plant molluscicides for schistosomiasis control, the characteristics of a range of molluscicidal plants are measured against those of the synthetic molluscicide of choice, niclosamide, and against the postulated attributes of practically useful plant molluscicides.

Medicinal plants for suppressing soil-borne plant diseases. I. Screening for medicinal plants with antimicrobial activity in roots

Abstract: Most plants exhibit inhibitory and stimulatory biochemical interactions with other plants and microorganisms, referred to as “allelopathy.” Especially, through root exudates, higher plants are able to affect the microfiora in the rhizosphere. Production of biological active substances by higher plants that prevent phytopathogens (bacteria, fungi, and nema-todes) from infecting crops has been reported (Yoshihara et al. 1988; Schenk et al. 1991). In addition, many species of plants which have been widely used for medicinal purpose also exert an allelopathic effect (Fujii et al. 1991).

Role of allelopathy as a possible factor associated with the rising dominance ofBunias orientalis L. (Brassicaceae) in some native plant assemblages.

Abstract: Leaf extracts ofBunias orientalis were shown to inhibit seed germination of a variety of cultivar plant species and of species cooccurring withB. orientalis in the field. Root exudate solutions and leaf litter leachates ofB. orientalis were tested for their allelopathic activity using seedling growth assays. Additionally, in comparative seedling growth assays soil cores removed from denseB. orientalis stands were tested bimonthly for elevated allelopathic effects. The impact of root exudates on seedling growth was generally weak and varied between species. Similar results were obtained for the effect ofB. orientalis leaf litter leachates on seedlings grown in sand culture relative to the effect of leaf litter leachates of a plant species mixture. When soil as a growth substrate was used, no consistent differences in seedling growth were obtained between the two litter leachate treatments. In the soil core experiment seedlings grown in soil cores collected from a denseB. orientalis stand unexpectedly showed better performance than seedlings grown in soil cores collected from a nearby mixed plant stand withoutB. orientalis, at least in early spring and late autumn. Predominating nutrient effects are, therefore, assumed to conceal a potentially increased allelopathic effect of soil beneath denseB. orientalis stands. It is concluded that other factors than allelopathy must be investigated to explain the rapid establishment of dense stands of this alien plant species.

Allelochemicals in tomato leaves affect a specialist insect herbivore Manduca sexta negatively but with no ill effects on a generalist insect predator, Podisus maculiventris

Abstract: To understand the role of allelochemicals in tritrophic interactions, it is important to consider how allelochemicals affect both insect herbivores and their predators. In one experiment, a specialist insect herbivore (Manduca sexta: Sphingidae) was fed artificial diet either without allelochemicals, or containing a combination of allelochemicals found in tomato leaves (tomatine, rutin and chlorogenic acid). When fed artificial diet containing allelochemicals, the herbivores consumed less food, their developmental time was extended and their final weight was lower than those fed artificial diet without allelochemicals added. In another experiment, a generalist insect predator (Podisus maculiventris: Pentatomidae) was given prey (M. sexta) fed artificial diet either without allelochemicals, or with the combination of allelochemicals. The allelochemicals in prey diet did not affect nymphal growth, nymphal survivorship, adult female longevity, number of eggs produced, number of egg masses produced, developmental period of the eggs, viability of the eggs, or weight of the first instar progeny. Thus, this study documents a case in which a plant would benefit by producing allelochemicals because the specialist herbivore would consume less plant material and by ingesting the allelochemicals have poorer growth, and the predator would be unharmed by the presence of allelochemicals within the diet of its prey.

Interference factors responsible for resistance of forb-grass cover types to tree invasion on an electric utility right- of-way

Abstract: An investigation of factors responsible for re- sistance of forb-grass cover types to tree invasion was car- ried out from 1992 through 1994 on an electric transmission right-of-way (ROW) in central Pennsylvania. Unprotected seedspots and seedspots protected by wire cages were in- stalled on the ROW to investigate the effect of the important interference factors of wildlife depredation, plant competition, and allelopathy. This field study was supplemented by pot culture tests of the effect of plant competition, seedbed con- dition, and allelopathy on tree seed germination and seedling growth in an environment where wildlife depredation, soil moisture, frost damage, and insect and disease attacks were controlled. The major factors that interfered with tree seed germination and seedling growth were wildlife depredation and plant competition by the dominant plant species of the forb- grass cover type, namely, poverty grass (Danthonia spicata), rough goldenrod (Solidago rugosa), and hayscented fern (Dennstaedtia punctilobula).

Allelopathic potential of well water fromPluchea lanceolata-infested cultivated fields.

Abstract: Pluchea lanceolata, an allelopathic perennial weed, has an extensive deep root and rhizome system. The objective of the present study was to determine the allelopathic potential of well water collected from weed-infested cultivated fields. Results indicate that well water recovered fromP. lanceolata-infested cultivated fields inhibited the shoot growth of pea, chick pea, mustard, and wheat under greenhouse conditions. Two phenolic compounds, phenol and phloroglucinol, were isolated and identified from collected well water using UV spectroscopy. The allelopathic potential of the aqueous extract of the two compounds was determined by growth experiments with 104 M solutions of the compounds. As a consequence of repeated irrigation with well water fromP. lanceolata-infested fields, higher levels of phenolics can accumulate in the soil, which may contribue to increased interference to crop plants. The present study is of significance since it cautions on the use of well water for irrigating cultivated fields infested with the perennial allelopathic weed (P. lanceolata) with dense subterranean systems and emphasizes the importance of controlling such weeds in cultivated fields.