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Phytopathogens have characteristics that make them desirable candidates as biological control agents for aquatic weeds: 1. numerous and highly diverse, 2. easily disseminated and self-maintaining, 3. often host-specific, 4. non-pathogenic to animals and 5. capable of limiting populations without eliminating the species. Phytopathogens have been little investigated for the biological control of water weeds. Recent efforts have revealed several diseases with the potential for exerting a degree of control over populations of water hyacinth (Eichhornia crassipes), hydrilla (Hydrilla verticillata) and alligator-weed, (Alternanthera philoxeroides). These include a blight and leafspot of water hyacinth caused by Rhizoctonia solani and Cephalosporium zonatum respectively, a root and crown rot of water hyacinth of unknown cause, a virus-induced stunt of alligator-weed, a Penicillium lysogenic to hydrilla and a pythium-induced blight of hydrilla.

Stem cuttings of alligatorweed [Alternanthera philoxeroides (Mart.) Griseb.] were subjected to various light and chemical inhibitor treatments to obtain information about the physiological nature of the hypoxic quiescence induced by dark submergence. White or red light at 40 μE m−2 s−1 stimulated growth from submerged stem cuttings but far-red at 5 μE M−2 s−1 did not. Photo-system II inhibitors, such as 3-(3,4-dichlorophenyl) 1,1-dimethylurea (DCMU) at 1.4 × 10−5M or 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) at 10−5M, completely inhibited the growth that normally occurs in a submerged state under continuous white light at 40 μE m−2 s−1. These concentrations of DCMU or simazine did not reduce nonphotosynthetic growth from underwater nodes of emersed stem cuttings partially exposed to air in the light for 1 week. Hydrogen peroxide at 50 mg/1 added every other day partially relieved the simazine-induced inhibition of growth from submerged, illuminated cuttings. These data indicated that sprouting and early growth of submerged, illuminated alligatorweed depended on the oxygen produced by photosystem II to support respiration and to overcome hypoxic quiescence.

Leaves of Alternanthera philoxeroides, alligator weed, developed at a photosynthetic photon flux density (PPFD, light energy at wavelengths of 400 to 700 nm) of 790 ,umol sec-' m-2 (High Light) had less surface area, were thicker, had a higher maximum Pn (net rate of CO2 uptake), and required a higher PPFD for saturation of PnX than leaves developed at 160 ,umol sec-' m-2 (Low Light). Mesophyll thickness at Low Light was within 19% of maximum 2 days after emergence but at High Light, thickness increased 79% between 2 and 16 days after leafemergence. The ratio of mesophyll surface area to leaf surface area decreased during development in both light treatments; the ratio, however, was over 70% greater in fully expanded High Light leaves than in Low Light leaves. Maximum Pn expressed on a leaf surface area basis was 158% greater in High Light leaves than in Low Light leaves, but Pn was only 58% greater when expressed on a mesophyll surface area basis. It was estimated that fully expanded High Light leaves fixed 72% more CO2 per leaf (Pn expressed per unit surface area times the total surface area per leaf) than fully expanded Low Light leaves when Pn was measured at the PPFD leaves expanded under. Both High and Low Light leaves would fix about the same amount of CO2 per leaf when Pn was measured at 160 ,umol sec-' m-2 because the larger surface area of the Low Light leaves offset small differences in Pn

Based on studies with host-specific weed-feeding insects, approximately 11–13 years of research may be needed to develop a classical biological control program for a single weed species. This includes the initial assessment of the problem and a survey of indigenous natural enemies, foreign surveys, the study and clearance of the most promising control organisms, and up through initial release. Using estimates of the costs and benefits from the successful alligatorweed project (Alternanthera philoxeroides (Mart.) Griseb.), plus examples of several terrestrial biological control of weeds projects, further support for research on classical biological control is economically justified. In addition to the classical approach, biological control of weeds may also be implemented through the use of non-selective weed feeders (e.g., in the case of aquatic weeds, herbivorous fish, crayfish, snails) although periodic surveillance and manipulation are required to avoid unwanted side effects and optimize weed control. Information on the costs and benefits of specific biological control of weeds projects is lacking or sketchy, adding to the present difficulty of making an economic analysis of this method of weed control.

Alligator weed (Amaranthaceae), a species found in habitats varying in the amount of light received, was grown at four photosynthetic photon flux densities (PPFD) to determine the effect of PPFD on production and partitioning of biomass. After 56 days of growth, the average dry weight of plants at the highest PPFD (40 mol m-2 day-1) was greater than ninefold that of plants at the lowest PPFD (8 mol m-2 day-1). The relationship between PPFD treatment and plant dry weight on day 56 was linear. Among PPFD treatments, leaf area per plant was not as dissimilar as dry weight per plant was; as a result, the ratio of leaf area to plant dry weight tended to increase as PPFD treatment decreased. The highest PPFD treatment produced plants with the highest ratio of leaf dry weight to leaf area. Although the rate of leaf emergence was linear for all plants, the rate of leaf emergence was reduced in the two lowest PPFD treatments. We estimated that the efficiency of dry weight production for PPFD received increased at ...

Larvae of the flea beetle Disonycha argentinensis Jacoby from Argentina completed their development and produced adults on only 3 of 57 South American plant species tested: its natural host Alternanthera philoxeroides (Mart.) Griseb. (alligatorweed), which is a pest in North America; A. paronychioides St. Hilaire, which does not occur in North America; and Beta vulgaris L. Cicla group (leaf beet). The few eggs laid by adults reared on leaf beet did not hatch. In the laboratory, adults lived an average of 147 days (maximum 306 days) and females laid an average of 409 eggs each. A generation in the laboratory (at mean temperatures of 25.9°C for immature and 22.6°C for adults) required 49 days: 4.0 days for the egg, 10.0 days for the feeding larva, 11.0 days for the prepupa and pupa, 11.4 days for pre-ovipositing adults, and 12.6 days for adults from beginning to peak oviposition. The larvae had three instars and pupated under litter. Both adults and larvae fed on the youngest leaves and the growing bud, but not on flowers and little on stems. In field cages, females oviposited under litter at the base of the plants. Populations were low in the field.

The herbicide MSMA is used extensively for grass control in non‐edible crops and for chemical mowing along roadside rights‐of‐way. Herbicide may reach adjacent water bodies either by accidental application or by runoff from sprayed plots. This study utilized floating, submerged and rooted plant species in hydroponic solution to monitor the uptake of trace levels of the herbicide from aqueous concentrations of 5 and 10 μg/ml, respectively. Plant species included Eichhornia crassipes, Ceratophyllum demer‐sum, Alternanthera philoxeroides and Hygrophila lacustris. Duplicate plants were analyzed over the 6 weeks of the study using the silver diethyldithiocarbamate (SDDC) procedure. Rates of uptake, partitioning of the herbicide in roots, stems and leaves and bioaccumulation ratios were determined for each plant species.

An experimental approach was taken to examine the processes of detritus decomposition in river sediments.Addition of macrophyte detritus (Alternanthera philoxeroides (Mart.) Griseb) to river sediment resultedin an increase in carbon mineralization from a “sbasal” rate of 200 up to 500 mg C m−2 d−1.Carbon mineralization after addition of oak detritus was only slightly higher than mineralization in sediments thatreceived no addition (∼ 200 mg C m−2 d−1). Bacterial biomass and production in sediments \s+ alligator-weedwere higher than in sediments + oak or zero-addition. In these experiments the major fate of addedalligatorweed was mineralization. For alligatorweed detritus, microbial metabolism depletes organic carbonrather than leading to increases in food quality. Therefore, a pulse input of alligatorweed detritus would notbe available as a long-term source of organic carbon. Oak detritus was not rapidly decomposed, and sopersists in these sediments for a longer period.

The post-emergent herbicide, MSMA, is used extensively for weed control in non-edible crops and for chemical mowing along roadside rights-of-way. Herbicide may gain access to adjacent water bodies by accidental application or by runoff from sprayed plots. This study utilized floating and rooted plant species in hydroponic solution to monitor the uptake of trace levels of the herbicide from an aqueous concentration of 24 μg/ml. Plant species evaluated included Eichhornia crassipes, Alternanthera philoxeroides, Hydrophila lacustris and Lemna minor . Plants were analyzed for total arsenic over the 6 weeks of study using the silver diethyldithiocarbamate (SDDC) procedure. Bioaccumulation ratios were then determined for each plant species.

Propagules (stem cuttings) of alligatorweed [Alternanthera philoxeroides (Mart.) Griseb.] were subjected to various treatments of submergence, emergence, light, dark, and oxygen to relate hypoxia to the suppression of alligatorweed growth by dark submergence. In the dark, submergence completely inhibited alligatorweed growth. A nitrogen atmosphere inhibited growth from emersed propagules in the dark. The suspension of growth by dark submergence was relieved by light (40 μ einsteins/m2× s photo-synthetically active radiation), emergence (whereby air is transported to underwater nodes via the aerenchyma), or exposure to 100 mg · l-1 of hydrogen peroxide solution renewed at 48-h intervals. Suspension of growth by a nitrogen atmosphere was relieved by inclusion of 16% oxygen in the ambient atmosphere. Dark to light transfers showed that the suspension of growth was immediately relieved if the requisite conditions were restored; this phenomenon, as described, thus appears to be hypoxic quiescence. The suppression of growth of two other amphibious species, mild smartweed (Polygonum hydropiperoides Michx.) and creeping water-primrose (Jussiaea repens L. var. glabrescens Ktze.), by dark submergence suggests that hypoxic quiescence may be a factor in the life history of amphibious species other than alligatorweed.

The Agricultural Research Service of the USDA has been actively engaged in research on the biological control of aquatic weeds since 1959. Research emphasis until 1967 was on alligatorweed, Alternanthera philoxeroides (Mart.) Griseb. As a result of this research, three species of insects from Argentina were released in the southeastern United States. Alligatorweed control with these natural enemies has been variable; but indications are that control will be substantial over most of the range of the weed. One species of weevil, Neochetina eichhorniae Warner, has been released against water hyacinth, Eichhornia crassipes (Mart.) Solms, in the USA as a result of research in Argentina. A second closely related species, N. bruchi Hustache, is presently undergoing final clearance procedures. Several other arthropods are being studied in Argentina as possible biological control agents of water hyacinth. A USA sponsored programme in Yugoslavia under the direction of Dr M Lekic resulted in the discovery o...

Using K‐rich plants as biological K fertilizer is an innovation in physiological ecology of plant nutrition and a possible solution to the problem of K deficiency in soils and crops in China and other developing countries. Since 1978, over 70 water plants, herbs and a few crops have been tested, of which 20 had a higher K content (>2.5% DM) than rice straw (1.67–2.5% DM). They were defined as K‐rich plants. Alligator alternanthera [Alternanthera philoxeroides (Mart.) Griseb] contains as much as 9.75% K on a dry matter basis. The results of pot cultures and field trials carried out in 1982–1984 showed that the application of dried Alligator alternanthera at the rate of 1500 kg/ha increased rice yields by 17.4% and was equally effective as or even more effective than KCl or rice straw. It should be noted that biological K fertilizers are superior to chemical ones in improving crop yield and quality because K‐rich plants not only supply crops with K but also with other nutrients and organic matter. ...

Pressure volume curves for Alternanthera philoxeroides (Mart.) Griseb. (alligator weed) grown in 0 to 400 millimolar NaCl were used to determine water potential (Ψ), osmotic potential (ψs), turgor potential (ψp) and the bulk elastic modulus (e) of shoots at different tissue water contents. Values of ψs decreased with increasing salinity and tissue Ψ was always lower than rhizosphere Ψ. The relationship between ψp and tissue water content changed because e increased with salinity. As a result, salt-stressed plants had larger ranges of positive turgor but smaller ranges of tissue water content over which ψp was positive. To our knowledge, this is the first report of such a salinity effect on e in higher plants. These increases in e with salinity provided a mechanism by which a large difference between plant Ψ and rhizosphere Ψ, the driving force for water uptake, could be produced with relatively little water loss by the plant. A time-course study of response after salinization to 400 millimolar NaCl showed Ψ was constant within 1 day, ψs and ψp continued to change for 2 to 4 days, and e continued to change for 4 to 12 days. Changes in e modified the capacity of alligator weed to maintain a positive water balance and consideration of such changes in other species of higher plants should improve our understanding of salt stress.

In the decussate plants Alternanthera philoxeroides and Hygrophila sp. the opposite axillary bud primordia are of unequal size from the time of their inception ; the larger or + buds lie along one helix and the smaller or buds along another (helicoidal system). In decapitated plants of Alternanthera both buds grew out, but unequally; if the node was vertically split growth of the two shoots was more equal, and if the + buds were excised growth of the shoots approximately equalled that of control + shoots. In decapitated shoots of Hygrophila grown in sterile culture only one bud, the + or larger one, grew out at each of the upper nodes. In excised cultured nodes, also, only the + bud grew out; but if the nodes were split longitudinally both buds grew out, initially rather unequally. These experiments support the view that the regulation of branching in these species has two components, apical dominance and the dominance of the larger (+) bud over the smaller ( ) bud at the same node. The restriction of growth potentiality imposed on the bud is not permanent but can be modified. Further correlative effects on bud outgrowth include those of the subtending leaves and of buds at other nodes.

The active delta of the Mississippi River was sampled in August 1968 to determine plant species composition, plant coverage, and soil and water chemistry. Hurricane Camille struck this area in August 1969, with winds in excess of 200 km/h and tides raging upward to 5.2 m above MSL. The delta was resampled 2 weeks following the hurricane to evaluate the immediate effects on vegetation, soil, and water, and again 1 year after the hurricane to determine the recovery rate of vegetation. The hurricane resulted in a drastic reduction of vegetation. Regrowth was rapid in the delta marshes and after 1 year plant coverage approached pre—hurricane levels of abudance; however, recovery was slower in ponds and lakes. The loss of vegetation was mainly a result of the sweeping action of wind and water, and plants were either uprooted or ripped apart and carried away by the current. Water salinity increased with the hurricane but declined by the following year and appeared to have only slight effect on marsh vegetation. Plant species caried in their response to the hurricane. Bacopa monnieri showed practically no effect, and Phragmites communis and Spartina alterniflora were reduced only slightly. Myriophyllum spicatum, Panicum repens, and Alternanthera philoxeroides were greatly reduced by the storm: and after 1 year, only Alternanthera philoxeroides showed significant recovery.

Vogtia malloi Pastrana was introduced into the United States from Argentina in April 1971 as a biological control agent of alligatorweed, Alternanthera philoxeroides (Mart.) Griseb. Vogtia were released at 10 different locations from Wilmington, North Carolina, to Ft. Pierce, Florida. Populations have become established at four of these release sites. Population studies conducted at the Lake Alice release site, on the University of Florida campus, Gainesville, Florida, indicated the new population dispersed randomly over the stand of alligatorweed. Vogtia reduced the number of aerial alligatorweed stems per square foot from 52.5 to 4.0 in four generations. The alligatorweed did not have a competitive advantage by the end of the fourth generation; mixed vegetation was replacing the deteriorating mats of alligatorweed.

Occurrence, coverage and chemical constituents of aquatic flora were studied in two Indian ponds over a period of 39-month in order to gain an insight into their associations and infestation for implications in conservation and management. Species diversity was recorded in presence of two invasive species ( Alternanthera philoxeroides (Martius) Griseb. and Lemna aequinoctialis Welwitsch). These species should be managed in view of their beneficial uses. Nymphaea pubescens Willd, a threatened species, was recorded. Positive association of Nymphoides hydrophylla (Loureiro) O. Kuntze with Alternanthera philoxeroides and Vallisneria spiralis L. showed that spatially separated habitats are useful for conservation. Azolla pinnata R. Brown, an useful species and Rotala rotundifolia (F. Hamilton ex Roxburgh) Koehne, an uncommon species, were able to produce high coverage in their brief occurrence - important for their conservation. Similar feature as observed in Cladophora glomerata (L.) Kutz and Hydrodictyon reticulatum (L.) Lagerh. is useful for management of these species due to their negative impacts. Key words: Aquatic flora, Species composition, Occurrence, Coverage, Nitrogen, Phosphorus, Management DOI: 10.3329/bjpt.v14i1.519 Bangladesh J. Plant Taxon. 14(1): 13-24, 2007 (June)

The host specificity of Amynothrips andersoni O'Neill was determined in a series of feeding behavior and starvation tests conducted in the laboratory in Argentina and Uruguay. The host plant spectrum tested involved 21 different plant species belonging to 5 families and 11 genera. A slight amount of adult feeding (1–2%) was obtained on the test plant, Polygonum aviculare L., but was not observed to occur on field plants. Observation and study of 46 plant species in nature also demonstrated an absence of thrips or their feeding. The results of these laboratory tests and observations confirm earlier observations indicating that this thrips is associated only with Alternanthera philoxeroides (Mart.) Griseb. and A. hassleriana Chod.

Pang Qi Ju (Alternanthera philoxeroides Griseb), a Chinese herb, used for the prevention and treatment of respiratory diseases, was tested in this laboratory for its inhibitory effect on the growth of several virus strains in tissue culture and chick embryos. It was found that its alcoholic infusions and tablets made of these infusions could inhibit the growth of several virus strains, including influenza virus types A, B and parainfluenza virus type I (Sendai strain). In addition, they could inhibit the growth of 2 other virus strains (A1/W.M./ Feng/81, and A3/W.M./9/82), which were isolated during the 2 consecutive epidemic outbreaks in 1981 and 1982 in Wuhan. The infusions of herbs of 3 different origins manufactured by the same procedure exerted similar inhibitory effect. Even after the removal of tannic acid by gelatin treatment their inhibitory effect remained unaffected. It is suggested that this herb may contain some antiviral active principles which remain quite stable even through pharmaceutical processing. Clinically, this herb has been used to treat influenza patients on a double blind basis during the 2 epidemic outbreaks and the results obtained were in conformity with those of laboratory tests.

Phenology and carbohydrate literature for waterhyacinth (Eichhornia crassipes (Mart.) Solms), hydrilla (Hydrilla verticillata L.f. Royle), Eurasian watermilfoil (Myriophyllum spicatum L.), and alligatorweed (Alternanthera philoxeroides (Mart.) Griesb) was surveyed to assess the feasibility of using phenology/carbohydrate relationships for improving control tactics. Many studies have examined phenology of waterhyacinth, hydrilla, and Eurasian watermilfoil, but not alligatorweed. Phenology of monoecious and dioecious biotypes of hydrilla differs in growth pattern and propagule development. The monoecious biotype appears to be better adapted than the dioecious biotype to live at Northern latitudes because of its ability to produce more tubers and turions at lower water temperatures. A few investigations involving Eurasian watermilfoil and alligatorweed suggested that control efforts directed at the low ebb of carbohydrates will decrease biomass production. Little information on carbohydrate partitioning has been reported for waterhyacinth and hydrilla. Previous studies of these plants have not evaluated the role of starch reserves for plant survival. Environmental factors (e.g., temperature, light, and nutrients) have been shown to influence phenology and, by inference, carbohydrate partitioning. How these factors control carbohydrate partitioning in these plants is unknown. Phenological and carbohydrate relationships have not been fully developed to allow plant control programs to take advantage of weak points in a plant's life cycle. Keywords: Weed control; Aquatic weeds.

Alternanthera philoxeroides, alligator weed, was grown at five different NaCl concentrations to determine the effect of salinity on factors related to the net rate of CO(2) uptake (P(n)). Over the range of 0 to 400 millimolar NaCl, P(n) declined 51%. Stomatal conductance declined in parallel with P(n) and as a result there was no reduction in intercellular CO(2) concentration and therefore no reduction in the amount of CO(2) available for photosynthesis. The CO(2) compensation point did not change with salt stress. Increases in leaf thickness tended to compensate slightly for the negative effects of salinity on leaf cell metabolism, at least in relation to P(n). On a mesophyll cell area basis, soluble protein was relatively constant in leaves developed at 100 to 400 millimolar NaCl while total chlorophyll decreased at all salinities. Dry weight production and P(n) were closely correlated in alligator weed grown at different salinities. Plants produced less leaf area per unit dry weight as salinity increased, which may aid in water conservation.

Proteins extracted from the leaves of Alternanthera philoxeroides, Lemna minor, and Pistia stratiotes were evaluated for their nutritional quality using rat feeding experiments. It was found that a...

Techniques were developed for evaluating herbicides on submersed, floating, and emersed aquatic weeds. Among 75 herbicides evaluated on three species of submersed weeds only 1:1′-ethylene-2:2′-dipyridylium (diquat); 1:1′-dimethyl-4:4′-dipyridylium (paraquat); di-N,N-dimethylcocoamine salt of 3,6-endoxohexahydrophthalic acid (endothal); and acrylaldehyde (acrolein) gave 85 percent or better control at 1 ppmw in still-water tests. Only acrolein and the di-N,N-dimethylcocoamine salt of endothal were effective on submersed weeds at 1 ppmw in the limited-exposure test. The evaluation of 17 herbicides on three species of floating aquatic weeds indicated that diquat was effective when applied at rates of 1 or 2 lb/A. The tertiary fatty acid amines of 2,4-dichlorophenoxyacetic acid (2,4-D) were more effective on floating weeds than an ester of 2,4-D. Many of the 78 herbicides evaluated on alligator-weed (Alternanthera philoxeroides (Mart.) Griseb.) killed the tops, but only two retarded the sprouting of underwater nodes longer than 6 weeks. Applications of 20 lb/A of 2-(2,4,5-trichlorophenoxy)-propionic acid (silvex) in two formulations retarded sprouting of underwater nodes for 8 weeks.

Alternanthera philoxeroides (Mart.) Griseb., a South American weed of the family Amaranthaceae, has been found in the lakes and water pools in the eastern parts of India, namely, West Bengal and Bihar. This species was introduced long ago in the tropics of the Old World, but its introduction into India has taken place during late years. In 1875, Otto Kuntze found this species growing in the vicinity of Java, where it has now become established in stagnant or slow-moving water1,2. In the Calcutta Herbarium there is a specimen from Victoria Lake in Rangoon district, Burma, collected in 1932 by C. E. Parkinson. This note is probably the first record of its occurrence on the Asiatic mainland. Apparently the species has made further ingress in Eastern India. Like several other American weeds, it seems probable that a few viable seeds of this species might have reached India along with some packing material during the Second World War. This is conceivable in view of the fact that this species was collected for the first time in India near an aerodrome at Calcutta. During recent years, a large number of neotropical weeds have been found to naturalize on Indian soil and spread like wildfire3. Further, in this species reproduction takes place vegetatively by means of subterranean shoots, and thus under favourable conditions it spreads rapidly, forming dense masses.

Silvex, [2-(2,4,5-trichlorophenoxy)propionic acid], impregnated (20% ae) on clay granules, applied at a rate as low as 20 lb/A ae gave excellent control of well-rooted alligatorweed [Alternanthera philoxeroides (Mart.) Grieb] growing in less than 18 inches of water. The 2-ethylhexyl ester of silvex was more effective than the potassium salt. Silvex was not effective on floating-mat alligatorweed or in water over 18 inches deep.