The effect of the armored scale,Rhizaspidiotus donacis (Hemiptera: Diaspididae), on shoot growth of the invasive plant Arundo donax (Poaceae: Arundinoideae)

The effect of feeding by the armored scale, Rhizaspidiotus donacis (Leonardi, 1920) (Hemiptera: Diaspididae) on the growth of the plant Arundo donax L. (Poaceae) was evaluated under field conditions in its native range. The study was designed to evaluate the impact of R. donacis, a candidate agent for biological control of A. donax which is invasive in arid riparian ecosystems of the Southwestern USA and Mexico. The study was carried out at five A. donax sites in the Province of Alicante, Spain, differing in altitude and climate. At each site, 30 infested lateral shoots were selected and 15 were randomly treated monthly with imidacloprid insecticide. Shoot lengths were measured monthly over a 1-year period in a comparative growth analysis. Shoots infested with R. donacis had an over 2-fold reduced growth rate as compared to treated shoots. Growth of shoots varied by site, and the effect of R. donacis on growth was most pronounced in the late spring, when mature females produced first instar scale crawlers. The impact of R. donacis on A. donax growth under field conditions in the native range, combined with its narrow host specificity, indicate that R. donacis is a promising candidate for biological control of A. donax in North America and other areas invaded by this weed.     

Evaluation of Spanish Arundo scale Rhizaspidiotus donacis (Hemiptera; Diaspididae) survival and fecundity on three new world genotypes of Arundo donax (Poaceae; Arundinoideae)

A pre-release evaluation of survival and fecundity of the arundo scale, Rhizaspidiotus donacis, was conducted on three invasive genotypes of the riparian weed, Arundo donax. The three A. donax genotypes were collected from Laredo, Austin and Balmorhea, TX, which represented the majority of the genotypic diversity found in Texas watersheds. Although R. donacis developed on all three genotypes of the plant, the Austin A. donax genotype, followed by the Laredo genotype, were the most suitable in terms of the size of first-generation immature and adult scale populations that developed after crawler release. Both the Laredo and Austin genotypes of A. donax are likely to be of Spanish origin and are close genetic matches with scale's original host plant genotype in Alicante, Spain. In comparison, survival was lowest on the phylogenetically distant genotype of A. donax from Balmorhea, TX. Although the population size of settled, immature second-generation scales varied in a manner similar to that of the first generation, the fecundity of isolated first-generation females was not significantly different across the three plant genotypes, suggesting that R. donacis is not a genotype specialist in terms of nutrient assimilation for reproduction. Rather, differences in genotype suitability affect rates of success of crawler settling. These results indicate that selection of scale genotype from the native range may have a moderate influence on the success of R. donacis and ultimately the biological control programme.     

Evaluation of biogeographical factors in the native range to improve the success of biological control agents in the introduced range

Biogeographical factors associated with the invasive weed Arundo donax were evaluated at 22 different locations in four countries in its native range in reference to its key herbivore, an armoured scale insect, Rhizaspidiotus donacis. Data on climate, plant health and quality, soil conditions and anthropogenic influences were analysed for each site and compared to populations of R. donacis. Climate modelling from location data in Spain and France accurately predicted the native range of the scale in the warmer, drier parts of Italy and Greece and was used to predict its distribution in North America. Presence of the scale was not associated with specific soil type or characteristics. However, it was positively associated with a higher percentage of dead stems and significantly lower biomass of A. donax. Micronutrient sampling using leaf material found that sulphur was negatively correlated with aluminium and positively correlated with boron for scale density. Disturbance of field sites by cutting and/or addition of supplemental irrigation during summer appeared to disrupt the synchronised seasonal phenology of A. donax and R. donacis, leading to more robust stands. These biogeographical factors from the native range indicate that R. donacis should have the greatest impact in warm, dry climates in the introduced range where A. donax is undisturbed.     

Impact of the Arundo scale Rhizaspidiotus donacis (Hemiptera: Diaspididae) on the weight of Arundo donax (Poaceae: Arundinoideae) rhizomes in Languedoc southern France and Mediterranean Spain

Arundo donax L. (Poaceae) is native to Mediterranean Europe and invasive in the Rio Grande Basin of North America. Rhizomes from nine sites in France and Spain infested with a candidate control agent, the armoured scale Rhizaspidiotus donacis (Hemiptera: Diaspididae) weighed 50% less than those from nine sites without scale.     

Host range of the European leaf sheath mining midge,Lasioptera donacis Coutin (Diptera: Cecidomyiidae), a biological control of giant reed,Arundo donax L.

The fundamental host range of the arundo leafminer, Lasioptera donacis a candidate agent for the invasive weed, Arundo donax was evaluated. L. donacis collects and inserts spores of a saprophytic fungus, Arthrinium arundinis, during oviposition. Larvae feed and develop in the decomposing leaf sheath channel tissue. Thirty-six closely related and economic grass species along with several key habitat associates were evaluated in no-choice tests. L. donacis and its associated saprophyte completed development only on A. donax, in concurrence with published reports from its native range in Mediterranean Europe. The arundo leafminer feeding leads to premature defoliation, constituting a different mode of attack on the host plant as compared to two previously released insects, the arundo wasp and arundo scale, which feed on shoot tips and rhizomes, respectively. Defoliation of A. donax is expected to increase light penetration into stands of A. donax which increases visibility for law enforcement, reduces the survival of cattle fever ticks, and enhance recovery of the native riparian vegetation along the Rio Grande and other habitats where this weed is invasive.     

Ecological significance of wing polymorphism in Fulgoroidea which inhabit tidal salt marshes

• 1 The vegetation of New Jersey tidal salt marshes is composed primarily of two grasses, Spartina patens, which occupies a narrow elevational zone of high marsh and varies little in structure from site to site, and Spartina alterniflora, an intertidal species which occurs as two spacially separated growth forms (tall and short). Fulgoroids, polymorphic for wing length, inhabit these grasses.
• 2 Populations of the common fulgoroid inhabiting short form S.alterniflora were composed of equal numbers of macropters and brachypters. Mesothoracic wings of brachypters were subequal in length to the abdomen allowing for short but inefficient flights compared to macropters.
• 3 Fulgoroids residing in S.patens produced mostly brachypters having small meso-and vestigial metathoracic wings and were incapable of flight.
• 4 Brachypter density of all fulgoroids was correlated with the seasonal increase in biomass of the host grass, while macropter density was not.
• 5 Peak macropter density occurred shortly before maximum biomass of the host grass was attained.
• 6 The production of macropterous forms was correlated with high levels of crowding incurred during nymphal stages.
• 7 Spatial and temporal variation in the structure of the host grasses and habitat reliability are suggested as important factors dictating the wing-polymorphism strategies of fulgoroids.

     

Tripius gyraloura n. sp. (Aphelenchoidea: Sphaerulariidae) parasitic in the gall midge Lasioptera donacis Coutin (Diptera: Cecidomyiidae)

A new nematode, Tripius gyraloura n. sp., is described from the arundo gall midge, Lasioptera donacis Coutin (Diptera: Cecidomyiidae). This gall midge is being considered as a biological control agent for use in North America against the introduced giant reed Arundo donax (L.) (Poaceae: Cyperales). Thus the present study was initiated to investigate a nematode parasite that was unknown at the time studies with L. donacis were initiated. The new species has a rapid development in the fly host and the mature parasitic female nematodes evert their uterine cells in the hosts’ hemolymph. Because large numbers of nematodes sterilise the host, eradication of the parasite from laboratory colonies of the midge may be necessary before populations of the fly are released.     

Phenotypic plasticity of <Emphasis Type="Italic">Spartina alterniflora</Emphasis> and <Emphasis Type="Italic">Phragmites australis</Emphasis> in response to nitrogen addition and intraspecific competition

Phenotypic plasticity of the two salt marsh grasses Spartina alterniflora and Phragmites australis in salt marshes is crucial to their invasive ability, but the importance of phenotypic plasticity, nitrogen levels, and intraspecific competition to the success of the two species is unclear at present. Spartina alterniflora Loisel. is an extensively invasive species that has increased dramatically in distribution and abundance on the Chinese and European coasts, and has had considerable ecological impacts in the regions where it has established. Meanwhile, Phragmites australis Cav., a native salt marsh species on the east coast of China, has replaced the native S. alterniflora in many marshes along the Atlantic Coast of the US. This study determined the effects of nitrogen availability and culm density on the morphology, growth, and biomass allocation traits of Spartina alterniflora and Phragmites australis. A large number of morphological, growth, and biomass parameters were measured, and various derived values (culm: root ratio, specific leaf area, etc.) were calculated, along with an index of phenotypic plasticity. Nitrogen addition significantly affected growth performance and biomass allocation traits of Spartina alterniflora, and culm density significantly affected morphological characteristics in a negative way, especially for Spartina alterniflora. However, there were no significant interactions between nitrogen levels and culm density on the morphological parameters, growth performances parameters, and biomass allocation parameters of the two species. Spartina alterniflora appears to respond more strongly to nitrogen than to culm density and this pattern of phenotypic plasticity appears to offer an expedition for successful invasion and displacement of Phramites australias in China. The implication of this study is that, in response to the environmental changes that are increasing nitrogen levels, the range of Spartina alterniflora is expected to continue to expand on the east coast of China.     

The effect of plant- and parasitoid-induced egg mortality on the interspecific distribution of an oligophagous herbivore

Plant-mediated egg mortality varied greatly for the oligophagous leafhopper, Carneocephala floridana, a common inhabitant of the salt marshes along Florida's Gulf coast. In the laboratory, survivorship from egg to first instar was generally greater on two herbaceous plants. Borrichia frutescens and Salicornia virginica (80 and 81% respectively) than it was on two grasses, Distichlis spicata and Spartina alterniflora (41 and 77% respectively). Although C. floridana laid significantly more eggs per clutch on Sp. alterniflora than on the two herbaceous species, this increase in egg number was offset by the higher mortality of eggs laid on this species. The greatest source of identifiable plant-mediated egg mortality was death due to desiccation of the leaf tissue surrounding the egg clutch. In addition, field experiments in which the four host species were infested with eggs of C. floridana at natural densities consistently yielded higher parasitism rates by two mymarid wasps on the grasses, regardless of the background plants. C. floridana switches host plants seasonally, using the grass species mainly during the winter months, when the herbaceous species experience a substantial dieback. The herbaceous species are nutritionally superior to the two grass species as a food source for C. floridana. C. floridana reared on the herbs produce larger, more fecund, adults than they do on the grasses (Rossi 1991). However, during cold winter snaps the grasses, while less attractive, may provide the most abundant nutritional and ovipositional resources available to C. floridana. The results of this study indicate how variable rates of plant-and parasitoid-mediated egg mortality may work synergistically with the interspecific nutritional status of the plants to explain host switching for this insect.     

Impact of the biological control agent Tetramesa romana (Hymenoptera: Eurytomidae) on Arundo donax (Poaceae: Arundinoideae) along the Rio Grande River in Texas

Five years post-release of the arundo gall wasp, Tetramesa romana, into the riparian habitats of the lower Rio Grande River, changes in the health of the invasive weed, Arundo donax, or giant reed, have been documented. These changes in plant attributes are fairly consistent along the study area of 558 river miles between Del Rio and Brownsville, TX, and support the hypothesis that the arundo wasp has had a significant impact as a biological control agent. Plant attributes were measured prior to release in 10 quadrats at each of 10 field sites in 2007, and measured again at the same undisturbed sites, 5 years after the release of T. romana, in 2014. Above ground biomass of A. donax decreased on average by 22% across the 10 sites. This decline in biomass was negatively correlated to increased total numbers of T. romana exit holes in main and lateral shoots per site in 2014 compared to 2007. Changes in biomass, live shoot density and shoot lengths, especially the positive effect of galling on main and lateral shoot mortality, appear to be leading to a consistent decline of A. donax. Economically, this reduction in A. donax biomass is estimated to be saving 4.4 million dollars per year in agricultural water. Additional impacts are expected as populations of the wasp increase and as other biological control agents such as the arundo scale, Rhizaspidiotus donacis, become more widespread.     

Olfactory responses of Cotesia flavipes (Hymenoptera: Braconidae) to target and non-target Lepidoptera and their host plants

The attraction of Cotesia flavipes Cameron to volatiles from a range of non-target lepidopteran larvae and their host plants (grasses and trees) or food substrate (honeycomb) was evaluated using a Y-tube olfactometer. The non-target host larvae used in the study included Galleria mellonella (L.), Charaxes cithaeron Felder, Bombyx mori L., and Eldana saccharina Walker. The target insects, Chilo partellus (Swinhoe) and Chilo orichalcociliellus (Strand), were used as controls. Host plants included Afzelia quanzensis Welw., Morus alba L., Cyperus papyrus L., Pennisetum purpureum Schumach, and Zea mays L. The response of C. flavipes to volatiles from the non-target larvae and their food was variable. Attraction to uninfested maize was not significantly different from uninfested plants of non-target hosts or honeycomb. Only maize and honeycomb were preferred over clean air. C. partellus infested maize plants were significantly more attractive than M. alba, A. quanzensis, and honeycomb infested with their herbivores. Infested maize and C. papyrus were more attractive than uninfested ones. When odors from naked larvae were tested, C. flavipes preferred odors from C. partellus larvae over those of E. saccharina and C. cithaeron and larvae of C. partellus and G. mellonella were preferred to clean air. The implications of these findings for biological control and its effect on non-target organisms are discussed.     

Biomass and aboveground production of four angiosperms in Cantabrian (N. Spain) salt marshes

New data of aboveground biomass and production of four angiosperms over a 12 month period for the Cantabrian Sea salt marshes (Bay of Biscay, N. Spain) are presented. Based on harvest methods, maximum aboveground total biomass values for Spartina maritima (Curtis) Fernald, Spartina alterniflora Loisel, Salicornia ramosissima J. Woods and Halimione portulacoides (L.) Aellen were 628, 1109, 480 and 1267 gm^-2, respectively. We conclude that although a slight latitudinal gradient in biomass is revealed in the data compiled with reference to some of the species studied, more work is neccesary in order to assess the potential productivity of these ecosystems on the coasts of Europe and/or to make comparisons with salt marshes of the American coasts. Annual net aerial primary production estimates using Smalley's method were: 296, 1160, 486 and 952 gm^-2yr^-1, for Spartina maritima, Spartina alterniflora, Salicornia ramosissima and Halimione portulacoides, respectively. These results together with turnover rate estimates point to the lack of vigour of the native S. maritima, while the exotic S. alterniflora, which seems to be spreading along the Cantabrian estuaries, behaves like a veritable pionner throughout the low marshes in this region.     

Enhanced production of pink pineapple mealybug,Dysmicoccus brevipes (Hemiptera: Pseudococcidae)

A mass rearing program was developed for the pink pineapple mealybug (PPM), Dymsicoccus brevipes (Cockerell) (Hemiptera: Pseudococcidae), to provide host material for producing the encyrtid parasitoid Anagyrus ananatis (Gahan). PPM individuals produce honeydew that accumulates on heavily infested squash and entraps crawlers and older instars. A new protocol was tested to reduce accumulated honeydew with minimal mortality to PPM. Butternut and kobocha squash were placed in rearing containers and covered with coarse vermiculite (>2.36?mm diameter) after being infested with PPM. Use of vermiculite removed the honeydew from the squash surface. PPM produced using vermiculite were easily harvested from the host squash, but mealybugs produced on squash without vermiculite were embedded within the honeydew. When individual kobocha squash fruit were inoculated with 300–400 mature PPM adults (>0.6?mm length), about 700 adult PPM (appropriate for A. ananatis production) were produced for each dollar value (USA) of squash fruit (i.e., ～1500?PPM per individual squash).     

Reduction of riparian arthropod abundance and diversity as a consequence of giant reed (Arundo donax) invasion

The non-indigenous perennial grass, Arundo donax, is an aggressive invader of riparian areas throughout California and many sub-tropical regions of the world, and is hypothesized to provide poorer quality habitat for native wildlife in riparian systems. We sampled aerial and ground-dwelling insects and other terrestrial arthropods associated with Arundo, native willow vegetation (Salix spp.), and mixtures of the two vegetation types during two seasons to determine how Arundo influences invertebrate composition in a low gradient stream in central California. The total number of organisms, total biomass and taxonomic richness of aerial invertebrates associated with native vegetation was approximately twice that associated with Arundo vegetation, while mixed vegetation supported intermediate arthropod levels. Shannon-Weaver (Weiner) diversity associated with native vegetation stands was also higher than that of Arundo vegetation. Ground-dwelling assemblages did not show differences as great as aerial assemblages which are more critical to foraging avian species. These results indicate that vegetation type is a significant factor reducing the abundance and diversity of invertebrates in this, and presumably in many other riparian ecosystems where this invasive species has become a dominant component. Arundo invasion changes the vegetation structure of riparian zones and in turn, may increasingly jeopardize its habitat value for birds and other wildlife whose diets are largely composed of insects found in native riparian vegetation.     

Ascomycete fungal communities associated with early decaying leaves of Spartina spp. from central California estuaries

Ascomycetous fungi play an important role in the early stages of decomposition of Spartina alterniflora, but their role in the decomposition of other Spartina species has not been investigated. Here we use fingerprint (terminal restriction fragment length polymorphism) and phylogenetic analyses of the 18S to 28S internal transcribed spacer region to compare the composition of the ascomycete fungal communities on early decay blades of Spartina species (Spartina alterniflora, Spartina densiflora, Spartina foliosa, and a hybrid (S. alterniflora × S. foliosa)) collected from three salt marshes in San Francisco Bay and one in Tomales Bay, California, USA. Phaeosphaeria spartinicola was found on all samples collected and was often dominant. Two other ascomycetes, Phaeosphaeria halima and Mycosphaerella sp. strain 2, were also common. These three species are the same ascomycetes previously identified as the dominant fungal decomposers on S. alterniflora on the east coast. Ascomycetes appeared to exhibit varying degrees of host specificity, demonstrated by grouping patterns on phylogenetic trees. Neither the exotic S. alterniflora nor the hybrid supported fungal flora different from that of the native S. foliosa. However, S. densiflora had a significantly different fungal community than the other species, and hosted at least two unique ascomycetes. Significant differences in the fungal decomposer communities were also detected within species (two clones of S. foliosa), but these were minor and may be due to morphological differences among the plants.     

Origin,diffusion and reproduction of the giant reed (Arundo donax L.): a promising weedy energy crop

Giant reed (Arundo donax) is a promising energy crop of the Mediterranean areas. It has long been associated with humans and has been cultivated in Asia, southern Europe, North Africa and the Middle East for thousands of years. It is a perennial herbaceous plant (Poaceae) found in grasslands and wetlands throughout a wide range of climatic zones. Amplified fragment length polymorphism (AFLP) analysis was used to assess genetic inter and intrarelationships between A. donax and other Arundo species. Furthermore, the development of the sexual apparatus was analysed to understand the basis of sterility in the accession examined. The dendrograms obtained by phenetic and cladistic analysis support the monophyletic origin of giant reed and suggest that it originated in Asia and began to spread into the Mediterranean without traces of hybridisation with the other Arundo species. In particular, samples from Mediterranean areas are characterisd by a lower gene diversity and incidence of rare AFLP fragments indicating that these populations are recent in origin. Moreover, results indicate the occurrence of post-meiotic alterations in the ovule and pollen developmental pathway. Thus, the success of giant reed can be attributed mainly to its rapid clonal spread by rhizome extension, flood dispersal of rhizome and culm fragments.     

Community-level consequences of invasion: impacts of exotic clonal plants on riparian vegetation

Biological invasions by exotic species are occurring at exceptional rates and spatial scales worldwide and are increasingly recognized as key forms of global environmental change. Despite this growing prominence, surprisingly few ecological studies have quantified the impacts of exotic taxa on the plant communities they invade, and this is especially evident in riparian ecosystems. Along the Russian River in northern California, we used both comparative and experimental studies to investigate the influence of two exotic clonal plant species—giant reed (Arundo donax) and blue periwinkle (Vinca major)—on the composition of riparian plant communities. Our results indicate that Arundo invasion was associated with significantly lower richness of native perennial plant species on stream banks and floodplains, whereas there was no relationship on gravel bars. Additional research showed that plots invaded by Arundo and Vinca, both individually and collectively, exhibited significantly lower native and exotic species richness and abundance of both established plants and seedlings than uninvaded plots. Finally, after 2 years, experimental reductions of Arundo biomass via cutting and herbicide resulted in significantly increased native plant species richness and abundances of both established plants and seedlings, while having no effects on other exotics. In summary, our results indicate that Arundo and Vinca have strongly negative effects on diverse components of a riparian plant community, which must be addressed via effective control and restoration efforts.     

EFFECT OF AN AMMONIUM NITRATE PULSE ON THE GROWTH AND ELEMENTAL COMPOSITION OF NATURAL STANDS OF SPARTINA ALTERNIFLORA AND JUNCUS ROEMERIANUS

A nitrogen (ammonium nitrate) pulse of 200 kg ha“¹ was added to stands of tall (1.0–1.5 m) Spartina alterniflora, short (< 0.5 m) Spartina alterniflora, and Juncus roemerianus in a Georgia salt marsh in July. The major response ten weeks later was an increase in the aerial biomass and a sharp reduction in the C/N ratio in short Spartina alterniflora. One year after the treatment the difference between the biomass in enriched and control plots was greater than ten weeks after treatment, but the C/N ratio in the plants in the treated plots had risen to that of the controls. The availability of nitrogen appears to limit growth in the middle elevation Georgia salt marsh (short S. alterniflora), but not in the lower (tall S. alterniflora) or higher (J. roemerianus) portions.     

Influence of Mycorrhizal Inoculation, Inundation Period, Salinity, and Phosphorus Availability on the Growth of Two Salt Marsh Grasses, Spartina alterniflora Lois. and Spartina cynosuroides (L.) Roth., in Nursery Systems

Restoration of salt marsh ecosystems is an important concern in the eastern United States to mitigate damage caused by industrial development. Little attention has been directed to the mycorrhizal influence on plantings of salt marsh species to stabilize estuarine sediments and establish cover. In our study, seedlings of two salt marsh grasses, Spartina alterniflora and Spartina cynosuroides, were grown in soil with a commercial, mixed species inoculum of arbuscular mycorrhizal fungi. Plants were grown in experimental “ebb and flow” boxes, simulating three levels of tidal inundation, to which two levels of applied phosphorus (P) and two levels of salinity were imposed. After 2.5 months, S. alterniflora was poorly colonized by arbuscular mycorrhizae, developing only fungal hyphae and no arbuscules, but S. cynosuroides became moderately colonized. Mycorrhizal inoculation marginally improved growth and P and nitrogen (N) content of both plant species at low levels of P supply but significantly increased tillering in both plant species. This factor could be beneficial in enhancing ground cover during restoration procedures. Greater P availability increased the mycorrhizal status of S. cynosuroides and improved P nutrition of both plant species, despite a reduction in the root‐to‐shoot ratio. Increasing salinity reduced mycorrhizal colonization of S. alterniflora but not of S. cynosuroides. Growth and nutrient content of S. alterniflora was improved at higher levels of salinity, but only increased nutrient content in S. cynosuroides. Increased duration of tidal inundation decreased plant growth in both species, but tissue P and N concentrations were highest with the longest time of inundation in both species.     

Non-target host risk assessment of the idiobiont parasitoid Bracon celer (Hymenoptera: Braconidae) for biological control of olive fruit fly in California

Non-target risk posed by an African parasitoid, Bracon celer Szépligeti (Hymenoptera: Braconidae), was assessed for a classical biological control program against olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae: Dacinae), in California, USA. Behavioral and reproductive responses to non-target tephritid species were tested with beneficial (Chaetorellia succinea [Costa] and Parafreutreta regalis Munro) (Tephritidae: Tephritinae) and native (Rhagoletis fausta [Osten Sacken]) (Tephritidae: Trypetinae) fruit fly species in successive no-choice and choice experiments under close confinement in quarantine. Non-target host-plant substrates exposed to B. celer were yellow-starthistle flower heads containing C. succinea, Cape ivy stem galls containing P. regalis, and bitter-cherry fruit containing R. fausta. The parasitoid probed all three infested non-target plant substrates, but significantly less than olives infested with B. oleae. It produced offspring from P. regalis in Cape ivy stem galls, but appeared unable to penetrate yellow-starthistle flower heads with its ovipositor. Bracon celer killed some B. oleae and R. fausta larvae without parasitism. Reproduction on P. regalis indicates that B. celer has a broad physiological host range, which, combined with the parasitoid's acceptance of all three host-plant substrates, indicates a strong potential to negatively impact non-target species. Although physical and temporal barriers to host attack may reduce risk to most non-target tephritids by B. celer in California, the parasitoid should not be released due to its risk of harming the beneficial P. regalis. Release of P. regalis is still under consideration, however, and final risk assessment should depend on whether the fly proves useful for weed control.