Non-target Plant Species Research Articles

Assessing the Risks to Non-Target Terrestrial Plants from Herbicides

Use of chemical herbicides to reduce weed competition is a major contributing factor to the high productivity of conventional intensive agricultural cropping systems. However, because of their inherent phytotoxicity, movement of herbicides from target crops and soils can adversely affect non-target terrestrial plants. We review current trends in herbicide usage, evidence for effects of herbicides on non-target plants, and risk assessment methodology used to determine potential non-target effects of herbicides. Persistent questions regarding whether or not standard plant tests and analysis protocols provide adequate information for risk assessments, lead us to suggest research needed to improve the risk assessment methodology for effects of potential herbicide drift on non-target plants. This research includes spatial analysis to identify non-target plant species at risk, and development of new biochemical/molecular, phytotoxicological, and ecologically based tests.

Phytotoxic effects of antifouling compounds on nontarget plant species.

Phytotoxic effects of antifouling compounds on nontarget plant species.

Establishment and impact of Galerucella calmariensis L. (Coleoptera: Chrysomelidae) on Lythrum salicaria L. and associated plant communities in Michigan

Abstract Purple loosestrife, Lythrum salicaria L. (Lythraceae) is an invasive wetland perennial plant of Eurasian origin that is widely established in North America and is considered a threat to native wetland flora and fauna. Two European beetles, Galerucella calmariensis L. and Galerucella pusilla Duft. (Coleoptera: Chrysomelidae) have been introduced and widely distributed in North America for biological control of Lythrum salicaria . Experimental releases of Galerucella spp. beetles were made in three locations in Michigan in 1994. In 1997 we initiated a project to rear, redistribute, and evaluate the impacts of Galerucella calmariensis in 19 additional sites throughout Michigan. G. calmariensis became established at 100% of the 24 release locations monitored in these studies and have persisted for up to seven years while G. pusilla apparently failed to establish. Large populations of G. calmariensis developed from each of the 1994 releases and caused 100% defoliation of L. salicaria. From 1995 to 2000, L. salicaria stem height was reduced 73–85%, percent plant cover was reduced 61–95%, and richness of nontarget plant species increased significantly at four out of five sites. By 2001, L. salicaria stem height and percent cover were reduced 38–81% and 32–74%, respectively, and nontarget plant species richness increased significantly at all five sites in contrast to the situation in 1995. Beetles have spread 3–10 km from these original release sites. Of the 19 additional sites monitored for 3–5 years post-release, 50% (4/8) of the 1997 releases have developed into large G. calmariensis populations and produced severe damage to L. salicaria . Thirty-three percent (2/6) of the 1998 releases have generated moderate impacts while all 1999 releases (5/5) remain without clear impacts. The successful establishment, spread, and impacts of G. calmariensis indicate the critical need for additional research on its role in the restoration of desirable plant communities in areas formerly dominated by L. salicaria .

Exploring the host range of Fusarium tumidum, a candidate bioherbicide for gorse and broom

The fungus Fusarium tumidum, a naturally occurring pathogen of gorse (Ulex europaeus) and broom (Cytisus scoparius) in New Zealand, is being evaluated as a potential bioherbicide against these weeds. The susceptibility to F. tumidum of 20 non-target plant species was evaluated in glasshouse trials that were conducted under conditions favourable for infection and disease development. Results show that F. tumidum is capable of infecting and causing disease on a wide range of legumes under ideal conditions. However, only plants in the same tribe as gorse and broom, such as tree lupin (Lupinus arboreus) and tree lucerne (Chamaecytisus palmensis), and one plant from the same subfamily (young white clover, Trifolium repens), showed levels of necrosis similar to the target weeds in response to infection by F. tumidum. The fungus generally had less effect on more distantly related legumes that are native in New Zealand, or are used there as economic crops or as cover crops in plantation forests. Species from plant families other than the Fabaceae were not significantly damaged by the pathogen. Overall, younger plants and those with soft herbaceous tissues were more susceptible to the fungus. Results will be used to prepare advice on the appropriate use of this potential bioherbicide, in the event of its commercialisation.

Host-specificity of Candidate Agents for the Biological Control of Onopordum spp. Thistles in Australia: An Assessment of Testing Procedures

This paper describes a series of host-specificity tests carried out to evaluate the safety of eight insects for release in Australia as biological control agents of Onopordum spp. thistles; Larinus latus L., Lixus cardui Ol. and Trichosirocalus briesei Alonso-Zarazaga & Sanchez-Ruiz (Coleoptera: Curculionidae), Tephritis postica Loew and Urophora terebrans Loew (Diptera: Tephritidae), Botanophila spinosa Rondani (Diptera: Anthomyiidae), Tettigometra sulphurea Mulsant & Rey. (Hemiptera: Fulgoroidae) and Eublemma amoena (Hbn.) (Lepidoptera: Noctuidae). Preliminary tests were first carried out against key test plants in the country of origin to determine whether it was worth proceeding with formal testing under quarantine conditions in Australia. In the formal testing procedure, the test plant list was based solely on phylogenetic relationships. The life-stage of each insect tested was selected with respect to its biology and behaviour, e.g. only oviposition was tested for insect species with immobile endophagous larvae, while larval host utilization was tested for those with mobile larval stages. The initial laboratory experiments for each species used were caged no-choice tests, as confinement without choice can elicit extreme behavioural responses, making negative results extremely robust. Where positive results occurred, insects where re-exposed to the plant, but this time given a choice between the target and non-target plants. The results of these tests, plus data from open-field preliminary tests in the country of origin, helped interpret results and determine the risk posed by each candidate biological control agent to non-target plant species. Following submission, all eight candidates were approved for release by the Australian plant biosecurity and conservation authorities. Based on a comparison of the eight species tested, it is recommended that host-specificity testing be kept flexible and pragmatic, rather than moving towards a formulaic risk assessment procedure. Moreover, given the improved state of knowledge of plant phylogenies and the evolution of host utilization, it is time to base testing procedures purely on phylogenetic grounds, without the need to include less related test species solely because of economic or conservation reasons.

Utilization of the Exotic Weed Pluchea odorata (Asteraceae) and Related Plants by the Introduced Biological Control Agent Acinia picturata (Diptera: Tephritidae) in Hawaii

The flower-head feeding fly Acinia picturata (Diptera: Tephritidae) was deliberately introduced from Mexico into Hawaii in 1959 for biological control of the exotic weed Pluchea odorata (Snow) (Asteraceae). Neither field efficacy nor possible non-target effects of the fly have been evaluated in the 40 years since the introduction. We assessed the impact of the fly on both its target host and on seven non-target plant species. The impact on the target weed was limited, with only 5-13% of the developing seeds in P. odorata flowerheads being destroyed by larval feeding. We did not detect any host range expansion of A. picturata onto flowerheads of two exotic or 5 endemic non-target plant species in the family Asteraceae.

Control of Seven Grasses with a Mixture of Three Fungal Pathogens with Restricted Host Ranges

Abstract Three fungi indigenous to Florida, Drechslera gigantea, Exserohilum longirostratum, and E. rostratum, were isolated from large crabgrass (Digitaria sanguinalis), crowfootgrass (Dactyloctenium aegyptium), and Johnsongrass (Sorghum halepense), respectively. In greenhouse trials, these pathogens controlled the following seven grasses: crowfootgrass, guineagrass (Panicum maximum), Johnsongrass, large crabgrass, southern sandbur (Cenchrus echinatus), Texas panicum (Panicum texanum), and yellow foxtail (Setaria glauca). Four-week-old seedlings were inoculated with spore suspensions of each pathogen (2 × 105 spores/ml) or a mixture of the three pathogens (1:1:1 by volume; total 2 × 105 spores/ml). The spore suspensions as well as the control (water only) were amended with 0.5% Metamucil and the seedlings were sprayed, incubated in a dew chamber for 12 h at 28°C, and then held in a greenhouse. All seven grasses were susceptible to each of the pathogens and the pathogen mixture, each with 100% disease incidence. Two weeks after inoculation, disease severity ranged from 83 to 100% for the different grasses. In a host-range trial, 52 plant species were tested, and all nontarget plant species were safe from the individual pathogens and the pathogen mixture inoculum amended with 0.5% Metamucil. An emulsion-based inoculum preparation of the pathogen mixture was also not injurious to the crop species tested (21 species). Thus, D. gigantea, E. longirostratum, and E. rostratum and a mixture of these pathogens were nonpathogenic to the crop species tested, including Poaceae members. It is preferable to have more than one or even two pathogens in the grass pathogen mixture to achieve a broad spectrum of weed control and provide insurance against any possible failure of one or even two of the pathogens in any given combination under field conditions. More pathogens (at least three instead of two) with different modes of action and/or sites of action in a combination have a much greater chance of reducing potential risk of development of resistance in weed populations than a single pathogen used repeatedly. The use of a mixture of these pathogens appears to have the potential to be developed further as a bioherbicide system to control weedy grasses.

Developmental Host-Specificity of Mozena obtusa (Heteroptera: Coreidae), a Potential Biocontrol Agent for Prosopis Species (Mesquite) in Australia

Mozena obtusa Uhler (Heteroptera: Coreidae) was examined in quarantine for its potential as a biological control agent of Prosopis species (mesquite) in Australia. Trials were conducted on 16 nontarget plant species to estimate its developmental host range. Complete development occurred on all Prosopis species that have become naturalized in Australia as well as on four Australian native species (Neptunia species and Paraserianthes lophantha), although reproductive diapause prevented assessment of subsequent fecundity. Development through the first feeding nymphal instar also occurred on other plant species representing two subfamilies. Nymphal performance was highly variable on both target and nontarget species, possibly because variation in plant nitrogen composition affected plant quality. The correlation between environment, plant nitrogen, and plant quality is likely to be sufficiently strong to determine whether a plant species can support development. Plant quality should therefore be considered when predicting the field host range of M. obtusa and of sap-sucking coreids generally. Nonetheless, our preliminary results suggest that M. obtusa may not be sufficiently specific for release in Australia, although insufficient understanding of its oviposition behavior in the field and the effect of plant quality on development means that its rejection would be premature. r 1999 Academic Press

Host-Range and Distribution ofEucerocoris suspectus(Hemiptera: Miridae), a Potential Biological Control Agent for the Paperbark TreeMelaleuca quinquenervia(Myrtaceae)

The Australian paperbark tree, Melaleuca quinquenervia (Cavier) S. T. Blake, is a serious economic and environmental pest in Florida. One of the most damaging insects found attacking M. quinquenervia during surveys for biocontrol agents in its home range (Australia) was the leaf-blotching bug Eucerocoris suspectus Distant (Hemiptera: Miridae). Adults and nymphs of E. suspectus feed on young leaves and shoots. Their feeding kills leaf tissue surrounding the feeding site, leaving a distinctive, brown, blotch scar. Laboratory host-range studies showed 6 nontarget plant species to be at risk from E. suspectus. However, our extensive field survey data indicate that none of these plants are used as field hosts by E. suspectus. We conducted 8 intensive field searches for E. suspectus feeding damage on >60 plant species at 6 sites. Damage was only noted on Melaleuca spp., except on 1 occasion, where minor feeding damage was found on 2 Lumnitzera racemosa trees adjacent to a more heavily damaged M. quinquenervia tree. Thus, although E. suspectus completed its life cycle on several plant species in the laboratory (albeit at a much lower level than on M. quinquenervia ), in the field, feeding damage is restricted to Melaleuca spp. in the M. leucadendra (L.) L. complex, and rarely, Callistemon spp. The narrow host-range, broad habitat tolerances, and extensive damage caused by this insect should make it a valuable biological control agent if released in Florida.

Influence of autumn applied herbicides on summer and autumn food available to birds in winter wheat fields in southern England

Herbicides applied to control problem weed species can directly reduce the availability of non-target plant species and, indirectly, invertebrates important as food for birds. Therefore, the effects of an autumn herbicide application on the flora and invertebrate fauna were studied within the field headland of winter wheat ( Triticum aestivum L.) crops over three years. Replicated plots were either treated with a herbicide or left untreated. Floral percentage cover and diversity were assessed in quadrats on two dates, and invertebrates sampled using a vacuum sampler on five dates, between May and July each year. A significantly greater floral cover ( p < 0.001), species diversity ( p < 0.001) and higher numbers of many arthropod groups, such as Heteroptera ( p < 0.001), Auchenorrhyncha ( p < 0.001) and Coleoptera ( p < 0.001), important in the diet of farmland birds, were found on all untreated plots. Selective pesticide use is suggested as a method that could help reverse the decline found in many species of farmland bird, by improving the availability of weed and invertebrate food in an intensively farmed landscape.

Biology ofMozena obtusa(Hemiptera: Coreidae), a Candidate for the Biological Control of Mesquite,Prosopisspp. (Fabaceae)

The leaf-footed bugMozena obtusaUhler is an important natural enemy of honey mesquite,Prosopis glandulosaTorrey var.glandulosa, in the southwestern United States and northern Mexico. The nymphs and adults severely damage mesquite by feeding on new vegetative and reproductive growth. The temporal distribution of all life stages indicated thatM. obtusahas five nymphal instars and is bivoltine in central Texas. In the laboratory, the generation time forM. obtusaon honey mesquite was ca. 70 days: 12.7 days for the egg stage, 32.7 days for the nymphal stage, and a preovipositional period of 24.7 days. Adult longevity was ca. 167 days for females and 144 days for males. Females produced an average of 510 eggs in 39 masses with 13 eggs per mass during their lives.Mozena obtusaalso developed normally on the Argentine vinal,Prosopis ruscifoliaGrisebach, although the nymphal stage was longer (49.5 days). In the field, a complex of hymenopterous egg parasitoids [Anastatus semiflavidusGahan (Eupelmidae),Ooencyrtus johnsoni(Howard) (Encyrtidae), andGryon atrumMasner (Scelionidae)] and the tachinid flyTrichopoda pennipesF. appeared to be the principal biotic mortality factors regulating populations ofM. obtusa. Parasitism of all life stages ofM. obtusawas found to be 40%. Because it has the potential to significantly reduce seed production, this insect may be a good candidate for introduction into other countries for classical biological control of mesquite (Prosopisspp.) providing host range tests demonstrate that it does not damage beneficial or nontarget plant species.

Rapid Determination of Glyphosate Injury to Plants and Identification of Glyphosate-Resistant Plants

Drift of glyphosate may cause injury to nontarget plant species. Herbicidal damage caused by glyphosate may be attributed to the herbicides that inhibit acetohydroxyacid synthase (AHAS) or acetyl CoA carboxylase (ACCase), because the time taken to show herbicidal damage and the visual injury symptoms caused by these three types of herbicides are similar. Glyphosate inhibits the biosynthesis of aromatic amino acid biosynthesis which causes accumulation of shikimate in plants. A modified, simpler method of extraction and assay for detection of shikimate in plants has been adapted from previously published procedures. With this assay, rapid accumulation of shikimate was observed in glyphosate-sensitive plants that have been treated with glyphosate. Furthermore, the accumulation of shikimate in herbicide-sensitive plants was only due to glyphosate and not due to an AHAS or an ACCase inhibitor. Therefore, high levels of shikimate in a damaged plant indicate glyphosate injury. With this assay, no accumulation of shikimate was seen in a glyphosate-resistant variety of soybean. Therefore, lack of accumulation of shikimate in a glyphosate-treated weed or crop species indicates that the plant is resistant to glyphosate.

Assessment of effects on non-target plants from sulfonylurea herbicides using field approaches

Since their introduction in the early 1980s, there have been a number of field studies conducted to assess the effects of sulfonylurea herbicides on non-target plants (i.e. plants not labeled for use). In these studies a wide variety of plant response assessment techniques have been used to measure effects on non-target plants. This paper examines the relationship of short-term plant response measurements to plant productivity measurements such as yield or quality. Whether short-term plant response measurements have a practical degree of accuracy and precision appropriate for hazard assessment on non-target plants from sulfonylureas is discussed. A comprehensive review of published literature and unpublished field studies of the effects of sulfonylureas on the yield and quality of non-target plant species is reported. When this information is coupled with exposure factors and environmental fate characteristics, the risks to non-target plants from sulfonylureas are similar to those from other herbicides used at higher application rates. © 1998 SCI.

Composition and Diversity of Plant and Small Mammal Communities in Tebuthiuron-Treated Big Sagebrush (Artemisia tridentata)

Sagebrush control has historically involved mechanical and chemical (2,4-D) treatments designed for total control and which detrimentally affect nontarget plant species, resulting in decreases in native wildlife abundance and diversity. Tebuthiuron, a potentially selective herbicide with thinning capabilities, was applied at various rates to big sagebrush plots near Ten Sleep, WY in 1979 and Hyatteville, WY in 1983. Plant and small mammal communities were evaluated in 1992 and 1993. Big sagebrush cover in untreated areas was 31 ± 1% in 1992 and 34 ± 1% in 1993 at Ten Sleep, and 44 ± 4% at Hyatteville (α = 0.10). Big sagebrush control increased as application rate increased. Productivity of herbaceous species (graminoids, forbs, or both) tended to be greatest at about 11 to 17% big sagebrush cover. In general, plant community diversity tended to be greatest where sagebrush was thinned to this level. Small mammal community diversity was least at both sites where big sagebrush cover was less than 5%, and was strongly correlated with plant community diversity at Ten Sleep (R2W= 0.99; 4 degrees of freedom). In addition, greater abundance of or better habitat quality for endemic, stenotypic (habitat specialist) species was associated with about 15% big sagebrush cover. This suggests (albeit retroductively) that biodiversity at both local (alpha) and global (epsilon) scales might be conserved by thinning big sagebrush with tebuthiuron.

Identification, Pathogenicity, and Safety of Alternaria eichhorniae from Egypt as a Bioherbicide Agent for Waterhyacinth

On the basis of conidial measurements, growth characteristics, and pigmentation in culture, two of three Egyptian Alternaria spp. (isolates 3 and 5) isolated from waterhyacinth (Eichhornia crassipes) were identified as A. eichhorniae and the third, isolate 6, as A. alternata. Isolate 5 (Ae5), the most virulent, caused a severe disease, characterized by leaf blight and discrete leaflesions. The disease was initiated with either conidial or mycelial inoculum of Ae5, to yield a similar level of disease severity. Different broth media and cultural conditions were evaluated for the ability to produce highly pathogenic mycelial inoculum. Fresh potato dextrose broth, shake-culturing, and incubating cultures under diurnal light for 1 week followed by continuous darkness for an additional week were most effective. Empirically, mycelia subjected to > or < 6 s of mechanical shear in a blender were less infective than those blended for 6 s. Disease severity increased with increasing inoculum density up to 5% mycelial wet weight; a higher inoculum density did not provide greater disease severity. Exposure of inoculated leaves to at least 10 h of dew was conducive to a high level of disease, and the use of a hydrophilic mucilloid as a humectant with the mycelial inoculum augmented the disease levels. None of 97 economically important, nontarget plant species and cultivars evaluated in host range trials was susceptible to Ae5. Thus, the results of this study affirm A. eichhorniae to be an aggressive, safe, and desirable pathogen for development as a bioherbicide for waterhyacinth in Egypt.

Biology and Host Specificity of Ageniosa electoralis (Coleoptera: Chrysomelidae), a Prospective Biological Control Agent for Chrysanthemoides monilifera (Asteraceae)

Abstract The southern African shrub Chrysanthemoides monilifera (L.) T. Non. (Asteraceae) invades native vegetation and threatens nature conservation objectives throughout its range in Australia. In a survey for biological control agents, adults and larvae of the chrysomelid Ageniosa electoralis (Vogel) were found at two sites in Natal, South Africa, where they fed on the foliage of Chrysanthemoides monilifera rotundata (DC.) T. Norl. In laboratory-based starvation tests, A. electoralis completed larval development or oviposited on 15 nontarget test plant species from the Asteraceae and 1 from the Apiaceae. The number of larvae completing development to adults on Arctotheca calendula (L.) M. Levyns, Cymbonotus preissianus Steetz, and Tussilago farfara L. was similar to that on C. monilifera . Also, the number of eggs laid by adults fed Calendula oflicinalis L. or Daucus carota L. was not significantly different from the number of eggs recorded for adults fed on C. monilifera . In multiple-choice tests that included C. monilifera , larvae fed on six nontarget test plant species. Ageniosa electoralis is not being considered for release as a biological control agent for C. monilifera in Australia until a satisfactory level of host-specificity is shown under field conditions in South Africa.

Evaluation of two herbicide techniques on electric transmission rights-of-way: Development of relatively stable shrublands

Postmanagement vegetation patterns were studied on five transmission rights-of-way subjected to over a decade of basal or stem-foliar herbicide applications designed to eliminate tall-growing trees. The basally treated lines had a mean of 100% greater shrub and 50% less herbaceous cover than stem-foliar treated lines due primarily to the lack of overspray damage to nontarget plant species with the basal technique. Persisting tree growth was also 50% less with basal treatments whenSassafras albidum, a rootsuckering problem species on all areas, was excluded. Tree seedling establishment on basally treated rights-of-way was 34% less than on stem-foliar treated lines. The creation of stable shrublands can potentially reduce the amount of future herbicide usage. These findings also lend support to the Initial Floristic Composition concept in vegetation development proposed by Egler. In southern New England, commercial basal applications can effectively control unwanted tree growth on rights-of-way while promoting the development of relatively stable shrublands which tend to inhibit the invasion of tree seedlings.