The RustPuccinia abruptavar.partheniicola,a Potential Biocontrol Agent of Parthenium Weed: Environmental Requirements for Disease Progress

The rust fungusPuccinia abruptavar.partheniicola,a potential biological control agent of parthenium weed (Parthenium hysterophorus), was evaluated under controlled environmental conditions. A range of spore germination temperatures as well as dew period durations and temperatures were investigated to determine some of the environmental requirements for disease establishment and disease progress. Plants were inoculated with urediniospores and exposed to dew periods between 3 to 12 h at temperatures of 10, 15, or 20°C. For disease expression, the inoculated plants were then grown in a glasshouse at one of two temperature regimes (30/26°C or 18/13°C; day/night). Urediniospores germinated best at 12 ± 1°C, with lower germination rates at 5°C or above 20°C. No infection occurred when the plants were exposed to dew periods of ≤3 h, regardless of the incubation temperature. The disease progressed most rapidly when plants were inoculated and incubated for a dew period of at least 12 h at a temperature of 15 ± 1°C. The disease progressed most slowly following inoculation at dew periods of 6 h or less. Disease progress was more rapid when the plants were exposed to a cool-temperature regime (18/13°C) than when exposed to a warm-temperature regime (30/26°C). This suggests that good infection of parthenium weed could be obtained when the urediniospores arrive on the plants during the afternoon in the cooler months of the central Queensland autumn when relatively long dew periods are expected.     

Bone-seed (

Bone-seed, Chrysanthemoides monilifera ssp. monilifera (L.), is an environmental weed of coastal vegetation communities scattered throughout New Zealand. To assess the long-term implications for native forest regeneration in sites where bone-seed is present, we selected four study sites around Wellington, New Zealand, where bone-seed was abundant. We compared seed bank composition in bone-seed-invaded sites with nearby native forest patches, and monitored bone-seed and native seedling recruitment with and without control of mature bone-seed plants. We also tested the potential effects of fire on bone-seed recruitment in these communities by heating seeds prior to germination. Bone-seed, gorse (Ulex europaeus), and native species emerged from seed bank samples taken from bone-seed-invaded sites, but only native species and (less) gorse emerged from seed bank samples taken from native forest patches. Gorse germination was strongly promoted by heat but bone-seed germination was less affected by heat. Bone-seed seedling abundance increased dramatically following canopy removal, whereas native seedling abundance decreased dramatically. This suggests that disturbance of any form is likely to favour recruitment of bone-seed (and gorse) over native species, although in the long term, native seedlings can establish beneath the canopy of mature bone-seed plants. It is not yet known if, in the absence of further disturbance, regenerating native vegetation will eventually replace bone-seed in New Zealand.     

Suitability of Agonopterix ulicetella (Lepidoptera: Oecophoridae) as a Control for Ulex europaeus (Fabaceae: Genisteae) in New Zealand

The larvae of Agonopterix ulicetella (Stainton) (Lepidoptera: Oecophoridae) feed on the green foliage of gorse, Ulex europaeus L., and this insect is a potential biological control agent of this weed in New Zealand. The biology of the insect is described and its known parasitoids are listed. In experiments to measure oviposition preference, 46 plant species from 11 families were exposed to adult moths. Gorse was highly preferred over other plants, and there was no oviposition on 33 species tested. Eggs were found on Spartium junceum, Chamaecytisus palmensis, Lupinus arboreus, L. polyphyllus, Genista tinctoria and occasionally on eight other species. In experiments to measure the ability of first instar larvae to feed on 70 test plant species, 59 did not support development beyond the first instar and only seven species supported development to the pupal stage. These results show that under laboratory conditions this moth can lay its eggs and complete development on five members of the tribe Genisteae other than gorse. A. ulicetella was released in New Zealand in 1990 but has not yet established.     

Insect assemblages in a native (kanuka –

In New Zealand, the European shrub gorse (Ulex europaeus) is becoming the initial post-disturbance shrub, replacing the native myrtaceous manuka (Leptospermum scoparium) and kanuka (Kunzea ericoides) scrub in this role. Change in the dominant vegetation is likely to affect the native invertebrate community. To quantify these changes, we compared the assemblages of four selected insect taxa (Coleoptera, Lepidoptera, and two groups of Diptera, the Tachinidae and the fungus gnats, represented in New Zealand by the families Ditomyiidae, Keroplatidae and Mycetophilidae) in neighboring stands of kanuka and gorse using Malaise and pitfall traps set during December. We sorted 34 387 specimens into 564 recognisable taxonomic units. Ordinations showed that insect assemblages associated with each habitat were distinct for all four insect groups. The gorse habitat was species rich compared with kanuka for tachinids, fungus gnats and Malaise-trapped beetles, and both habitats contained few adventive species. Many species were unique to each habitat. Some species loss might occur if the kanuka-dominated community continues to be replaced by gorse, but gorse is nevertheless considered to be valuable as a habitat for native invertebrates.     

Factors influencing pathogenicity of Fusarium tumidum on gorse (Ulex europaeus)

Factors promoting pathogenicity of Fusarium tumidum on gorse (Ulex europaeus) were determined to develop a novel strategy for delivering this potential mycoherbicide using insects as vectors of inoculum. Fusarium tumidum sprayed as a suspension of 1×10⁶ conidia mL^?1 on at least 50% of a gorse plant reduced shoot dry weight by 45% (P<0.05). A minimum of 910 viable conidia were required to cause a lesion on leaves. The leaves and flowers were more susceptible to infection than stems, spines and pods. Generally, wounding of gorse leaves and stem increased F. tumidum infection, most likely through releasing nutrients that enhanced conidial germination and hyphal growth. We showed in a separate experiment that conidial germination (93%) and germ tube length (407 µm) were greater when incubated in 0.2% gorse extract solution for 24 h than in water (62% germination, germ tube length 42 µm). Inoculation of gorse with a F. tumidum conidial suspension supplemented with 0.2% gorse extract resulted in a shoot dry weight reduction (P=0.012) equivalent to that of plants that were wounded and inoculated. It is concluded that wounding of older tissues (which mimics insect damage) is required to facilitate F. tumidum infection of mature gorse plants.     

Biology, Impact and Preliminary Host-specificity Testing of the Rust Fungus, Uromyces salsolae , a Potential Biological Control Agent for Salsola kali in the USA

Russian thistle, Salsola kali (=Salsola australis) (Chenopodiaceae) of Eurasian origin is a troublesome weed in the drier regions of the western USA. The weed commonly infests crops, disturbed wastelands and overgrazed rangelands. A rust fungus, Uromyces salsolae , has been found to cause considerable damage to the weed in Eurasia. Field observations in Turkey revealed that S. kali plants infected by the rust were covered with a powdery brown mass of urediniospores and had stunted growth. Under laboratory conditions, U. salsolae severely infected Salsola plants from France, the USA and Turkey (control). The urediniospores germinated when in contact with water within a minimum period of 2 h and over a wide range of temperatures. S. kali plants were also infected at a wide range of temperatures and incubation periods with simulated dew. Fungal attack was very severe and caused mortality or much reduced growth of infected plants without seed production. Preliminary host specificity testing using 17 plant species or varieties from six families revealed that the rust infected only the Russian thistle. U. salsolae was imported recently into the USA for further host specificity testing under quarantine conditions. Its use as a biological control agent for S. kali in the USA is recommended.     

Seedling Blights of Cyperaceae Weeds Caused by Curvularia tuberculata and C. oryzae

Two Curvularia tuberculata isolates (93-020 and 93-022) and one C. oryzae isolate (93-061) were obtained from diseased Cyperus difformis , C. iria , and Fimbristylis miliacea , respectively, in the Philippines in 1993. When inoculated onto their hosts at 1 ×10 8 conidia m -2 , and provided with 24-h dew at 28°C, a severe and rapid blighting of the leaves caused the weed seedlings to die within two weeks. The three Curvularia isolates were cross-pathogenic to C. difformis , C. iria , F. miliacea , and C. rotundus but exhibited varying degrees of virulence depending on the weed species being attacked. C. tuberculata isolates 93-020 and 93-022 effectively controlled C. difformis and C. iria but were less effective on F. miliacea.

C. oryzae was equally virulent on C. difformis , C. iria , and F. miliacea . C. rotundus was not killed by any of the three isolates and exhibited only minor flecking and leaf tip die-back. Sporulation of the three Curvularia isolates on necrotic leaf tissues occurred on the susceptible ( C. difformis , C. iria , and F.miliacea ) but not on the resistant ( C. rotundus ) weed hosts.     

Secondary forest succession differs through naturalised gorse and native kānuka near Wellington and Nelson

The dominant native woody species forming early-successional vegetation on formerly forested sites in lowland New Zealand were kānuka (Kunzea ericoides) and mānuka (Leptospermum scoparium) (Myrtaceae). These have been replaced extensively by gorse (Ulex europaeus, Fabaceae), a naturalised species in New Zealand. Because gorse typically gives way to native broadleaved (angiosperm) forest in about 30 years, it is often considered desirable for facilitating native forest restoration. We tested three hypotheses, derived from the New Zealand literature, on gorse and kānuka: (1) kānuka stands have a different species composition and greater species richness than gorse stands at comparable successional stages; (2) differences between gorse and kānuka stands do not lessen over time; and (3) several native plant taxa are absent from or less common in gorse than in kānuka stands. We sampled 48 scrub or low-forest sites in two regions, Wellington and Nelson. Sites were classified into one of four predefined categories – young gorse, young kānuka, old gorse, old kānuka – based on canopy height of the succession and the dominant early-successional woody species. Few characteristics of the sites and surrounding landscapes differed significantly among site categories, and none consistently across regions. The vegetation composition of gorse and kānuka and their immediate successors differed in both regions, mainly in native woody species. Species richness was often lower in gorse and there were fewer smallleaved shrubs and orchids in gorse. Persistent differences at the older sites suggest the successional trajectories will not converge in the immediate future; gorse leads to different forest from that developed through kānuka. Gorse-dominated succession is therefore not a direct substitute for native successions. We suggest areas of early native succession should be preserved, and initiated in landscapes where successions are dominated by gorse or other naturalised shrubs.     

胶孢炭疽菌婆婆纳专化型侵染波斯婆婆纳的影响因子的研究

通过盆栽试验,研究了真菌自身生物学特性、杂草生长状况和环境因素等对胶孢炭疽菌婆婆纳专化型菌株QZ－97a侵染波斯婆婆纳的影响。结果表明,子叶期和衰老斯波斯婆婆纳感病性最强;培养7－14d后的孢子侵染力最强;病害发生的最佳温度范围是15－25℃;在保湿2－3d的条件下,露期中间的光照时间越短,病害发生越严重;保湿也可通过添加玉米粉和黄粉等介质来解决;达到理想致病效果的该菌株孢子悬浮液浓度必须在10^7个.ml^-1以上,由此可见,菌株QZ－97a在波斯婆婆纳发生时期的环境条件下可有效控制该杂草。     

The EVect of Release Size on the Probability of Establishment of Biological Control Agents: Gorse Thrips ( Sericothrips staphylinus ) Released Against Gorse ( Ulex europaeus ) in New Zealand

Many biocontrol agents released against alien weeds and pests fail to establish in the field. Here, we ask whether better release strategies could improve the likelihood of successful establishment. A manipulative field experiment was used to investigate the relationship between the probability of establishment and the number of individuals released for a weed biocontrol agent. In this experiment, replicated releases of 10, 30, 90, 270 and 810 gorse thrips, Sericothrips staphylinus Haliday, were made on to isolated gorse bushes in New Zealand. The sampling eY ciency was determined using a further experiment in which known numbers of thrips were released on to bushes. The data obtained showed that in approximately nine out of 10 releases of 10 thrips, at least one thrips would be found. The thrips in the size of release experiment were sampled 1 year after their release. A higher proportion of the small releases became extinct during this time period: thrips were recovered from 100% of the releases of 270 and 810 thrips, but only from 33% of releases of 10, 30 and 90 thrips. Using gorse thrips as an example, a protocol was developed to determine the optimal release size for biocontrol agents. It is suggested that for a fixed number of insects available for release, smaller releases may increase the overall establishment rate. W hile a single large release can easily become extinct by chance, it is extremely unlikely that a large number of small releases will do so over the same time period. The optimal release size (i.e. that which maximizes the average number of successful establishments) for gorse thrips in New Zealand might be fewer than 100 thrips/ release site. This contrasts with the current strategy in New Zealand of 1000 thrips/release and the suggestion in the biocontrol literature that large releases optimize establishment. Over 1 year of observation the thrips had no eVect on gorse growth rate. The EVect of Release Size on the Probability of Establishment of Biological Control Agents: Gorse Thrips ( Sericothrips staphylinus ) Released Against Gorse ( Ulex europaeus ) in New Zealand     

The host range ofTetranychus lintearius (Acarina: Tetranychidae)

The host range ofTetranychus lintearius was examined experimentally to determine if the mite could be safely introduced into New Zealand for the biological control of gorse,Ulex europaeus (Leguminosae: Genisteae). The rationale for choosing test plants was the same as that employed for testing insect species as biological control agents. Outdoors, mite colonies could be transferred successfully from gorse plant to gorse plant, but could not re-establish on any of 39 other plant species progeny to develop, was measured on 58 plant species other than gorse. Apart fromUlex europaeus andU. minor, development was completed only onPhaseolus vulgaris andGlycine max. Further experiments using 22 bean cultivars showed that mites could not complete a second generation on detached leaf cultures, could not form permanent colonies on potted plants in the glasshouse, and remanned only a short time when transferred to bean plants in the field. Tetranychus lintearius has never been recorded from any plant butUlex species. This fact, coupled with the results of host-range testing, suggests that the mite is sufficiently host-specific to be safely used as a biological control agent for gorse in New Zealand.     

Fusarium nygamai, a potential bioherbicide for Striga hermonthica control in sorghum

Glasshouse trials were performed to investigate the control of the parasitic weed Striga hermonthica by Fusarium nygamai and the performance of the host plant sorghum (Sorghum bicolor) using different inoculum substrates and inoculum amounts of the fungus. Optimal constant and alternating temperatures for the growth of the fungus were 25°C and 30/20°C, respectively. Striga incidence was decreased up to 100% when the fungus was incorporated into the soil preplanting. Emerged Striga plants at different stages of growth up to the flowering stage were killed by the fungus when the fungus was applied postemergent. In root-chamber trials none of the Striga seeds germinated when 10 ml inoculum suspension of 8 × 10⁶ spores/ml of F. nygamai was applied on seeds of the parasitic weed sprinkled on the surface of filter paper. F. nygamai has potential as a bioherbicide for Striga control. Further studies regarding its performance under field conditions and its safety to the environment and humans should be assessed.     

Effect of Epidemiological Factors on the Impact of the Fungus Plectosporium tabacinum on False Cleavers ( Galium spurium )

The fungus Plectosporium tabacinum has been evaluated as a bioherbicide for control of false cleavers ( Galium spurium ), but the limiting factors and optimal conditions for successful control using this pathogen are not known. False cleavers mortality and dry weight reductions caused by P. tabacinum were assessed under single or combined factors, including pathogen inoculum concentration, plant growth stage, dew period (duration, frequency, and timing), and dew period temperature. The minimum inoculum concentration required to kill false cleavers seedlings was 1 ×10 7 conidia mL -1 at an application rate of 150 mL m -2 . False cleavers seedlings in the cotyledon or 1-whorl growth stage were the most susceptible. Increasing inoculum concentration increased weed control efficacy on older false cleavers seedlings. When an adequate dew period was provided, 100% mortality and dry weight reduction occurred. The minimum dew period to achieve 100% mortality was 16 h. Delaying the initiation of the dew period by 24 h significantly reduced disease development. Short, repetitive dew periods only improved false cleavers control to a limited extend and the length of initial dew is a critical factor influencing false cleavers mortality due to P. tabacinum . The optimal dew period temperature for disease development was above 15°C.     

Drechslera sp. (Pyrenophora chaetomioides (Speg.)), a Potential Biocontrol Agent for Bromus sterilis and Other Bromus spp.

Infection by a Drechslera sp. (perfect stage, Pyrenophora chaetomioides (Speg.)), isolated from Bromus sterilis , killed B. sterilis , B. commutatus and B. secalinus. B. diandrus and B. hordeaceus were both infected but not killed. Successful infection required a 24-h dew period. Reduction of the dew period to 8 h significantly reduced the infection of all Bromus spp. tested as determined by leaf necrosis. Inoculation with a low inoculum concentration (2 104 conidia/ml) produced little dry weight reduction, but at 2 105 conidia/ml with an 8-h dew period the dry weights of B. commutatus , B. diandrus , B. secalinus and B. sterilis were reduced by 11-25%. Extending the dew period to 24 h resulted in 77% mortality of B. sterilis and 93% mortality of B. commutatus and B. secalinus.     

Environmental weeds in Australia and New Zealand: issues and approaches to management

Environmental weeds are plants that invade natural ecosystems and are considered to be a serious threat to nature conservation. Australia and New Zealand, where biota with a high degree of endemism have evolved, are particularly susceptible to environmental weeds. Environmental weeds have been implicated in the extinction of several indigenous plant species, and they also threaten ecosystem stability and functional complexity. Historically, emphasis has been placed on the chemical or manual ‘control’ of weed infestations, often with little consideration of the long‐term effectiveness or the ecological consequences of such an approach. As the threat from environmental weeds is becoming more fully recognized, an integrated, strategic and ecological approach to weed management is being recommended. In both countries, systems for screening new plants before allowing entry for cultivation have been developed. For already established plants, management is conducted within a legislative and policy framework such as the Regional Pest Management Strategies that operate through the Biosecurity Act 1993 in New Zealand. Noxious weed legislation in Australia has historically focused on agricultural weeds, but some Acts are (or have recently been) undergoing revision to give greater emphasis to environmental weeds and the involvement of the community in weed management. Quarantine, legislation, research and on‐ground management are complemented by education programmes about the impact and control of environmental weeds. This paper provides an overview of the ‘tool‐kit’ needed to manage environmental weeds in Australia and New Zealand, comparing and contrasting the approaches taken in the two countries. It also provides a broad framework for the case studies that make up this special issue on the ecology and management of environmental weeds in both countries.     

Factors affecting the cost of weed biocontrol programs in New Zealand

Many national schemes for setting priorities for invasive weed management have emphasized the current or future impacts of the weed more than the cost or feasibility of control, perhaps because the latter may be difficult to estimate. As part of a project to improve prioritization of weed biocontrol targets in New Zealand, we investigated factors that were hypothesized to influence the cost of conducting weed biological control, using data from New Zealand programs. Taxonomic isolation of the target weed, relative to commercially important plants and native flora was not a significant influence on program cost, although we present evidence that disease, which to date has only affected agents released against taxonomically isolated weed targets, has masked the importance of taxonomic isolation in New Zealand. Opposition to biocontrol has caused delays, but has not had a major influence on the cost of biocontrol in New Zealand, probably because weed species with the greatest potential for opposition were identified during feasibility studies and avoided, or because conflicts were resolved by conducting cost-benefit analyses that were minor components of the total program costs. Only two factors explained virtually all the variance in program cost: program type (repeat programs were cheaper than novel/pioneering programs); and the number of agent species released. The predicted cost of future weed biocontrol programs can now be incorporated into decision-making tools ranking New Zealand weed biocontrol targets. Efficiencies in future programs are most likely to be gained by better agent selection so that fewer agents are released. For repeat programs this could be achieved by waiting until monitoring has been conducted overseas, so that the best agents or combination of agents can be selected for any particular weed. This reiterates the need for better post-release evaluation of weed biocontrol agent effectiveness worldwide.     

Factors Affecting Disease Development by Rhynchosporium alismatis in Starfruit (Damasonium minus), a Weed of Rice

The fungal pathogen Rhynchosporium alismatis is being developed for biological control of starfruit (Damasonium minus), an important aquatic weed in Australian rice fields. The development of R. alismatis in starfruit differs between juvenile and adult plants. Juvenile starfruit plants are stunted as a result of fungal infection, while in adult plants, the main effect is necrosis and chlorosis of floating leaves. A conidial concentration of 1×10⁴ conidia mL^-1 was adequate to cause disease symptoms on floating leaves, but the stunting effect on juveniles was caused by concentrations of at least 1×10⁵ conidia mL^-1. To successfully inoculate juvenile plants, the water must be drained before inoculation to expose plants to the inoculum. The artificial addition of dew periods did not enhance disease development in plants. The stunting of juvenile starfruit plants caused by the infection of R. alismatis may give rice plants a competitive advantage over the weed at the seedling stage     

Reproductive isolation betweenTetranychus lintearius and two related mites,T. urticae andT. turkestani (Acarina: Tetranychidae)

Gorse,Ulex europaeus L. (Leguminosae), is a serious weed in New Zealand and some other temperate parts of the world.Tetranychus lintearius Dufour (Tetranychidae) has been released in New Zealand as a biological control agent for the weed. Before it could be introduced from Europe, it was necessary to show thatT. lintearius is reproductively isolated from closely related pest mites.Crosses and reciprocal crosses were made betweenT. lintearius and four populations ofT. urticae Koch, and betweenT. lintearius and one population ofT. turkestani (Ugarov and Nikolski). In a second experiment, males of a second population ofT. lintearius were crossed with females of fiveT. urticae populations. The sex-ratio of F₁ progeny in both experiments suggested thatT. lintearius was reproductively isolated from the other species, and could therefore be used as a biological control agent for gorse.     

Biological Control of Kudzu ( Pueraria lobata ) with an Isolate of Myrothecium verrucaria

An isolate of the fungus Myrothecium verrucaria ( MV ) was evaluated for biocontrol potential against kudzu ( Pueraria lobata ). In greenhouse tests, MV was highly virulent against kudzu in the absence of dew when conidia were formulated in 0.2% Silwet L-77 surfactant (SW). Inoculum concentrations ≥2 ×10 7 conidia ml -1 were required to satisfactorily control plants in the third leaf stage and larger. In controlled environment experiments, kudzu mortality was greater at higher temperatures (25-40°C) than at lower temperatures (10-20°C), although pathogenesis and mortality occurred at all temperatures tested. In field tests, transplanted kudzu seedlings in the 2-3 leaf growth stage treated with MV at 2 ×10 7 conidia ml -1 in 0.2% SW, exhibited leaf and stem necrosis within 24 h following inoculation, with mortality occurring within 96 h. After 7 days, 100% of inoculated kudzu plants were killed in plots treated with the fungus/surfactant mixtures. Similar results were observed in a naturally occurring kudzu population, where 100% control occurred within 14 days after inoculation with 2 ×10 7 conidia ml -1 in 0.2% SW. In summary, MV effectively controlled kudzu in the absence of dew over a wide range of physical and environmental conditions and under field conditions. These results indicate that, when properly formulated, MV has potential as a valuable bioherbicide for controlling kudzu.     

Factors influencing biocontrol of jimsonweed (Datura stramonium L.) with the leaf-spotting fungus Alternaria crassa

In greenhouse tests, Alternaria crassa (Sacc.) Rands killed > 80% of inoculated jimsonweed (Datura stramonium L.) seedlings within 14 days following a 9-h dew period at 25°C with 1 × 10⁵ spores/ml, and after 8 h of dew at 1 × 10⁶ spores/ml. At least 10 h of dew with 1 × 10⁵ spores/ml and 9 h of dew with 1 × 10⁶ spores/ml were required to obtain 100% mortality of fungus-inoculated plants. Growth stage and inoculum concentration studies revealed that higher concentrations of inoculum were required to obtain 100% mortality of larger plants. Weed control was significantly reduced by day/night air temperatures of 35°C and 24°C, respectively, at all inoculum concentrations as compared to the controls at lower air and dew temperature regimes. The results of these studies indicate that A. crassa has potential as a biological herbicide for the control of jimsonweed.