Pilosella officinarum (mouse-ear hawkweed)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Plant Type
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Habitat List
- Hosts/Species Affected
- Biology and Ecology
- Latitude/Altitude Ranges
- Air Temperature
- Rainfall Regime
- Soil Tolerances
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Pathway Vectors
- Plant Trade
- Impact Summary
- Economic Impact
- Impact: Biodiversity
- Social Impact
- Risk and Impact Factors
- Uses List
- Similarities to Other Species/Conditions
- Prevention and Control
- Links to Websites
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Pilosella officinarum Vaill.
Preferred Common Name
- mouse-ear hawkweed
Other Scientific Names
- Hieracium albofloccosum (Nägeli & Peter) Prain
- Hieracium kemulariae Üksip
- Hieracium melanops (Peter) J.Weiss
- Hieracium paradoxum Kem.-Nath.
- Hieracium pilosella L.
- Hieracium tricholepium (Nägeli & Peter) Prain
- Hieracium trichosoma (Peter) J.Weiss
- Pilosella angustella Norrl.
- Pilosella melanops (Peter) Dostál
- Pilosella micradeniophorum (Zahn) Dostál
- Pilosella officinarum F.W.Schultz & Sch.Bip.
- Pilosella tricholepia (Nägeli & Peter) Dostál
- Pilosella urnigera Norrl.
International Common Names
- English: mouseear hawkweed
- Spanish: pelosilla; pilosella
- French: épervière piloselle; oreille de souris; piloselle; véluette
- Portuguese: polosela-das-boticas
Local Common Names
- Austria: kleines habichtskrau; langhaariges habichtskraut; mausohr-habichtskraut
- Germany: Kleines Habichtskraut; Langhaariges Habichtskraut; Mausohr; Mausohr-Habichtskraut; Mausöhrlein
- Italy: orecchio di topo; pelosella; pelosetta
- Netherlands: muizeoor
- Sweden: graafibbla
- Switzerland: kleines habichtskraut; langhaariges habichtskraut; mausohr-habichtskraut; oreille de souris
- HIEPI (Hieracium pilosella)
Summary of InvasivenessTop of page
P. officinarum is a prostrate herb which has spread rapidly to exotic locations (e.g. New Zealand, North America and South America) after introduction as a garden ornamental or contaminant of agricultural seed. As it continues to be available as an ornamental and can be easily transported by machinery, P. officinarum is likely to spread further. It is an undesirable invader on account of its vigorous growth due to stolon production and wind-dispersed seeds. P. officinarum displaces the inter-tussock vegetation leading to loss of forage and biodiversity.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Asterales
- Family: Asteraceae
- Genus: Pilosella
- Species: Pilosella officinarum
Notes on Taxonomy and NomenclatureTop of page
P. officinarum is often referred to by the synonym Hieracium pilosella. The scientific name Hieracium is of Greek origin and means 'hawk'. Hawkweed refers to the fact that many species of this genus grow at higher altitudes which are only accessible by hawks. According to other sources hawks sharpened their faces with the latex sap of hawkweeds (Zahn, 1987). During the sixteenth and seventeenth centuries, botanists used to include various other yellow-flowering Asteraceae under the name Hieracium, e.g. Sonchus spp., Tragopogon spp., Crepis spp., Hypochoeris spp., or Leontodon spp. (Marzell, 1972). Hieracium species are perennial rhizomatous herbs comprising 850-1000 species worldwide with most species occurring in western Europe, where especially mountainous regions are species-rich (Gottschlich, 1996). The genus Hieracium consists of the three subgenera Hieracium, Pilosella and Stenotheca and H. officinarum was thought to belong to the subgenus Pilosella, section Pratensina. Most species in this subgenus produce stolons for vegetative reproduction in contrast to species in the subgenera Hieracium and Stenotheca which do not produce stolons.
Sell and West (1976) and other authors prefer to consider Hieracium and Pilosella as separate genera and hence the name Pilosella officinarum. The recognition of a distinct genus is thought to be justified both morphologically (Pilosella is distinct from Hieracium by cypsela features) and phylogenetically (Bräutigam and Greuter, 2007). Detailed justification for this name change can be found in Bräutigam and Greuter (2007). For the purpose of this datasheet and in keeping with The Plant List (2013) the name Pilosella officinarum will be applied. Pilosella refers to the Latin word 'pilosus', which means 'hairy' (Zahn, 1987).
DescriptionTop of page
P. officinarum is a prostrate, monocarpic herb with a rosette of small, setose, oblanceolate, entire leaves and a single terminal shoot apex. Leaves are elliptic, 3-10 cm long, 1-5-2 cm in width, with distinctive white midvein. The lower leaf surface is covered with a dense layer of stellate hairs, and long, simple eglandular hairs cover both upper and lower leaf surfaces and the leaf margin (Sell and West, 1976). P. officinarum has a single flower head per stem. Florets are yellow, often with a red stripe on the outer face, resembling those of dandelions (Taraxacum spp.). Floral evocation results in the development of one or more axillary buds into stolons that bear further apical meristems at their tips and further dormant buds in the axils of their scale-leaves, which can reach a final length of 10-30 cm, occasionally with a terminal capitulum. Under certain conditions, stolon axillary buds may break dormancy and produce branching stolons. Each branch is potentially capable of developing into a new rosette. These daughter rosettes root adventitiously and their stolon connections atrophy. Daughter rosettes may also develop in situ from the axillary buds of the parent rosette. These growth patterns result in mat-forming growth (Bishop and Davy, 1985; Gottschlich, 1996). Since rosettes are monocarpic (semelparous), the parental rosettes will senesce and die (Bishop and Davy, 1985). The fruit is an achene up to 3 mm long, purple-black at maturity, with a pappus.
Plant TypeTop of page
DistributionTop of page
P. officinarum is native throughout Europe from close to 65° N to northern Portugal, Spain and Turkey in the south, and the Urals and Caucasus in the east (Zahn, 1987; Gottschlich, 1996). In Southern Norway it occurs up to 1000 m and in the Central Alps up to 3000 m (Meusel and Jäger, 1992). It is now widely naturalized in similar climates in New Zealand and North America, and possibly also in South America.
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.Last updated: 17 Feb 2021
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|Bosnia and Herzegovina||Present||Native|
|Federal Republic of Yugoslavia||Present||Native|
|Russia||Present||Present based on regional distribution.|
|Canada||Present||Present based on regional distribution.|
|-Newfoundland and Labrador||Present||Introduced||Invasive|
|-Prince Edward Island||Present||Introduced||Invasive|
|-Tasmania||Absent, Formerly present||2001|
|New Zealand||Present, Widespread||Introduced||1878||Invasive|
History of Introduction and SpreadTop of page
P. officinarum has been introduced to many other parts of the world either deliberately as a garden ornamental, or accidentally as a contaminant of pasture seed or packing material (Makepeace, 1985a; Birdsall and Quimby, 1996). In New Zealand, P. officinarum has been present since 1878 (Webb et al., 1988) and was probably introduced as a contaminant of agricultural seed (Makepeace, 1985b). Remaining relatively rare until the 1950s, where species of Hieracium/Pilosella have since spread dramatically (McMillan, 1992). In terms of overall geographical extent and the abundance within affected areas, P. officinarum is the most significant species (Hunter, 1992).
Risk of IntroductionTop of page
Further spread is highly probable, owing to the risks of both accidental movement as a seed contaminant of agricultural seed or deliberate introduction as an ornamental species. This is encouraged by the availability from commercial nurseries via web-sites. P. officinarum is listed as a quarantine pest in Oregon and Washington State (USDA-NRCS, 2016), New Zealand (Webb et al., 1988) and Australia (Rudman et al., 2002).
HabitatTop of page
Within its native range, P. officinarum is a plant of open, sandy and semi-dry grasslands. It occurs on sheep-grazed grasslands, along roadsides and on soil exposed by disturbance such as after construction work or locally in pastures where the soil is poor or stony. Furthermore, this species grows under sparse bushes, in sunny pine and oak forests and as a pioneer plant in ruderal habitats such as gravel and clay pits, quarries, and on fallow fields (Gottschlich, 1996). Soil conditions at these sites are moderately dry, alkaline, and rich in limestone to moderately acidic (Gottschlich, 1996).
In New Zealand, it is invasive in tussock grasslands, lawns, wasteland, river terraces, roadsides, rock outcrops, and pastures (Webb et al., 1988). The optimal rainfall range for vigorous hawkweed-dominated communities appears to be 600 to 1200 mm. Species of Hieracium/Pilosella show reduced vigour in very dry sites, and are known to occur in areas where the annual rainfall exceeds 3000 mm (Hunter, 1992). P. officinarum typically occurs on dry northerly slopes, areas of thin soil, and areas of depleted, open or intensively grazed land (Hunter, 1992). In North America, P. officinarum is a troublesome weed of fields and pastures (Fernald, 1950; Scoggan, 1979).
Habitat ListTop of page
|Terrestrial||Managed||Cultivated / agricultural land||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Managed grasslands (grazing systems)||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Disturbed areas||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Rail / roadsides||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Urban / peri-urban areas||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Natural / Semi-natural||Natural forests||Present, no further details|
|Terrestrial||Natural / Semi-natural||Natural grasslands||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Natural / Semi-natural||Riverbanks||Present, no further details||Harmful (pest or invasive)|
Hosts/Species AffectedTop of page
Biology and EcologyTop of page
P. officinarum typically possesses 2n=18, 36, 45, 54, 63 chromosomes (Sell and West, 1976) but laboratory crossings also revealed individuals with 72, 81 and 90 chromosomes (Gottschlich, 1996). Diploid populations (2n=18) are generally sexually reproducing and self-incompatible. Polyploid plants with an even chromosome number generally reproduce sexually (although some are also apomictic) whereas plants with uneven chromosome numbers reproduce by apomixis (Gottschlich, 1996). However, Rotreklova et al. (2002) recorded sexual reproduction of pentaploid P. officinarum, findings which increase the diversity of possible reproduction modes of those cytotypes having odd chromosome numbers.
In New Zealand, diploids are absent, and both tetraploids and pentaploids are facultative apomicts, though obligate sexual tetraploid biotypes of P. officinarum also occur (Houliston and Chapman, 2000). Pentaploids comprise approximately 60% of most field populations (Houliston and Chapman, 2000). The presence of various ploidy levels and a plethora of morphological variation has been recorded (Chapman and Brown, 2001). However, current New Zealand populations are probably composed of a complex of intra-specific hybrids and possibly interspecific hybrids, which are at least partially capable of sexual reproduction and thus back-crossing (Chapman and Brown, 2001).
Hybridization is possible with numerous other species of Hieracium/Pilosella. Examples of resulting species include H. x iseranum (P. floribunda x P. officinarum), H. x stoloniflorum (P. aurantiaca x P. officinarum) and H. x flagellare (P. caespitosa x P. officinarum).
In the northern hemisphere, rosettes of P. officinarum start producing stolons in April. Flowering occurs in May and June but later flowering can also occur. Seed is wind dispersed. Ripe flower heads contain approximately 54 (31-77) seeds (Winkler and Stöcklin, 2002). No persistent seed bank is evident for P. officinarum either in Europe (Roberts, 1986) or in New Zealand (Jenkins, 1992). In New Zealand, initiation of inflorescences and stolons of P. officinarum begins around November, with flowering becoming evident one to three weeks later (Jenkins, 1992). Because rosettes are monocarpic and die after setting seed, there can be a high turnover of rosettes within P. officinarum populations, with Makepeace (1985b) recording 5-173 new rosettes per 100 existing rosettes. Makepeace (1985b) also found that within existing P. officinarum populations in New Zealand, spread occurs mainly by vegetative means (i.e. stolon production) and rosettes originating from seed accounted for only 1% of all new plants in one area. Similar results were obtained for P. floribunda, an invasive hawkweed of Eurasian origin in North America, where only 1% of new plants in a population were derived from seedlings (Thomas and Dale, 1975). Nonetheless, seeds remain important for long distance spread. A mixed strategy of clonal growth and reproduction by seeds in P. officinarum may be necessary to maintain populations of this species in the presence of high interspecific competition and a shortage of open space (Winkler and Stöcklin, 2002).
Physiology and Phenology
P. officinarum rosettes originate either from seedlings or are produced vegetatively at the end of leafy, sometimes branched stolons up to 30 cm long (Gottschlich, 1996). Occasionally, daughter rosettes may also develop in situ from the axillary bud of the parent rosette, without a stolon, or from the leaf axil of stolon leaves. In spring, the terminal apex of rosettes undergoes transition to flowering and produces one, or sometimes two flower heads. At the same time, one or a few of the axillary meristems of the rosette leaves form stolons with new terminal rosettes that root and thus become independent. The mother rosettes decay after flowering and the stolon connections between mother and daughter rosettes also decay. The flowering probability of a rosette depends on its diameter. Winkler and Stöcklin (2002) showed that a 3 cm rosette in calcareous grassland in Switzerland has a flowering probability of 0.08 whereas larger rosettes of 5 cm diameter have a flowering probability of 0.65. The mean number of ripe seeds per flower head was 54 (Winkler and Stöcklin, 2002). Seed of P. officinarum germinate rapidly without after-ripening (Makepeace, 1985a) and seedlings that establish successfully reach their final rosette size in 8 to 10 weeks (Makepeace, 1985a).
Makepeace (1985a) found that vegetative propagation of P. officinarum increased with fertilizer application. Calcium nitrate increased the number of daughters produced and molybdenum-fortified superphosphate increased stolon length. In a glasshouse experiment, an inverse relationship was found between seed production and total stolon length per plant (Makepeace, 1985b).
P. officinarum contains umbelliferone, caffeic acid and chlorogenic acid (Makepeace et al., 1985). Umbelliferone is the most active compound present in P. officinarum leaves, from where it is washed into the soil when leaves die and is deleterious to root development under certain circumstances in field conditions (Makepeace et al., 1985). However, Makepeace et al. (1985) could not detect measurable levels of umbelliferone in the soil. Henn et al. (1988) also found umbelliferone and apigenin-glucoside in the roots; however, it is not known whether they serve a distinct role in plant defence against herbivory or allelopathy.
Within its native range, P. officinarum is an indicator plant of dry, nutrient-poor sites (Caputa, 1984). It occurs in warm temperate climates with occasional frost in winter (e.g. UK), temperate humid climates with a distinct but not very long winter (e.g. Germany), in the boreal zone with long winters but an average temperature of the warmest month above 10°C (e.g. Sweden), and also in continental climates.
In New Zealand, species of Hieracium/Pilosella are particularly abundant in sub-humid to humid montane to lower sub-alpine bio-climates. The optimal rainfall range for vigorous communities appears to be 600-1200 mm (Hunter, 1992). However, P. officinarum also occurs locally where annual rainfall exceeds 3000 mm (Hunter, 1992). P. officinarum is well adapted to both low soil moisture and low soil fertility (Rose et al., 1998). Rose et al. (1998) developed a preliminary 'grassland decline' model for P. officinarum invasion in short-tussock grasslands comprising five main factors: environment, disturbance, vegetation structure and composition, availability of P. officinarum propagules and life-history attributes of P. officinarum. Predisposing and trigger factors, as well as interactions between multiple factors, may increase the likelihood of P. officinarum invasion. Predisposing factors include: low rainfall, low soil moisture and fertility, long history of anthropogenic disturbance (i.e. grazing, browsing or burning), low stature, low canopy cover, abundant safe sites for establishment, many native species poorly adapted to grazing and trampling, proximity of P. officinarum populations (i.e. external seed rain but also local seed rain and vegetative spread), and life-history attributes of P. officinarum such as drought tolerance, tolerance to low soil fertility, rapid response to nutrient and moisture pulses, and vegetative and seed dispersal (Rose et al., 1998). Makepeace (1985a) investigated the growth and reproduction of P. officinarum at several sites in New Zealand where this species is dominant. The soil was yellow brown earth at all locations but with different depths and humidity levels: shallow dry hydrous, moderate dry hydrous, deep dry hydrous and hydrous. P. officinarum grows well at high nitrogen levels but is usually outcompeted by other plant species.
Latitude/Altitude RangesTop of page
|Latitude North (°N)||Latitude South (°S)||Altitude Lower (m)||Altitude Upper (m)|
Air TemperatureTop of page
|Parameter||Lower limit||Upper limit|
|Absolute minimum temperature (ºC)||-29|
|Mean annual temperature (ºC)||6||11|
|Mean maximum temperature of hottest month (ºC)||15||19|
|Mean minimum temperature of coldest month (ºC)||-4||3|
RainfallTop of page
|Parameter||Lower limit||Upper limit||Description|
|Mean annual rainfall||500||3000||mm; lower/upper limits|
Rainfall RegimeTop of page
Soil TolerancesTop of page
Special soil tolerances
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
|Aulacidea pilosellae||Herbivore||Plants|Leaves; Plants|Stems|
|Aulacidea subterminalis||Herbivore||Plants|Stems||to genus||New Zealand, Canada, USA||P. officinarum, H. flagellare and P. aurantiaca|
|Cheilosia psilophthalma||Herbivore||Plants|Growing point; Plants|Stems||to genus||New Zealand||P. aurantiaca, P. caespitosa, H. lepidulum, P. officinarum and H. praealtum|
|Cheilosia urbana||Herbivore||Plants|Roots||to species||Canada, USA, New Zealand||P. officinarum|
|Macrolabis pilosellae||Herbivore||Plants|Growing point; Plants|Inflorescence||to genus||New Zealand||P. caespitosa, H. lepidulum, P. officinarum and H. praealtum|
|Oxyptilus pilosellae||Herbivore||Plants|Whole plant||to genus||New Zealand||P. aurantiaca, H. lepidulum, P. officinarum and H. praealtum|
|Puccinia hieracii var. piloselloidarum||Pathogen||Plants|Leaves||to genus||New Zealand||‘self-introduced’, P. officinarum|
|Tephritis ruralis||Herbivore||Plants|Inflorescence; Plants|Seeds|
Notes on Natural EnemiesTop of page
Within its native range P. officinarum is not a weed, possibly due to the presence of specialized herbivores which develop on this species and thus reduce the plants' competitive ability. A number of specialized phytophagous insects attack P. officinarum in Europe (Grundy, 1989; Grosskopf, 1996; Sárospataki, 1999). The larvae of Tephritis ruralis (Loew.), a common tephritid in the flower heads of P. officinarum in Europe destroys up to 100% of the seeds with the fly larvae feeding on florets and the seeds. However, since vegetative propagation seems more important for the maintenance and expansion of existing populations, the main emphasis for biocontrol is on insects developing in the vegetative parts of the plant.
Five insects chosen for further investigation as biocontrol agents, of European origin, are at least genus-specific, and are permitted to be field-released in New Zealand (Syrett et al., 1999; Grosskopf et al., 2002; Klöppel et al., 2003). Oxyptilus pilosellae (Lepidoptera, Pterophoridae) develops on the above-ground plant parts of P. officinarum; Aulacidea subterminalis (Hymenoptera, Cynipidae) and Macrolabis pilosellae (Diptera, Cecidomyiidae) galls the stolon tips, meristems in leaf axils and rosette centres; Cheilosia urbana larvae (Diptera, Syrphidae) feed externally on the roots; and Cheilosia psilophthalma larvae (Diptera, Syrphidae) feed in leaf axils, at the base and tips of stolons and in the rosette centre.
Means of Movement and DispersalTop of page
Propagation occurs via stolons, rhizomes and seeds. Seeds are wind-dispersed.
All introductions of P. officinarum can be traced to anthropogenic sources (i.e. through human activity). Disturbance plays an important role for successful establishment of P. officinarum seedlings and expansion of existing populations (Rose et al., 1998; Jesson et al., 2000). Rosettes, seeds or plant fragments may be spread by machinery, dumping of contaminated garden refuse or transport of contaminated soil (DPIWE, 2003). P. officinarum was accidentally introduced into New Zealand, probably as a contaminant of agricultural seed (Makepeace, 1985b). P. officinarum was first recorded in 1861 in Michigan; it was originally collected in cemeteries, lawns, and waste areas in the USA, it is believed to have arrived in packing material rather than as a seed contaminant in North America (Birdsall and Quimby, 1996).
Deliberate introduction of P. officinarum is quite likely, as it is used as an ornamental plant and was used for medicinal purposes in the past. Such introduction is encouraged by the availability of seed and plants from commercial nurseries (Rudman et al., 2002; DPIWE, 2003).
Pathway VectorsTop of page
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Fruits (inc. pods)||weeds/seeds|
|Growing medium accompanying plants||weeds/leaves; weeds/roots; weeds/seeds|
|True seeds (inc. grain)||weeds/seeds|
|Plant parts not known to carry the pest in trade/transport|
|Stems (above ground)/Shoots/Trunks/Branches|
Impact SummaryTop of page
|Fisheries / aquaculture||None|
Economic ImpactTop of page
In New Zealand, P. officinarum invades and displaces the inter-tussock vegetation and at some sites subsequently displaces the fescue tussock, subsequently reducing the herbage available for grazing and the diversity of native vegetation (Makepeace, 1985b). Negative economic effects of this species thus include loss of production and negative impact on stock health (Grundy, 1989). It is estimated that invasive Hieracium/Pilosella species reduce the value of high country agricultural production in New Zealand by between NZ$1.1 and NZ$4.4 million annually (Grundy, 1989).
Impact: BiodiversityTop of page
Due to its mat-forming growth, P. officinarum has the potential to invade open space and thus outcompete native plants or forage species. By invading and displacing the inter-tussock vegetation, P. officinarum is able to increase to up to c. 80% ground cover (Makepeace, 1985b).
Social ImpactTop of page
In New Zealand, farmers have had to abandon their farms due to the drop in profitability caused by heavy infestation of species of Hieracium/Pilosella.
Risk and Impact FactorsTop of page
- Proved invasive outside its native range
- Highly adaptable to different environments
- Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
- Has high reproductive potential
- Negatively impacts agriculture
- Negatively impacts tourism
- Reduced amenity values
- Reduced native biodiversity
- Competition - monopolizing resources
- Highly likely to be transported internationally accidentally
- Highly likely to be transported internationally deliberately
- Difficult/costly to control
UsesTop of page
Grundy (1989) note several actual or potential benefits of species of Hieracium/Pilosella in New Zealand, including a source of umbelliferone (used in sun-screens and sun tan lotions), food source for stock, soil conservation, horticultural plants, pollen source for honey production, suppression of other weeds and seed for herbal purposes. However, the conclusion is that these benefits are negligible with regard to the negative impacts of this plant.
Uses ListTop of page
Similarities to Other Species/ConditionsTop of page
In Europe, P. officinarum can be confused with P. peleteriana, H. hoppeanum and P. tardans. However, the stolons of P. officinarum and P. tardans are long and slender and their leaves become smaller towards the tip, whereas the stolon leaves of P. peleteriana and H. hoppeanum do not get smaller towards the stolon tip and are closer to each other. Also, the involucral bracts of P. peleteriana and H. hoppeanum are 1.5-4 mm wide, whereas those of P. officinarum are (0.5-)1-2 mm wide (Gottschlich, 1996). In contrast to P. officinarum, the involucral bracts of P. tardans are without glandular hairs and are whitish due to presence of short silky hairs (Zahn, 1987).
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
The main method of control at present is to improve pasture land by application of fertilizer and oversowing with pasture species. However, species of Hieracium/Pilosella remain a problem on areas of limited potential economic development, abandoned land, reserves and national parks (Grundy, 1989). Timely oversowing and top dressing combined with intensive grazing show promise for control (Robertson, 1979). Makepeace et al. (1985) found that of all the plant species investigated, clover is the best competitor. Where perennial grasses, legumes, and other beneficial forbs are present in the plant community, fertilizers can help control Hieracium/Pilosella species by increasing the competitive ability of more desirable species.
Due to its low, mat-forming growth, mowing is not effective. Mechanical control is ineffective since small fragments of plants can root and form new populations. In addition, plants or plant parts can be accidentally transported by machinery and establish elsewhere.
Species of Hieracium/Pilosella have proved resistant to most herbicides, so that chemical control of the weed does not appear practical (Grundy, 1989). P. officinarum can be controlled with 2,4-D amine or ester, and a mecoprop + MCPA + dicamba formulation, although results have been variable. This variability in effectiveness was thought to be related to the time of application. The 2,4-D ester usually yielded better results than the amine formulation (Meeklah, 1980). However, total kill is unlikely and follow up with fertilizer and top dressing is considered essential (Grundy, 1989). A problem with chemical control is that the chemicals have as much, or more, impact on many desirable pasture species than they do on P. officinarum (Grundy, 1989). In many areas in New Zealand chemical control is uneconomic and thus not considered on a large scale (Grundy, 1989).
Since chemical and mechanical control methods are ineffective and/or not economical, a programme to develop biological control with insects and a pathogen was initiated in 1992 (Syrett and Smith, 1998). P. officinarum is not attacked to any noticeable degree by phytophagous insects in New Zealand (Syrett and Smith, 1998), therefore presenting a competitive advantage over native rangeland species. The rust fungus Puccinia hieracii var. piloselloidarum was chosen as a potential biological control agent. However, during the investigations prior to its introduction, it was detected in the field in New Zealand but further strains may need to be tested and released to infect the various biotypes of P. officinarum (Morin and Syrett, 1996). In addition to this rust fungus, five herbivorous insects of European origin, Oxyptilus pilosellae (Lepidoptera, Pterophoridae), Aulacidea subterminalis (Hymenoptera, Cynipidae), Macrolabis pilosellae (Diptera, Cecidomyiidae) Cheilosia urbana (Diptera, Syrphidae) and Cheilosia psilophthalma (Hymenoptera, Syrphidae) were studied and are approved for release in New Zealand (Syrett et al., 1999; Grosskopf et al., 2002; Klöppel et al., 2003). The insects attack different parts of the plant and are at least genus-specific.
A biocontrol programme for North America is in progress. However assessment of O. pilosellae,M. pilosellae, A. hieracii and C. psilophthalma have been discontinued. A. pilosellae causes small galls on the midrib of leaves, stolons and flower stalks of several Hieracium/Pilosella target species, and appears to have a restricted host range. The wasp is being studied in collaboration with Agriculture and Agri-Food Canada (AAFC) and Montana State University (MSU). A joint petition for field release of the gall wasp Aulacidea subterminalis in to the USA and Canada was submitted and approved in 2010. Since summer 2011, several releases have taken place in British Columbia, Canada and Montana, USA on H. flagellare and P. aurantiaca, and sites are being monitored. So far, establishment has only been confirmed on H. flagellaris. P. officinarum is the primary host of this gall wasp and is therefore very likely to establish when further releases are made on this target in North America.
A joint petition for the field release of the root-feeding hoverfly Cheilosia urbana in to North America was submitted to the United States Department of Agriculture – Animal and Plant Health Inspection Service (USDA-APHIS) Technical Advisory Group (TAG) and the Canadian Biological Control Review Committee in December 2014. The agent was approved for release in Canada by the Canadian Food Inspection Agency (CFIA) in April 2016 and recommended for release by TAG for the USA in May 2016. Surveys in Switzerland to collect the hoverfly in view of future releases in Nord America started in 2016.
All risks which predispose short-tussock grasslands to P. officinarum invasion should be minimized (Rose et al., 1998). Instead, emphasis should be placed on sound land management including adequate fertilizing, avoidance of heavy grazing and burning, rabbit control, sowing of competitive pasture species, controlled grazing in the absence of P. officinarum flower heads and the use of classical biological control agents which stress or even kill P. officinarum (Grundy, 1989; Wilson and Callihan, 1999).
ReferencesTop of page
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