Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Gaultheria shallon



Gaultheria shallon (salal)


  • Last modified
  • 27 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Host Plant
  • Preferred Scientific Name
  • Gaultheria shallon
  • Preferred Common Name
  • salal
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • G. shallon is an ericaceous shrub typically found as part of the understory of coniferous forests in the west coast of North American, from California to Alaska. It can form dense to almost impenetrable thicket...

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Gaultheria shallon (salal); habit, showing foliage and flowers. Mount Higgins Trail 640, Mount Baker-Snoqualmie National Forest, Washington State, USA. June, 2009.
CaptionGaultheria shallon (salal); habit, showing foliage and flowers. Mount Higgins Trail 640, Mount Baker-Snoqualmie National Forest, Washington State, USA. June, 2009.
Copyright©Walter Siegmund/via wikipedia - CC BY-SA 3.0
Gaultheria shallon (salal); habit, showing foliage and flowers. Mount Higgins Trail 640, Mount Baker-Snoqualmie National Forest, Washington State, USA. June, 2009.
HabitGaultheria shallon (salal); habit, showing foliage and flowers. Mount Higgins Trail 640, Mount Baker-Snoqualmie National Forest, Washington State, USA. June, 2009.©Walter Siegmund/via wikipedia - CC BY-SA 3.0
Gaultheria shallon (salal); leaves.
CaptionGaultheria shallon (salal); leaves.
Copyright©Crown Copyright 2011/GB Non-native Species Secretariat
Gaultheria shallon (salal); leaves.
LeavesGaultheria shallon (salal); leaves.©Crown Copyright 2011/GB Non-native Species Secretariat
Gaultheria shallon (salal); flowers. nr. Dungeness Recreation Area, Sequim, Washington State, USA. July, 2008.
CaptionGaultheria shallon (salal); flowers. nr. Dungeness Recreation Area, Sequim, Washington State, USA. July, 2008.
Copyright©Walter Siegmund/via wikipedia - CC BY-SA 3.0
Gaultheria shallon (salal); flowers. nr. Dungeness Recreation Area, Sequim, Washington State, USA. July, 2008.
FlowersGaultheria shallon (salal); flowers. nr. Dungeness Recreation Area, Sequim, Washington State, USA. July, 2008.©Walter Siegmund/via wikipedia - CC BY-SA 3.0
Gaultheria shallon (salal); habit, showing fruits and foliage. August, 2013.
CaptionGaultheria shallon (salal); habit, showing fruits and foliage. August, 2013.
Copyright©Darren Giles/via wikipedia - CC BY-SA 3.0
Gaultheria shallon (salal); habit, showing fruits and foliage. August, 2013.
FruitsGaultheria shallon (salal); habit, showing fruits and foliage. August, 2013.©Darren Giles/via wikipedia - CC BY-SA 3.0


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Preferred Scientific Name

  • Gaultheria shallon Pursh

Preferred Common Name

  • salal

Other Scientific Names

  • Brossaea shallon (Pursh) Kuntze
  • Shallonium serrulatum Raf.

International Common Names

  • English: shallon

Local Common Names

  • Germany: shallon-rebhuhnbeere; shallon-scheinbeere

EPPO code

  • GAHSH (Gaultheria shallon)

Summary of Invasiveness

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G. shallon is an ericaceous shrub typically found as part of the understory of coniferous forests in the west coast of North American, from California to Alaska. It can form dense to almost impenetrable thickets that dominate the site, reducing forest regeneration and shadowing native plant species. In its native range it has moderate to low invasiveness. Outside of this range it has been reported as a particular problem in the UK, where it can form dense thickets in acid soils which prevent other more valuable pasture species from establishing. Minor introductions have also been reported in France, Germany, Ireland and New Zealand.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Ericales
  •                         Family: Ericaceae
  •                             Genus: Gaultheria
  •                                 Species: Gaultheria shallon

Notes on Taxonomy and Nomenclature

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The genus Gaultheria was first created by the German American botanist Pehr Kalm in his “Guide of Canada”, in homage to the French Canadian botanist Jean Françoise Gaultier.

The names shallon and salal are of Amerindian origin, probably from the Chinook language sallal, recorded during Lewis and Clack expedition as shelwel, shellwell (Oxford Dictionary, 2014).


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G. shallon is a perennial, evergreen shrub with a growth form from sprawling to erect. G. shallon can reach 0.2-5 m tall, growing strongly from rhizomes. Leaves are evergreen, alternate, round to ovate, pointed, glossy green, with a leathery texture. The lower side of the leaf is rough and lighter green. Each leaf has a base rounded or cordate, margins finely serrulate (with the “teeth” fimbriate apically), apex mucronate/apiculate or aristate, surfaces glabrous, reaching 5-10 cm long (Flora of North America Editorial Committee, 2015). Young shoots are red. Mature bark and twigs of G. shallon are grayish-brown and smooth. The twigs change angles between each node, giving it a zigzag appearance. The flowers are hermaphroditic (have both male and female organs) and are pollinated by insects. The inflorescence consists of a bracteate raceme, one-sided, with 5 to 15 flowers at the ends of branches. Flowers are white to pale pink, urn-shaped and they appear in late spring and early summer. Each flower is composed of a deeply five-parted, glandular-haired calyx and an urn-shaped pink to white, glandular to hairy, five-lobed corolla, 7-10 mm long. Flowers mature to fleshy, reddish to blue, rough-surfaced, hairy, nearly spherical fruit 6-10 mm in diameter (Pojar and MacKinnon, 2004).

Plant Type

Top of page Perennial
Seed propagated
Vegetatively propagated


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The centre of origin of G. shallon comprises the west coast of North America; Alaska, British Columbia, Washington, Oregon and California.

A record for G. shallon in Nei Menggu, China has been reported (CPNWH, 2015) but it is likely that this record is invalid.

Distribution Table

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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.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasivePlantedReferenceNotes


ChinaPresentConsortium of Pacific Northwest Herbaria, CNPWHRecorded in Nei Menggu. Record likely to be invalid.

North America

CanadaPresentPresent based on regional distribution.
-British ColumbiaPresentNative Natural Consortium of Pacific Northwest Herbaria, CNPWH
USAPresentPresent based on regional distribution.
-AlaskaPresentNative Not invasive Natural Consortium of Pacific Northwest Herbaria, CNPWH
-CaliforniaPresentNative Not invasive Consortium of Pacific Northwest Herbaria, CNPWH
-OregonPresentNative Not invasive Natural Consortium of Pacific Northwest Herbaria, CNPWH
-TexasPresentIntroducedDiscover Life, 2015
-WashingtonPresentNative Natural Consortium of Pacific Northwest Herbaria, CNPWH


FrancePresentIntroduced Invasive EPPO, 2014; Meyer, 2015
GermanyPresentIntroducedDiscover Life, 2015; Encyclopedia of Life, 2015
IrelandPresentIntroduced1961 Invasive EPPO, 2014Introduced in 1961 for food and to provide cover
NetherlandsPresentIntroduced Invasive EPPO, 2014
SpainPresentIntroduced Not invasive Discover Life, 2015Present in a botanical garden
UKWidespreadIntroduced1828 Invasive Pojar and Mackinnon, 2004; EPPO, 2014; Encyclopedia of Life, 2015


AustraliaPresentPresent based on regional distribution.
-TasmaniaPresentIntroduced1972Council of Heads of Australasian Herbaria, 2014
New ZealandPresentIntroduced1954 Invasive Webb et al., 1988

History of Introduction and Spread

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G. shallon was introduced to Britain from North America in 1828 by David Douglas, who intended the plant to be used as an ornamental (Pojar and Mackinnon, 2004). By 1914 it could be seen growing in the wild. After establishing in heathlands as a mild invasive species, its spread was traditionally controlled by cattle ranchers. Probably as a result of these practices and in view of its potential as forage, G. shallon was introduced into Ireland in 1961 (EPPO, 2014).

Further introductions in Europe are likely to be associated with releases from botanical gardens or collectors. In New Zealand is believed that G. shallon has been naturalized since 1946 (Webb et al., 1988). It was introduced into Tasmania, Australia in 1973 where it has also naturalized (Council of Heads of Australaisan Herbaria, 2014).


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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Ireland UK 1961 Forage (pathway cause) Yes EPPO (2014)
New Zealand North America 1946-1954 Yes Webb et al. (1988)
UK North America 1828 Ornamental purposes (pathway cause) Yes Pojar and Mackinnon (2004)

Risk of Introduction

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The risk of G. shallon being introduced into new areas is likely related to its availability in the North American market for ornamental purposes. The risk of spread, however, is probably low east of the Rocky Mountains, as the climatic conditions in continental North America are unfavourable for this species. This species is however readily spread by birds eating the berries and translocating them into new areas.


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G. shallon forms thickets at forest edges and in recently cut coniferous to mixed stands, becoming less dense as the tree canopy is more developed. G. shallon tolerates open sun and some shading. If heavily shaded, plants become elongated and eventually die. It grows in the understory, dominant in a variety of lowland to montane, coniferous or mixed evergreen forests. It is often a component in Douglas-fir (Pseudotsuga menziesii) forests and western hemlock (Tsuga heterophylla) or western hemlock-western redcedar (Thuja plicata) forests. In full sun, it forms dense thickets whilst in shade, it is more spindly. It is ericaceous and can tolerate drought, but is not tolerant of severe frost. In the UK it thrives on lowland heath, a rare habitat, which provides acidic soil and is warmer than upland heath.

Habitat List

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Terrestrial – ManagedManaged forests, plantations and orchards Principal habitat Natural
Disturbed areas Secondary/tolerated habitat Natural
Rail / roadsides Secondary/tolerated habitat Natural
Terrestrial ‑ Natural / Semi-naturalNatural forests Principal habitat Natural
Riverbanks Secondary/tolerated habitat Natural
Wetlands Secondary/tolerated habitat Natural
Rocky areas / lava flows Secondary/tolerated habitat Natural
Coastal areas Principal habitat Natural
Coastal dunes Secondary/tolerated habitat Natural

Hosts/Species Affected

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G. shallon affects many pasture species mainly by overshadowing them and forming dense thickets that do not allow other plant species to emerge and grow.

Biology and Ecology

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G. shallon has a chromosome number of 22 (Chinnappa and Chmielewski, 1987).

Reproductive Biology

G. shallon can reproduce both from seed and from vegetative regeneration. However, new seedling establishment is apparently insignificant where plants have already established. In these areas, the expansion of existing clones occurs through layering, sprouting of rhizomes, root suckering and sprouting from the stem base (Haeussler and Coates, 1986).

Physiology and Phenology

G. shallon has a wide native range and through local adaptation it exhibits variable annual and geographic phenological development. Plants generally flower in late spring or early summer, from May to July (Kruckeberger, 1982). Fruit ripening occurs from August through to October and fruits may persist on the stem until December (Whittaker, 1954; Dimock et al., 1974; Haeussler and Coates, 1986).


This species is an evergreen woody shrub that once established expands vigorously from rhizomes. Longevity of individual plants is unknown, but the clones remain on site many decades.

Environmental Requirements

G. shallon can be found on soils derived from a wide range of parent rocks, including diorite, breccia and basalt, serpentine, granite and metamorphic rock (Whittaker, 1954; Whittaker, 1960; Sawyer et al., 1977; Halverson et al., 1986). Elevation ranges from sea level to approximately 1000 m, with the limit lowering in the northern reaches of the distribution limit. Generally, G. shallon grows better on moist sandy or peaty soils, but it can be found on a wide variety of mineral and organic soils, including shallow rocky soils, sand dunes, coarse alluvium, glacial till and peat (Hawk and Zobel, 1974; Haussler and Coates, 1986). G. shallon requires little nutrients and it can grow on poor to moderately rich soils (Klinka et al., 1989; Prescott et al., 2003). This shrub prefers soils with a neutral to slightly acid pH, but it can grow well in acid soils up until pH 4.0. The growth form of G. shallon can change depending on site conditions, with plants assuming a dwarfed or mat-like growth form on shallow, droughty soils. G. shallon commonly grows on decaying wood and stumps. It can also grow as an epiphyte on living trees in extremely humid areas (Hauessler and Coates, 1986).

Preferred habitats for G. shallon are sunny edges, dappled shade or shady edges of woodlands. G. shallon grows in cool, humid to perhumid, mesothermal climates (Klinka et al., 1985, 1989). Winters are typically mild with little snow accumulation (Haussler and Coates, 1986). G. shallon reaches its greatest size and abundance in the foggy maritime temperate forests along the Pacific Coast (van Meter, 1985). Plants can survive to temperatures as low as -15 ºC, but they are sensitive to frost (Haussler and Coates, 1986).


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C - Temperate/Mesothermal climate Preferred Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Tolerated Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter Tolerated Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)
Df - Continental climate, wet all year Tolerated Continental climate, wet all year (Warm average temp. > 10°C, coldest month < 0°C, wet all year)

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
30 60

Air Temperature

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Parameter Lower limit Upper limit
Absolute minimum temperature (ºC) -15

Rainfall Regime

Top of page Winter

Soil Tolerances

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Soil drainage

  • free
  • seasonally waterlogged

Soil reaction

  • acid
  • neutral

Soil texture

  • light
  • medium

Special soil tolerances

  • infertile
  • shallow

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Boeremia exigua Pathogen Adults/Seedlings not specific N/A
Mycosphaerella pyrolae Pathogen British Columbia
Phyllosticta gaultheriae Pathogen Adults/Seedlings to genus

Notes on Natural Enemies

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A number of fungal pathogens have been reported on G. shallon. These include, Phoma exigua [Boeremia exigua] Phyllosticta gaultheriae and Phyllostic pyrolae [Mycosphaerella pyrolae] (Shamou and Zhao, 2005; Zhao and Shamou, 2006).

Means of Movement and Dispersal

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Natural Dispersal

G. shallon is naturally dispersed over short distances through the production of rhizomes.

Vector Transmission

The berries are attractive to birds and are consumed and excreted into new areas facilitating its spread.

Intentional Introduction

G. shallon was introduced into the British Isles as forage and cattle cover in the early nineteenth century and again in mid twentieth century. It was also planted for game cover in woods and on heaths. It was also introduced into botanical gardens for ornamental purposes where it has since escaped.

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Host and vector organismsSeeds transported to new areas after ingestion and egestion by birds Yes Plant Life, 2015

Environmental Impact

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Impact on Habitats

G. shallon is a strong competitor for nutrients. In nutrient poor sites it can outcompete trees or other shrubs by being the first species to reach and use the available nutrients (especially nitrogen), reducing other species growth (Prescott et al., 2003; Prescott and Sajedi, 2008). G. shallon can also influence the mineralization of nitrogen through the release of tannins (Prescott et al., 1996).

Impact on Biodiversity

G. shallon can form dense thickets through the development of suckers from roots and rhizomes. As a result, G. shallon can rapidly take over large areas as the thickets can shade out any vegetation underneath and provide very little growing space for other species. This can decrease plant diversity in particular that of shade intolerant species.

Risk and Impact Factors

Top of page Invasiveness
  • Invasive in its native range
  • Proved invasive outside its native range
  • Has a broad native range
  • Abundant in its native range
  • Tolerant of shade
  • Highly mobile locally
  • Long lived
  • Has high reproductive potential
  • Has propagules that can remain viable for more than one year
  • Reproduces asexually
Impact outcomes
  • Conflict
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Modification of nutrient regime
  • Negatively impacts agriculture
  • Negatively impacts forestry
  • Reduced native biodiversity
Impact mechanisms
  • Allelopathic
  • Competition - monopolizing resources
  • Competition - shading
  • Competition - smothering
Likelihood of entry/control
  • Highly likely to be transported internationally deliberately


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Economic Value

In the Pacific Northwest, G. shallon is the heart of a local but important industry of cut flowers and therefore has some economic value. Wild G. shallon boughs are harvested and used as a floral green in floral arrangements (Ballard and Huntsinger, 2006).

Social Benefit

G. shallon berries were a large component of traditional North American diets due to their abundance and ease of harvest. Several tribes have used the berries as part of feasts, mixed with salmon eggs and the leaves as hunger suppressant (Pojar and MacKinnon, 2004). G. shallon can be sustainably harvested for a large number of years before the growth of the plant is reduced, as it is frugal in nutrient needs and regenerates quickly. G. shallon berries taste similar to, the bilberries (Vaccinium myrtillus), another member of the Ericaceae family. Fruits can be eaten raw, cooked or dried for later use (Grieve, 1971; Hedrick, 1972; Simmons, 1972; Facciola, 1998; Pojar and Mackinnon, 2004). Dried fruits are used as sweeteners and in jams, preservatives, or drinks (Facciola, 1998). The leaves can be used for making tea (Turner, 1979). Several traditional and natural dyes have been created from G. shallon. From the berries it is possible to obtain a dark purple dye and green-yellow dye from the infusion of the leaves (Moerman and Eierman, 1998). 

In traditional medicine, G. shallon has been used as an astringent, a poultice and a stomach tonic. The poultice consists of a mixture of the toasted, pulverized leaves. The plaster can be applied to cuts and insect bites and leaves can be chewed and applied to burns and sores. The stomach tonic is made from an infusion of the leaves and helps to reduce internal inflammation such as stomach ulcers, heart burn, treat diarrhea, period pain, coughs and tuberculosis (Moerman and Eierman, 1998).

Environmental Services

Environmental services within forest and wetland ecosystems provided by G. shallon in its native range include supporting services such as primary production, nutrient recycling and soil formation, regulating services such as carbon sequestration, erosion control and soil stability and hydrological stabilization. Mammals which may use the berries as food include the red squirrel (Sciurus vulgaris), Townsend's chipmunk (Neotamias townsendii), Douglas' squirrel (Tamiasciurus douglasii) and the black bear (Ursus americanus). In the UK cattle will also feed on the berries. In its native range the fruit are a good food source for birds such as the blue grouse (Dendragapus species) and the band-tailed pigeon (Patagioenas fasciata). In addition to this, in both its native and introduced range many species of songbirds feed on the fruit when available. Hummingbirds may also feed on the flowers.

G. shallon is also an important plant in gardening, especially in its native range and in many parts of North America. It is often used as a ground cover plant for a shady position under trees which spreads slowly by means of suckers (Brickell, 2010). G. shallon may also be used to make green fences for which seedlings should be spaced about 90 cm apart each way (Thomas, 1970). The reason for this is that G. shallon can grow very rapidly and densely. G. shallon is often used to “deer-proof” gardens as the foliage is very dense and usuaally not favored by deer. However, other thicket forming species may better serve in this role as reports exist of mule deer (Odocoileus hemionus), black-tailed deer (O. hemionus columbianus) elk (Cervus canadensis) and small mammals such as beaver (Castor species) feeding on foliage.

Uses List

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Animal feed, fodder, forage

  • Invertebrate food


  • Erosion control or dune stabilization
  • Land reclamation


  • Botanical garden/zoo
  • Ornamental

Human food and beverage

  • Beverage base
  • Emergency (famine) food
  • Fruits
  • Leaves (for beverage)


  • Dyestuffs

Medicinal, pharmaceutical

  • Traditional/folklore

Detection and Inspection

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G. shallon can be identified using the 'Key to Genera and Species for Ericaceous' plants provided by the Flora of North America Editorial Committee (2015).

Prevention and Control

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Public Awareness

Outside of its native range it is important that foresters, cattle ranchers, protected areas managers and the general public are made aware of the existence of this shrub in the regions that they work so they can try to control its spread.


Physical/Mechanical Control

Mechanical control is often ineffective with G. shallon owing to its capacity to sprout from rhizomes. In fact, if applied carelessly it may be counter effective and increase spread (USDA Forest Service, 2015).

Fire is not recommended as an eradication measure, as fire can consume the aboveground part, but the shrub can survive by regeneration from the underground structures (Yerkes, 1960; Hawkes et al., 1990).

Biological Control

Control of this species by biological control is currently being considered. Potential biocontrol agents include a number of fungal pathogens identified as natural enemies of G. shallon (Shamoun and Zhao, 2005; Zhao and Shamoun, 2006).

In the UK, cattle ranching can be used to break continuous thickets and reduce G. shallon to a mere component of heathland vegetation.

Chemical Control

Fertilization in mixed forests with presence of G. shallon ensures adequate levels of nutrients for trees and other canopy vegetation, reducing the competitive effect of G. shallon (Prescott et al., 2003; Blanco, 2007). G. shallon is resistant to many herbicides including 2,4-D, 2,4,5-T, amitrole, picloram and silvex (fenoprop) (Stewart, 1974a; Bovery, 1977; Otchera-Boateng and Herming, 1990). Mode of herbicide application, season and site characteristics all have a great influence on the response of G. shallon to herbicides (Stewart, 1974b; D’anjou, 1990). Herbicides are however often impractical or prohibitively expensive to be effective, owing to the need for repeated application. G. shallon is most susceptible to foliage sprays at budbreak, although many plants recover later from damage (Stewart, 1974b).

Gaps in Knowledge/Research Needs

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Additional research on the ability to reduce the spread of G. shallon through changes in soil fertility (fertilization and other soil amendments, planting of preferred species) is recommended.


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22/04/15 Original text by:

Yueh-Hsin Lo, Universidad Pública de Navarra, Spain.

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