California Pest Rating for
Vachellia nilotica: Prickly acacia
Solanales: Febaceae (Caesalpinioideae)
Pest Rating: A | Proposed Seed Rating: P
PEST RATING PROFILE
Initiating Event:
Vachellia (Acacia) nilotica is a federal noxious weed and is one of the 20 worst weeds in Australia because of its invasiveness, potential to spread, economic and environmental impacts. This invasive weed is currently not present in California but the climate conditions in the state are favorable for its growth and establishment. There is currently no pest rating designated for V. nilotica. A pest rating proposal is needed to assign a permanent rating.
History & Status:
Background: Vachellia nilotica (L.) P.J.H. Hurter & Mabb. is a medium sized tree that can reach a height of 10 m. The crown is flat or round and branches can droop downward. Young branches are smooth and grey to brown in color. Leaves are twice compound. The flowers are yellow, borne in small heads 1 cm in diameter and appear from September to January depending upon the rainy season. Pods are flat, straight or slightly curved, are fleshy when young with reddish hairs and are deeply constricted between each seed; they do not split but break open. This species occurs in wooded grassland and scrub escarpment, low lying forests, in deep soil and along rivers (South Africa National Biodiversity Institute, 2005).
Vachellia nilotica was introduced in Australia as a source of gum arabic and was cultivated as a fodder and shade plant for livestock in semi-arid pastures. It is also grown as garden ornamental in drier inland areas in Australia (Environmental Weeds of Australia, 2016).
Vachellia nilotica prefers semi-arid, warmer temperate, and sub-tropical regions but is also found in tropical environments and will grow near water sources in arid areas. It is most commonly found growing in grasslands, pastures and open woodlands. Within these plant communities it inhabits floodplains, open plains, gullies, areas near waterways (i.e. creeks and streams) and areas near other water sources (i.e. dams and bores). It also grows on recently cleared land, near stockyards and farm buildings, and along roadsides. (Environmental Weeds of Australia, 2016).
Worldwide Distribution: Vachellia nilotica is native to the arid and semi-arid regions of Africa and western Asia, the Indian sub-continent (i.e., India, Pakistan, and Myanmar) and the Arabian peninsula (i.e., Oman and Yamen). It has been introduced in China, Australia, the Caribbean, Indian Ocean islands, Mauritius, the United States, Central America, South America and the Galápagos Islands. It has naturalized in several countries where it has been introduced as a medicinal, forage and fuelwood plant (GRIN Database).
In the United States, it has been introduced in Arizona, California and Florida, Puerto Rico and Virgin Islands in the past. (Scher et.al, 2015).It has been introduced in China, Australia (in Northern Territory and Queensland where it is considered to be a pest plant of national importance), the Caribbean, Indian Ocean islands, Mauritius, the United States, Central America, South America and the Galápagos Islands. It has naturalized in several countries where it has been introduced as a medicinal, forage and fuelwood plant. It has been introduced in China, Australia (in Northern Territory and Queensland where it is considered to be a pest plant of national importance), the Caribbean, Indian Ocean islands, Mauritius, the United States, Central America, South America and the Galápagos Islands. It has naturalized in several countries where it has been introduced as a medicinal, forage and fuelwood plant.
Official Control: Vachellia nilotica is a federal noxious weed (Federal Noxious Weed Regulations, 2010) and is listed as a harmful organism in French Polynesia, Honduras and New Zealand (PCIT-PExD).
California Distribution: Vachellia nilotica is not found growing in the natural environment in California.
California Interceptions: Vachellia nilotica has never been intercepted by CDFA through any detection activities (border stations, high risk pest exclusion, detection surveys etc.).
The risk Vachellia nilotica (prickly acacia) would pose to California is evaluated below.
Consequences of Introduction:
1) Climate/Host Interaction: Vachellia nilotica has the ability to grow in warm deserts, the south coast area of California is a possible habitat as these areas provide warmer and near tropical environments for its growth. However, the risk of invasion is high in near tropical areas where there are both good water supply to promote high seed production and presence of livestock to disperse seeds. It receives a Medium (2) in this category.
Evaluate if the pest would have suitable hosts and climate to establish in California. Score:
– Low (1) Not likely to establish in California; or likely to establish in very limited areas.
– Medium (2) may be able to establish in a larger but limited part of California.
– High (3) likely to establish a widespread distribution in California.
2) Known Pest Host Range: Weeds do not need one host but grow wherever ecological conditions are favorable. Vachellia nilotica receives a High (3) in this category.
Evaluate the host range of the pest. Score:
– Low (1) has a very limited host range.
– Medium (2) has a moderate host range.
– High (3) has a wide host range.
3) Pest Dispersal Potential: Vachellia nilotica reproduces mainly by seed. It flowers in 3-4 years in ideal conditions. Mature tree can produce 200-3000 pods, each pod carrying 8-16 seeds. Seed production is higher during wet years where trees are close to water channels (Carter, 1998). Seeds are dispersed by large herbivores like cattle and sheep. Transportation of livestock that have ingested seeds can lead to dispersal over long distance. Seeds can also spread by water, particularly during floods after heavy rains and by mud adhering to legs of animals or vehicles. Strong winds can also carry seeds pods over short distances (Environmental Weeds of Australia, 2016). Vachellia nilotica receives a Medium (2) in this category.
Evaluate the natural and artificial dispersal potential of the pest. Score:
– Low (1) does not have high reproductive or dispersal potential.
– Medium (2) has either high reproductive or dispersal potential.
– High (3) has both high reproduction and dispersal potential.
4) Economic Impact: The spread of Vachellia nilotica trees can reduce the amount of available pasture for livestock. Dense thickets of V. nilotica trees can restrict access, impede the movement of vehicles and livestock, and may even reduce land values. Irrigation systems can become more expensive to operate because the tree can use some of the water (CABI 2017). Being a federal noxious weed and if it were to establish in California, it could impact international trade. (USDA APHIS Weed Risk Assessment). It receives a (High) in this category.
Evaluate the economic impact of the pest to California using the criteria below.
Economic Impact: A, C, G
A. The pest could lower crop yield.
B. The pest could lower crop value (includes increasing crop production costs).
C. The pest could trigger the loss of markets (includes quarantines).
D. The pest could negatively change normal cultural practices.
E. The pest can vector, or is vectored, by another pestiferous organism.
F. The organism is injurious or poisonous to agriculturally important animals.
G. The organism can interfere with the delivery or supply of water for agricultural uses.
Economic Impact Score: 3
– Low (1) causes 0 or 1 of these impacts.
– Medium (2) causes 2 of these impacts.
– High (3) causes 3 or more of these impacts.
5) Environmental Impact: Vachellia nilotica can outcompete pasture grasses for water in open forest and woodlands, and grasslands. Such losses of groundcover can facilitate water and wind erosion and leads to soil degradation. Serious invasion by this species can heavily disrupt natural communities. Approximately seven million hectares of the Mitchell grass plains in northern Australia have been infested by V. nilotica. Establishment of this species can cause a significant change in vegetation structure and can threaten the integrity and biodiversity of grassland communities. Changes in vegetation can pose a threat to survival of endangered species in these areas (Environmental Weeds of Australia, 2016). It receives a High (3) in this category.
Environmental Impact: A, B, C
A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.
B. The pest could directly affect threatened or endangered species.
C. The pest could impact threatened or endangered species by disrupting critical habitats.
D. The pest could trigger additional official or private treatment programs.
E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.
Score the pest for Environmental Impact. Score:
– Low (1) causes none of the above to occur.
– Medium (2) causes one of the above to occur.
– High (3) causes two or more of the above to occur.
Consequences of Introduction to California for Vachellia nilotica (prickly acacia): High (13)
Add up the total score and include it here.
–Low = 5-8 points
–Medium = 9-12 points
–High = 13-15 points
6) Post Entry Distribution and Survey Information: Vachellia nilotica has never been found in the environment and receives a Not established (0) in this category.
Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.
–Not established (0) Pest never detected in California, or known only from incursions.
–Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).
–Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.
–High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.
Final Score:
The final score is the consequences of introduction score minus the post entry distribution and survey information score: High (13).
Uncertainty:
Vachellia nilotica is a listed as a federal noxious weed that may be introduced to California for cultivation as a fodder and shade plant for livestock in pasture areas and also as garden ornamentals in the inland areas. Because this species is economically useful, introduction can be possible through international transport by passengers. There are nine species in the Vachellia nilotica species complex; this can make it difficult to identify. Early detection surveys can confirm the presence of Vachellia nilotica. Since it has not established in California, its ability to invade the warm, dry areas of California is unknown.
Conclusion and Rating Justification:
Vachellia nilotica has not been found in the natural environment of California. If this species were to be cultivated deliberately or if introduced accidently, it could cause significant economic and environmental impacts. Therefore, as it is not yet established in California and invasion is possible, an “A” rating is justified.
References:
CABI, 2017. Acacia nilotica. In: Invasive Species Compendium. Wallingford, UK: CAB International. Accessed 10/11/2017
http://www.cabi.org/isc/datasheet/2342
CARTER, J. O. 1998. 7.2 Acacia nilotica: A tree legume out of control. Pp. 338–351 in H. M. Shelton and R. C. Gutteridge (eds.), Forage tree legumes in tropical agriculture. Tropical Grassland Society of Australia, St. Lucia, Queensland. Accessed 10/12/2017
https://www.cabdirect.org/cabdirect/abstract/19940601700
Environmental Weeds of Australia for Biosecurity Queensland 2016. Vachellia nilotica
Accessed 10/12/2017.
https://keyserver.lucidcentral.org/weeds/data/media/Html/vachellia_nilotica.pdf
Germplasm Resources Information Network (GRIN) Database 2015. Vachellia Nilotica (L.) P.J.H. Hurter & Mabb. Accesses 10/11/2017
https://npgsweb.ars-grin.gov/gringlobal/taxonomydetail.aspx?465206
Phytosanitary Certificate Issuance & Tracking System (PCIT), Phytosanitary Export Database (PExD), USDA, APHIS. Accessed 10/10/2017
https://pcit.aphis.usda.gov/PExD/faces/ReportFormat.jsp
South African National Biosecurity Institute 2005. Biodiversity of Life. Vachellia nilotica subsp. Kraussiana. Accessed 10/10/2017
http://pza.sanbi.org/vachellia-nilotica-subsp-kraussiana
Scher, J. L., D. S. Walters, and A.J. Redford. 2015. Federal noxious weed disseminules of the U.S., Edition 2.2. California Department of Food and Agriculture, and USDA APHIS Identification Technology Program. Fort Collins, CO. [10/11/2017]
http://idtools.org/id/fnw/factsheet.php?name=14575
Update of Federal Noxious Weed Regulations 2010. A Rule by USDA Animal and Plant Health Inspection Services.
https://www.federalregister.gov/documents/2010/11/10/2010-28346/update-of-noxious-weed-regulations
Weed Risk Assessment for Acacia Nilotica (L.) Willd. Ex Delile. Version 6, June 2, 2009. USDA Animal and Plant Health Inspection Services. National Weed Program Risk Assessment.
https://www.aphis.usda.gov/plant_health/plant_pest_info/weeds/downloads/wra/AniloticaWRA.pdf
Author:
Raj Randhawa, 1220 ‘N’ Street, Room 221, Sacramento CA 95814, (916) 654-0317, plant.health[@]cdfa.ca.gov
Responsible Party:
Dean G. Kelch, Primary Botanist; California Department of Food and Agriculture; 1220 N Street, Sacramento, CA 95814; Tel. (916) 403-6650; plant.health[@]cdfa.ca.gov.
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Pest Rating: A | Proposed Seed Rating: P
Posted by ls
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