California Pest Rating Proposal
Asclepias physocarpa (balloon plant)
Current Pest Rating: Q
Proposed Pest Rating: C | Proposed Seed Rating: None
Asclepias physocarpa is currently Q-rated and was recently intercepted at the Benton Border Station (PDR BE0P06666758). A pest rating proposal is required to support an official pest rating.
History & Status:
Background: Asclepias physocarpa, commonly called balloon plant, is native to southeast Africa. It is an upright, shrubby perennial that typically grows 4-6′ tall and has lanceolate green leaves. This milkweed family member is perhaps best noted for its soft, spherical (balloon-like), lime-green seed pods, which are 5-7.5 cm long and covered with soft spines 7-10 mm long7. Pods change in color to tan before splitting open in the fall to release large numbers of small, black seeds, which measure approximately 4.5 mm long by 2 mm wide and are topped with a tuft of silky-white hairs approximately 3 cm long. These seeds are wind-dispersed1, 3.
Asclepias physocarpa is a food plant for the larvae of the monarch butterflies (Danaus spp.). The caterpillars are immune to the poisonous alkaloids in Asclepias physocarpa and have developed the ability to store them and pass them on to the pupa and adult butterfly, that are then unpalatable and/or poisonous to predators5.
Asclepias physocarpa is sometimes placed in the segregate genus Gomphocarpus, but recent evidence support retaining it in the large genus Asclepias (milkweeds) 2.
Worldwide Distribution: Asclepias physocarpa is native to South Africa, Swaziland, and Mozambique. It was introduced to various Mediterranean countries, China, India, Mexico, Central America, tropical South America, and Western Australia1.
Official Control: Asclepias physocarpa is not considered to be a noxious weed by any state government authorities6. However, it is listed as an invasive weed in Hawaii, French Polynesia, the Canary Islands, New Caledonia, China, Australia, Cuba, Jamaica, India, and Italy1.
California Interceptions: One recent interception record (PDR BE0P06666758) was reported in the Pest and Damage Record Database by CDFA4. A few voucher specimens have been collected from gardens and in disturbed areas near new developments in southern CA.
The risk Asclepias physocarpa (Balloon Plant) would pose to California is evaluated below.
Consequences of Introduction:
1) Climate/Host Interaction: Asclepias physocarpa can grow in waste places, disturbed sites, and roadsides. It may able to establish in a larger but limited part of California. Therefore, it receives a Medium (2) in this category.
Evaluate if the pest would have suitable hosts and climate to establish in California:
– 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: Asclepias physocarpa does not require any one host, but grows wherever ecological conditions are favorable. It receives a High (3) in this category.
Evaluate the host range of the pest.
– 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: Asclepias physocarpa spreads by seeds and each seed has a tuft of silky hairs that facilitates dispersal by wind and water. They may also be dispersed as a contaminant of crops, fodder, soil, or in mud attached to animals or machinery1. Each plant produces several hundred seeds per year. It receives a Medium (2) in this category.
Evaluate the host range of the pest.
– 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: Asclepias physocarpa has been cultivated in California for decades, but apparently has rarely escaped gardens. It exudes a milky white latex that is poisonous to livestock and humans, so an infestation could reduce the productivity of pastures1. It receives a High (3) in this category.
Evaluate the economic impact of the pest to California using the criteria below.
Economic Impact: D, F
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: 2
– 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: Asclepias physocarpa has so far not invaded wildland in California. It could be expected to invade flood plains or other disturbed areas. In wet, tropical areas, such as Hawaii, it can form dense thickets in pastures. It is unlikely to do this in the drier climate of California. As a garden weed, it could trigger additional private treatment programs. It receives a Medium (2) in this category.
Environmental Impact: D
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.
Environmental Impact: Score: 2
– 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 Asclepias physocarpa (Balloon Plant): Medium (12)
-Low = 5-8 points
–Medium = 9-12 points
–High = 13-15 points
Evaluate the environmental impact of the pest on California using the criteria below.
6) Post Entry Distribution and Survey Information: No official records indicating this species is established in the environment of California have been found, so it 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.
The final score is the consequences of introduction score minus the post entry distribution and survey information score: Medium (12)
Uncertainty: This plant is not known to be established in California. No official survey has been conducted to confirm its presence. However, it has been growing in the environment of California as a common garden plant and has never been noticed as invasive weed.
Conclusion and Rating Justification: Conclusions of the harm associated with this pest to California using all of the evidence presented above: Proposed Rating: Based on the score listed above, Asclepias physocarpa is medium risk. However, its low frequency in California after years of cultivation suggest that it will not become invasive, so a “C” rating is justified.
Crop protection Compendium (Cabi). Accessed August 24, 2017: http://www.cabi.org/isc/datasheet/114618
Fishbein M., Chuba D., Ellison C., Mason-Gamer R. J., Lynch S. P. 2011. Phylogenetic relationships of Asclepias (Apocynaceae) inferred from non-coding chloroplast DNA sequences. Systematic Botany 36: 1008–1023. Missouri Botanical Garden online. Accessed August 24, 2017:
Pest and Damage Record Database, California Department of Food and Agriculture, Plant Health and Pest Prevention Services. Accessed August 24, 2017:
South Africa National Biodiversity Institute, Plantzafrica, online. Accessed August 24, 2017:
USDA Phytosanitary Certificate Issuance & Tracking System (PCIT) Phytosanitary Export Database (PExD). Accessed August 24, 2017.
Weeds of Australia, Biosecurity Queensland, online. Accessed August 24, 2017. https://keyserver.lucidcentral.org/weeds/data/media/Html/gomphocarpus_physocarpus.htm
Javaid Iqbal, California Department of Food and Agriculture; 1220 N Street, Sacramento, CA 95814; Tel. (916) 403-6695; plant.health[@]cdfa.ca.gov.
Photo of Ballon plant (Asclepias physocarpa), photographed in Tonga. Photo By: Tauʻolunga, via Wikimedia Commons