Myrtle Spurge | Euphorbia myrsinites


California Plant Pest Rating
Myrtle Spurge (Euphorbia myrsinites)
Former Pest Rating:  Q
CURRENT Pest Rating: A  |  Proposed Seed Rating: R
Initiating Event:

Collection in Lassen County by county staff and submission to the CDFA Botany Lab.

History & Status:

Background: Myrtle spurge is a deciduous, perennial herb (to 10 cm tall by 40 cm wide) native to southeastern Europe through Asia Minor. It is a semi-succulent plant with prostrate branches and awl-shaped, blue leaves without a petiole approximately 2 cm long. The flowers (cyathia) are borne in spring. The floral bracts are bright greenish yellow. Like all true spurges, the branches and leaves exude an irritating white latex when damaged. It arrived in CA as a garden plant, and it can be found at nurseries in the north and at higher elevations. It’s is extremely cold hardy, but evidently doesn’t thrive in areas with severe summer drought.

California Distribution: Myrtle spurge is currently restricted in California. There are 2 small populations, persisting but not spreading, known along the coast in Alameda and Ventura Counties. It was once collected in Kern County. A small population in Quincy, Plumas County has evidently been eradicated. The recent find, in Lassen County, is reportedly spreading from nearby cultivation. A similar case exists east of Macarthur, Shasta County.

United States: Myrtle spurge is highly invasive in Utah and other western, interior states including Wyoming, Colorado, Eastern Oregon, Washington and New Mexico. It has also been collected as waif in a few eastern states such as Wisconsin and Virginia.

International: Myrtle spurge is native to southeastern Europe through Asia Minor.

Regulation: Myrtle spurge is listed as a noxious weed in Colorado, Oregon, Washington and Utah.

This risk Myrtle spurge will pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Risk is Medium (2), as the plant could naturalize throughout higher elevation mountains and in the “sagebrush” area of northeastern 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) Pest Host Range:  Risk is High (3) as weeds do not require any one host, but grow wherever ecological conditions are favorable.

Evaluate the host range of the pest: 3

– 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:  Risk is Medium (2). The plant reproduces via numerous, rather large seeds that are thrown some distance from the mother plant. Nevertheless, its ability to disperse seems limited, as populations do not spread rapidly. It is unlikely to be found in commercial crop seed.

Evaluate the dispersal potential 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: Risk is High (3) as Myrtle spurge, where established, lowers the rangeland productivity, is unpalatable to livestock, and, where common, will necessitate herbicide treatments for control. As it is a noxious weed in several western states, infested commodities could be excluded from those states that list it as noxious.

Evaluate the economic impact of the pest to California using these criteria:

Economic Impact: A, C, D

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 by other states or countries)

D. The pest could negatively change normal production cultural practices

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:  Risk is High (3). In California, Myrtle spurge could disrupt natural bunchgrass and sagebrush scrub communities. Once established, it would trigger additional treatment programs to control it, as in Utah. It would crowd out native species that coexist with or foster rare species.

Evaluate the environmental impact of the pest on California using the following criteria:

The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

Environmental Impact: B, C, D

A. The pest could directly affect threatened or endangered species

B. The pest could impact threatened or endangered species by disrupting critical habitats

C. The pest could trigger additional official or private treatment programs

D. Significantly impacting cultural practices, home/urban gardening, or ornamental plantings.

Environmental Impact Score: 3

-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 Myrtle spurge:

Rating (Score): Add up the total score and include it here

Low = 5-8 points

Medium = 9-12 points

High = 13-15 points

Total points based on above criteria: High (13).

6) Post Entry Distribution and Survey Information: 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.

Score: 0

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:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: 13

Uncertainty:

Because there is ample evidence of its invasiveness in Utah, Oregon and Colorado, there is little uncertainty that this plant can establish and become invasive in similar climatic areas of California.

Conclusion and Rating Justification:

Conclusions of the harm(s) associated with this pest to California using all of the evidence presented above: Proposed Rating: Based on the score listed above the pest is a High risk. It has the ability to spread more widely in California. Its current limited distribution in California makes the feasibility of eradication high. An A rating is justifed.

References:

Baldwin, B. G., D. H. Goldman, D. J. Keil, R. Patterson, T. J. Rosatti, and D. H. Wilken, editors. 2012. The Jepson manual: vascular plants of California, second edition. University of California Press, Berkeley.

Consortium of California Herbaria (cjeps.berkeley.edu/consortium/). 2014.

Global Compendium of Weeds: http://www.hear.org/gcw/species/euphorbia_myrsinites/

Jepson Flora Project (eds.) 2013. Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html, accessed on Mar 28 2014

Washington State Weed Control Board; Myrtle Spurge. Accessed 6/18/2017: http://www.nwcb.wa.gov/weeds/myrtle-spurge


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


Comment Period: CLOSED

45-day comment period:  7/17/17 – 8/31/17


NOTE:

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Pest Rating: A  |  Proposed Seed Rating: R