Plant Invasive Species

CISR: Russian Thistle

Anonymous — Mon, 20 Jan 2020 20:58:52 +0000

CISR: Russian Thistle Anonymous (not verified) Mon, 01/20/2020 - 12:58 More Blog Posts CISR Team October 22, 2009

The Situation: Russian thistle, commonly known as tumbleweed, is a profusely branched annual herb. Its efficient taproot, abundant seed production and reduced leaf surface adapt this weed well to disturbed semiarid agricultural environments, rangeland and nonagricultural areas such as vacant resident lots and railroad or highway rights-of-way. It has become pervasive as an exotic weed species throughout California and the western United States.

Damage: Russian thistle is damaging as a seed contaminant, as a forage weed that may contain toxic levels of soluble oxalates and nitrates, and as an alternative host of several economically significant insect species. The mature plants break off at ground level, creating spiny, brittle, windblown tumbleweeds that fill drainage canals, catchments and swimming pools, and pile up against fences and dwellings, becoming eyesores, fire hazards, and foci for the accumulation of other windblown debris.

Economic Impact: In addition to being a nuisance, Russian thistle is an expense to both public and private property owners. While the economic impact to the state of California has not been well documented, costs include clean-up of public roadways and thoroughfares, loss of seed crops due to contamination by thistle seed and illness or even death of foraging livestock, and degradation of California’s valuable and highly diverse wilderness areas.

Distribution: Russian thistle is a summer annual native to southeastern Russia and western Siberia and was originally introduced into the United States as a contaminant of flax seed in South Dakota in 1873. Within 20 years, it had spread to 16 western states and several Canadian provinces. It is now widespread throughout western North America, including virtually all arid and semi-arid regions of California and Russian thistle infests around 100 million acres of land.

Research: Russian thistle is an exotic weed species and is a good candidate for biological control. A pith-boring moth and a case-bearing moth have been established as biocontrol agents in California, but are ineffective. Additional insect enemies from the weed’s native central Asia should also be introduced and evaluated. Mites, moths, and beetles that exhibit sufficient host specificity may potentially be effective natural enemies of this weed. Phytopathogens may also offer promise and should be investigated as possible biological control agents. The California Department of Food and Agriculture and the University of California Exotic Pests and Diseases Research Program has supported foreign exploration by USDA and UC entomologists in recent years, and natural enemies have been studied at the USDA European Biological Control Laboratory in southern France.

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CISR: Saltcedar

Anonymous — Mon, 20 Jan 2020 20:57:28 +0000

CISR: Saltcedar Anonymous (not verified) Mon, 01/20/2020 - 12:57 More Blog Posts CISR Team October 22, 2009

Damage: Once established, saltcedar is tolerant to high salinity and secretes salt at a high rate which is deposited on the soil surface to the detriment of native plant species. Saltcedar increases fire frequency within the riparian habitats it dominates because of its high levels of dead leaves and branches that provide fuel for fires. After fires, saltcedar sprouts rigorously, while native riparian trees and shrubs generally do not. Saltcedar groves push out native species, affecting their reproductive potential and contributing to a loss of natural biodiversity. Research implies that saltcedar could impact the structure and dynamics of streams by trapping and stabilizing sediments, increasing overbank flooding following high flow events and creating permanent sand bars in rivers. This pest also contributes to the decline of wetland communities as habitat refuge for wildlife. Species affected by the spread of saltcedar include the entire gamut of animals and plants associated with riparian communities, including several threatened or endangered species (i.e., desert pupfish, bighorn sheep, southwestern willow flycatcher, etc.).

Economic Impact: Saltcedar depletes the genetic diversity of California riparian communities, resulting in direct environmental damage and indirect economic impact on the state. It also may impact recreation opportunities in riparian areas. The dominance of saltcedar in natural communities can be seen as both a cause and a consequence of habitat degradation due to human activities, including dams and agricultural run-off. Saltcedar could also pose a substantial threat to agriculture due to its high use of water and its tendency to clog irrigation canals. It has been estimated that the cost incurred by salt cedar infestations in the southwest USA with respect to water supply, flood control, and wildlife to the benefits of eradicating this weed would be a net total benefit between $3.8 billion to $11.2 billion over a 55 year period (Zavaleta 2000, pp. 261-300 in Mooney & Hobbs, Invasive Species in a Changing World).

Distribution: Estimates of the saltcedar invasion in the southwest include over one million hectares of sensitive habitat ranging from northern Mexico to southern Canada which have become dominated by this species. States affected include California, Arizona, New Mexico, Texas, Colorado, Utah and Wyoming.

Research: Saltcedar control and eradication programs are being conducted throughout the western U.S. In most cases, the goal is to preserve or recover sensitive areas. Research on chemical control, prescribed burning and mechanical removal by bulldozers for the control of saltcedar has been initiated in small plots along several major riparian areas with good results, but these efforts do not lend themselves to large scale control of saltcedar. Preliminary research on biological control agents, in particular leaf feeding chrysomelid beetles, Diorhabda elongata. This beetle has caused spectacular mortality of saltcedar in some release areas in the southwest USA. However, the beetle has not been effective in all areas because of its diapause requirements. Additional strains of the beetle that have different diapausing requirements are being sourced from the home range of the beetle in Eurasia and will most likely provide establish and provide control in areas where the beetle has failed previously.

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CISR: Giant Reed, or Arundo

Anonymous — Mon, 20 Jan 2020 20:19:53 +0000

CISR: Giant Reed, or Arundo Anonymous (not verified) Mon, 01/20/2020 - 12:19 More Blog Posts CISR Team October 30, 2009

The Situation:Arundo donax, also known as giant reed or arundo, is native to Eastern Asia but has been widely planted around the world because this plant has a variety of practical uses. Arundo has been used for walking sticks, fishing poles, musical instruments, and recently it is being investigated as a biofuel source. Arundo was first planted in California in the 1820’s to provide roofing materials and for erosion control in the Los Angeles Basin area. Arundo has also been widely planted in parts of the USA, Mexico, Central and South America, the Mediterranean, the Caribbean, Australia, and New Zealand. In many of these areas it is now considered an invasive weed (e.g., California, Texas [especially the Rio Grande River Valley], Hawaii, Nevada, Utah, Missouri, Virginia, New Mexico, and Florida).

The Problem: Arundo is an exceptionally fast growing plant, growing about 4 inches per day and reaching a mature height of 25 feet in about 12 months. An acre of arundo can produce about 25 tons of biomass per acre for each of two annual harvests. The plant is very tolerant of a variety of environmental conditions and can be found growing in damp riparian areas, and it is tolerance of moderately saline soils too. Because stands of arundo are so dense native plants are typically displaced and the animals associated with these native plants are unable to utilize arundo so decline their populations decline also. In California, arundo infestations are particularly problematic because this weed chokes out native willows, it can provide a lot of fuel for fires which are typically very uncommon in riparian areas (arundo appears to be very well adapted to fire so fires promote arundo invasions in these sensitive habitats). In the Santa Ana River Basin in Southern California, the fire fuel load in riparian areas has almost tripled because of arundo infestations. During floods, large rafts of dislodged arundo can cause bridges to collapse as tons of arundo pile up around bridge supports. Because of the serious and widespread nature of arundo infestations in California, several counties have formed task forces specifically to manage to this weed (e.g., The Santa Ana River Arundo Management Taskforce, and Team Arundo del Norte). In North America arundo appears to reproduce asexually and seldom produces viable seeds even though this plant produces flowers. The major mode of propagation is via vegetative reproduction either by underground rhizomes, or from plant fragments.

Economic Impact: The economics of arundo’s impact on water use has been estimated using data from transpiration rates. Arundo transpires 56,200 acre-feet of water per year on the Santa Ana River, compared to an estimated 18,700 acre-feet that would be consumed by native vegetation. If arundo were not drawing water from the Santa Ana River Basin there would be enough water to serve a population of about 190,000 people. If that amount of untreated water (37,500 acre-feet) was purchased from the Metropolitan Water Association it would cost approximately $12,000,000 in 1993 dollars (1993 was the year this economic study was conducted.)

Research Programs on Arundo: University of California scientists are studying aspects of the invasion ecology of this plant, control strategies that utilize herbicides or mechanical removal from infested areas. One promising long-term control strategy that is being developed by USDA-ARS researchers in Texas is biological control. In California and other parts of the USA there are no organisms that cause substantial feeding damage or mortality to arundo. This lack of herbivory has in part allowed arundo to flourish in areas that it has invaded. Foreign exploration for herbivores feeding on arundo in its native range have found several host specific natural enemies that may be able to substantially reduce the vigor of arundo by simply feeding on this plant. The herbivores of interest are all insects and include Arundo wasp, Tetramesa romana; the Arundo scale, Rhizaspidiotus donacis; and the Arundo fly, Cryptonevra sp. Safety evaluations suggest that these insects are very host specific and pose no substantial threat to other plants. Consequently, efforts are now under to mass rear and establish these natural enemies in areas with severe arundo infestations.

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CISR: African Fountain Grass

Anonymous — Mon, 20 Jan 2020 02:36:19 +0000

CISR: African Fountain Grass Anonymous (not verified) Sun, 01/19/2020 - 18:36 More Blog Posts CISR Team November 24, 2009

The Situation: African fountain grass, Pennisetum setaceum (Forssk) Chiov., is invasive outside its native range in Northern Africa and has been damaging native ecosystems in Hawaii. It is now an increasingly problematic weed in California. As a common landscape ornamental, it is now widely planted in southwestern states. Fountain grass seeds may disperse readily from existing populations via wind, animals, and automobiles. Repeated introductions through landscape plantings are important in the spread of other invasive plants in California, and are likely important in range expansion of fountain grass. It is a state-listed noxious weed in Hawaii, and has been listed as a Moderate threat by the California Invasive Plant Council.

Damage: The impacts of fountain grass on natural habitats in California are unknown and are currently under research by University of California Riverside scientists. However, in Hawaii it has been shown that fountain grass alters fire cycles and microhabitats. After invasion, due to increased fire and other effects, fountain grass may cause a forest community to be converted into grassland. For example, fountain grass can form single-species stands that promote the spread of fire. After fire, it has shown the ability to rapidly colonize burned areas and prevent other plants from establishing. Native communities like coastal sage scrub in southern California have already been impacted extensively by the combined effects of changes in fire cycle as well as invasion by exotic grasses. Computer modeling has indicated that areas that support coastal sage scrub, grassland, and desert habitats have climates that are potentially suitable for establishment of fountain grass.

Economic Impact: Unknown. Potential losses due to increased community flammability and fire-carrying characteristics could be in the millions of dollars ($US).

Distribution: From the native range in Northern Africa (Sudan, Ethiopia, Egypt), fountain grass has spread to Australia, New Zealand, Micronesia, Hawaii and the mainland USA All southwestern states in the USA have naturalized populations of fountain grass. Early herbarium records in California show introduction of fountain grass to the Los Angeles area sometime before 1917. It now occurs in 11 counties in California. Fountain grass is commonly seen on California roadsides and road cuts and it is now increasingly seen occurring in large stands on southwest-facing hillsides and rocky outcrops in coastal sage scrub, chaparral edges, and desert slopes and washes. Cultivars of fountain grass that are presumed sterile are commonly used in landscape plantings, as well.

Research: Researchers at the University of California, Riverside are looking at the potential distribution of fountain grass in California, conducting research to predict corridors for spread, and evaluating the potential impacts of fountain grass on native species (such as out-competing native species for light and water) in coastal sage scrub and the desert. This research has been funded by the Shipley-Skinner Riverside County Endowment (http://ccb.ucr.edu/shipley.html), and the Community Foundation (http://www.thecommunityfoundation.net/home/index.html). Research results will be used to develop recommendations for management based on the risk of fountain grass invasion in southern California.

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