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Non-Native Flora and Fauna
Whether introduced for a specific purpose or accidentally, an increasing number of non-native species are devastating native habitats and croplands. The spread of noxious and invasive weeds and insects adds significant costs to the use and management of natural resources throughout the state. Non-native plants and animals, if not kept in check, have the ability to spread rapidly, resist controls, exclude native species, interfere with crop and forage production, degrade wildlife habitats, promote wildfire, leave soils vulnerable to erosion, and alter entire ecosystems.
Non-Native Flora
With increased globalization and human mobility Nevada's ecosystems are at greater risk of exposure to undesirable plants. The growing number of state-designated noxious weed species illustrates the threat posed by invasive plant species or weeds in Nevada. In 1992, there were 29 weed species officially designated by the Nevada Department of Agriculture (NDOA) as noxious (Table 3-11). By 2001, 13 additional non-native species were classified as noxious. In 2002, two more plants will be added to the noxious weed list - Fountain grass (Pennisetum setaceum) and Giant salvinia (Salvinia molesta) - raising the total to 46 noxious weeds in the state (Nevada Department of Agriculture, 2002).
Nevada, like most states, has a law for designating certain weeds as "noxious." Nonnative plant species designated as noxious are characterized as prolific, and are difficult to control or eradicate. They displace desirable plants on agricultural lands and natural sites, and causes significant environmental and/or economic damage.
"Invasive weed" is a separate, unofficial, category of damaging alien plants. The key distinction is that noxious weeds are considered to be manageable and may be eliminated. An invasive weed species has become so widespread that eradication is infeasible. State law requires landowners to control noxious weeds that occur on their property (NRS 555.130). Unfortunately, resources to prevent or limit the spread of nonnative plants are limited, so public and private land managers must decide whether to control the plants that already are dominating plant diversity, or those that may become dominant in the future if not immediately controlled.
Noxious weeds have impacted several land cover types. Floodplains and riparian zones have been smothered with perennial pepperweed and whitetop. Tamarisk obstructs stream channels. Croplands are infested by Russian knapweed and yellow star thistle. Musk thistle and diffuse knapweed choke out native plants from pastures and other ranchlands. Shrublands, pasture, cropland, and riparian zones appear to be the most heavily impacted cover types.
The serious economic and ecological damage caused by noxious and invasive weeds makes preventing new introductions a top priority for state and federal agencies. To coordinate early control efforts, Conservation Districts (CDs), federal and state land use management agencies, scientists, ranchers, and farmers and others are assisting with mapping the occurrence of noxious weeds. Preliminary mapping and reporting of the extent of noxious weed infestations has produced a rough estimate of 276,000 acres (Table 3-13). However, this number underestimates (perhaps grossly) the statewide impact. Field mapping is incomplete, and some landowners have not inventoried or reported data on infestations yet.
Cheatgrass (Bromus tectorum) is the most widespread "invasive" plant in Nevada. Cheatgrass and its southern cousin, red brome, exemplify the vulnerability of the state's rangelands. Cheatgrass has invaded sagebrush zones in numerous basins. Scientists have observed the plant invading mountain shrub zones, indicating it may be adapting to other climate zones. Following repeated wildfires, cheat grass forms a monoculture. During the growing season, livestock, wild horses, and other grazers can eat and gain nutritional value from cheat grass. However, after cheatgrass cures in early to late spring, the nutritional value and edibility of the plants declines.
Domestic and wild grazing animals, upland birds, and other wildlife must go elsewhere to meet their nutritional and other habitat needs. According to the report Nevada's Coordinated Invasive Weed Strategy prepared by the Nevada Weed Action Committee, approximately nine million acres in northern Nevada (about 13 percent of the total state) has succumbed to the cheatgrass invasion.
Much is being done to combat the introduction and spread of noxious weeds. Nevada's 28 Conservation Districts, which cover the entire state, have traditionally focused much of their resources on the control of invasive  weeds located within the district. In addition, with the increased awareness of the threats posed by invasive species, the formation of weed control districts in Nevada has increased from six in 1992 to 10 in 2000. Conservation Districts and weed control districts typically consult and work closely with experts at their local University of Nevada Cooperative Extension and the Natural Resources Conservation Service offices.
Increased awareness in large part is due to efforts of the NDOA. In 1995, the NDOA created an interagency working group whose mission was to coordinate and facilitate local, county, state and federal agency programs and projects for the control and management of noxious and invasive weeds in Nevada. The group was named the Nevada Weed Action Committee (NWAC). A result of the formation of this group is the creation of the state weed plan, The Nevada Coordinated Invasive WeedStrategy. The strategic plan emphasizes five key objectives: weed control; prevention of new infestations; education and awareness; cooperative and coordination of control efforts; and, research.
The NWAC has taken on the challenge of effectively coordinating public and private resources and efforts toward proactive prevention, control, and management of invasive weed species in Nevada to benefit all land users in the state. The NWAC emphasizes prevention of additional invasions and quick action to eradicate new introductions, primarily because these are the most cost effective approaches. An example is the program to inspect for and certify hay and forage as "weed free." Another priority is mapping the occurrences of noxious and invasive weed species on a real-time basis to ascertain the level of threat, update management priorities, and assist with coordinated weed management plans. Other NWAC priorities include improved communication and education, and finding project funding (Nevada Weed Action Committee, 2002).
Non-Native Fauna
Invasive invertebrate species continue to be introduced into Nevada at an alarming rate. In recent years both the Turkestan cockroach and the Africanized honeybee have expanded to fill niches in southern Nevada. In 1999 and 2000, nine sites infested with red imported fire ants were eradicated in Clark County. Surveys for gypsy moth and Japanese beetle have both been negative in recent years. Surveys and inspection efforts for these and other threatening species have been increased (Nevada Department of Agriculture, personal communication, 2001). All survey, detection, monitoring and control activities relating to invasive invertebrate species are closely coordinated between the Nevada Department of Agriculture and the USDA Animal and Plant Health Inspection Service.
Control of Plant and Animal Infestations
In general, the choices for methods to control or eliminate noxious weeds are mechanical, biological, and chemical. Each has its advantages and disadvantages, depending upon the species, site conditions, and type of land use. The use of herbicides, insecticides, and fungicides (i.e., pesticides) to control noxious weeds and other pests requires special care and oversight because contamination of soil and water can pose serious health threats to people and other life forms. Even with proper use, some chemicals that are mobile, persistent, or degrade into other toxic chemical compounds may accumulate in surface and groundwater bodies. Using pesticides at higher rates or in a place or manner of use different from label specifications is against the law.
State laws give the NDOA authority to manage pesticide use and coordinate with other organizations in monitoring use and effects. The agency trains and certifies pesticide applicators, investigates complaints concerning pesticide use, and monitors the use of pesticides. The Nevada Agricultural Statistics Service compiles data contained in mandatory monthly reports submitted by custom applicator licensees to NDOA. Licensed applicators in 2000 reported that approximately 133,140 acres of farm and ranch land were treated with one or more types of pesticide. This is not a complete summary in that it does not include chemical applications by individual farmers and ranchers who may apply chemicals on their own operations (Nevada Agricultural Statistics Service, 2002).
The NDOA, USGS, and NDEP periodically monitor groundwater quality in areas where pesticides are used. The presence of pesticides has been detected in the groundwater around urban and agricultural areas, but at levels below drinking water maximum contaminant levels. Local University of Nevada Cooperative Extension offices have experts in the area of noxious weed and insect pest controls and can provide state of the art information on the responsible use of pesticides.
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