A weed is generally defined as any plant growing where it is not wanted. Any plant that interferes with the management objectives for a given area of land at a given point in time may be considered a weed. This broad definition includes lawn grass in a flowerbed or corn plants in a field of wheat. More commonly, plants are chosen because of subjective characteristics or attributes that are objectionable because they interfere with human activities or are detrimental to the welfare of humans as harmful to crops, animals or quality of life. These characteristics include an ability to grow or spread aggressively, possess spines, thorns, allergenic sap, resins, or have an objectionable odor. Natural Resources Management Group Priority Weed List.
Noxious: A noxious weed is an undesirable, non-native plant species requiring management or control because of legislative action or statute. Most of the problematic plant species in Arizona are not designated as noxious weeds. The majority of species regulated, pose a risk to agriculture or another economic interest. Relatively few of the exotic invasive species that affect wildlands are designated as noxious by either state or federal regulation. State or Federal government may list any plant as noxious that is deemed an economic threat, an environmental threat or a threat to public health. Arizona has a State Noxious Weed List (R3-4-244 and R3-4-245). www.azda.gov/PSD/quarantine5.htm. Arizona is also under the jurisdiction of the federal noxious weed list http://www.aphis.usda.gov/ppq/weeds.
Arizona statute defines criteria that a species of plant, that is not indigenous to the state and is or likely to be detrimental, destructive, difficult to control or eradicate, may be listed as noxious. The Director of the Department of Agriculture may conduct an investigation and hearing to determine a species as noxious. Rules for abatement are published in Arizona Administrative Code (RS3-4-244 and RS3-4-245). Statutory authority for noxious weed law is contained in ARS 3-202, 3-203, 3-204, 3-205.01 and 3-206.
The current list includes 53 taxa, divided into three groups as regulated, restricted and prohibited. Species may be included in more than one category.
Seven species listed as regulated are to be controlled to prevent further infestation or contamination.
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Fifteen species are classed as restricted and are to be quarantined or allow commodities and land to be quarantined until eradication is complete.
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Fifty one species are termed prohibited from entering Arizona and shippers must obtain a permit to transport them through the state.
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Sixteen additional species are currently under consideration for inclusion.
Invasive: Most plants considered as weeds are not endemic to the area they are found growing and are labeled as exotic or non-native. Executive Order 13112, signed by President Bill Clinton on February 3, 1999 (see www.invasivespecies.gov) defines an invasive plant or alien species as one that grows and spreads rapidly, replacing desirable native plants. Many invasive plants are extremely prolific, competitive, sometimes harmful or destructive and are difficult to control. Four characteristics that identify these weeds are:
- Invasiveness - the ability to rapidly colonize disturbed environments in diverse geographic sites.
- Competitiveness - the capability to dominate a plant community in creating a monoculture of one single species.
- Persistence – the capability to becoming a permanent member of the local plant community.
- Aggressiveness - the colonization of undisturbed native plant communities.
These exotic species have been introduced from other biotic communities either: intentionally for their edible, medicinal, ornamental or forage properties; accidentally in ballast, or cargo; or as contaminants in seed, hay or straw. Because of the lack of competition or natural control mechanisms of predator or pathogen, the exotic species thrives and the native plant and animal communities sufffer.
In 1998, BioScience reported that invasive species constitute a greater threat to endangered species than pollution, over-harvesting and disease combined.
Invasive species compete for space, moisture and nutrients. They alter the fire regime, interrupt cycling of nutrients, disrupt stream flow and native plant regeneration patterns. This may contribute to habitat destruction and lead to a reduction in species diversity and species richness. Exotic invaders displace local species or cause their extinction. Species such as tamarix and russian olive can alter or disrupt flood regimes in desert washes and streams, causing loss of life and severe economic and environmental harm.
ADOT Natural Resources Management Section (NRMS) uses Integrated Plant Management (IPM) to minimize runoff, control noxious and invasive weeds, minimize impacts to the natural habitat and prevent pollution.
CONTROL STRATEGY:
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Inspect the roadsides to determine the scope of the problem and determine the noxious species present.
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Locate discrete weed populations by Global Positioning System (GPS) and map them.
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Evaluate the phenology and habitat requirement of the various species.
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Prioritize the sites for potential threat, with major emphasis on destroying the smaller populations first while stopping the spread of the perimeter of larger populations.
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Implement the best management practice using the various IPM treatment methods (fire, herbicides, tillage, mowing, re-seeding native species and biological agents) for control or eradication.
Authority – (Noxious weeds) Executive order 13112, 1999, Arizona Administrative Code (RS3-4-244 and RS3-4-245), (ARS 3-202, 3-203, 3-204, 3-205.01 and 3-206). (Native Plants, IPM) Executive Memorandum, Federal Register / 60. No. 154/1995 (Invasive Species) Executive order 2005-09, and www.swvma.org/ and http://www.usgs.nau.edu/swepic.
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