Generally, the term weed is used to describe any plant that is unwanted and grows or spreads aggressively. The term exotic weed describes an invasive unwanted non-native plant. Terms such as invasive weed or noxious weed are used somewhat interchangeably to refer to weeds that infest large areas or cause economic and ecological damage to an area.
The term noxious weed has legal ramifications in some states that maintain official lists of noxious weeds. What is considered a weed ion one area may not be a weed in another.
Native plants evolved over millions of years to fill unique ecological niches. What we know as weeds today (non-native, ecologically damaging plants) did not exist in the wilderness then. These plants developed in and are native to other countries. Like our native plants, they are kept in check in their native environment by insects or diseases and by competition with other species. In order to survive in their native ecosystems, many plants develop characteristics that make them especially hardy.
Early European settlers in North America inadvertently brought weed seeds with them, perhaps in the hay they brought for their animals or in the dirt they used as ballast for their ships or even in their clothes or bedding. Some activities, such as clearing the land, opened up niches that created places for weeds to grow. Settlers also purposely brought plants from their “home country” to reseed areas, make dyes for clothing and use as ornamental plants.
These plants have spread at an alarming rate because, unlike native species, there are no native insects, fungi or diseases to control their growth and spread in this country. What began as a handful of plants introduced in the 19th now number in the hundreds of millions. Noxious weeds destroy wildlife habitat and forage, threaten endangered species and native plants, increase erosion and groundwater loss and prevent recreational activities.
Weeds are continuing to spread rapidly in many areas across the country. Weeds spread to an estimated 4,000 acres (over six square miles) each day on public lands managed by the Bureau of Land Management and the US Forest Service.
Weeds have invaded approximately 17 million acres of public rangelands in the West – more than quadrupling their range from 1985 to 1995. In northern California, yellow star thistle expanded its range from 1 million acres in 1981 to 10 million acres in 1997.
But weeds know no boundaries. They also are spreading on private and park lands. In fact, no one really knows how fast or how far they are spreading.
The pictures below are beautiful but they are all noxious weeds: Blueweed, Buttercup, Orange Hawkweed, Purple Loosestrife, Scotchbroom and Oxeye Daisy.
Methods For Noxious Weed management
Weed management consists of developing a control plan to implement over a period of time. it is different than simple weed control which is just a reaction to weeds after they show up. There are three general weed management strategies: prevention, eradication and control.
PREVENTION is the first line of defense to keep weeds from ocurring or increasing in an area. Preventive techniques may include planting high quality, weed free crops or grass seed. Laws such as the Noxious Seed Act and Noxios Weed Law also help stop weed problems before they occur or help to stop their spread. An important preventive measure is to keep weeds from going to seed. This is particularly important for annuals and biennials because that is their only way to reproduce. Perennials reproduce from seed and often vegetatively from their root systems. (Annual weeds live for one growing season , biennials for two and perennials more than two). However, preventing seed is extremely important to keep perennials from starting new infestations some distance from existing ones.
ERADICATION is the removal of weeds from an area so they will not recur unless reintroduced. If eradication creates an open environment, though, a weed problem may be cured simply to create another one. When eradication is the goal, it is usually necessary to revegetate the land to prevent another weed infestation. Eradication is often desirable and possible for small patches, e.g. 10 to 100 feet in diameter, but not always for larger ones.
CONTROL, which is the most often used method, reduces a weed population in an area to a level where you can enjoy using and living off the land. Adequate control also may prevent future infestations. There are four main tools used for control; cultural, mechanical, biological and chemical.
- Cultural control methods are implemented to favor desireable plant growth. Fertilization, irrigation and planting at optimum densities are methods that offer the most competition from crop plants to weeds and least competition among crop plants. Weeds may respond to fertilization and/or iorrigation, but generally do not respond as well as crops do because weeds evolved under limited environmental conditions.
- Mechanical control methods physically disrupt weed growth. Mechanical weed control is the oldest and most often used method worldwide. Tillage, hoeing, hand pulling, mowing and burning are examples of mechanical weed control. Mulching (or smothering) is often considered a mechanical tool, even though it acts biologically on the plant to prevent its use of light rather than physically disrupting it growth.
- Biological control methods use a living organism to disrupt weed growth. Often, the organism is an insect or plant pathogen and a natural enemy of the weed. This is called classical biological control, but is not the only form of biological control. Livestock can be effective weed management tools for certain plants if used correctly. Generally, biological control is environmentally sound, paraticlarly classical biological control. However, improper livestock management (overgrazing) can be ectremely damaging to the environment and make the weed problems worse.
- Chemical control methods involve herbicide use to disrupt weed growth. The first rule is to READ THE LABEL before using the product and follow all directions and precautions. YOU MUST READ PRODUCT LABELS BEFORE USING CHEMICALS!
- Other non herbicidal methods: We are aware of tests performed with “weed burners” or boiling water, which appear to be somewhat effective. Keep in mind, these are non-selective methods and will not single out just the weeds. Also, several magazines have reported use of lemon juice or vinegar in controlling small, young weeds. Again, these products are non-selective and will injure other vegetation. A small sprayer bottle could help to keep these more “on target”.
A good weed management plan uses more than one strategy and two or more control methods. The key is to create a favorable situation for desirable plant growth with optimum fertilization and/or irrigation (cultural). Plant competition is a good tool that is often overlooked and should be used first, but not exclusively. Tilling, hoeing, hand pulling, mowing or mulching (mechanical) should be used where possible.
Herbicides are powerful tools to be used judiciously, not exclusively. Unfortunately, herbicides are used too often to make up for poor cultural or mechanical management decisions. Herbicides should be a component of the weed management system, not comprise the system solely. Biological controls can be part of a system, but they seldom eliminate their host. Livestock grazing, depending on the weed species, is effective when used with other methods.
