Weeds and exotics
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Weeds and Exotics. Dandelion. What is a weed?. a plant in the wrong place a plant out of place a plant whose virtues are yet to be discovered one person’s weed is another person’s herbarium specimen . What is an exotic?.

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What is a weed?

  • a plant in the wrong place

  • a plant out of place

  • a plant whose virtues are yet to be discovered

  • one person’s weed is another person’s herbarium specimen

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What is an exotic?

  • Exotic or alien species are species that are not native the area in question – i.e. an exotic in Illinois would be a species that did not occur here naturally and was somehow introduced to Illinois by human activity

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What is a weed?

  • In general, we consider weeds to be exotic or alien plants which have somehow become problem plants –

  • Problem plants typically have the following two characteristics –

  • 1) the plant has achieved a threshold level of abundance, and

  • 2) someone is concerned about the plant

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Perspectives on Weeds

  • There appear to be three dominant perspectives on weeds: agricultural-ranching, suburban, and ecological.

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Agricultural-Ranching Perspective

  • The agricultural perspective considers any plant a weed if it competes with crops for the available nutrients and moisture in a field. Such plants can lower crop yield or cause crop failure.

  • The ranching perspective considers any plant a weed if it presents a threat to livestock or reduces the quality of forage that is otherwise available.

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Suburban Perspective

  • The suburban perspective considers any plant a weed if it invades the lawns and gardens of suburban homeowners and other managed landscapes of mainstream society, which includes the lawns and gardens of banks, schools, churches, malls, government buildings, industrial parks, etc.

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Suburban Perspective

The ideal plant of the managed landscape in suburbia has the following characteristics: 1) It is often an introduced species that is poorly adapted to the surrounding environment. 2) It is a sterile hybrid or patented cultivar. 3) It is difficult to maintain and often short-lived.4) It doesn't spread readily to places where it doesn't belong. 5) It has obvious aesthetic or culinary properties.6) It has to be purchased at a store or through a catalog (maybe – heirloom plants may be passed from one gardener to another).

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Suburban Perspective

  • The weediness of a plant is defined by the absence of the preceding characteristics. Thus, suburbia considers any plant a weed that is well-adapted to its environment, prone to reproduce itself and spread, requires little or no effort to maintain, and has no obvious aesthetic or culinary properties.

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Ecological perspective

  • One ecological perspective considers any plant a weed if it is a pioneer species that thrives in a degraded habitat with a history of disturbance through human agency. Such weeds may be native or introduced.

  • There are also superweeds that have the capacity to invade high quality natural areas. Superweeds are usually introduced plants with few natural enemies in the area of invasion. Some ecologists are only concerned with superweeds.

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Problem Plants

  • Perennial herbs – many examples are found in wetlands like purple loosestrife and grasslands like Canada Thistle and our woods like garlic mustard (a biennial)

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Perennial Herb Problems

Purple Loosestrife Garlic Mustard

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Problem Plants

  • Perennial grasses – replace native grasses in grazed rangeland and pose a serious fire risk to native trees in forest ecosystems. Perennial grasses pose a double fire hazard: 1) they produce much greater bulk of flammable material than was produced by native plants and thus lead to more intense fires, and 2) the timing of their flammability is different than native plants so that fires occur at times of the year for which native plants are not adapted – Smooth Brome and Phalaris arundinacea

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Perennial Grass Problems

Smooth Brome Phalaris arundinacea

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Problem Plants

  • Vines – Serious pests in woods and disturbed habitat – field bindweed and kudzu

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Vine Problems

Field Bindweed Kudzu

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Problem Plants

  • Shrubs – Very serious pests in most climates – often become severe pests in areas where native vegetation has been overgrazed – multiflora rose

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Shrub Problems

Multiflora Rose

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Problem Plants

  • Trees – trees are potentially disastrous for nature conservation and watershed management. Often invasive trees do well in disturbed, edge habitat and become the canopy dominants, out-competing native trees – among our problem trees are autumn olive (small, almost a shrub), black locust, tree-of-heaven

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Tree Problems

Autumn Olive Black Locust Tree of Heaven

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Illinois Noxious Weed Act

Section 220.10 Duty of Every Person

a) It shall be the duty of every person to control the spread of and to eradicate all noxious weeds on lands owned or controlled by him in the State of Illinois.

b) All noxious weeds shall be controlled or eradicated by methods approved and adopted pursuant to the Act and these rules.

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Section 220.60 Noxious Weeds

The following plants within the sovereign territory of the State of Illinois are designated and declared noxious weeds:

a) Marihuana (Cannabis sativa L.);

b) Giant Ragweed (Ambrosia trifida L.) within the corporate limits of cities, villages, and incorporated towns;

c) Common Ragweed (Ambrosia artemisiifolia L.) within the corporate limits of cities, villages, and incorporated towns;

d) Canada Thistle (Cirsium arvense);

e) Perennial Sowthistle (Sonchus arvensis);

f) Musk Thistle (Carduus nutans);

g) Perennial members of the sorghum genus, including johnsongrass (Sorghum halepense), sorghum almum, and other johnsongrass X sorghum crosses with rhizomes; and

h) Kudzu (Pueraria labata).

(Source: Amended at 26 Ill. Reg. 14644, effective September 23, 2002)

Illinois Noxious Weeds

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Are weeds of some positive value?

1) Some weedy species are pioneers of degraded landscapes where the soil is worn-out or nearly destroyed. Such weedy species are necessary to the healing process of the landscape, as their decaying organic matter improves the quality of the soil and the sets the stage for the succession of non-weedy plants – alfalfa, red clover

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Are weeds of some positive value?

2) Some weedy species are pioneers of disturbed landscapes where the soil is high quality, but exposed to erosion by wind and water. Such weedy species quickly cover the exposed soil and prevent erosion from occurring until they are replaced by non-weedy plants – annual ryegrass

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Are weeds of some positive value?

3) Weedy plants are often important sources of food and cover to various kinds of wildlife, including mammals, birds, and insects. For example, the caterpillars of Papilio polyxenes asterias (Black Swallowtail butterfly) feed on Daucus carota (Wild Carrot) and Pastinaca sativa (Wild Parsnip).

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Are weeds of some positive value?

4) Weedy plants are potentially important sources of food, medicines, herbicides, and other products to modern society. For example, our major food crops are almost all weeds in terms of being exotic species for the Midwest and some of them such as apples can survive outside of cultivation. A powerful herbicide has been derived from Centaurea biebersteinii (Spotted Knapweed), while the fiber of Cannabis sativa (Marijuana) can be used to make paper, rope, or clothing.