Weed Science: definitions, concepts, and characteristics Flashcards
- Study of vegetation management in agricultural production systems,
natural areas, and managed properties in residential and urban areas - is vegetation management
– the employment of many
techniques to manage plant populations in an area. - might be considered a branch of applied ecology that attempts to modify the environment against natural evolutionary trends
Study of vegetation management in agriculture, aquatics, horticulture, right of ways, essentially anywhere plants need to be managed
Weed science
These are many definitions of a weed and the following are the most common:
- A plant whose virtues are not yet discovered (_____1912)
Emerson,
These are many definitions of a weed and the following are the most common:
- A plant growing where it is not wanted (_______ 1912)
Blatchley,
These are many definitions of a weed and the following are the most common:
- Unwanted plant in a human made setting (________ 1916)
Georgia,
These are many definitions of a weed and the following are the most common:
- A plant grown out of place (_____ 1961)
Kingman,
These are many definitions of a weed and the following are the most common:
- Any undesirable plant (____ 1961)
Salisbury,
These are many definitions of a weed and the following are the most common:
- A plant or part of a plant interfering with the objectives of human beings (Blatcley, 1912)
Salisbury,
Characteristics of Weeds
The common idea that weeds are noxious is attributed to their _____.
invulnerability
Although weeds and crops may have the same characteristics, weeds after have evolved adaptive traits that increase their persistence or competitiveness. Some of their secrets of success
are:
- Weeds produce more ______ than cultivated crops.
seeds
Some of their secrets of success
are:
- Weed seeds ripen _______. Mature seeds readily shatter to the ground and grow into new plants. In effect, they become self-seeding.
non-synchronously
Some of their secrets of success
are:
- Viable weed seeds are in various stages of ______. ______ among seeds may be genetic or due to environmental conditions such as deep burial, low oxygen supply, unfavorable temperature and water logging. As soon as the condition becomes favorable weed seeds germinate.
dormancy
Some of their secrets of success
are:
- Weed species have adapted efficient methods of __________.
seed dispersal
Structures that seed and fruit use to adhere to animal fur, skin or clothing.
spines and hooks
5 characteristics or adaptive
traits that weeds have evolved that increase their persistence or competitiveness.
- Weeds produce more seeds
- Weed seeds ripen non-synchronously.
- Viable weed seeds are in various stages of dormancy.
- Weed species have adapted efficient methods of seed dispersal.
- Weeds may reproduce by more than one method
Classification of Weeds
They are classified according to the following categories (5):
- According to their life cycle
- According to their habitat
- According to morphology
- According to growth habit
- According to body texture
Classification of Weeds
According to their life cycle (3):
a) Annual
b) Biennial
c) Perennials
Classification of Weeds
– weeds having a life cycle of less than a year to one year or within one growing season.
* Examples:
Phyllanthus niruri
Euphorbia hirta
Annual
Classification of Weeds
- weeds that complete their life cycle within a period of two years. They germinate, emerge, and usually form a rosette in the first year.
- Examples: Wild carrot (Daucus carota subsp. maximus)
Biennial
Classification of Weeds
– weeds that
thrive for more than two
years and reproduce
vegetatively or by seeds.
Perennials
Classification of Weeds
2 Types of perennials
- Simple perennials
- Creeping perennials
A type of perennial propagated only by seeds.
Examples:
Chromolaena odorata
Sida acuta
Simple perennials
This type of perennials are propagated by seeds and vegetative parts such as rhizomes, runners, stolons, tubers and bulblets.
Examples:
Centella asiatica
Commelina diffusa
Creeping perennials
Classification of Weeds
According to their habitat (3)
a) Terrestrial
b) Aquatic
c) Epiphytic
The category of weeds living on land.
Terrestrial
Subcategories of Terrestrial weeds (6)
- Rice field weeds
- Garden weeds
- Grassland weeds
- Wasteland weeds
- Forests weeds
- Weeds in fields
Classified according to their habitat these are the weeds that are found living in water.
Aquatic
Subcategories of Aquatic weeds (3):
- Floating
- Emergent
- Submergent
These sub-type of aquatic weeds are not anchored in the soil. They grow on the water surface.
Example: Eichhornia crassipes
Floating
This sub-type of aquatic weeds have their roots attached to the soil and the leaves above the water surface.
Example: Monochoria vaginalis
Emergent
This sub-type of aquatic weeds have their roots attached to the soil and are totally under water.
Example: Hydrilla verticillata
Submergent
Classified according to their habitat, this group of weeds needs a host plant for support, it has no roots but cling to trees by tiny scales.
* Example: Lichens, algae, ferns,
orchids
Epiphytic
Classification of weeds according to morphology (3)
a) Grasses
b) Sedges
c) Broadleaves
This sub-group of weeds belong to family Graminae. They have cylindrical hollow stem composed of nodes and internodes. The leaves are narrow with parallel veins. A membranous outgrowth at the junction of the leafsheath and leafblade called ligule varies in length among species.
∙ with long leaf blades with parallel veins
∙ belong to the Graminae or Poaceae families
∙ with distinct nodes and internodes
∙ alternate leaf arrangements
∙ presence of round stems
Grasses
This sub-group of weeds belong to family Cyperaceae. Similar to grasses and can be distinguished by a triangular solid stem without
node and internode.
∙ with long leaf blades with parallel veins
∙ no nodes and internodes
∙ absence of ligule
∙ fusion of leaf sheath forming a tube around the stem
∙ with angular or triangular stems.
∙ With whorl leaf arrangements
Sedges
This sub-group of weeds belong to other families. They have expanded leaves that are net vein with various size, shape and arrangement.
∙ those belonging to the other families of dicots and
monocots
∙ leaf blades are broad and fully expanded
Broadleaves