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
Weeds classification According to growth habit (3)
a) Vines
b) Shrubs
c) Trees
According to growth habit, it is a sub-group of weeds with parts that creep on the ground; these are usually common among plantation crops like in banana, pineapple, etc.
Vines
According to growth habit, it is a sub-group of weeds that are common in cattle ranches in the Philippines examples are the Chromolaena odorata and Lantana camara
Shrubs
Classification of weeds according to body texture (2)
a) Herbaceous
b) Woody
The _______ of weeds is concerned with the establishment, growth and reproduction of weeds as well as the influence of the environment on these processes.
biology
________ and environment are the master factors governing life. ________ determines what an organism becomes-that is, a dog or a corn plant by controlling the life form, growth potential, method of reproduction, length of life, and so on.
Heredity
The ______ largely determines the extent to which these life processes proceed.
environment
________ is the relationship of organisms to their environment.
Ecology
Factors affecting the ecology of weeds (3)
Climatic
Physiographic
Biotic
Climatic factors (5)
a. light
b. temperature
c. water
d. wind
e. atmosphere
Physiographic factors (2)
a. edaphic
b. topographic
Physiographic Factors which include soil factors including pH, fertility, texture, structure, organic matter content, CO2, O2, water drainage
edaphic
Physiographic factors that include altitude, slope, exposure to the sun
topographic
Biotic factors (2)
a. plants
b. animals
This type of reproduction requires pollination of a flower which in turn produces a seed.
Sexual
This type of reproduction is carried out by stems, roots, leaves, or modifications of these basic organs such as rhizomes (underground horizontal stem), stolon (above ground horizontal stem), tubers, corms, bulbs, and bulblets.
Vegetative
Major factors influencing flowering and seed production (4)
1) Photoperiod
2) Vegetative growth
3) Temperature
4) Growth regulators
the period of time each day during which an organism receives illumination; day length
Photoperiod
The period of growth between germination and flowering is known as what phase of plant development
Vegetative growth
This factor has diverse effects on sexual reproduction of weeds being a factor that can influence all the physiological and biochemical processes within the plant body.
Temperature
Major factors influencing Asexual Reproduction (4)
- Soil texture
- Daylength
- Light intensity
- Mineral sufficiency
Weed seeds are scattered by (7):
- crop seed, grain feed, hay and straw
- wind
- water
- animals, including man
- machinery
- weed screenings
- in rare cases, explosive mechanism
– cropping period wherein the crop is very sensitive to weed competition. The duration at which there is optimum yield is the critical period of competition.
Critical Period of Competition
– the presence of weed above a tolerable density will cause a significant reduction in yield the density at which optimum yield is obtained.
Critical threshold level
Factors affecting the competitive ability of a crop against weeds (4)
- Weed species, density and duration of competition.
- Seeding method
- Crop variety or selection
- Level of nutrition
The growth rate in plants is primarily a function of _______ assimilation in the photosynthetic process.
carbon
Major factors for competition (3)
- Competition for nutrients
- Competition for water
- Competition for light
Among the essential nutrients taken from the soil, ____ appears to be the most critical for most crop weed competition.
nitrogen
_____ which is associated with upland rice typifies a weed species that can respond to nitrogen fertilization. In competition with rice, it can drastically reduce nitrogen
uptake and consequently the yield of rice, the reduction being greater when additional
nitrogen is applied to the soil.
Cyperus rotundus
The overall competitive ability of a plant is partly controlled by
its_______.
root system
LAI is the ground per area
whereas LTR (%) is the ratio of light intensity at ground level to that above the canopy.
leaf area index
______ is restricted to the harmful effect of one plant or another through the production of toxins or inhibitors that escape into the environment.
Allelopathy
_____ is the inability of the seed or any vegetative organ or tissue to germinate under favorable conditions.
Dormancy
Two types of Dormancy
A. Innate dormancy
B. Enforced dormancy
Innate dormancy – seed is inherently dormant as it leaves the parent plant.
4 Reasons:
- Rudimentary embryo
- Much restrictive and impermeable seed coat
- Presence of germination inhibitors
- nature of the seed coat
Germination process of a seed is divided into five steps
- Imbibition
- The period of metabolic activity
- Root or root-like elongation
- emergence of the shoot
- period of independent growth
1st step - ______ can be divided into two phases:
1. Phase I – is purely a physical process which involves the absorption of water by starch and can take place in living and dead seeds
2. Phase II – is a physiological process and is the water absorption by the embryo. This phase marks the initiation and progress of starch hydrolysis.
imbibition
This is triggered by the breakdown of the food reserve. During this period, cell division and cell elongation proceed at a fast rate supported by a rapid synthesis of materials. The end result is a perceptible growth of the embryo.
2nd step, the period of rapid metabolic activity:
Under field conditions, the root-like structures break through the
seed and grow into the soil. The emergence of the shoot follows
which, under field condition, is considered the first sign of weed
growth.
3rd step, root or root-like elongation becomes evident.
Some of the important soil factors that can affect the weed seedling growth and development are _______ (3).
nutrient level, pH, and salinity
in most weed species, this stage is the most vulnerable and the most practical stage for control.
seedling stage
4 Major factors affecting seedling growth and development
- Soil factors
- Light
- Adaptation to growing conditions
- Competitive power of weed
- Which of the following weed species is an example of a broadleaf?
a. Cyperus rotundus
b. Imperata cylindrica
c. Monochoria vaginalis
d. Cynodon dactylon
c. Monochoria vaginalis
- A weed that has vegetative parts and can also reproduce by seeds; A weed that is able to live for more than two years is ________.
a. Annual weed
b. Dicot weed
c. Biennial weed
d. Perennial weed
d. Perennial weed
- Cyperus rotundus is able to persist because:
a. It produces asexually
b. It is a broadleaf
c. Its seeds have long viability period
d. It has cylindrical stem
a. It produces asexually
- Which of the following weeds could be found in lowland rice environment?
a. Euporbia hirta
b. Amaranthus viridis
c. Lantana camara
d. Monochoria vaginalis
d. Monochoria vaginalis
- Identification of weeds at the seedling stage is quite difficult because:
a. Weeds belong to the same family and are very similar in appearance in this stage.
b. Weeds cannot be easily seen due to their small size
c. Weeds tend to grow taller than crops
d. Weeds do not grow at this time
a. Weeds belong to the same family and are very similar in appearance in this stage.
- A weed that is totally submerged in water is known as:
a. emergent
b. floating
c. submergent
d. terrestrial
c. submergent
- An example of a woody weed is:
a. Euphorbia hirta
b. Cyperus rotundus
c. Lantana camara
d. Eleusine indica
c. Lantana camara
- The release of substances toxic to crop plants, all resulting in abnormal growth and lower crop yields is known as:
a. Apathy
b. Allelopathy
c. Apocalypsy
d. Allepathy
b. Allelopathy
- The presence of weeds above a certain density that will cause a significant reduction in yield is:
a. Critical threshold level
b. Critical period of competition
c. Economic threshold level
d. Economic injury level
a. Critical threshold level
- The tubers of Cyperus rotundus would remain dormant if:
a. There is continuous cultivation
b. Cyperus rotundus plants are left intact
c. Herbicides are not applied
d. The area where they are planted is weeded
Correct answer
b. Cyperus rotundus plants are left intact
- Weeds compete with crop plants for:
a. Space
b. Soil nutrients and water
c. Solar radiation
d. B and C
d. B and C
- In innate dormancy, seed is inherently dormant as it leaves the parent plant. Reasons for this include the following EXCEPT:
a. Rudimentary embryo
b. Much restrictive and impermeable seed coat
c. Absence of germination inhibitors
d. Nature of the seed coat
c. Absence of germination inhibitors
