UGA Weed Science Exam 1 - Basinger

weed science

the discipline that investigates the biology and ecology of weeds and how best to manage these plant species for the betterment of mankind

weed

"a plant out of place"; "a plant growing where it is not wanted"

weed (Weed Science Society of America)

any plant that is objectionable or interferes with the activities or welfare of man

Ten characteristics of weedy plants

1.) germination requirements fulfilled in many environments

2.) discontinuous germination (internally controlled) due to great longevity of seed

3.) rapid growth through vegetative phase to flowering

4.) continuous seed production for as long as growing conditions permit

5.) self-compatibility but not autogamy or apomixis

6.) cross-pollination, when it occurs, bay unspecialized visitors or wind

7.) very high seed output in favorable environmental circumstances

8.) production of some seed in wide range of environmental conditions; tolerance and plasticity

9.) adaptations for short- and long-distance dispersal

10.) if perennial, vigorous vegetative reproduction or regeneration from fragments

11.) if perennial, brittleness, so that it is not easily drawn from the ground

12.) ability to compete interspecifically by special means

What do plants need to do in terms of growth and resource capture in order to be successful?

early and rapid establishment, rapid canopy development, rapid root growth; grows faster than its neighbors to get a disproportionate amount of available resources

C4 plants

plants which are considered more efficient at "fixing" carbon

What type of weeds tend to be C4?

summer annuals and perennials

What type of weeds tend to be C3?

winter annual

What characteristics do C4 plants tend to have>

-higher temperature and light optimum for photosynthesis

-higher photosynthesis rates per unit leaf area

-higher growth rates under optimum conditions-greater dry matter production per unit of water used

allelopathy

process by which a plant releases into the environment (air or soil) an organic chemical (an allelochemical) that adversely affects the growth and development of surrounding plants

intraspecific competition

occurs when two or more plants of the same species coexist in time and space and simultaneously demand a limited resource; when crop or weed plants of the same species compete with one another

interspecific competition

occurs when two or more species co-exist in time and space and simultaneously demand a limited resource

interference

the combination of competition and allelopathy under field conditions

competition

a process that occurs when the combined resource demands of plants within a given area exceeds the available supply

For which input is there the greatest competition between crop plants and weeds?

Light

Critical weed free period (CWFP)

The minimum period following crop emergence that the crop must be maintained; bottom to top curve on graph

Critical time of weed removal (CTWR)

the maximum length (after crop planting or emergence) that weeds can be allowed to compete with the crop and not reduce yield; top to bottom curve on graph

Critical period of weed control (CPWC)

the time interval between the two separately measured crop-weed competition components of critical time of weed removal and critical weed free period; the period during which weed control is necessary ro avoid a yield loss

AYL

acceptable yield loss; runs across top of graph

What is the relationship between new cultivars and competitiveness with weeds?

crops can be bred for greater ability to compete with weeds

How does tight row spacing affect the success of weeds?

Since high light intensity is required for the germination of some weeds, cultural practices like increasing turf density will prevent light from reaching the soil surface

What are the three types of direct losses associated with weeds?

1.) Reduced crop yields

2.) Reduced harvesting efficiency

3.) Reduced quality of harvested crop

What are the types of indirect losses associated with weeds?

1.) Increased crop production costs

2.) Crop damage

3.) Weeds may limit rotational choices

4.) Weeds may be alternate hosts for insects, diseases or nematodes that attack crops

Noxious weed (as defined by the Federal Noxious Weed act of 1974)

any living stage (including seeds and reproductive parts) of a parasitic or other plant of a kind which is of foreign origin, is new to or not widely prevalent in the U.S., and can directly or indirectly injure crops, other useful plants, livestock, poultry or other interests of agriculture, including irrigations, navigations, fish and wildlife resources or the public health

Federal Noxious Weed Act of 1974

gives the Secretary of Agriculture the authority to designate plants as noxious weeds by regulation. Movement of all such weeds in interstate or foreign commerce is prohibited except under permit. Also gives the Secretary the authority to inspect, seize and destroy products, and to quarantine areas to prevent spread of such weeds.

Examples of terrestrial noxious weeds

witchweed

benghal dayflower

onionweed

itchgrass

Examples of invasive aquatic weeds

Hydrilla

Water Hyacinth

Threshold

point at which a stimulus is just strong enough to produce a response

Weed Damage Threshold

The weed population at which a crop response can first be measured

Weed economic threshold

the weed population at which cost of control is equal to value of crop yield attributable to that control; or the weed population which reduces crop value to a level equal to the cost of control; or value of the loss equals the cost of the control

Factors that affect weed economic thresholds

1.) Potential crop yield in absence of the weeds

2.) Selling price of the crop

3.) Cost of treatment

What has to happen to make threshold increase?

treatment cost increases

yield potential decreases

selling price decreases

What has to happen to make threshold decrease?

treatment cost decreases

yield potential increases

selling price increases

Terrestrial plants

plants that live on land

Aquatic plants

plants that live in or around water

Aerial

Plants that don't root in soil, using other plants as support

Herbaceous plants

plants with non-woody aerial stems that usually die down each year

annuals

complete life cycle in one growing season; live for only one season; reproduce by seed

summer annuals

complete life cycle during period from spring to fall; seed germinates in spring, plants flower and produce seed in mid to late summer and die in the fall.

Examples of summer annuals

large crabgrass

common cocklebur

Winter annuals

complete life cycle during period from fall to spring; seed germinates in fall or throughout winter months OR early in the spring, plants flower and produce seed in mid to late spring and die early in summer

Examples of winter annuals

common chickweed

henbit

biennials

require two growing seasons to complete life cycle; seed germinates in spring, summer or fall of the first year and grow vegetatively, forming a rosette during the first season. Plants overwinter as a basal rosette of leaves with a thick storage root. After exposure to a period of cold, plants flower and produce seed in the summer of the second year and die that fall.

How do biennials reproduce?

by seed only

in what kind of environments are biennials rarely a problem?

tilled or other disturbed environments

examples of biennials

common evening primrose

wild carrot

common mullein

perennials

plants that produce vegetative structures that allow them to live for more than two years without having to reproduce from seed (although they can also reproduce from seed)

simple perennials

propagate by seed; overwinter by means of a vegetative structure but reproduce new plants entirely by seed; do not spread by means of vegetative structures

examples of simple perennials

dandelion, curly dock, buckhorn plantain

creeping perennials

can overwinter and produce new plants from vegetative structures. Most can also reproduce from seed

examples of creeping perennials

johnsongrass

purple/yellow nutsedge

common bermudagrass

woody plants

plants with woody aerial stems that persist from year to year

Federal Seed Act of 1939

Requires certain information is given on a seed label:

Cultivar Name

Germination Percentage

Percent Pure Seed

Presence of Weed Seed

Georgia Seed Law

Requires that the following information be printed on seed bags

1.Commonly accepted name of the kind and variety of seed

2.Percentage by weight of inert matter

3.Percentage by weight of agricultural seeds other than those named on label

4.Percentage by weight of all weed seeds, including noxious weed seeds

5.Percentage of germination, exclusive of hard seed, for the named agricultural seed

6.Percentage of hard seed, if present

7.Name and number per pound of each kind of restricted noxious weed seed present

AND deems it unlawful to sell or transport the following:

1.prohibited noxious weed seeds

2.restricted noxious weed seeds, except as allowed by the law

3.weed seed and inert matter percentage by crop

Natural asexual dispersal

usually short distance as compared to seed dispersal. Results from encroachment or "creeping" of weed as it grows and produces additional vegetative reproductive structures.

Artificial asexual dispersal

related to man's activities; can be long or short distance

Examples of artificial asexual dispersal

soil movement with vegetative structures within

tilling with stolons present within soil

External factors governing germination

water

oxygen

temperature

light

chemical stimulation

quiesence

quiesence

inactivity, stillness

Reasons for seed dormancy

1.) Impermeable seed coat

2.) Hard seed coat

3.) Immature embryo

4.) Hormonal imbalance

Implications of dormancy

when seeds are buried deeply and not exposed to oxygen they can remain in the soil seeds bank for a long time; result: allowing weeds to go to seed can have long term consequences

eradication

complete kill or removal of a weed species from a defined geographical area; implies that the weed will not come back unless reintroduced

Ways to manage weeds

Prevention

Mechanical or physical control

Cultural control