Herbicides

Question 1

What is a weed?

Answer 1

-plant out of place
-Non-native plant
-plant causing economic loss
-plants whos virtues haven’t been discovered
-a DECISION made by man

Question 2

Weeds my possess

Answer 2

-Abundant seed production
-rapid population establishment
-easy distribution by human activity
-long term survival of buried seed
-quick spreading

Question 3

Reasons weeds survive

Answer 3

-Hard seed coat
-deep burial
-germination inhibitors
-prolific seed production
-persistent vegetative structures: bulbs, tubers, rhizomes, stolons, and corms

Question 4

Effects of weeds

Answer 4

-Loss of yield and quality
-increased production costs
-nutrient and water competition

Question 5

Seed germination factors

Answer 5

-oxygen
-light
-temp
-water
-scarification

Question 6

What is an escape weed?

Answer 6

A weed that comes through despite herbicide efforts

Question 7

What is a monocot?

Answer 7

Plant with one cotyledon
-leaves are mainly parallel-veined
-mainly grasses and sedges

Question 8

What is a dicot?

Answer 8

A plant with two cotyledons
-leaves not usually veined
-primary vascular bundles in a ring
-hard seed coat

Question 8

What is an annual?

Answer 8

Plant that goes through entire life cycle in one year
-most weeds

Question 9

Summer annuals

Answer 9

germinate in the spring, grow vegetatively in the summer, flower in late summer/fall, then die
-ex) crabgrass, sicklepod, morning glory

Question 10

Winter annuals

Answer 10

Germinate in the fall, flower in spring
-ex) henbit, annual bluegrass

Question 11

What is a biennial?

Answer 11

Completes its life cycle in two years
-ex) thistle, carolina false dandelion, wild carrot

Question 12

biennial year 1

Answer 12

germination, vegetative growth, forms rosette of leaves, stores CHO in roots

Question 13

Biennial second year

Answer 13

-regrowth form stored CHO, grows vegetative, flowers, produces seed, dies

Question 14

What is a perennial?

Answer 14

Plant that lives for more than 2 years

Question 15

Perennial life cycle

Answer 15

First year
-germinates, grows veg, develops storage organ, flowers, produces seed, top dies, seed spreads
Second Year
- plant regrows from CHO and goes through life cycle,
-continues each year

Question 16

What are some perennial propagules?

Answer 16

-rhizomes
-stolons
-bulbs
-tubers

Question 17

What is a rhizome?

Answer 17

Horizontal, below ground stem
roots

Question 18

What is a stolon?

Answer 18

horizontal stems, grows at soil surface
-roots and shoots

Question 19

What is a bulb

Answer 19

Modified bulb with stem and fleshy scales compressed closely together

Question 20

What is a tuber?

Answer 20

enlarged terminal portion of rhizomes

Question 21

How do weeds spread?

Answer 21

-wind
-water
-animals
-forceful dehisence
-filaree
-machinery
-man
-accidental

Question 22

Germination

Answer 22

-imbibition of water
-increase in respiration
-mobilize CHO
-digest CHO

Question 23

Some environmental factors to germination

Answer 23

-moisture
-temp
-oxygen

Question 24

What is light quality determined by

Answer 24

phytochrome

Question 25

What is phytochrome?

Answer 25

a chemical photoreceptor in plants used to detect light

Question 26

Phytochromes exist in two forms

Answer 26

promoting and inhibiting

Question 27

Inactive form (pr)

Answer 27

Red light

Question 28

Active form (Pfr)

Answer 28

Far red light (730 nm) -inhibits germination

Question 29

What is epigeal emergence?

Answer 29

Cotyledons emerge ABOVE soil surface

Question 30

What is hypogeal emergence?

Answer 30

Cotyledons remain BELOW soil after emergence

Question 31

Dicot growing point

Answer 31

above ground

Question 32

Monocot growing point

Answer 32

below soil surface

Question 33

Pre-emergent in soil causes..

Answer 33

-Hypogeal dicots growing point death -epigeal is protected -hypogeal monocots growth point is typically below treated zone

Question 34

What is a photoperiod?

Answer 34

Length of daylight and darkness

Question 35

light competition starts

Answer 35

6 wks after emergence

Question 36

Light competition differs because

Answer 36

- there is no reservoir -only available part of the day

Question 37

Water competition increases

Answer 37

as the season progresses

Question 38

Most variable resource

Answer 38

water

Question 39

Moisture availability is governed by

Answer 39

-amount of seasonal suppy -root development and structure -water use efficiency -most severe competition between weeds and crops centered around moisture and supply

Question 40

Most limiting nutrient is

Answer 40

Nitrogen

Question 41

Nitrogen competition occurs at

Answer 41

4-6 wks

Question 42

When does P and K competition occur

Answer 42

Later in the season when roots begin to overlap

Question 43

Crops produce more before or after weeds emerge?

Answer 43

Before

Question 44

Damage thresholds are when

Answer 44

when weed populations cause a decrease in yield

Question 45

Economic threshold is when

Answer 45

weed density causes a loss of value and it exceeds the cost of control

Question 46

When is the critical time to get ahead of weed growth?

Answer 46

3-6 weeks after emergence - gives the crop a chance to shade out the weeds

Question 47

What are the four general methods of weed control

Answer 47

-mechanical -cultural -biological -chemical

Question 48

Characteristics of mechanical weed control

Answer 48

Use of a device to kill or or reduce weeds -advantage- no herbicide cost of residue potential -disadvantage- high labor input

Question 49

Characteristics of cultural weed control

Answer 49

-Smother crop -recommended varieties -proper planting dates -fertility and pH -insect and disease management -crop rotation -water management -sanitation

Question 50

Indicator plants

Answer 50

WEEDS -low pH (red sorrel) -low nitrogen (black medic) Excessive moisture (algae)

Question 51

What is a herbicide

Answer 51

a chemical that is used to control, suppress, or kill weeds

Question 52

What is a pre emergent herbicide?

Answer 52

Applied before weed seed germination (trifluralin) no control over emerged weeds

Question 53

What is a post emergent herbicide

Answer 53

Applied after weed emergence no control over unemerged weeds

Question 54

what is a contact herbicide?

Answer 54

causes localized plant tissue injury does not readily move through the plant (glufosinate)

Question 55

What is a systemic herbicide?

Answer 55

Readily moves through the plant tissue (glyphosate)

Question 56

What is a selective herbicide?

Answer 56

Kills some plant species but not others

Question 57

What are non selective herbicides

Answer 57

Generally kills all plant species (glyphosate)

Question 58

Modes of Action

Answer 58

mechanism used to kill plants/weeds

Question 59

Site of Action

Answer 59

Specific cellular location where toxicity occurs