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Pesticides > Herbicides > Flashcards

Herbicides Flashcards

1
Q

What is a weed?

A

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

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2
Q

Weeds my possess

A

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

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3
Q

Reasons weeds survive

A

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

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4
Q

Effects of weeds

A

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

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5
Q

Seed germination factors

A

-oxygen
-light
-temp
-water
-scarification

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6
Q

What is an escape weed?

A

A weed that comes through despite herbicide efforts

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7
Q

What is a monocot?

A

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

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8
Q

What is a dicot?

A

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

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8
Q

What is an annual?

A

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

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9
Q

Summer annuals

A

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

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10
Q

Winter annuals

A

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

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11
Q

What is a biennial?

A

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

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12
Q

biennial year 1

A

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

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13
Q

Biennial second year

A

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

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14
Q

What is a perennial?

A

Plant that lives for more than 2 years

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15
Q

Perennial life cycle

A

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

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16
Q

What are some perennial propagules?

A

-rhizomes
-stolons
-bulbs
-tubers

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17
Q

What is a rhizome?

A

Horizontal, below ground stem
roots

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18
Q

What is a stolon?

A

horizontal stems, grows at soil surface
-roots and shoots

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19
Q

What is a bulb

A

Modified bulb with stem and fleshy scales compressed closely together

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20
Q

What is a tuber?

A

enlarged terminal portion of rhizomes

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21
Q

How do weeds spread?

A

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

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22
Q

Germination

A

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

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23
Q

Some environmental factors to germination

A

-moisture
-temp
-oxygen

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24
Q

What is light quality determined by

A

phytochrome

25
Q

What is phytochrome?

A

a chemical photoreceptor in plants used to detect light

26
Q

Phytochromes exist in two forms

A

promoting and inhibiting

27
Q

Inactive form (pr)

A

Red light

28
Q

Active form (Pfr)

A

Far red light (730 nm)
-inhibits germination

29
Q

What is epigeal emergence?

A

Cotyledons emerge ABOVE soil surface

30
Q

What is hypogeal emergence?

A

Cotyledons remain BELOW soil after emergence

31
Q

Dicot growing point

A

above ground

32
Q

Monocot growing point

A

below soil surface

33
Q

Pre-emergent in soil causes..

A

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

34
Q

What is a photoperiod?

A

Length of daylight and darkness

35
Q

light competition starts

A

6 wks after emergence

36
Q

Light competition differs because

A
  • there is no reservoir
    -only available part of the day
37
Q

Water competition increases

A

as the season progresses

38
Q

Most variable resource

A

water

39
Q

Moisture availability is governed by

A

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

40
Q

Most limiting nutrient is

A

Nitrogen

41
Q

Nitrogen competition occurs at

A

4-6 wks

42
Q

When does P and K competition occur

A

Later in the season when roots begin to overlap

43
Q

Crops produce more before or after weeds emerge?

A

Before

44
Q

Damage thresholds are when

A

when weed populations cause a decrease in yield

45
Q

Economic threshold is when

A

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

46
Q

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

A

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

47
Q

What are the four general methods of weed control

A

-mechanical
-cultural
-biological
-chemical

48
Q

Characteristics of mechanical weed control

A

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

49
Q

Characteristics of cultural weed control

A

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

50
Q

Indicator plants

A

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

51
Q

What is a herbicide

A

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

52
Q

What is a pre emergent herbicide?

A

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

53
Q

What is a post emergent herbicide

A

Applied after weed emergence
no control over unemerged weeds

54
Q

what is a contact herbicide?

A

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

55
Q

What is a systemic herbicide?

A

Readily moves through the plant tissue (glyphosate)

56
Q

What is a selective herbicide?

A

Kills some plant species but not others

57
Q

What are non selective herbicides

A

Generally kills all plant species (glyphosate)

58
Q

Modes of Action

A

mechanism used to kill plants/weeds

59
Q

Site of Action

A

Specific cellular location where toxicity occurs

Pesticides (6 decks)

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