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APS206: Biotechnology & Food Security > Lecture 4: Chemical Control of Weeds > Flashcards

Lecture 4: Chemical Control of Weeds Flashcards

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1
Q

The global pesticide market was values at $___ in 2012 with the total value expected to reach ___ in 2017

A

$46.1 billion

$65.3 billion

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2
Q

Synthetic pesticides were worth a total of $__ in 2012 and ___ in 2017

A

$44 billion in 2012

$61.5 billion in 2017

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3
Q

Biopesticides were worth a total of $__ in 2012, and will surpass ___ in 2017

A

$2.1 billion in 2012

$3.7 billion in 2017

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4
Q

pesticide use is greatest in

A

developed countries

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5
Q

herbicides are chemicals used to control

A

weeds

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6
Q

herbicides make up __% of pesticides sales worldwide

A

45%

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7
Q

the greatest use of herbicides is in

A

developed countries

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8
Q

two type of herbicides:

A

contacts or systematic

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9
Q

2 type of treatment by herbicides

A

Pre-emergence or post-emergence of crops etc

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10
Q

classification of herbicides:

A
  • type of herbicide
  • type of treatment
  • chemical nature
  • mechanisms of action
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11
Q

contact herbicides:

A
  • only kill the portion of green tissue contacted (they are not taken up by the plant)
  • uniform spray converge is required to kill the plant
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12
Q

contact herbicides: how do they kill the plant?

A

due to their phytotoxicity (usually by rupturing cell walls)

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13
Q

contact herbicides are used against:

A

annual weeds only - do not kill perennial weeds

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14
Q

contact herbicides e.g.:

A
  • Paraquat for non selective control

- Methyl arsenic acid for control of grasses

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15
Q

Systematic herbicides:

A

-enter the plant and are translocated in the phloem and/or the xylem to other parts of the plant

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16
Q

systematic herbicides are applied as

A

either a foliar application or as a soil drench

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17
Q

systematic herbicides require how long to achieve good control

A

days to weeks

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18
Q

systematic are more effective against annual/ perennial weeds?

A

PERENNIAL

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19
Q

examples of systematic herbicides:

A
  • Glyphosate for non selective weed control

- Atrazine for certain annual grasses & broad-leaved weeds

20
Q

for systematic herbicides to be an effective weed management tool it must:

A
  1. contact the plant surface
  2. remain on the plant surface long enough to be absorbed
  3. reach a cellular site and disrupt a life supporting process (e.g.amino acid synthesis) or structure (e.g. membranes)
  4. Degrade into non-toxic metabolites
21
Q

contact herbicide positives:

A

-kill the plant quickly & they are not very persistent in the soil

22
Q

contact herbicide negatives:

A
  • have to be sprayed frequently often at quite high doses to kill weeds
  • only annual weeds are controlled
23
Q

systematic herbicide positives:

A
  • do not have to cover the whole plant therefore they can be applied at lower doses
  • can control perennial weeds
24
Q

systematic herbicide negatives:

A
  • must be applied carefully so that mist doesnt affect the crop plants
  • tend to be more persistent in the soil
25
Q

chemical structure of herbicides:

A

organic & inorganic compounds, some of which occur naturally & some of which are synthesised in labs by chemical companies

26
Q

type of treatment: total weed control-

A

herbicides are applied with the intention of killing all plants present e.g. on railway tracks or in industrial areas

27
Q

type of treatment: selective weed control:

A
  • application of a herbicide is meant to kill only the weed species
  • crop plants should not be harmed agricultural situations
28
Q

mode/mechanism of action of systematic herbicides:

A
  • inhibitors of normal growth (auxin mimics)
  • photosynthetic inhibitors
  • amino acid synthesis inhibitors
  • inhibitors of cell division
  • inhibitors of pigment synthesis
  • inhibitors of lipid biosynthesis
29
Q

inhibitors of normal growth (auxin mimics) are used primarily for controlling:

A

broadleaf perennial weeds in cereal crops e.g. picloram (cordon) fluroxypyr (starane)

30
Q

inhibitors of normal growth (auxin mimics) are absorbed where

A

through both roots & foliage and are translocated in the xylem & phloem

31
Q

inhibitors of normal growth (auxin mimics) have what effects on the plant

A
  • growth hormones regulate cell elongation, protein synthesis, and cell division
  • injury symptoms on susceptible plants include growth & reproduction abnormalities
32
Q

photosynthetic inhibitors:

A

disrupt photosystem || or photosystem 1 e.g. simazine or paraquat

  • plant but be undergoing active photosynthesis for the herbicide to be effective (tf more effective on sunny days)
  • injury symptoms may be sdelyeaed under cloudy conditions and become evident after the first sunny day after application
  • causes build up of e- in the leaves
33
Q

amino acid synthesis inhibitors: act by..

A

inhibiting an enzyme (acetolactate synthase -ASL) involved in a.a synthesis

34
Q

a.a synthesis inhibitors act over..

A

a number of days - weeks

35
Q

typical symptoms of a.a synthesis inhibitors:

A

chlorosis, purple colouration around the veins, secondary root proliferation

36
Q

a.a synthesis inhibitor example:

A

probably most famous herbicide - Glyphosate

37
Q

production of a herbicide:

A
  • chemicals (with specific or random structure) are produced in an chemistry lab
  • applied to a small number to TEST weed species as a spray or systematic application -PRIMARY SCREEN
  • any chemical which kills the plant goes to a 2nd CREEN (adult & seedling, stage, different concentrations etc.)
  • tested for toxicity on crop species animals & Humans
  • tested for persistence in the soil
  • long term field trials & more thorough tests on possible toxic side effects
38
Q

production of a herbicide takes __ years and costs how much

A

10-15 years from discovery to market & costs $10-15M

39
Q

advantages of herbicides:

A
  • they control multiple weed species
  • some can move into roots and control perennial weed species
  • some can move into roots & control perennial weed species
  • some possess residual soil activity and can control weeds over a long period of time
  • many cause little or no injury to the crop plant (As many are selective)
  • They can be applied over a large area rapidly
  • they control weeds quickly
40
Q

disadvantage of herbicides:

A

-may be toxic to humans & Other animals
-may negatively impact the soil ecosystem
-may leach into the water supply
may persist in the soil for too long and damage a susceptible crop
improper application may result in injury to the crop
-repeated use of a herbicide may lead to herbicide resistant weeds

41
Q

integrated weed management strategies involves:

A
  • carefully managed use of different control tactics - (e.g. biological, cultural, chemical or GM )
  • there are limitations to integrating these methods
  • need to understand the biology of the weed, the biological control agent and the chemical herbicide to determine the best time to spray
42
Q

e.g. of integrated weed management:

A

Control of the Water Hyacinth (Eichornia crassipes)

43
Q

Water Hyacinth (eichornia crassipes) facts

A
  • LAKE VICTORIA
  • native to S. America & was introduced into florida in 1880’s
  • very high growth rate - population doubles in 12 days
  • prevents sunlight & oxygen getting into the water
  • crowds & shades out submersed plants & reduces biological diversity
  • prevents fishing & blocks waterways
  • until the introduction
44
Q

Water Hyacinth (Eichornia crassipes) is now controlled by a combination of

A
  • classical biocontrol agents
  • mycoherbicide (innundative control)
  • occasionally a chemical herbicide
  • mechanical clearance
45
Q

classical biocontrol control agents used to control Water Hyacinth (Eichornia crassipes)

A
  • Water hyacinth weevils (Neochetina spp)
  • -both adults & larvae feed on various parts of the plants
  • Water hyacinth moth larvae (Sameodes spp)
46
Q

Mycoherbicide used to control Water Hyacinth (Eichornia crassipes)

A

-composed of spores of the fungus Cercospora rodmanii
• The pathogen exists at low levels in the population but because it is spread by rain splash it never reaches epidemic proportions.
• Therefore water hyacinths are inoculated with spores ro create an epidemic
• These control measures are used in Florida, Australia, Fiji, Honduras, India, Malaysia, S. Africa, Thailand (and other countries).

APS206: Biotechnology & Food Security (19 decks)

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