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Weed ecology and management

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Title: Weed ecology and management


1
Weed ecology and management
  • Martha Rosemeyer
  • Ecological Agriculture
  • November 4, 2003

2
Sustainable Agriculture
  • Three attributes Economically viable,
    environmentally sound, socially just
  • An integrated system including
  • natural resources land/soil, crops, animals,
    climate
  • socio-economic resources capital, labor and
    management

3
That are organized to satisfy the following goals
  • Provide food and fiber
  • Enhance environmental quality and natural
    resource base
  • Make the most efficient use of non-renewable and
    on-farm resources
  • Sustain the economic viability of farm
    operations
  • Enhance the quality of life for farmers, their
    families, communities and society as a whole

4
Outline
  • Definition
  • Weed ecology and succession
  • Weed problems and benefits
  • Weed management systems modifications vs. input
    subsitution

5
  • WEEDS ARE THE GREATEST BIOLOGICAL CHALLENGE TO
    AGRICULTURAL PRODUCTION, WHETHER CONVENTIONAL OR
    ORGANIC!
  • Labor 40-70 labor in traditional systems or
    herbicides to remove weeds

6
Pesticide use in major crops herbicides major
quantity
7
What is driving the system? Why are weeds so
important?
  • Disturbance and Recovery via Succession
  • Succession is the process by which one community
    gives way to another
  • Here referring to plants
  • Primary vs. secondary succession

8
Two approaches to agriculture
  • Dont let succession proceed
  • Invest much energy in the form of human, animal
    or fossil fuel
  • Herbicides are used to prevent succession from
    occurring
  • Try to mimic successional stages of the natural
    ecosystem, the analogue model
  • plant a corresponding successional stage, filling
    that niche. If the niche is filled a weed
    cant compete

9
Analogue Approach
  • Commonly used in tropics where forest is climax
  • Disturbance can be introduced at any stage to
    bring back to beginning stage of succession

10
Why we go to all the effort to bring it back to
early stages!
11
Annual NPP addition decreases while overall
biomass increases
12
Agroforestry
  • Defined as practices that intentionally retain
    trees on land used for crop production or
    grazing
  • Over space or time (rotations that use fallows
    with trees in it)
  • fallow
  • Trees can be spatially arranged for different
    effects

13
Roles of trees
  • Good foundation for developing the
  • emergent properties
  • of more complex ecosystems
  • Other roles
  • Gliessman p259
  • microsites for beneficials
  • reduction of wind

14
Optimizing the positive impacts
  • Potential negative effects
  • shading, allelopathic influence
  • microclimate effects that favor disease
  • branches etc. can fall on harvestable portion
  • Can be mitigated by planting plan

Fallow field not planted to a crop
15
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16
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17
What is a weed? A plant out of place
  • A weed is any plant, native or non-native, that
    interferes with crop production by doing more
    harm than good and encroaches where it is not
    wanted
  • A successful weed has closely adapted to the
    life-cycle of the crop and farming practices
  • Most of our crops and farming practices came via
    Europe with European weeds
  • Learn to work with succession instead of
    preventing it

18
When working against successionWeed problems
competition
  • Nutrients
  • Light
  • Water
  • Results in lower yields and poor crop quality

19
Interference with harvesting operations
  • Weed roots such as bindweed wrap around sub-soil
    blades used for undercutting root crops during
    harvest
  • European, extensive problem, difficult to
    eradicate, root system to 20, seeds viable for
    50 years
  • Reproduction by seed or rhizomes

Field bindweed, (Convulvulus arvensis),
Morningglory Family
20
Build up of soil seedbank vs crop seed bank (for
storing crops)
  • Weed seeds present in soil
  • Seedbank can increase rapidly in one season with
    fertilization and irrigation and ineffective
    control
  • One weed plant can produce thousands of seeds
  • Affected by management

21
Redroot Pigweed Amaranthus retroflexus
Amaranthaceae Fam.
  • Common throughout the West
  • One plant can produce thousands of seed
  • Relatives seed eaten by Andean populations
    (Grain amaranth, A. hypochondiacus)
  • North American indigenous crop (A. blitum)

22
Hairy Galisoga, Galinsoga ciliataAsteraceae Fam.
  • One of the most difficult-to-control weeds in
    vegetable production on fertile soil, esp. in NE
    US
  • Continually produces seeds throughout growing
    season
  • Can produced 7500 seeds/plant

23
Allelopathic affect on crop plant
  • Black walnut and tomatoes
  • Lambs quarters roots secret oxalic acid
  • Velvetleaf, quackgrass, Canada thistle, giant
    foxtail, black mustard and yellow nutsedge
  • Mechanism root secretion, decomposition of
    residues, effects microbial symbionts

24
Weeds can harbor diseases and pathogenic fungi,
esp. crop relatives
  • Classic case of wheat rust disease on wheat with
    alternative host European barberry
  • 1970-1990 caused 100 million annually
  • Barberry eradication project saved farmers 30
    million per year

25
Can be directly parasitic
  • Dodder (Cuscuta sp.) Convolulaceae (Morningglory)
    Family
  • Major problem in West US with alfalfa, clover,
    potatoes, safflower
  • First germinates root then when finds host
    becomes parasite

26
Striga is serious problem of corn and sorghum in
Africa
  • Striga in corn, Witchweed, Scrophulariaceae Fam.

27
Benefits of weeds
  • Enhance soil structure and water penetration
  • Improve soil tilth
  • Capture nutrients that would otherwise be lost
  • Provide habitat for beneficial insects

28
Indicate soil characteristics and suitability for
crops
  • Creeping buttercup, Ranunculus repens,
    Ranunculaceae Fam.
  • Introduced from Europe as ornamental
  • Reproduces from seed or rhizomes
  • Toxic to cattle
  • Could indicate moist soil conditions

29
From Beeby, J. 1997.
30
May be edible good weed/bad weed concept
  • Common purselane Portulaca oleracea Portulacaceae
    Fam.
  • Introduced from Europe
  • Seeds can remain dormant for years
  • Edible fresh or cooked, esp. used in Mexican
    cooking

31
Know your weed biology Critical to controlLife
habit classification
  • Annual A plant that completes its life cycle in
    one year
  • Summer annual
  • Purslane, galinsoga, pigweed, lambsquarters,
    pineappleweed

32
Winter annuals common chickweed, black mustard,
annual bluegrass
Brassica nigra Stellaria media Brassicaceae Cary
ophullaceae
33
Biennials
Biennials
  • A plant that completes its life cycle in two
    years above ground
  • Examples are wild carrot (Daucus spp.), bull
    thistle (Circium vulgare) and poison hemlock
    (Conium maculatum)

Wild carrot is a host of leafhopper-vectored
aster yellows phytoplasma
34
Perennials
  • A plant that lives a number of years, often
    producing seed once each year
  • Simple perrenials reproduce by seed
  • Examples are dandelion ((Taraxacum officinale),
    curly dock (Rumex crispus) and plantain (Plantago
    sp.)

Broadleaf plantain, (Plantago major)
35
Creeping perennials
  • Reproduce by seed and asexually through rhizomes,
    stolons (a horizontal above ground stem that
    roots at the nodes runners) tubers and rootstalk
  • Examples are Johnson grass, Bermuda grass,
    Nutsedge (Cyperus sp.), Field bindweed

36
Management Goal Balance with crop, not complete
eradication
  • Retain diverse community
  • Economic threshold concept
  • Do not start to modify agricultural practices
    unless it reaches a point where it pays to deal
    with it in long and short term
  • Can include ecological concepts as well
  • If ecological benefit then may want to leave

37
Weed control Systems approach vs. Input
substitution
  • Systems approach Direct intervention is last
    resort!
  • First modify
  • soil conditions
  • change crop rotation
  • cultivation and sowing practices
  • increase competitiveness of crop
  • introduction of animals as grazers

38
Farming practices affect weed community
composition
  • No-till increases percentage of perennial weeds
    (annuals shaded out by residue)
  • Decreased reliance on grass leys (2-3 yr
    rotation into grass (European) increases
    perennial weeds
  • grass shades and cutting reduces thistle
  • Organic production may have worse problems with
    perennials
  • Annuals increased by crop nutrition

39
  • Prevention because of system effect
  • Crop rotation
  • Tillage
  • Fallow
  • Mulches
  • black plastic, organic, living
  • Direct effects
  • Pesticides
  • Flame and soil sterilization
  • Chemicals- vinegar

40
Systems approach vs input substitution
  • Systems approach modifies system so that weeds
    are not a problem
  • Prevention of weed problems
  • Alternate summer and winter crops (where
    possible)
  • Rotate crops- different crops favor different
    weed., pest and disease populations

41
Crop Rotation effects on weeds
Warn season weeds
Cool season weeds
From Harwood
42
Weed-suppressive cover crops
  • Sudan grass, buckwheat, sesbania (hot summer
    areas)
  • Perennial rygrass (Lolium perenne) (PNW)- dense
    growth and allelochemicals suppress weeds (at
    organic farm)
  • Optimize planting time to ensure uniform cover

43
Tillage
  • Pre-plant tillage to allow weed seeds to sprout--
    removing part of weed seed bank
  • may till several times depending on weed pressure
  • One of main weed control methods of organic
    farmers
  • Can also use moldboard plow to bury the weed seeds

44
Fallow
  • For control of perennial weeds like
  • Johnson grass, crab grass and Bermuda grass
  • Tillage can actually increase infestation

45
Mulches
  • Black plastic mulch in strawberry (also warms
    soil)
  • Organic mulches- straw, sawdust, tree leaves,
    secondary succession vegetation
  • Living mulches
  • intercrop with a
  • cover crop

46
I. Direct intervention pesticideWhat is a
pesticide?
  • An umbrella term used to describe any chemical
    that controls or kills a pest
  • Classified by the type of pest they kill
  • insecticide
  • fungicide
  • bactericide
  • herbicide- kills plants
  • rodenticide- kills rodents
  • nematicide- kills nematodes
  • acaricide- kills mites

47
Who uses them?
  • Comparisons of pesticide use by area
  • Units are grams / ha

48
  • Contact herbicides
  • Paraquat persistent, high acute mam. Toxicity,
    slightly to high toxic aquatic
  • Triazine herbicides Atrazine- persistent, low
    acute mam. toxicity, carcinogen,
  • endo. disruptor, ground water
  • Systemic herbicides
  • glyphosate (OP)- not persistant, low acute mam.
    tox., slightly toxic aquatic, hormones
  • (2,4-D (auxin) 2,4,5-T) - not persistent,
    moderate acute mam. tox.,
  • poss. carcinogen sus. endo. disruptor,
  • potential ground water contaminant

49
Not only is there stimulation of cancer but new
story Endocrine disruptors
  • Theo Colborne, 1987. Our Stolen Future.
  • PhD UW, observations of birds of Great Lakes
  • Led to endocrine disruptor hypothesis
  • Data still emerging
  • National EPA still not released list of suspected
    chemicals, though Illinois EPA, Keith, Colborn
    and Benbrook list and Canada

50
Function of endocrine disruptors
  • They can act like a natural hormone and bind to a
    receptor. This causes a similar response by the
    cell, known as an agonist response.
  • They can bind to a receptor and prevent a normal
    response, known as an antagonistic response.
  • A substance can interfere with the way natural
    hormones and receptors are synthesized or
    controlled.

51
Source of Agricultural Endocrine Disruptors
  • Agricultural runoff /Atmospheric transport
  • Organochlorine Pesticides (found in
    insecticides, many now phased out)
  • DDT, dieldrin, lindane
  • Carbamate insecticides
  • Aldicarb (PAN-pesticide database)
  • Agricultural runoff
  • Pesticides currently in use
  • Atrazine, trifluralin, permethrin

52
Other sources of endocrine disruptors
  • Incineration, landfill
  • PCB (Polychlorinated biphenyls), PCD (PC dioxins)
  • Municipal effluent and agricultural runoff
  • Natural hormones produced naturally by (animals)
    synthetic steroids (contraceptives)
  • 17-b-estradiol, estrone, testosterone ethynyl
    estradiol
  • ECS Communications Last update September 15
    1999 http//www.ec.gc.ca/eds/fact/broch_e.htm

53
Atrazine (triazine herbicide)
  • 1 herbicide in corn in the MidWest
  • Now banned in EU because of human health and
    environmental concerns
  • Just re-approved in US
  • Discrediting of US scientists by Syngenta (e.g.
    Hayes), where Atrazine is 1/4 of total revenues
  • Proven endocrine disruptor-- in frogs changes
    testes to ovaries (Lumenstyk,2003 Chronicle of
    Higher Educ 50A26)

54
  • Atrazine detected
  • in groundwater
  • in Wisconsin

55
Other direct interventionsUsed by organic
farmers
  • Flaming
  • Solarization
  • Biological control
  • Vinegar (salt not recommended)

56
Flaming
Impt to have small seeds Can use propane gas tank
on small scale
57
Solarization with clear or black plastic
  • Useful to kill annual weed seeds
  • Can kill certain perennials, e.g. creeping
    buttercup in the PNW
  • Can be combined with
  • cabbage or cole crop
  • decomposition for
  • sterilization

58
Biocontrol of weeds using insects or plant
pathogens (a pathogen causes a disease)
  • One of major natural occurrences- Only 25 of
    weed seeds do germinate- thought to be due to
    insects and pathogens in the soil
  • Used only in specific circumstances-
  • ie not widely used,
  • unlike diseases of insects

Carabid beetle
59
Vinegar
  • 5 (household white vinegar)-10 concentrations
    of organic vinegar had 85-100 kill rate
  • Canada thistle- one of most susceptible with 5
    concentration with 100 kill rate
  • Spot spraying in corn cost 20-30 per acre
  • ARS researchers Radhakrishnan, Teasdale and
    Coffman
  • Not tested for effects on soil that cannot be
    replace by lime
  • Salt not recommended

60
The systems approach
  • How to avoid the use of direct intervention
    methods?
  • Organic farmers growing annuals use long (4-7 yr)
    rotations and a combination of other methods
  • How can we mimic the natural ecosystem to avoid
    the effects of weeds?
  • How do does letting succession take place avoid
    problems with weeds?

61
References
  • Weed photos identification and management
    www.ipm.ucdavis.edu
  • Whitson et al. 2000. Weeds of the West (9th
    Edn).Western Society of Weed Science.
  • Taylor, R. 1990. Northwest Weeds. Mountain Press,
    Missoula
  • Uva, R., J. Neal, J. DiTomaso. 1997. Weeds of the
    Northeast. Comstock Press.
  • Beeby, John. 1997. Test Your Soil with Plants.
    Ecology Action Self-teaching Mini-Series Booklet
    29

62
Questions
  • Would you consider the lack of weeds an emergent
    property of an agroecosystem? Explain.
  • Ch 17 Question 1, 2 (spend some time on this),
  • Upper division Ch 17 4, 6
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