Transcript Weed ecology and management - The Evergreen State College

Weed ecology and
management
Martha Rosemeyer
Ecological Agriculture
November 4, 2003
Sustainable Agriculture
 Three attributes: Economically viable,
environmentally sound, socially just
 An integrated system including:
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natural resources: land/soil, crops,
animals, climate
socio-economic resources: capital, labor and
management
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 nonrenewable 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
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Outline
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Definition
Weed ecology and succession
Weed problems and benefits
Weed management: systems modifications
vs. input subsitution
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
Pesticide use in major crops:
herbicides major quantity
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
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Here referring to plants
 Primary vs. secondary succession
Two approaches to agriculture
 Don’t let succession proceed
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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”
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plant a corresponding successional stage, filling
that niche. If the niche is filled a “weed” can’t
compete
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
Why we go to all the effort to
bring it back to early stages!
Annual NPP addition decreases
while overall biomass increases
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
Roles of trees
Good foundation for
developing the
“emergent properties”
of more complex
ecosystems”
Other roles:
Gliessman p259
 microsites for
beneficials
 reduction of wind
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
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
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Most of our crops and farming practices came
via Europe with European weeds
 Learn to work with succession instead of
preventing it
When working against succession
Weed problems: competition
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Nutrients
Light
Water
Results in lower yields
and poor crop quality
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
Field bindweed, (Convulvulus  Reproduction by seed
arvensis), Morningglory Family
or rhizomes
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
Redroot Pigweed Amaranthus
retroflexus Amaranthaceae Fam.
 Common throughout the
West
 One plant can produce
thousands of seed
 Relative’s seed eaten by
Andean populations (Grain
amaranth, A.
hypochondiacus)
 North American indigenous
crop (A. blitum)
Hairy Galisoga, Galinsoga ciliata
Asteraceae 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
Allelopathic affect on crop plant
 Black walnut and tomatoes
 Lamb’s 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
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
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
Striga is serious problem of corn
and sorghum in Africa
 Striga in corn,
Witchweed,
Scrophulariaceae Fam.
Benefits of weeds
 Enhance soil structure and water penetration
 Improve soil tilth
 Capture nutrients that would otherwise be
lost
 Provide habitat for beneficial insects
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
From: Beeby, J. 1997.
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
Know your weed biology:
Critical to control
Life habit classification
 Annual: A plant that completes its life cycle
in one year
 Summer annual
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Purslane, galinsoga, pigweed, lambsquarters,
pineappleweed
Winter annuals: common chickweed,
black mustard, annual bluegrass
Brassica nigra
Brassicaceae
Stellaria media
Caryophullaceae
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
Perennials
Broadleaf plantain, (Plantago
major)
 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.)
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
Management Goal: Balance with
crop, not complete eradication
 Retain diverse community
 Economic threshold concept
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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
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If ecological benefit then may want to leave
Weed control: Systems approach
vs. Input substitution
 Systems approach: Direct intervention is
last resort!
 First modify:
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soil conditions
change crop rotation
cultivation and sowing practices
increase competitiveness of crop
introduction of animals as grazers
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
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grass shades and cutting reduces thistle
 Organic production may have worse
problems with perennials
 Annuals increased by crop nutrition
 Prevention because of system effect
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Crop rotation
Tillage
Fallow
Mulches
• black plastic, organic, living
 Direct effects
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Pesticides
Flame and soil sterilization
Chemicals- vinegar
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
Crop Rotation effects on weeds
Warn season weeds
Cool season weeds
From: Harwood
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
Tillage
 Pre-plant tillage to allow weed seeds to
sprout-- removing part of weed seed bank
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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
Fallow
 For control of perennial weeds like
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Johnson grass, crab grass and Bermuda grass
 Tillage can actually increase infestation
Mulches
 Black plastic mulch in strawberry (also
warms soil)
 Organic mulches- straw, sawdust, tree
leaves, secondary succession vegetation
 Living mulches
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intercrop with a
cover crop
I. Direct intervention: pesticide
What 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
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insecticide
fungicide
bactericide
herbicide- kills plants
rodenticide- kills rodents
nematicide- kills nematodes
acaricide- kills mites
 Contact herbicides
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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
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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
Not only is there stimulation of
cancer but new story: Endocrine
disruptors
Theo Colborne, 1987. Our Stolen Future.
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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
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.
Source of Agricultural Endocrine
Disruptors
 Agricultural runoff /Atmospheric transport
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Organochlorine Pesticides (found in
insecticides, many now phased out)
• DDT, dieldrin, lindane
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Carbamate insecticides
• **Aldicarb (PAN-pesticide database)
 Agricultural runoff
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Pesticides currently in use
• **Atrazine, trifluralin, permethrin
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 50:A26)
Atrazine detected
in groundwater
in Wisconsin
Other “direct” interventions
Used by organic farmers
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Flaming
Solarization
Biological control
Vinegar (salt not recommended)
Flaming
Impt to have
small seeds
Can use propane
gas tank on small scale
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
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- Carabid beetle
ie not widely used,
unlike diseases of insects
Vinegar
 5% (household white vinegar)-10%
concentrations of organic vinegar had 85100% kill rate
 Canada thistle- one of most susceptible with
5% concentration with 100% kill rate
 Spot spraying in corn cost $20-30 per acre
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ARS researchers Radhakrishnan, Teasdale and
Coffman
 Not tested for effects on soil that cannot be
replace by lime
 Salt not recommended
The systems approach
 How to avoid the use of direct intervention
methods?
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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?
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How do does letting succession take place
avoid problems with weeds?
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 MiniSeries Booklet #29
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