Weed diversity in agroecosystem

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Weed diversity in agroecosystem
Fabian Menalled Land Resource and Environmental
Science Montana State University
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What is a Weed?

• A plant that is growing where it is not wanted
• Roberts et al. 1982. Weed Control Handbook

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Weed Management is Achieved Through
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Approximately 20-30 of input costs
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Pesticide Application to
U.S.A. Agricultural Land
Herbicides
Insecticides/acaricides
Fungicides
Fumigants/nematicides
Other
(USEPA 1999)
0
50
100
150
200
250
Million kg
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Thirty-nine herbicide active ingredients are
classified by the U.S.A. Environmental Protection
Agency as probable1, likely2, or possible3
carcinogens.1 e.g., acetochlor 2 e.g.,
alachlor3 e.g., atrazine, cyanazine, metolachlor
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Wheat Herbicides and Health

• Clorophenoxy herbicides (2,4-D and MCPA)
• Schreinemachers, D.M. 2003. Birth malformations
  and other adverse perinatal outcomes in four US
  wheat-producing states. Env. Health Perspectives
  111 1259-1264
• Schreinemachers, D.M. 2000. Cancer mortality in
  four northern wheat producing states. Env. Health
  Perspectives 108 873-881

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Atrazine in River Water
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Atrazine and Frogs

• Hayes et al. 2002. Hermaphroditic, desmaculinized
• frogs after exposure to the herbicide,
  atrazine,
• at low ecologically relevant doses. Proc.
  Nat.
• Acad. Sci. 995476-5480.
• Exposure 10,000 - 30,000 times beneath levels
  previously identified as non-toxic to frogs

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Herbicide Resistance
The ability of a plant to survive and reproduce
after treatment with a dose of herbicide that
would normally kill the plant
Susceptible
Resistant
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Herbicide Resistance

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What is a Weed?

• A plant that is successful in colonizing
  disturbed, but potentially productive sites and
  at maintaining their abundance under conditions
  of repeated disturbances
• Mohler, 2001. Ecological Management of
  Agricultural Weeds

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Disturbance

• A discrete event that disrupts ecosystem,
  community or population structure
• Changes resources, substrate availability or the
  physical environment
• Pickett and White, 1985

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In Summary

• 1. Weed scientists are re-thinking our approach
  to weed management
• 2. There is growing interest in reducing chemical
  inputs in agroecosystems
• Increased interest in low-input and organic
  farming

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What is the Impact of Cropping System on Weed
Diversity?
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Study Site 42 ha-
100 m
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Weed Biomass
g / m2
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Species Density (no. species m-2)

no. species / m2
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What is the Functional Importance of Weed
Diversity?
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Experimental Manipulations of Diversity
Large-scale manipulations in grasslands
Cedar Creek
BIODEPTH
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Diversity and Ecosystem Function

• Positive relationship between diversity and
  ecosystem functioningthough there has been quite
  a bit of debate about these experiments

Resistance to invasion
productivity
stability
diversity
diversity
diversity
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Diversity and Ecosystem Function

• Positive relationship between diversity and
  ecosystem functioningthough there has been quite
  a bit of debate about these experiments

• Which of these ecosystem functions are
  important in weed management?

Resistance to invasion
productivity
stability
diversity
diversity
diversity
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Weed Diversity and Pest Management

• Weeds provide resource for beneficial insects
  (parasitoids, ground beetles)

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Does Weed Diversity Impact Resource Availability
and/or Soil Feedbacks?
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Cellulose boards Plant biomass
Phase 1
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Soil Pasteurization and Weight Loss of Cellulose
Boards Means Averaged Across All Treatments
SE, n 96
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Response of Spring Wheat to Previous Species,
Pasteurization, and N
Soil NOT pasteurized after phase I
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6
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Wheat dry weight Phase II (g)
4
3
2
1
control
oat
rag
wheat
Previous species (phase I)
Fertilized
No fertilizer
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In Conclusion

• We are rethinking our approach to farming
• Definition of weeds
• Methods to farm
• Farming system impacts weed diversity
• More number of species in organic and low input
  systems
• Weed diversity impacts ecosystems function
• But we are just scratching the surface

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Question?
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What is a Weed?
Source WSSA web site. Ian Heap
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Resources
Light Water Nutrients Space