Weed Control and Management

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Weed Control and Management

• INAG 116 / ANSC 110
• February 19, 2008

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Why Should I Worry?

• 1 Acre Weed Free Pasture/Horse 40 to 60 of
  Yearly Feed Bill.
• 2 Acres Weed Free Pasture/Horse 90 of Yearly
  Feed Bill (Haying Required)
• Feed Ration is Unknown When Weedy
• Some Weeds are Poisonous or Noxious
• Weeds Reduce the Quality Value of Hay

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Weed Overview

• Interfere with forage establishment, yield, and
  quality
• Compete for resources
• Light
• Space
• Nutrients
• Water
• Weeds are indicators of deficiencies in a forage
  management program

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Weed Overview

• Classified based on life span, season of growth
  and method of reproduction
• Annuals
• Complete life cycle in one year and germinates in
  spring or summer
• Biennial
• Complete life cycle in two consecutive growing
  seasons and germinates in late summer or early
  fall
• Perennials
• Persist for more than 2 years and reproduce from
  seed or asexually

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Weed Overview

• Designations
• Native part of North America plant communities
  before Europeans colonized the continent
• Invasive exotic species that pose a special
  threat because they lack natural enemies to limit
  population growth
• Noxious weeds that are regulated by law

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Weed Management

• To plan an effective weed management program, a
  producer must be able to identify weeds and
  understand how weed biology and ecology affects
  where weeds are found and their value or
  detriment.
• Weed control decisions are based largely on
  visual thresholds and intuition.
• Begins long before crop establishment.

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Weed Management

• Some things to consider
• New establishment?
• Established pasture?
• Management strategy
• Incremental goal-setting

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Where to start?

• Pasture-invading weed species should be assessed
  for
• Competitive ability potential to reduce
  desirable forage species
• Invasiveness potential to multiply and increase
• Yield quality nutritive value relative to
  desirable forage species
• Cost and effectiveness of control measures
  cultural, mechanical and chemical

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Causes of an Unprofitable Pasture

• Overstocking
• Cutting Strategies
• Climate
• Fertility and pH
• Pest Control

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Weed Management Strategies

• Prevention
• removing weed seed and vegetative material from
  farming implements before preparing a seedbed for
  forage grasses
• Planting seed that is not contaminated with weed
  seed
• Control
• process of minimizing weed interference with
  desirable plants to meet economic and production
  goals

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Weed Management Strategies

• Eradication
• complete elimination of weed
• requires removal of living plants and destruction
  of seed in the soil
• Early detection followed by swift, intensive and
  aggressive effective control measures during
  early invasion are essential to eliminate the
  invader.

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Weed Control Measures

• Cultural
• Mechanical
• Chemical
• Biological

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Cultural Control

• Includes anything that makes a crop more
  competitive against weeds
• Focuses on improving the health of native
  plants
• Practices include
• Fire
• Grazing
• Haying
• Revegetation or reseeding
• Plant competition
• Liming
• Fertilizing

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Cultural Control Things to consider

• Consider seedbed preparation, planting date,
  fertilization, planting population, and
  high-quality crop seed and select adapted species
  and varieties
• Prevention is the most important tool for
  managing weeds on established pastures
• Managing a dense, competitive forage is key to
  preventing weed invasion and interference

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Cultural Control Things to consider

• Overseed in open areas
• Test soils fertilize annually
• Rotational grazing systems
• Prevent dispersal of seeds

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Cultural Control - Fire

• Useful and essential practice to meet land
  management objectives
• Used to control woody plants
• Can help increase nutritive value of dominant
  grasses
• Increase grass seed production

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Transition Pasture SystemsAnnual Forages

• Renovate and reseed pastures until pasture
  problems are solved.
• Use annual forages to correct or overcome pasture
  deficiencies or failures.
• Use annual forages to develop successful
  perennial pastures.

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Mechanical Control

• Involves either removal of the aerial portions of
  the weed or removal of enough of the root and
  crown to kill the plant
• Practices include
• Tilling
• Mowing
• Removal by hand

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Mechanical Control Things to consider

• Repeated mowing can
• reduce competitive ability
• deplete root carbohydrates
• prevent seed production
• Mow at a height above grass seedlings when weeds
  are 8 to 10 inches tall to reduce shading

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Mechanical Control Things to consider

• If you see a new weed, dig it, pull it, or remove
  the seedhead before seeds can disperse
• Mowing can kill or suppress annual and biennial
  weeds
• High cost of these more energy intensive
  treatments limits their widespread use

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Chemical Control

• Herbicides provide a convenient, economical and
  effective way to help manage weeds
• Allow fields to be planted with
• Less tillage
• Earlier planting dates
• Additional time to perform the other tasks that
  farm or personal life require
• Spot spraying is most economical alternative for
  scattered infestations of weeds

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Biological Control

• Release of organisms that attack plants to
  control weeds
• Aim is to shift the balance of competition
  between the weed and the crop in favor of the
  crop and against the weeds
• Historically insects and mites have been most
  important

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Biological Control

• Tools currently utilized
• Insects
• Mites
• Nematodes
• Pathogens
• Grazing Animals
• Can be cost effective, environmental safe,
  self-perpetuating, and well suited to an
  integrated weed management program

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Biological Control Strategies

• Conservation
• involves manipulation of the environment to
  enhance the effect of existing natural enemies
• usually used to manage native weeds
• Augmentation
• employs periodic release of natural enemies
• restricted to managing weeds in high-value food
  crops

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Biological Control

• Importation
• known as classical biological control
• the planned relocation of natural enemies of
  exotic weeds from their native habitats onto
  weeds in their naturalized habitats
• seeks to reestablish weed and natural enemy
  interactions that reduce the weed population to
  an acceptable level in the new environment

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Beneficial InsectsCanada Thistle
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Beneficial Insects
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Grazing Animals

• Can be used to minimize the spread of certain
  weeds and to control large infestations
• Does not completely eradicate weeds
• Common animals
• Cattle
• Sheep
• Goats
• Horses

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Biological Control
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Biological Control Limitations

• Success in the past 200 years has been variable
• Hard to control alone due to environmental
  changes
• Although slow in coming, it may have a major
  impact on managing problem weeds in pasture
  systems in the future

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Integrative Management

• A program that combines cultural, mechanical,
  chemical, and perhaps biological tools
• Can provide a effective economical weed
  management program in pasture systems
• Prevention is the most important consideration
  for managing weeds in established pasture systems

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Adaptive Management

• Complements integrated programs
• Requires manager to
• Establish management goals
• Develop and implement management programs based
  on goals
• Monitor and assess impacts of management efforts
• Modify goals and invasive plant management in
  light of new information