Weeds L6 Flashcards
Biological weed control
control of a weed species by their natural enemies to maintain the weed population below the level of economic injury
Lotka-Volterra equation/Predator-prey model
Simplified model about predator-prey relationship
Economic injury level (EIL)
the lowest pest population density that will cause economic damage equal to the cost of the control
Economic threshold (ET)
the level of pest infestation at which management action is justified
Types of biocontrol agents
Invertebrates (insects, worms, etc.)
Pathogens
Mammals
Birds
Fish
Advantages of weed biocontrol
offers permanent solution to problem
agents are often self-perpetuating and self-dispersing
Risks are known and evaluated before release
Good cost ratio for successful programs
Example of unsuccessful biocontrol
Attempt to control beetles in sugarcane with the cane toad. Didn’t work because beetles just flew to tops of sugarcane and toads just ate everything else
Disadvantages of weed biocontrol
control is slow and weed eradication is impossible
establishment may fail
# of control agents may be low if target weed is closely related to crop
some risks are not known and cant be evaluated
Classical weed biocontrol
The intentional introduction of host-specific natural agents from a different country to achieve control of an invasive weed species (importation)
Non-classical weed biocontrol
inoculation, augmentation, inundation, conservation
2 main requirements for the classical weed biocontrol method
- invasive weeds species was freed from its natural enemies when it was introduced to the new habitat
- the natural agent being imported should not have enemies in the new habitat
it can take __________ years to achieve control (plus millions of dollars)
5-10
example of classical weed biocontrol success
Purple loosestrife was brought from Europe/Asia to North America and is invasive to wetlands
Released beetles Galerucella calmariensis and G. pusilla to control it
What are the core assumptions of classical weed biocontrol programs that are needed to reunite pest species with their coevolved natural enemies?
Natural agent can control target weed
agent is specific (not attack other plants)
can be reared in captivity
can self-disperse and reproduce in new habitat
Steps to developing a classical biocontrol program
- determine suitability of weed for biocontrol
- search for potential enemies
- evaluate ecology of natural enemies
- select candidate species and conduct host range testing
- small-scale experimental releases
- post-release evaluation
- large scale general release
Example of successful classical weed biocontrol in North America
Leaf beetles were introduced from Europe to control St. Jon’s Wort Hypericum perforatum in Canada and the USA
Example of classical biocontrol in Australia
Moth Cactoblastis cactorum was brought from Argentina to control the Prickly Pear Cactus in Australia
Thistle Biocontrol examples
Thistle head weevil and Canada thistle stem-mining weevilintroduced from Eurasia to control thistle
Curly dock Biocontrol example
Rumex rust fungal pathogen introduced from Europe to control curly dock
Fish biocontrol example
White amur introduced from East Asia to control weeds in waterways
When is biocontrol likely to fail?
Natural agent fails to establish, cause ecological instability, or attack/targets non-target plants
Inoculative weed biocontrol
Introducing a natural agent that is already in the country to a new location or environment
main requirements for inoculative weed biocontrol
agents are able to reproduce
impact is season long
further releases necessary if secondary outbreak of target weed occurs
Augmentative weed biocontrol
intervention to enhancing or restoring the function of a natural agent that is already in the habitat, location, or environment
Main requirements for Augmentative weed biocontrol method
Impact should be season-long
further releases necessary if secondary outbreak of target weed occurs
Inundative weed biocontrol
the massive release of a natural agent into a certain environment to quickly suppress a weed infestation
Main requirements for Inundative weed biocontrol
Agent is able to rapidly suppress target weed population
Agent doesn’t have to reproduce
Easy to mass-rear
Impact is similar to herbicide
Conservation weed biocontrol
Improving agricultural practices to enhance the functioning of natural agents
Main requirements of Conservation weed biocontrol
No bio controls are released
rely on agents ability to suppress weed populations
focus is on the species ecology
Weed seed predation
Predators that attack seeds of target weed species
Pre-dispersal seed predation
carried out by specialist insects that attack the seedheads and destroy the seeds
Post-dispersal seed predation
carried out by non-specialist invertebrates and vertebrates that attack seeds on the soil surface and destroy them
