Weeds- Mid Term Flashcards
Pest -def
An organism detrimental to humans or human concerns
generally insects, weeds, pathogens
Parasitc weeds are directly
dependant on the host
We want the host plant to be ___ to herbicides
resistant
When was chemical weed controlled developed
WW2 commercialized in 1950s
Major Herbicide Classifications based on Physiology
- Inhibition of photosynthesis
- Inhibition of plant growth
- Inhibition of Biosynthetic processes (amino acid synthesis, lipid synth)
Mechanism of Action (def)
The precise biochemical (inhibition of sp. enzyme) or biophysical (inhibition of electron flow) reaction or series of reactions that create a herbicides final or ultimate effect
(site of action, specific target of an herbicide)
Mode of Action (def)
The sequence of events that occur from herbicides first contact with a plant until its final effect (often plant death) is expressed.
(All events from application to death)
Ways that herbicide resistant crops are developed
- naturally tolerant
- Developed using tradition breeding methods
- Mutagensis
D. Genetic Engineering (majority)
Ways that Herbicide resistant weeds happen
Naturally evolved
Resistant Crop (to herbicide def)
The inherited ability of a crop to survive and reproduce following exposure to a dose of herbicide normally lethal to the original crop
Stacked resistance (crops to herbicides)
Crop that is resistant to 2+ herbicides
Herbicide resistance
Why do weed control failures not necessarily mean herbicide resistance?
- improper dosage
- lack of coverage
- stage of weed growth at application
- climactic conditions
Herbicide Resistance in Weeds definition
The Inherited ability of a plant to survive and reproduce following exposure to a dose of herbicide that was previously known to control the population
How does herbicide resistance develop in weeds
A change in the population over time where resistance individuals survive and reproduce and begin to dominate the population
There is naturally extensive genetic variation in weeds that allows for this possibility. Crops only have one genotype.
population
A field of not controlled palmer
Herbicide Tolerance -definition
The inherent ability of a species to survive and reproduce after use of a dose of herbicide that controls a susceptible species.
Implies no selection or genetic manipulation. Naturally tolerant. Has never been controlled by that herbicide
No change in population over time
Why do herbicide resistant weeds evolve (from a management perspective)
Extensive/repeated use of herbicides
continuous threat to weed management
fewer herbicide options and increased costs
Cross resistance (herbicide resistance in weeds)
Resistance to two or more classes of herbicides in the same group acting on the same target site.
Resistance to two or more groups of herbicides dues to a single common mechanism of resistance.
When changing herbicides we need make sure the ___ changes as well
mechanism
Why would single herbicide resistance be preferred by growers?
It’s easier to find other herbicides that work.
Single Resistance (to herbicides in weeds)
Resistant to only one herbicide
Multiple Resistance (to herbicides in weeds)
Resistant to two or more herbicides with different target sites or mechanisms
Resistant by multiple mechanism
Why might a weed sp. develop multiple resistance to herbicides?
Continuous applications of a single herbicide of MOA, and selection for HR biotypes, followed by repeated applications of another herbicide and selection for biotypes.
Low-level resistance visual scoring
Plant response from slightly injured to nearly dead
majority of plants display immediate response
High-level resistance visual scoring
Plants are slightly injured or uninjured
Few plants have an intermediate response
-plants look untouched even at a high dose
Herbicide Tolerance in crops is based on ___ principle
selectivity
Herbicide Resistance in crops is based on
Genetic manipulation
Selective Herbicide definiton
Herbicide that kills or significantly retards growth of weed without significantly damaging the crop
Herbicide Metabolism def
Breakdown of herbicides into non-toxic compounds
-refers to a change in the chemical structure of the herbicide molecule. A minor change can drastically change the herb. activity
Phases of herbicide metabolism
- oxidation, reduction, and hydrolosis
- Conjugation reaction to limit mobility and stop herb. metabolic activity
- Form secondary conjugates, is non-toxic and can be move elsewhere
Factors influencing herb metabolism rate
- plant is under environmental stress = less efficient
- Excessive herb. rates (misapplication) can reduce plants ability to metabolize herb.
- Other pesticides, chemicals (competition for enzymes, or inhibition of enzymes by insecticides)
Altered Target Site - Resistant Crop Enabled
-how is it done
The target site is insensitve to herbicides
Ge based- INsertion of insensitive target gene via genetic engineering
Conventional breeding- insertion of insensitive target from wild species.
Negative Cross Resistance (weeds to herbicides)
Resistant to one MOA of herbicide by highly susceptible to the other MOA of herbicides
How to confirm herbicide resistance in a weed
- Full analysis of application
- Past experience (has this happened nearby or elsewhere)
- Seed collection from the resistant population and a nearby susceptible population
- Greenhouse dosage studies
- Must show the trait is heritable
GR50
Amount of herbicide required to reduce the plant population by 50%
NTSR Mechanism in weeds
Non-Target Site Resistance
- Altered herbicide absorption, translocation, or sequestration
- Enhance metabolism/detoxification (most common)
TSR Mechanisms in weeds
Target Site Resistance
- Mutations in the target gene
- Target gene amplification (allows plant to continue to function normally)
- Over-expression of target gene/enzyme
Implications of NTSR in weed management
- Many genes are involved
- slow to develop
- cross resistance
- Weeds may have evolved resistance to unknown herbicides
Implications of TSR in weed management
- Major genes involved
- Develops quickly
- Generally high level of resistance
- Resistance spreads rapidly
