Exam 2 herbicide questions
Preplant herbicide applications in ag refers to treatment _____________ the crop is planted
before
Preemergence herbicides in crops can be used ___________ and ____________ weeds emerge but ONLY __________ crop emerges
before after before
The inherent sensitivity to herbicide at cellular level refers to the ________________ basis of herbicide selectivity
biochemical
Herbicides are absorbed through the process of _____________
diffusion
2 forms of directed herbicide application
drop nozzle and ropewick
____________ herbicides are wax and oil soluble, fast moving, and less sensitive to water stress
non polar
2 reasons herbicide resistance occurs
1. A small portion of weeds within a population are naturally resistant. 2. Repeated use of herbicides that inhibit the same site of action select for the resistant plants.
4 Factors affecting cuticle thickness
1. Age 2. Species 3. Light exposure 4. Moisture status of the developing plant
4 mechanisms of herbicide resistance
1. Altered binding sites 2. Overproduction of binding sites 3. Metabolism 4. Compartmentalization this website helps http://pesticidestewardship.org/resistance/Herbicide/Pages/Mechanisms-of-Herbicide-Resistance.aspx
3 methods of herbicide placement
1. Broadcast 2. Banded 3. Directed
3 Pros and COns of PRE herbicides
1. Can be applied when planting 2. Less work required to apply than PPI 3. Great for Band apps Cons: 1. Needs rain 2. Envmt controls when app can be made 3. Used before the problem can be seen
2 forms of protectve barriers used during herbicide application
1. Charcoal barriers 2. Spray shields
3 ways roots absorb herbicide through DIFFUSION
1. Concentration gradient 2. in a soil solution 3. in vapor phase
Leaves are the most important site for herbicide absorption by plants. What 3 anatomical characteristics of a leaf impact it's ability to absorb? What characteristic has the biggest impact on absorption?
1. Cuticle 2. Cell wall 3. Plasmodesmata Cuticle
5 factors that affect foliar absorption
1. Cuticle thickness 2. Herbicide (and all factors considered with each) 3. Environment 4. Moisture status of the plant 5. The use of adjuvants
2 ways plants can metabolically alter herbicides to improve efficacy
1. Deactivation 2. Activation
3 morphological characteristics of herbicide selectivity
1. Differential Interception 2. Differential retention 3. Growing point location
3 factors that effect Rate of Spread of Resistance
1. Dominant vs. Recessive traits of the plant 2. Nuclear vs Non-nuclear plant genes 3. Weed biology (seed and pollen mvmt potential)
2 forms of non-selective herbicides
1. Foliar active 2. Soil active (Fumigants, sterilants)
3 areas of a leaf where cuticle is generally thinner
1. Guard cells of the stomata 2. Cells over vascular tissue 3. Cells of trichomes
2 morphological factors effecting herbicide RETENTION by a plant
1. Leaf surface 2. Orientation
3 ways herbicides can be absorbed through the roots
1. Mass Flow 2. Root interception 3. Diffusion
5 biological factors effecting herbicide selectivity
1. Morphological 2. Growth Habit 3. Physiological 4. metabolic 5. biochemical
3 Characteristics of PRE herbicides
1. Must have residual 2. Relatively non volatile 3. Requires rainfall
3 characteristics of PPI (Preplant incorporation) herbicides
1. Must have residual effect 2. May be volatile 3. Good crop tolerance
3 Pros and Cons of PPI herbicides
1. No interference at time of planting 2. Less dependent on rainfall than PRE 3. Less trips across field Cons: 1. Less flexibility to change 2. Not as effective in reduced till systems 3. Higher costs
4 characteristics of POST
1. Non volatile 2. May be soil active or foliar ative 3. May be selective or non selective 4. Systemic and non systemic
3 advantages of herbicides
1. Reduce labor costs 2. Reduce tillage 3. Reduce crop injury risk
5 practices to reduce risk of herbicide resistant weeds
1. Rotate chemistry with different site of action 2. Scout 3. Rotate crops with differing life cycles 4. Mechanically remove weeds 5. Avoid transport of resistant weed seeds
3 cons of POST herbicides
1. Timing 2. requires scouting 3. when applying very sensitive to envmt
3 ways plants biochemically affect a herbicides efficacy
1. altering binding site 2. plant has multiple forms of binding sites 3. Overproduction of binding sites
There are _____ Sites of Action, _______ modes of action, and _________ chemical herbicide families
12, 10, 24
When was the start of the "pesticide era"
1945
When was EPA invented?
1970
How long can soil sterilant persist in the soil? Fumigants?
2 years for sterilants >2 days for fumigants
2 ways PRE herbicides can be applied
Broadcast Banded
The formation of chemical complexes
Conjugation
Resistance to two or more herbicides with the same site of action.
Cross resistance
In 1972, what pesticide was banned?
DDT
For PPI herbicides, what piece of equipment is generally a poor choice
Disk machine
The inherent ability of a plant to survive and reproduce following exposure to a dose of herbicide normally lethal to the wild type refers to????
Herbicide resistance
4 PHYSICAL factors affecting herbicide selectivity
Herbicide; 1. Rate 2. Placement 3. Protective barriers 4. Formulations
In 1948 Mueller won the Nobel Peace Prize for....
His discovery of the high efficiency of DDT as a contact poison against several arthropods
Until the late 1940s, what was the most widely used pesticide?
Lead arsenic
3 morphological factors effecting herbicide interception by plant
Leaf 1. Size 2. Shape 3. Orientation
Resistance to two or more herbicides with different sites of action.
Multiple resistance
Preplant ____-____________ herbicides can be used days to months before planting of crops. Preplant ________________ herbicides can be used within a month of planting crops. ________ preplant herbicides can be used 10-45 days before planting/. Often this method is used in no till systems adnd utilizes rain for incorporation
Non-Selective Incorporated Early
Herbicides that work well on perennial weeds prior to planting
PPI
______ herbicides are water soluble, slow moving, and are very sensitive to water stress.
Polar
3 ways herbicides are classified
Selectivity, mode of Action, method of application
Who is Paul Mueller?
Synthesizer of DDT as an insecticide
Form or herbicide that disrupts physiological processes in the plants
Systemic
In 1995 "Our Stolen Future" discussed what?
The Endocrine Disrupter Hypothesis
The amount of pesticide residue permitted by federal law to remain in or on a crop"
Tolerance