Exam 3 Flashcards
What is an example of biological weed control?
Using the thistle head weevil to control Musk (Nodding) Thistle
How does the thistle head weevil control musk (nodding) thistle?
- lays its eggs in the head of the thistle
- larvae hatch and feed on the thistle head
What is the concern with chemical weed control?
Resistance building up in weeds to herbicides.
What are the “goals” of chemical weed control?
1- Permit weed control where tillage isn’t possible.
2- Allow for no-till farming
3- reduce # of tillage operations required
4- reduce amount of labor related to weed control
5- controls weeds that were previously difficult and costly to control
6- allow for more flexibility for crop management
What is an example previous practice that chemical control has allowed us to replace because of its costliness and difficulty?
Clean fallowing
What are some of the issues with chemical weed control? (5)
- Kills non-target plants (via drift, runoff, etc.)
- harms animals indirectly ( via algae)
- Poor public reception
- perception by some that herbicide can resolve all weed issues
- problems caused improper selection, storage, handling, and application.
What plant was found to be resistant to 4 classes of herbicide across the state of Missouri?
Water Hemp
What herbicides were predominantly used between 1900-1940?
Inorganic Herbicides
What is the example family of herbicides used between 1900-1940?
Chlorates
What herbicides were predominantly used between 1940-1980?
Organic Herbicides
What herbicides were predominantly used between 1980-1995?
Selective Post-Emergent Herbicides
What herbicides were predominantly used between 1995-Present?
Trangenic crops with herbicide tolerance
What is an example “family/brand” of the herbicides used between 95-present?
Roundup Ready Beans/Corn
What does 2,4-D control? What is significant about this?
- Broadleaf plant species
- Was the 1st to provide complete control of creeping perennial broadleafs
How does 2,4-D control weeds so effectively?
It is translocated throughout the plant
What is the #1 herbicide for weed control in corn?
Atrazine
What was significant about Paraquat? How toxic is it?
- allowed for no-till practices to become common
- 1st non selective kill-all herbicide
- very toxic
What does glyphosate control?
-perennial grasses and perennial broadleafs
What is the max amount of Atrazine app. allowed on soils with 30% residue on surface?
2lbs/Ac
What is Karst Terrain?
Areas that are underlain by limestone that have been opened up by water flow so that sinkholes, caves, and channels are common topographic features.
What are the distance restrictions with Atrazine for these features:
- wells and sinkholes?
- streams or rivers?
- lakes or resiovors?
- 50ft
- 66ft
- 200ft`
Why were 2,4,5-T and Silvex removed from the US market? What is significant about these herbicides?
Because they contained trace amounts of vioxin which is a carinogenic compound.
Were used as agent orange in vietnam.
What is an example family of post-emergence herbicides?
sulfonylurea herbicides
(T/F) The total amount of herbicides applied annually have increased sinced 1982
False
What are the 4 ways herbicides are named?
- Chemical Name
- Biological Active Ingredient
- Common Name
- Trade Name
Example of chem name, active ingredient, common name, and trade name?
chem name: N-(phosphonomethyl) glycine
active ingredient: isopropylamine salt
common name: Glyphosate
trade name: Roundup-ultra
What are the 2 types of plant responses? Examples of each?
selective
ex- atrazine (corn is tolerant, pigweeds are not)
non-selective
ex- glyphosate (kills most plants)
What are the 2 types of applications? Example of each.
-soil applications
Ex- atrazine
-foliar applications
Ex- Glyphosate
What are the 4 classes of length of persistence?
What do they each mean?
What is an example of (r) and (hp)?
-no residual: doesn’t hurt other crops
-residual: will kill/injure germinating seedlings for relatively short period of time.
Ex- Scepter (53 days)
-persistent: can harm crops planted in rotation after treated crop is harvested.
-highly persistent: harms crops planted during 2nd season after original crop is harvested.
Ex-Lightning (40 months)
What are 3 different coverage methods?
- broadcast
- banded
- spot-spraying
What are 4 methods of spraying (time-wise)?
- early preplant
- preplant
- preemergence
- postemergence
What are the 4 types of post emergence spraying (time wise)?
- early postemergence
- late postemergence
- directed postemergence
- layby application
What were the 2 methods of soil applications?
- surface applied
- preplant incorporated
What are the 4 ways chems are distributed through plants?
- symplastic translocation (phloem translocation)
- apoplastic translocation (xylem translocation)
- contact (no translocation)
- modes of action (cover later)
What are the 3 herbicide families named?
- Sulfonylurea
- Triazine
- Other ones
What is vapor drift? What herb. has this really been an issue with lately?
Herb. hits target, then some of it vaporizes and moves with the wind.
-Dicamba
What is the issue that has been causing dicamba problems? Explain it.
Air Inversion- warm and cool air flip causing sideway wind
Who labels Herbs in US?
EPA
Can each state select its legal herbs?
Yes
What is hazard formula?
Hazard=toxicity * exposure
What is tolerance level?
max amount (dosage) of herb. allowed in crop
How is toxicity measured?
LD50
What is LD50?
amount of dose required to kill half of test pop.
How is LD figured?
mg of chemcal/kg of body wt.
(T/F)Once EPA approves registration, it is a legal document?
True
What is FIFRA? What’s it do?
Federal Insecticide, Fungicide, and Rodenticide Act
Also requires labelling of herbicides
(T/F) If a product is pasture labelled, you can assume it is good for all plants found in pastures ( including clovers)?
True
Will herbicides be specifically labelled by livestock type such as Horse?
No, will only say livestock.
