1. Intro to Chemical Weed Control Cont.
Plant Science 280
Mr. Gomes

3. Classifications Of Herbicides
Crop Use
Observed Effect
Site of Uptake
Contact Vs. Systemic
Selectivity
Time of Application
Chemical Structure
Site of Action

4. Crop Use The first method of classification at the herbicide birth
Beans, Corn, Wheat, Turf Grass, etc
Has become outdated and incomplete as specificity as taken over
2,4-D in wheat at it’s inception versus it’s uses now
Now, we look at things like soil applied, pre-emergence, post-emergence, combinations, etc.

6. Observed Effect
This system is designed based on the effects observed after emergence
Very good at describing the effects of burning, chlorosis, or gradual chlorosis. Ex..??
Describes what we see, but not how the herbicide actually works
Also effective on hormones which effect hormone function.. Ex???
Growth abnormalities make this challenging, so burning and chlorosis only

8. Site of Uptake Distinguishes between foliar and soil applied
Herbicide that acts after contact is foliar, soil applied is soil active…
Often times rate of application is the determining factor
Diphenyl ether (Reflex) PPOII, most phenoxy acids (2,4-D)??, arsenicals, selective oils - foliar
translocation readily
Imidazolinone (Raptor) ALS, Triazine (Princep) PPOII, chloracetamides (Dual Magnum) Fatty – soil
Still an inaccurate portrayal

10. Contact Vs Systemic Contact literally means killing on contact
Which Causes??
No translocation. Leafy parts go bye bye. As little as one day
Systemic allows for movement throughout he plant
Kills roots, tubers, stems, etc
Generally takes longer to kill

11. Selectivity Plant age and stage of growth Plant morphology Absorption
Translocation
Type of treatment
Time and method of application
Herbicide formulation
Environmental conditions

12. Time of Application Pre-Planting Pre-Emergence Post-Emergence
Usually several weeks prior to planting
Usually soil incorporation
Pre-Emergence
Before crop, weed, both emergence
Post-Emergence
After emergence and affects leaf tissue usually

13. Chemical Structure Isolate the actual molecular bonding
No simple relationship between chemical structure and biochemical behavior
As of 2007, there were 67 chemical groups and 24 actions
In 1967 there were 29 different

14. Site of Action
The study of chemistry, biochemistry, and plant physiology
Determines the exact area of effect
PPO Inhibitor versus ALS Inhibitor vs growth regulator vs seedling growth inhibitors
The entire chain of events from first contact to ending