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

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

Crop Use The first method of classification at the herbicide birth Beans, Corn, Wheat, Turf Grass, etc Has become outdated and incomplete as specificity as taken over 2,4-D in wheat at it’s inception versus it’s uses now Now, we look at things like soil applied, pre-emergence,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

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

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

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

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

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

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

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