PLNT*6800 Special Topics in Plant Science (Herbicide Activity)

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The following description is for the course offering in Fall 2021 and is subject to change. It is provided for information only. The course outline distributed to the class at the beginning of the semester describes the course content and delivery, and defines the methods and criteria to be used in establishing the final grades for the course.

This course provides a comprehensive study of the major herbicide groups used in Ontario. The various herbicide groups will be discussed under the following topics: herbicide uptake and translocation, herbicide mode of action, herbicide selectivity, weeds controlled and crop injury.

Campus: Ridgetown (video conference to Guelph campus)


Teaching Assistant:

Credit Weight:


Course Level:

  • Graduate

Academic Department (or campus):

Department of Plant Agriculture



Semester Offering:

  • Fall

Class Schedule and Location:

B29, Ridgetown Campus

Learning outcomes:

Upon successful completion of this course the student will be able to:

  1. identify the biological and environmental factors that underpin chemical weed control, using commonly-found weed species and commercially-available herbicides in Ontario;
  2. integrate knowledge of points of uptake, methods of translocation and site of inhibition for the various modes-of-action of herbicide groups commercially available in Ontario;
  3. differentiate the injury symptoms and basis of selectivity of the various herbicide modes-of-action;
  4. discuss the various mechanisms by which weeds become resistant to herbicides based upon review of current peer-reviewed literature;
  5. integrate knowledge of the biochemical and physiological aspects of two different herbicide resistance mechanisms with their genetic background;
  6. construct a plan to manage and delay the development of herbicide-resistant weeds.

Lecture Content:

Lecture #1: Herbicide absorption and translocation and site-of-action

Lecture #2: Herbicide selectivity

Lecture #3: Group 1 Herbicides - Aryloxyphenoxypropionates, Cyclohexanediones and phenylpyrazolines

Lecture #4: Group 3 Herbicides – Dinitroanilines

Lecture #5: Group 2 Herbicides – Sulfonylureas, Imidazolinones & triazolopyrimidines & sulfonyl-aminocarbonyl-triazolinones

Lecture #6: Test #1 (15%)

Lecture #7: Group 4a Herbicides - Phenoxy carboxylic acids, benzoic acids, pyridine carboxylic acids & arylpicolinates

Lecture #8: Group 5 Herbicides – Triazines & triazinones

Lecture #9: Group 6a Herbicides - Benzonitriles & benzothiadiazoles

Lecture #10: Group 9 Herbicides - Glycine (Organophosphorus)

Lecture #11: Test #2 (15%)

Lecture #12: Group 10 Herbicides – Phosphinic acid (Organophosphorus)

Lecture #13: Group 13 Herbicides – Isoxalidinones

Lecture #14: Group 22 Herbicides – Bipyridyliums

Lecture #15: Group 14 Herbicides – Phenylpyrazoles, pyrimidinediones, aryl triazolones, N-phenylphthlamides & diphenylethers

Lecture # 16 Test #3 (15%)

Lecture # 17 Group 15 Herbicides - oe-chloroacetamides & isoxazolines

Lecture #18: Group 27 Herbicides - Isoxazoles, Triketones, Pyrazolones, & Benzoylpyrazoles

Lecture #19: Herbicide Activity – Why do herbicides provide poor weed control?

Lecture #20: Herbicide Activity – Why do herbicides cause crop injury?

Lecture # 21: Exam (35%)

Labs & Seminars:


Week 1:  Herbicide Resistance: A “Global perspective of herbicide-resistant weeds" 
Overview of Term Assignment: Developing an IWM Plan to Minimize the Potential for Herbicide Resistance
Week 2:  Target Site and Non-Target Site Based Resistance
Diversity in Target Site Herbicide Resistance
Week 3:  Variance in Resistance Among Families within a Herbicide Group
Week 4:  No Seminar - test # 1
Week 5:  2,4-D – Review of Properties and Uses Auxinic Resistance and the Auxin Signal Transduction Pathway
Week 6: Current State of Herbicides in Herbicide-Resistant Crops
Week 7:  No Seminar - test # 2
Week 8:  State of Knowledge of Group 9 Resistance – Use Patterns and Mechanisms of Resistance
Week 9: Unintended Effects of Shifting Herbicide Strategies to Manage Herbicide Resistant Weeds 
Week 10: No Seminar - test # 3
Week 11:  Student Presentations - Developing an IWM Plan to Minimize the Potential for Herbicide Resistance
Week 12:  No Seminar - Final Exam

Course Assignments and Tests:

Assignment or Test Contribution to Final Grade



Term Paper


Participation in weekly Discussion


Student-lead Discussion of one group of papers


Final examination:

There is no final examination scheduled for this course.

Course Resources:

Required Texts:

Guide to Weed Control – Publication 75 (2012-2013)

Other Resources:

All papers for discussion will be available as PDF files on Courselink.

Course Policies:

Grading Policies:

Academic consideration will be made for missed or late assignments/tests/midterms for medical, psychological or compassionate reasons only.  No other reasons are eligible for consideration – late assignments will not be accepted.

Course Policy on Group Work:

Not applicable.

Course Policy regarding use of electronic devices and recording of lectures

Electronic recording of classes is expressly forbidden without consent of the instructor.  When recordings are permitted they are solely for the use of the authorized student and may not be reproduced, or transmitted to others, without the expressed written consent of the instructor.

Other Course Information:

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