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

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The following description is for the course offering in Fall 2015 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, crop injury and herbicide resistance.  Weekly discussions will be held to detail current knowledge and management implications of mechanisms of resistance.

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:

To be determined.

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:

Week Topic

Herbicide mode of action, Herbicide selectivity, Herbicide movement

Discussion – Mechanisms of herbicide resistance – target site (mutation, overexpression), non-target site (decreased absorption, decreased translocation, sequestration, metabolism).


Group 1a Herbicides - Aryloxyphenoxypropionates & Cyclohexanediones

Group 3 Herbicides – Dinitroanilines

Discussion – Group 1 herbicide resistance mechanisms


Group 2a Herbicides – Sulfonylureas, Imidazolinones &   Triazolopyrimidines

Discussion – Group 2 herbicide resistance mechanisms


Group 4a Herbicides – Phenoxies, Benzoic Acids &  Carboxylic Acids

Discussion – Group 4 herbicide resistance – auxinic resistance and the auxin signal transduction pathway


Group 5 Herbicides – Triazines

Group 6 Herbicides – Benzonitriles & Benzothiadiazoles

Group 7 Herbicides - Substituted Ureas

Discussion – Group 5 resistance mechanisms, PQ binding and the potential for fitness penalties


Group 9 Herbicides – Organophosphorus

Discussion – Group 9 herbicide resistance – constitutive overexpression by gene amplification


Group 10 Herbicides – Organophosphorus

Group 11 Herbicides – Triazoles

Group 22 Herbicides – Bipyridyliums

Discussion – Group 22 resistance and restricted translocation of paraquat


Group 14 Herbicides – Triazolones, Diphenylethers, Dicarboximides and Pyrimidinediones

Discussion – Group 14 resistance: amino acid deletion – an unusual target-site based mechanism of resistance


Group 15 Herbicides – Chloroacetamides

Group 8 Herbicides – Thiocarbamates

Group 13 Herbicides – Isoxalidinones

Discussion – Group 15 resistance


Group 27 Herbicides - Isoxazoles, Triketones, Pyrazolones, & Benzoylpyrazoles

Discussion – What are the management implications of multiple herbicide resistance?


Herbicide adjuvants

Herbicide resistant weeds

Discussion – What are the management implications of cross herbicide resistance?


Herbicide resistant crops

Integrated weed management

Discussion – Do all target site resistance mutations endow high level resistance?

Labs & Seminars:

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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