CROP*4240 Weed Science

course node page

The following description is for the course offering in Fall 2022 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.

Weeds will be studied in relation to agricultural practices. Principles of chemical, mechanical and biological control will be outlined. Principles of chemical, mechanical and biological control will be outlined. Laboratories will include weed identification, weed control methods, and demonstrations of the effects of various herbicides. Laboratories will include weed identification, weed control methods, and demonstrations of the effects of various herbicides.

This course aims at discovering these plants we don’t want and we call weeds.

  • What are they?
  • Why are they causing problems?
  • How can we manage them?

Prerequisite(s): AGR*2470


Teaching Assistant:

Isabelle Aicklen

Credit Weight:


Course Level:

  • Undergraduate

Academic Department (or campus):

Department of Plant Agriculture



Semester Offering:

  • Fall

Class Schedule and Location:

Please refer to WebAdvisor for class schedule and location.

Learning outcomes:

By the end of this course, you should be able to:

  1. Synthesize knowledge, facts and information from different sources, pertaining to weed biology and management and be able to explain how they are interrelated; demonstrated through successful completion of assignments and exams.
  2. Critically assess the value of different weed management strategies; demonstrated through successful completion of assignments, exams and lab exercises.
  3. Identify 80 of Ontario’s most common weeds and understand their key characteristics; demonstrated though successful completion of weed identification quiz.
  4. Identify herbicide injury through analysis of symptomology and selectivity.
  5. Synthesize and understand facts explaining an aspect of herbicide mode of action.

Lecture Content:

Topics to be covered in lecture include:

  • Introduction to weeds and their biology; problems due to weeds; biological characteristics of weeds
  • Life cycles of weeds; seed dormancy; germination; dispersal in space and time
  • Vegetative reproduction; strategies for invasion; the role of weeds in succession
  • Competition and allelopathy, managing competition
  • A holistic approach to weed management
  • Cultural control
  • Biological Control
  • Physical and mechanical control
  • Herbicide formulation and application
  • Herbicides and soil 
  • Herbicide uptake and movement
  • Herbicide metabolism and selectivity
  • Herbicide target sites, how do herbicides kill weeks
  • Photosynthesis inhibitors
  • Pigment synthesis inhibitors
  • Amino acid synthesis inhibitors
  • Auxin mimics
  • Fatty acid synthesis inhibitors
  • Cellulose synthesis and tubulin assembly inhibitors
  • Herbicide resistant crops
  • Herbicide resistant weeds
  • Future of weed management
Labs & Seminars:

There will be two different activities in the lab:

  1. Weed identification: the instructor and the TA will introduce the characteristics of the 80 weed species that will be studied in pre-recorded PowerPoint presentations. These will be available online prior to the actual lab periods and it will be the responsibility of the students to review them prior to the hands-on lab. The lab period will allow the students to examine live weed specimens and will then be asked to fill in an assignment.
  2. Herbicide injury diagnostic: prior to the labs, the main symptoms due to herbicides on crops and weeds will be explained in a virtual presentation. The hands on lab period will allow students to examine trays containing weeds and crops that have been treated with various herbicides and will be able to fill-in the assignment.

Course Assignments and Tests:

Assignment or Test
Contribution to Final Grade




Weed ID Assignments



Weed ID Quiz 15%  

Herbicide diagnostic assignment



Final Exam



Final examination:

Please refer to WebAdvisor for class schedule and location.

Course Resources:

Required Texts:


Recommended Texts:

For the weed identification portion of the lab, we will be using mostly the Identification Guide to the Weeds of Ontario. There are a few ways to obtain the book:

  1. A hard copy can be ordered from the publisher's web site for on demand printing at a cost of $37.51
  2. You can download a PDF of the book for free at
  3. if you prefer an e-reader format you can go to

More details are available at:

Lab Manual:


Other Resources:

Any material produced by the instructor in a written format will be distributed in class and be made available on D2L.

Field Trips:

Not applicable.

Additional Costs:

Not applicable.

Required Resources
System and Software Requirement (Software)

This course will use a variety of technologies including:

  • CourseLink (main classroom)
  • Zoom
  • Kahoot!
  • Mentimeter

To help ensure you have the best learning experience possible, please review the list of system and software requirements.

Polling Software
The instructor will make use of polling softwares such as Kahoot! and Mentimeter throughout the semester. This is to keep track of the learning in a more informal way and also help as review tools. The instructor has access to an institutional Kahoot! licence which gives more functionalities than the free version. In return, the instructor and the students will have to fill a quick survey on their Kahoot! experience in December.
CourseLink System Requirements

You are responsible for ensuring that your computer system meets the necessary system requirements. Use the browser check tool to ensure your browser settings are compatible and up to date. (Results will be displayed in a new browser window).

Course Technologies

This course is being offered using CourseLink (powered by D2L's Brightspace), the University of Guelph's online learning management system (LMS). By using this service, you agree to comply with the University of Guelph's Access and Privacy Guidelines. Please visit the D2L website to review the Brightspace privacy statement and Brightspace Learning Environment web accessibility standards.

Technical Support

If you need any assistance with the software tools or the CourseLink website, contact CourseLink Support.
Tel: 519-824-4120 ext. 56939 Toll-Free (CAN/USA): 1-866-275-1478
Support Hours (Eastern Time):

Monday thru Friday: 8:30 am–8:30 pm
Saturday: 10:00 am–4:00 pm
Sunday: 12:00 pm–6:00 pm

Course Policies:

Grading Policies:

Rescheduled exams: The midterm and final exam must be written on the date scheduled unless there is a documented timetabling conflict. Please advise the instructor in writing of any scheduling conflict prior to week 5.

Course Policy regarding use of electronic devices and recording of lectures:

Recording of classes, either electronically or otherwise, 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 express written consent of the instructor.

Other Course Information:

University Policies

Academic Consideration

When you find yourself unable to meet an in-course requirement because of illness or compassionate reasons, please advise the course instructor in writing, with your name, id#, and e-mail contact. See the academic calendar for information on regulations and procedures for Academic Consideration:

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The Academic Misconduct Policy is detailed in the University Calenders:


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