Understanding Herbicides

This course will give participants a good grounding in the principles of using herbicides to control weeds.

Key Facts

• Start date: 4 May 2026
• Cost: $1,800 + GST
• Duration: 10 weeks
• Delivery mode: Online
• Time commitment: Approximately 50 hours, including 2-hour open book exam

Overview

This course is designed primarily as a stand-alone course to give participants a good grounding in the principles of using herbicides to control weeds.

Who This Course Is For

People working in the herbicide industry within New Zealand. It is also useful for people working in agriculture, horticulture, and regional councils who need to control weeds with herbicides as part of their job.

What You'll Get

Successful participants will receive an official certificate of completion, and the material will count as 5 credits at the 300 level towards a university qualification.

Learning Outcomes

On successful completion, a participant should be able to understand herbicides well enough to be able to select the most appropriate compound for any weed situation and obtain maximum effectiveness from that herbicide without causing damage to desirable plants or the environment.

Course Content and Structure

This course is online and uses course material and recorded lectures. Participants study at a time convenient for them between May and July, and an online, open-book exam is in July.

Topic 1 – Introduction

This topic will cover:

• An explanation of various things about the course
• Introduction to participants to various terminology about herbicides
• Herbicide mode of action

Topic 2 – Herbicide Toxicity and Legislation

This topic will cover:

• Safety testing of herbicides
• Relative toxicity of herbicides
• New Zealand legislation
• Withholding periods
• The GROWSAFE scheme
• The 2,4,5-T and glyphosate controversies
• Herbicide residues in food

Topic 3 – Herbicide Formulation

This topic will cover:

• Solutions
• Emulsions
• Wettable powders
• Granules
• Dusts
• Surfactants
• Chemical drift through the air
• Common and trade names
• Calculations

Topic 4 – Behaviour of Herbicides in Plants

This topic will cover:

• Interception and uptake of foliage-applied herbicides
• Availability and uptake of soil-applied herbicides
• Transport of herbicides in the plant
• Factors affecting these processes
• Herbicide selectivity

Topic 5 – Behaviour of Herbicides in the Soil

This topic will cover:

• Adsorption
• Volatilization
• Leaching
• Photochemical degradation
• Chemical decomposition
• Microbial decomposition
• Rates of degradation of herbicides
• Bioassays
• Activity of soil-applied herbicides
• Selectivity of soil-applied herbicides
• Effects of weather on herbicides

Topic 6 – Herbicide Application

This topic will cover:

• Conventional spraying equipment
• Calibration of a sprayer
• Back-pack sprayers
• Problems with conventional sprayers
• Improvements in spraying equipment
• Wiper applicators

Topic 7 – Knockdown Herbicides

This topic will cover:

• Characteristics of importance in decision making
• Broad-spectrum herbicides
• Translocated knockdown of dicots in grass crops
• Contact knockdown of dicots in grass crops
• Selective knockdown of grasses in dicot crops
• Sulfonylureas
• Other knockdown herbicides

Topic 8 – Residual Herbicides

This topic will cover:

• Residual herbicides used primarily for non-selective control
• Herbicides used primarily for depth protection
• Selective residual herbicides which primarily control dicots
• Selective residual herbicides which primarily control grasses

Topic 9 – Economics of Weed Control

This topic will cover:

• When weeds reduce yields through competition
• When weeds exert indirect effects in pasture
• When weeds cause other effects difficult to measure
• How most weed control decisions are made

Topic 10 – Weed Control in Pastures and Lucerne

This topic will cover:

• Problems caused by weeds
• Keeping pastures competitive
• Discouraging weeds that establish
• Weed control in new pastures
• Weed control in established pastures
• Control of specific problem weeds
• Clearing scrub weeds
• Weed control in riparian plantings
• Weed control in lucerne using management
• Weed control in lucerne using herbicides

Topic 11

This topic involves two modules: either do Topic 11A or 11B.

Topic 11A – Weed Control in Annual Crops

This module will cover:

• Problems caused by weeds in annual crops
• Finding suitable herbicide information
• Weed control in cereals
• Weed control in maize and sweet corn
• Weed control in forage brassicas
• Weed control in fodder beet
• Weed control in peas
• Weed control in onions

Topic 11B – Weed Control in Trees and the Environment

This module will cover:

• Problems caused by weeds in the situations listed below
• Finding suitable herbicide information
• Weed control in orchards and vineyards
• Weed control in forestry
• Weed control in conservation estates
• Weed control on roadsides, urban areas, and waste places
• Control of aquatic weeds

Topic 12 – Herbicide Resistance

This topic will cover:

• Herbicide tolerance vs herbicide resistance
• Development of herbicide resistant weeds
• Factors affecting development of resistance
• Mode of action coding system
• Herbicide resistance in New Zealand
• Managing herbicide resistance
• Making use of herbicide resistance

Meet Your Facilitator

Adjunct Associate Professor Kerry Harrington

PhD, MAgrSc(Hons), BAgrSc(Hons)

Associate Professor in Weed Science

Until his semi-retirement in late 2023, Kerry was the weed science specialist at Massey University. As well as teaching aspects of weed biology, identification, and control, he supervised postgraduate students and undertook his own research. Kerry still runs the Understanding Herbicides short course each year for Massey University and deals with questions about New Zealand weeds.

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• Farm Dairy Effluent: System Design & Management
• Introduction to New Zealand's Agricultural Greenhouse Gas Emissions & Management
• Intermediate Freshwater Farm Planning
• Advanced Freshwater Farm Planning
• Analysis of New Zealand Agricultural Systems
• Introduction to Life Cycle Assessment

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• Massey Business School
• College of Creative Arts
• College of Health
• College of Humanities and Social Sciences
• College of Sciences

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