Revision: May 25, 2005
Original Date Published: 1991

• Introduction
• Weed Identification Guide Index
• Glossary

Material for this publication was prepared by the Weed Science Services Section of the Plant Industry Branch of the Nova Scotia Department of Agriculture and Marketing and the Plant Health Section of the Plant Industry Branch of the New Brunswick Department of Agriculture.

This publication was a joint effort among Agriculture Canada and the provinces of Nova Scotia and New Brunswick with financial assistance of the Canada/Nova Scotia Livestock Feed Development Agreement and the Canada/New Brunswick Livestock Feed Development Agreement.

Assistance provided by Charles Surette (photography), Sharon Campbell and Margaret Mann is gratefully acknowledged. Appreciation is extended to Dr. Doug Doohan whose suggestions, advice, and editorial comments were invaluable.

Lise LeBlanc
Weed Project Coordinator
NSDAM

Kevin McCully
Weed Specialist
NBDA

Introduction

A weed is any plant growing in an area where it is not wanted. We try to control weeds because they compete with crops for light, moisture, space and nutrients. Certain weed species can harbour plant diseases and insect pests. Other species may be poisonous, allergenic or irritant to humans and/or livestock. Medical and economic problems such as illness, death, rashes, hayfever, or a reduction in quality of fur, meat and milk products may result.

Weeds have many unique characteristics which make them extremely difficult to control. Most produce a tremendous number of seeds. The seeds of some weed species may be dormant for many years, with only a small percentage germinating each year. Weeds generally mature earlier than the crop and often seeds will be dropped before crop harvest and remain in the field. Weeds are generally more competitive than crops and can often survive under unfavorable growing conditions.

Early identification of emerged weed species is critical for choosing the best weed control methods. This guide will enable you to identify weeds at three growth stages.

Summer annuals complete their lifecycle from seed to maturity in less than one year. They germinate in the spring, mature, set seed and die in the fall. Winter annuals germinate in the fall, overwinter as seedlings or small rosettes and mature, set seed and die the following spring or early summer. Some weeds are capable of both the summer and winter annual lifecycle.

Biennials complete their lifecycles in less than two years. Germination and the production of an overwintering rosette of leaves occur the first year. The second year, flowering, seed production , and plant death occur. Control is best obtained during the first year.

Perennials live for more than two years. They reproduce vegetatively from roots, rhizomes, buds, or tillers, or from seed, or both. They can be especially difficult to control because of their persistent root systems.

Several weed control options are available. Prevention is the most practical and economical form of weed control. Always use certified seed, clean off farm implements when travelling from field to field, control weeds in fence lines, right-of-ways, irrigation ditches, etc. Be alert for new weeds on your farm, so they can be controlled before they become a serious problem. Mechanical control may utilize hoeing, timely cultivation (excellent for seedlings and annuals), and mowing to prevent seed production. Cultural control may utilize techniques such as proper grazing management, good soil fertility practices, proper drainage, rotation and choosing good competitive crop varieties to encourage maximum crop competition. Biological control is the control of weeds with plant pathogens or insects. Several of our most troublesome pasture weeds can be controlled with this method. For example, tansy ragwort is controlled by the cinnabar moth. Chemical control utilizes various herbicides to control weeds. Weeds must be correctly identified in order to select a herbicide that will be effective. Herbicides will be most effective on annual and biennial weeds during the seedling stage. Herbicides will be most effective on perennial weeds during the seedling stage or just prior to flowering (bud stage) or in the fall.

Remember to always read the label of the herbicide to determine crops registered, weeds controlled and safety precautions.

The best weed control program will not rely on one control method, but rather will integrate several methods of weed control.

Glossary