Understanding Herbicide Safety and Efficacy for

Invasive Plant Management

Brian Jones

Extension Agronomist

Introduction

• Chemical methods are well adopted for invasive plant management

• Relative to other management methods, herbicides are:– Inexpensive– Easy to use– Fast acting

• Must be used judiciously and safely…

Outline

• Herbicide Basics– Product Labels– Product Formulations– Herbicide Classification

• Impacts of Chemical Methods– How herbicides work (review)– Effects of herbicides on human health and

environment

• Basic Herbicide Tactics

Herbicide Basics: Labels

• The label is the law– Legally binding agreement between the EPA,

the company and the end user

• Label provides:– Directions for proper use– Safety information (PPE, REI)– Product name, common name, chemical

name

Herbicide Basics: Labels

• Signal Words– Warning– Caution– Danger or

Danger/Poison

• Hazard Level– Low– Moderate

– High

Herbicide Basics: Formulations

• Formulations include active and inert ingredients

Herbicide Basics: Formulations

• Adjuvants can have greatest impact on herbicide activity– Surfactants (surface acting agents)

• Improve contact, droplet retention, and spread

– Antidrift agents• Minimize non-target impacts

– Color, odor or emetics• Improve human safety from ingestion

Herbicide Basics: Formulations

• Many types of formulations– Water-soluble powder– Liquid– Wettable powder– Emulsifiable concentrates– Dry granule– Pellet

• Provided on the label

Herbicide Basics: Classification

• A working knowledge of classification is essential for:– Proper selection– Diagnosing injury symptoms– Managing herbicide resistance– Predicting herbicide interactions in the

environment

How Herbicides Work

• Kill or suppress plants by interfering with essential plant processes (e.g. photosynthesis)

• Interactions between a herbicide and a plant from application to the final effect are known as the Mode of Action

Diagram of leaf cross-section showing mode of action of a foliar-active, systemic herbicide (e.g., atrazine) that inhibits photosynthesis. In this example, the herbicide is applied to and absorbed through the leaf, is translocated to the chloroplasts (site of action), and subsequently inhibits photosynthesis (mechanism of action)

Mechanism of Action

• Avoid the repeated use of the same mechanism of action…why?

• Reduce the risk of developing herbicide-resistant populations

Effects of Herbicides

• Goal of pesticide regulation is no unreasonable adverse effects

• Achieve this through risk management

RISK = EXPOSURE x TOXICITY (how likely) (how bad)

Exposure (how likely)

• Minimize exposure by following label and understanding the fate of herbicide after application

• Four modes of entry into body:– Dermal (through the skin)– Oral (swallowing)– Inhalation (breathing in)– Ocular (through the eyes)

Exposure (how likely)

• Most at risk for exposure when mixing and loading

• Easiest way to avoid exposure???

• WEAR PERSONAL PROTECTIVE EQUIPMENT…

• LABEL WILL TELL YOU…

Exposure (how likely)

• Processes that affect environmental fate of herbicides (transfer and degredation):

Toxicity (how bad)

“The dose makes the poison.”Paracelsus - 1493 - 1541

“What is it that is not a poison? All things are poison and nothing is without poison. It is the dose

only that makes a thing not a poison.”

Toxicity (how bad)

• Acute and chronic toxicity

CO

NC

EN

TR

AT

ION

TIME

Symptoms

Threshold

Toxicity (how bad)

• Measured by the median LD50– The dose that is lethal to 50% of the treated

population (mg of compound / kg of body weight)

Herbicide Application Tactics

• Tactics will vary according to:– Target species– Site conditions– Herbicide properties

Understanding Application Rate

• Illegal to apply more than label states

• Rates are given in terms of amount of formulated product per acre

• Applicator must determine the pounds of active ingredient per acre to be applied

Understanding Application Rate

• EX: Glyphosate formulation has 3 lbs active ingredient (ai) per gallon of product

• Label application rate is 2 quarts product per acre

3 lb ai

gallonX

0.5 gallon

acre=

1.5 lb ai

acre

Summary

• Herbicides are important tools for invasive plant management

• Understand the fundamentals of:– Classification– Mode of action and formulations

• Must be used according to the label– Avoid RISK– Take the time…wear the proper PPE

• Understand the application tactics

THANK YOU!