Unit 8: Toxicity, Resistance, Residues, Licensing Chapters 13-16.

Unit 8: Toxicity, Resistance, Residues, Licensing

Chapters 13-16


• Unit 7 Objectives:– Discuss precautions and risks– Prevention and treatment concerns– Guarding against residues– Licensing concerns and procedures


• Toxicity of Herbicides– Toxicity – capacity of a substance to produce

injury• Effects

– Immediate (acute)– Cumulative (chronic)– Depends on:

» Exposure» Dose» Herbicide» Duration


• Other factors– Species (animal or plant)

» Age, sex, nutritional status– Route of exposure

– Human Toxicity• Manufacturers required to test for toxicity levels

– Tested on experimental animals» Mice, rats, rabbits

• Expression of acute toxicity– LD50

» Lethal dose in mg/kg BW» Kills 50% of test population


• Label indicates extent of toxicity w/ signal words– What are they?– Signal word applies to most serious method of exposure– Danger-Poison

» Herbicides w/ endothall or paraquat» Wear goggles, face shield, rubber gloves, rubber

apron, avoid breathing spray mists– Danger-Corrosive

» Irreversible eye or skin burns – wear goggles or face shield, rubber gloves, apron

» Eyes - Flush w/ water 15 minutes, get medical attention promptly

» Skin – wash thoroughly, seek medical attention if irritation occurs


– Warning» Moderate toxicity through oral, dermal, or inhalation

exposure» Warnings and risks are listed thoroughly

– Caution» Any label that doesn’t have Warning or Danger on

the label» Low oral, dermal, or inhalation toxicity risk» Little/no irritability of eyes or skin

– Environmental Toxicity• Toxicity regarding fish and wildlife

– Labels may warn of specific toxicities


– Fish, groundwater, etc.

– Read the labels thoroughly, see the tables in the book for specific ingredients

• Weed Resistance to Herbicides– Resistance is a continual problem

• Incidence has increased the last decade

– Populations within a species of weed can develop resistant tendencies not observed in the typical population

– First reports of resistance in early 1950’s (dandelions, wild carrots)


– >170 weeds reported to have resistance qualities– Herbicide resistance

• Inherited ability of plant to survive and reproduce following exposure to chemical

• Normal lethal dose

– Herbicide tolerance• Inherent ability of a species to survive and reproduce after a

chemical treatment

– Resistance – plant is resistant when species is usually susceptible

– Tolerance – species has never been susceptible to the herbicide


– Cross-Resistance • Resistance to a herbicide the plant may not have

previously been exposed to• Similar mode of action to a previous herbicide

– Multiple-Resistance• Resistance to more than one class of herbicides• Different modes of action• More than one basis for resistance may be

involved


– Ex – developing resistance to atrazine and simazine in continuous corn

• Cross resistance• Multiple resistance

– Origin of Resistance• Mutation Theory

– Genetic mutation occurs following herbicide application– Mutation confers resistance to the plant– Not widely accepted, not much evidence to support


• Natural-selection Theory– Regarded as most plausible theory– Herbicide resistant types have always existed in low

populations– Only those who survive and reproduce will make seed

for the future– “Survival of the fittest”

• If same herbicide is used each year, resistant varieties will survive and flourish

– Relying on the same herbicide creates more resistance– 3 components

» Herbicide w/ single site action» Repeated use of same herbicide» Absence of other control measures


– Basis for Weed Resistance• Alterations in the target sites of the herbicide

– Herbicide activity is site specific in the plant» Disrupts a particular plant function/process

– Some alteration may interrupt chemical ability to work effectively

– Most resistance is developed in this manner

• Enhanced Metabolism of the Herbicide– Plant “digests” the chemical to detoxify itself– May inactivate the herbicide before it has the chance to

work


– Management Strategies to Minimize Herbicide-Resistant Weeds

• Goal is to prevent the selection of herbicide resistant weeds

• Don’t necessarily want to develop a new herbicide for each new weed problem

– Improve management techniques

• Strategies:– Scout regularly to identify resistant weeds

» Record and response quickly to changes in weed populations

» Restrict resistant weed development


– Rotate herbicides w/ different sites of action» No more than 2 applications consecutively

– Apply herbicides w/ multiple action sites» Tank mixes, prepackaged, sequential mixes» Chemicals must have substantial activity against

resistant weeds– Cautious use of herbicide resistant or tolerant crops

» Still honor 2 consecutive application rule– Combine mechanical and herbicide controls– Clean tillage and harvest equipment to prevent cross-

contamination– Pay attention to RR, highway depts., etc. and their

control methods» May need to help them adjust to prevent a resistant

development


• Correct Diagnosis of Resistant Weed problems– All other causes of herbicide failure are eliminated

» What might they be?– Other labeled weeds are effectively controlled– History of continuous use of the same herbicide– Weed was controlled effectively in the past

• Identified by just a few weeds left standing after herbicide should have controlled

– May be confined to small patches– Patches may grow

– Lets review the scenario on pg. 336


• Herbicide Persistence and how to Test for Residues in Soils– Factors Affecting Herbicide Persistence

• Herbicides applied for season-long control• Length of time herbicide remains active called “soil

persistence” or “soil residual life”– Anything that affects the herbicide may affect

persistence

• Factors affecting herbicide persistence– Soil factors– Climatic conditions– Herbicidal properties


– Soil Factors• 3 categories

– Physical» Soil composition - % sand, silt, clay» Organic matter content

– Chemical» Soil pH» CEC» Nutrient status

– Microbial» Type and abundance of soil microorganisms» How can this affect herbicides?


• Soil composition affects phytotoxicity & persistence– Adsorption, leaching, volatilization– Soils high in: clay, organic matter

» Higher potential for herbicide carryover» Increased adsorption to soil colloids» Decreased leaching & volatilization» Results in decreased initial plant uptake & herbicidal

activity» More herbicide held in reserve – may injure future

crops


• Triazines– Very affected by soil pH

» Lesser amounts of herbicide are held to soil colloids at higher pH

» Remain in soil solution (only herbicide in soil solution can be taken up by the plant)

• Chemical/Microbial breakdown slower at higher pH• CEC

– Some herbicides more available in the presence of some cations

– Others “tied up”


• Soil Microorganisms– Types and amounts determine rate of herbicide

decomposition– What factors affect microbial activity?

– Climatic Conditions• Factors involved:

– Moisture– Temperature– Sunlight

• Positive relationship between herbicide degradation and temp & moisture

– Why? What is the primary culprit?


• Cool/dry conditions create possibility for carryover• Wet/mild winters increase likelihood of herbicide

persistence• Photodecomposition

– May occur in surface applied herbicides– Soil incorporation will decrease the risk

– Herbicidal Properties• Important factors

– Water solubility» Determines leaching potential» Where might the herbicide go?

– Soil adsorption» Those adsorbing strongly have greater potential to

persist, less likely to leach


– Vapor Pressure» Determines its volatility (changing from

liquid/solid/gas)» Increases w/ temp» Certain herbicides must be incorporated to avoid

gaseous losses– Susceptibility to chemical/microbial degradation

» Ex. 2,4-D decomposes very quickly, atrazine – slow» Dependent on herbicide makeup and microbial

population


– Avoiding Herbicide Carryover• Apply correct rates of herbicide for the soil type

and weed problem– Lowest possible rate that produces the desired effect

» Determine acreage accurately» Measure chemical accurately» Proper calibration» Uniform application

• Proper method and time of application• Amount of tillage

– Tillage encourages herbicide decomposition


– Minimum and No-till leave more herbicide near the soil surface

– Persistent herbicides may affect susceptible crops– Higher herbicides rates often used in reduced tillage

systems» Some tillage may help dilute persistent herbicides

• Herbicide combinations– Reduces risk of carryover– Mixing will reduce application rates of both herbicides

while broadening control spectrum– Some herbicides may interact to cause crop injury, if

carryover in enough amounts


• Plant extraction also removes much herbicide from the soil

• Crop rotation– Awareness of carryover risks and following crop

susceptibility will minimize injury

– Testing for Herbicide Residues• Soil chemical test

– Can be expensive– Completed in a laboratory

• Bioassay– Cheaper– Field test

• May help make crop rotation adjustments if carryover injury risk is present


• Soil Collection & Preparation– Early to mid-spring before planting– Representative sample from no more than 20 ac

» Take separate samples from areas where excessive residues are expected (turnaround points & end rows)

– Sample at 6” depth– Sample an area not suspect (“check” area)

» Nearby fencerow» Untreated area

– Submit for analysis ASAP after sampling to improve accuracy

» Refrigerate if samples can’t be submitted promptly


• Bioassay– May predict potential crop injury– Cheap– Doesn’t measure amount of herbicide present in the soil– Field Bioassay

» Plant a test strip in the field» Realistic?

– Indoor Bioassay» Same procedure for soil collection» Air-dry samples» Plant test crop in pots and let them grow in a warm

area (greenhouse, inside your home, etc.)» May be more realistic?


• Testing for Specific Herbicide Groups– Triazine Residues

» Atrazine, Princep» Oat bioassay works best» Place in warm location w/ ample sunlight» Symptoms should occur within 10-14d» Characterized by chlorosis, then necrosis of leaf

tissue– DNA Residues (dinitroaniline)

» Treflan, Prowl, Pendimax» Sorghum or corn root bioassay» Wrap in moist paper towel 2-3d» Allow to germinate then plant


» Observe root formation at 10-14d» Looking for inhibited root development – stunting,

stubbing, lack of root hairs, leaves that don’t unroll, thickened hypocotyl

– Imazaquin, Imazethapyr, Chlorimuron Residues» Scepter, Backdraft, Pursuit, Pursuit +, Extreme,

Lightning, Classis, Canopy XL, Synchrony STS» Affect root and shoot development» Symptoms – inhibited root development, stunting,

leaf striping (interveinal chlorosis)» Use same sorghum/corn bioassay» Observe at 14-21d


– Command Residues» Inhibits production of photosynthetic pigments» Emerge lacking green color» May appear as chlorosis or bleaching» Test w/ oats and wheat» Observe at 10-14d» Affected plants will be white

• Pesticide Licensing Requirements & RUP Listings– IL Pesticide Act Licensing Requirements

• License required by anyone who purchases or applied RUP’s


• Anyone applying a RUP or general use pesticide in the course of employment

• One using a general pesticide on their own property is exempt

• Dept of Ag certifies and licenses– U of I Extension provides training and study materials

• Dept of Public Health certifies those using pesticides in/on manufactured structures

– Nuisance bird control, rodents, insects, etc– Not covered in this manual


• Types of Licenses– Private Applicator License

» Required for people applying pesticides to an ag commodity on property they own/control

» Must pass Grain Fumigation exam in order to fumigate their own bins

» $15 for 3 yr. license (w/ or w/out G.F. cert.)– Pesticide Dealer License

» Individual selling RUP» Test, license, fee required» Keep records of RUP sales for 2 yrs.» Commercial Applicators & Structural Pest Control

Operators are exempt from the test & fee, must register as a dealer


» $100 for 1 yr license» Certification exam good for 3 yrs

– Commercial Applicator & Operator License» Those who use or supervise the use of general or

RUP for hire» $45 for 1 yr applicator license, $30 for 1 yr operator

license» Exam good for 3 yrs

– Public Applicator & Operator License» Those who use or supervise general or RUP as an

employee of a state agency, municipality, or other governmental agency


» No fee, certification good for 3 yrs– Commercial Not-for-Hire Applicator & Operator License

» Those who use/supervise the application on an employer’s property as part of their responsibilities

» No fee, license good for 3 yrs

• Applicator vs. Operator License– Applicators

» Responsible for purchasing, storage, handling, use» Each organization must have at least one person

licensed as an applicator at each facility location» Usually: owner, supervisor, foreman, etc.» May supervise operators


» Pass general standards exam (100 questions) – general of aerial general

» Pass one or more category exam (50 questions ea) – specialized topics, depends on sites where company will use pesticides

» Complete the license application – after passing exams, send to Dept of Ag within 90d, must retest after 90d

» Provide certificate of insurance – property coverage, must also be sent w/ application

– Operators» User of pesticides on the job site» Tied to applicator’s license


» Cannot be licensed w/out being under an applicator» Operator cannot legally apply for a different licensed

applicator» Operator can only apply under direct supervision of

an applicator, only on areas covered by applicator’s licensure

» Operator cannot legally apply if applicator is out-of-town or unavailable

» Provide proof of employment by licensed applicator» Pass general standards exam» Complete license application


• Technical Categories of Licensure– Each category requires specific professional knowledge– Applicator license must encompass all areas in which

they might apply a pesticide– Aquatic

» Weed control in standing/running water– Demonstration & Research

» Use during research or teaching of pesticide/equipment use

– Field Crop Pest Control» Use in corn, SB, forages, etc.


– Forest Pest Control» Use in forest, forest nurseries, forest seed producing

areas– Fruit Crop

» Fruit & nut crops– Grain Facility

» Noncommercial use in/around grain elevators or grain holding facilities, transport facilities, etc.

– Grain Fumigation» Use by private applicators to treat stored grain on

own property– Livestock

» Livestock application or in barns


– Mosquito Control– Ornamental

» Trees, shrubs, ornamental plantings– Plant Management

» Portable plants used for interior landscaping– Regulatory Pest

» By government employees for control of regulated pests

– Right-of-Way Pest Control» Weed control on noncrop sites – parking lots, roads,

etc.– Sewer Line Root Control– Seed Treatment– Soil Fumigation– Turf Pests – turf & sod farms– Vegetable Crops


– Restricted Use Pesticides• Can only be sold to licensed applicators• Tracked carefully• New products carefully tested and classified

– Record-Keeping Requirements• Requirement of all licensed applicators

– Under the 1990 Farm Bill– In IL since the 1988 Pesticide Act

• No specific form, any form will work as long as all data is complete


• Private Applicators– Record w/in 14d of application– Maintain for at least 2 yrs– Records must include the following:

» Brand, product name, EPA registration #» Total amount applied» Location of the application» Size of the are treated» Crop, commodity, stored product, site to which RUP

was applied» m/d/yr of application» Name and certification # of applicator who

applied/supervised


– <1/10 ac application (spot application) – less stringent data collection required

» Greenhouses and nurseries excluded from spot application

• Commercial Applicators– Must supply records to the customer w/in 30d of RUP

application– Maintain records 2yrs from application date– Requirements

» Brand, product name, EPA registration #» Amount applied» Use site» m/d/yr of application


• For more information:– Contact your local U of I Extension office

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Unit 8: Toxicity, Resistance, Residues, Licensing Chapters 13-16.

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