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Final Exam Flashcards

1
Q

Triazine Injury on Soybeans

A
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2
Q

Group 14 PPO Inhibitors

Post Emergence Herbicides

A

Aryltriazinone

carfentazone → Aim

flumiclorac → Resource

fluthiacet → Cadet

Diphenylether

Acifluorfen → Blazer

Fomesafen → Flexstar, Reflex

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3
Q

Sharpen (Group 14)

A

Used for broadleaf weeds (pigweed, waterhemp, wild buckwheat)

Needs to have 0.5” water to activate

Tank-mixed with many herbicides

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4
Q

Triazines

A

Applied either as a soil (preemergence) or to the plant (post emergence)

If applied post then surfactants are normally added

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5
Q

Atrazine Herbicide Activity

A

Soil Applied

Herbicide translocated in the apoplast (xylem) and moves with transpiring water to the oldest leaves

Leaf Applied

Herbicide moves with water to the leaf margins

  • must have good coverage to get good control
  • Does not move to the youngest tissue
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6
Q

Site of Action for ALS Herbicides

A

Binds to and inhibit the enzyme acetolactate synthase (ALS enzyme)

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7
Q

Mode of action for ALS Herbicides

A

Blocks the formation of branched chain amino acids

  • Leucine
  • Isoleucine
  • Valine

This leads to stoppage of protein synthesis

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8
Q

ALS Symptoms

A

Purpling of soybean leaf veins

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9
Q

Symptoms of ALS Herbicides

A

Slow to develop

May see reddish - purple shoots

(this may be due to variety or nutrient deficiency)

Stunting 10 days or more after application

Pinched corn ears if applied after labeled growth stage

Chlorosis, Necrosis

Bottle brush roots

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10
Q

ALS Inhibitor Sympton

A

Bottle Brush Roots on Corn

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11
Q

Prerequisities for Effective Herbicide Use

A

Must come in Contact with the Plant

  • Has to Remain on the Surface of Seed or Leaf Long Enough to Penetrate
  • Surfactants to Hold Chemical on the Leaf
  • Rainfastness or Rain-free Period (30 minutes to 4 hours)

Must Reach the Site where it Disrupts the Vital Process or Structure

  • A photosynthetic Inhibitor does no good in the Root

High Enough Concentration or Long Enough to Injure the Plant

  • Reduced Rates may not have enough on Plant
  • Rainfastness
  • Soil Chemicals Leached to Levels below Optimum Rate
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12
Q

Methods of Classification

A

Time and Method of Application

Soil Persistence

Formulation

Herbicidal Activity

Herbicide Chemistry

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13
Q

Time of Application

A

Preplant (pp)

  • Treatment before the crop is planted
  • Need water to get herbicide into seed zone

Preplant Incorporated (ppi)

  • Applied propr to Planting and Worked into the Soil
  • Normally done because the Herbicide is Photodecomposed or Volatile

PP and PPI do not Interfere with Planting

PPI may not fit in a Minimum or No-till Operation

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14
Q

Time of Application

Preemergernce

A

Treatment made before Emergence of the Crop or Weed

Usually done at planting

Eliminates Early Cultivation

Treatment done without seeing the problem

  • Unless it’s a burndown

Subject to Environmental Conditions, Soil Influences

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15
Q

Post-Emergence Application

A

Made after the emergence of crop or weed

If after weed emergence but before crop emergence (burndown)

  • Can see the Problems
  • If herbicides have ONLY foliar activity and no soil residual crop does not need to be tolerant to the herbicide
  • Could use nonselective herbicides (e.g. Roundup, Liberty, paraquat)
  • Apply when weeds are small (less herbicide needed)
  • Done before critical weed free period (yield loss stopped)

If AFTER Crop Emergence

  • Crop must be tolerant and at the correct stage of growth
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16
Q

Time of Application

Layby

A

Treatment made with or just after last culitivation

May have passes critical weed-free period

Cleans the field for harvest

  • Rely on crop competition to keep any other weeds in check
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17
Q

Time of Application

Post Harvest

A

Done in Late Fall after Light Frost but before Killing Freeze

Controls Winter Annuals

Used to Give Better Controls for Perennials

  • Carbohydrates move into roots and herbicide transported there also
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18
Q

Coverage of Target Area

A

Broadcast

  • Applied to Entire Field

Band

  • Applied only over crop row (more of a precision ag part)

Spot

  • Localized application to scattered plants

Directed Sprays

  • Treatment to weed but miss crop

(using drop nozzles that goes between the plants)

Foliar

Soil

  • Surface/Incorporated or Knife
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19
Q

Type of Formulations

A

Water Soluble

Oil Soluble

Emulsifiable Concentrate

Ultra-Low Volume Concentrate (ULV)

Liquid Flowable or Slurry Type

Dry Flowable

Water Dispersible Granule (WDG)

Granules (G)

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20
Q

Soil Persistence

A

Persistent

When Applied at Recommended Rate will Harm Susceptible Crops in Normal Rotation (atrazine, picloarm)

Long Residual

Herbicide used as Soil Sterilants to Control for > 1 season

(use it around oil tankers/train tracks/pipeline)

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21
Q

Problems of Persistence Soil Herbicides

A

Crop Failure Neccesitates Replanting

Susceptible Crop Follow Short Season Crop within the Same Growing Season (sunflower,winter wheat)

Suscpetible Crop Follows year after Persistent Herbicide Applied (Trifluralin on Spring Wheat)

Decomposition is slow due to weather or soil conditions

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22
Q

Herbicide Formulation

A

Herbicidal prepartion designed for pratical use by the manufacturer for the grower

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23
Q

Herbicide Formulation

Made Up Of

A

Active Ingredients (AI) the part that is phytotoxic

Carrier - Serves to dilute the active ingredient (water,oil,clay)

Surfactants - to spread the herbicide on the folidge

Stickers

Other inert ingredients

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24
Q

Type of Formulations

Water Soluble (S or WS)

A

Active Ingredient totally water soluble (salts of acids like glyphosate, 2,4-D)

Easy to mix

DO NOT PENETRATE into plant weel

Must add a stickers to help get the herbicide into the plant

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25
Q

Type of Formulation

Emulsifiable Concentrate (E or EC)

A

Active Ingredient not water soluble, soluble in nonpolar solvents

Can penetrate the cuticle of the plant easier than water soluble

Problems with drift at high (> 80F) temperatures

Plant wax is nonpolar making the herbicide easy to get into the plant

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26
Q

Types of Adjuvants

Spray Modifiers (Type 1)

A

Dispersing agents

(Enhances the dispersal of a power in a solid-liquid suspension)

Thickener

(used to reduce the number of fine droplets from a nozzle)

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27
Q

Type of Adjuvants

Utility Modifiers (Type 2)

A

Compatibility Agents

  • Used to keep different types of formulations in suspension

Antifoam Agents

  • To reduce foaming in the tank

Emulsifiers

  • Material that aids in the suspension of fine drops of one liquid in another, like oil in water
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28
Q

Degree of Response

Selective Herbicide

A

Only some plants of a mixed population are injured

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29
Q

Degree of Response

Nonselective Herbicide

A

All plants of a mixed population are killed (paraquat and Roundup)

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30
Q

Herbicide Movement in the Plant

Contact

A

No movement in plant

Kills only the tissue that is treated

Complete coverage of the plant is needed to get good control (best applied when plant is small)

Examples

  • aciflorfen (Blazer) (soybean)
  • bentazon (Basagran) (soybean & corn)
  • paraquat (Paraquat) (orchards & other places)
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31
Q

Herbicide Movement in Plants

Translocated Herbicides

A

Moves in the plant from the site of application to other plant parts

Two Types of Movement

  • Symplastic (phloem)

Moves with the sugars/typically moves to the newest areas of the plant

  • Apoplastic (xylem)

Water moves in the xylem/going to the oldest tissue in the plant/applying to leaf it moves to the outer edges of the leaf

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32
Q

Symplastic Movement

A

Herbicide moves in the phloem

Moved with sugars

Moved to the YOUNGEST tissue were demand for energy greatest

Injury seen in youngest leaves and in the youngest roots

Good for control of perennials

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33
Q

Apoplastic Movement

A

Herbicides that move in the apoplast move in the xylem

Move with Water

  • Move to the oldest, most actively transpiring tissue

If taken up by roots move to the oldest leaves

If taken up by leaves stays in the treated leaf

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34
Q

Apoplastically Translocated Herbicides Examples

A

Trizines (atrazine, metribuzin)

Uracils (diuron, monuron)

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35
Q

Herbicide Mixtures

A

Often done to control many types of weeds (mix broadleaf and grass herbicides)

To have the operation be ‘one pass’ (to lessen application costs)

To get synergistic responses (better kill)

To lessen the costs of the ‘expensive’ herbicide by adding a cheaper tank mix partner

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36
Q

Type of Mixture

Premix

A

Sold by the Manufacturer

  • These already have what the manufacturer thinks is the best combination of ingredients
  • A premix may have similar active ingredients at different concentrations and be marketed under different names

Examples

Storm (29% bentazon + 18% acifluorfen) vs Galaxy (33% bentazon + 7% acifluorfen)

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37
Q

Type of Mixture

Tank-Mix

A

Mixed in the field not as the formulation

  • Caution must be taken
  • Incompatible Formulations

The solution turns into sludge

Having AI precipitate out of solution

Mixing chemicals bound to clay with chemicals that are adsorbed by clay

(i.e. glyphosate and DF formulations)

Combining antagonistic chemicals (get no or little plant response)

Getting too high a response (Burn crop or residual lasts too long)

Not understanding all the ingredients already in a formulation

When mixed there can be 4 types of responses that occur

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38
Q

Responses to Herbicide Mixtures

Additive Response

A

When the response of a plant to each herbicide alone or in the mix is the same

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39
Q

Responses to Herbicide Mixtures

Syngeristic Response

A

When mixing 2 chemicals get a greater response than either chemical alone

  • This can be good if get better weed control i.e. mix a some 2,4-D (cheap) with Tordon (expensive) and get a more phytotoxicity than either alone
  • Bad if get more crop injury
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40
Q

Responses to Herbicide Mixtures

Antagonistic Response

A

When the mixture of 2 or more herbicides results in less than expected response (i.e. less weed control) than when any of them are used separately

  • If you mix 2,4-D with some wild oat herbicides get no wild oat control

Graph Info

To get the same response as if the two chemicals were used alone, 1.2 to 1.5 times as much of either herbicide needes to be applied in the mix

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41
Q

Responses to Herbicide Mixtures

Enhancement

A

Mix a nonphytotoxic adjuvant (i.e. crop oil or other) with a herbicide and get a response that is greater than the herbicide is used alone

  • Phytotoxicity increased usually results from increased leaf absorption
  • May reduce crop selectivity (may get more injury such as burned leaves or stunted plants)
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42
Q

Mechanism of Action

A

Precise biochemical reaction that creates the herbicide’s ultimate effect

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43
Q

Herbicide Mode of Action

A

Sequence of events that occur from the herbicides contact with the plant until its final effect is expressed

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44
Q

Site of Action

A

Precise enzyme or target area affected by the herbicide

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45
Q

Mechanisms and Mode of Action

Auxin-type Growth Regulators

A

2,4-D

Dicamba

Picloram

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46
Q

Mechanisms and Modes of Action

Photosynthesis Inhibitors

A

Triazines

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47
Q

Mechanisms and Modes of Action

Disruption of Cell Permeability

A

Paraquat

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48
Q

Mechanisms and Modes of Action

Disruption of Cell Division (Mitosis)

A

Trifluralin

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49
Q

Mechanism and Mode of Action

Root and Shoot Inhibitors

A

Alachlor

Acetochlor

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50
Q

Mechansims and Mode of Action

Pigment Inhibitors

A

Clomozone

Balance

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51
Q

Mechanism and Mode of Action

Block Amino Acid Formation

A

Glyphosate (ESPS)

Immidiazilinone and Sulfonyl Ureas (ALS)

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52
Q

Mechanism and Mode of Action

Other

A

Aryloxy phenoxy

(stops long chain fatty acid syn)

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53
Q

Why Soil Applied

A

Herbicides not absorbed by foliage

  • only enters plants through roots

May be too volatile

May be photodecomposed and lost if not soil applied

  • Incorporation is needed

May have low water solubility

May only be root active and not translocated

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54
Q

Advantages of Soil Applied

A

Control weeds at very small growth stage

Not as much herbicide needed to kill weeds

Dont get much crop competition

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55
Q

Disadvantages of Soil Applied

A

Dont know which weeds will be the problem

Dont know where problem areas are

Some herbicides become environmental problems

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56
Q

Application Type

Soil Pre

A

Herbicides Applied to Soil (PRE Applications)

  • Meant to have residual effect (if not burndown)
  • Control germinating seedlings (if seedlings have emerged, some have no activity)
  • More environmental problems with soil applied herbicides
  • Some metabolites of the chemical remain toxic

Atrazine to deethylatrazine

Balance (isoxaflutole) (1/2 life 4 days) to DKN metabolite (highly active) (1/2 life 3 weeks plus) low sorption of each

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57
Q

Preemergence Herbicide/Soil/Plant Interaction

A

Must come in contact with developing plant

  • Depth of application must be correct or need to leach to the zone needed
  • Dormant structures are not affected

Herbicide must be there in high enough concentration

  • Reasons why the concentration may be low even if applied at the correct amount

Degradation (microbial or chemical)

Binding to soil (sorption decreases amount available to plant)

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58
Q

Herbicide Uptake from Soil

A

Soil Water Must be Present

  • Needed for seed germination, needed for herbicide uptake

Too Dry

  • Photodecomposition
  • Volatilization
  • No Seed Germination

Too Wet

  • Leach from Seed Zone
  • Runoff
  • Microbial Degradation
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59
Q

Chemical Fate in the Environment

Plant Uptake

A

1-10% of Applied Herbicide

Taken up either as

Toxic chemical or Nontoxic metabolite

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60
Q

Chemical Fate in the Environment

Fate in the Air

A

0 to 30% of Applied

Sprayed On - no movement (ideal and usually not the case)

Drift as spray droplets to nontarget areas (0 to 30% of applied)

Volatilization (vapor drift) with movement in the air deposition with rain and snow

Photodecomposition by UV light

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61
Q

Chemical Fate in the Environment

Fate in Soil

A

50-100% of applied

Sprayed On - lasts long enough to kill the target pest - no movement (ideal)

Remains where it’s at is nontoxic due to rapid breakdown (e.g. 2,4-D) or very high sorption (e.g. Roundup)

Remains where it’s at and continues to be toxic

Remains where it’s at degrades to another toxic product

Movement to offsite areas as parent or metabolite (can be toxic or nontoxic)

Mechanisms for movement (< 1% of applied but still detectable)

  • Runoff
  • Leaching
  • Erosion
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62
Q

Herbicide Uptake

A

Herbicide moves in soil to the point of contact

  • with water (mass flow)
  • as a gas (diffusion)

Herbicide DOES NOT move

  • Roots or shoots grow into and through the treated area (interception)

Note: Some herbicides cannot be taken by roots, some cannot be taken up by shoots

  • Can use these properties to design where the chemical is placed to control the weeds of interest and not injure the crop
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63
Q

Routes of Herbicide Entry for Root Uptake

3 Major Routes

A

All Passive (through nonliving tissue)

All Active (through cells and plasmodesmata)

Mixture of Passive and Active

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64
Q

Routes of Herbicide Entry for Root Uptake

All Passive

A

(Through nonliving tissue) (e.g. cell walls)

Entry with water and movement in nonliving tissue (cell walls) and xylem

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65
Q

Routes of Herbicide Entry for Root Uptake

All Active

A

Through Cells and Plasmodesmata

  • Requires energy, moves in cell and symplast
  • If phloem only - the herbicide moves to the root actively growing cells, usually the root tip
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66
Q

Casparian Strip

A

Major barrier to herbicide movement

  • reason for why some herbicides are not taken up
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67
Q

Herbicide Uptake

A

Underground Shoot Adsorption (Thiocarbamates)

  • Coleoptile node of grass seedlings is the entry point
  • This is part of the leaf so there is no Casparian Strip
  • Hypocotyl and shoot of broadleaves are other entry points for herbicide
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68
Q

Soil Applied Herbicides

Shoot Inhibitors

A

Group 8

  • Thiocarbamates
  • Lipid Synthesis, not ACCase

Gropu 15

  • Acid Amides also called acetamides
  • Inhibits very long fatty acid synthesis
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69
Q

Soil Applied Herbicides

Root Inhibitors by Microtubule Disruption

A

Group 3

  • Dinitroanilines
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70
Q

Soil Applied Herbicides

Bleaching Herbicides

A

Group 27

  • HPPD Herbicides
  • 3 Families
  • Inhibits plastiquinone biosynthesis

Group 13

  • DOXP Herbicides
  • Inhibits isoprenoid synthesis
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71
Q

Shoot Inhitors WSSA Group 8

Thiocarbamates

A

EPTC (Eptam) & butylate

  • Does not rely on post-application rainfall (but have to be incorporated due to high volatility)
  • Less loss from dry soil than from moist soil
  • Underground shoot absorption
  • Entry Point - coleoptile node of grass seedlings and hypocotyl hook of broadleaf
  • No problems with crop rotation restrictions
  • Only translocated in the xylem
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72
Q

Shoot Inhibitors WSSA Group 8

Inhibit Lipid Biosynthesis

A

Grasses may not emerge

Reduces cuticular wax formation

Leaves tightly rolled and do not unroll properly

Broadleaf plants may have small leaves or ‘bud seal’

Roots may be brittle, short and thick

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73
Q

WSSA Group 15

Acid Amides (acetanilides) and Isoxazolinone

A

Shoot Inhibitors

  • Stop very long chain fatty acid formation (VLCFA herbicides)

Drawstring (heart shaped) leaves

Acid amide injury to soybean

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74
Q

Symptoms of EPTC, butylate (Group 8) and acide (Group 15) Damage to Corn

A

Injury

Improper leaf unfurling

Twisted whorls

Buggy whipping

Conditions

Misapplication

Heavy rains soon after herbicide application that may leach away the herbicide safener

Stressed conditions (cool, wet soils)

Certain hybrids may be sensitive

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75
Q

Site and Mode of Action (Group 15)

A

Site of Action: Unknown

Mode of Action: Inhibits synthesis of very-long-chain fatty acids in the growing shoots

  • membrane disruption
  • Stops growth
  • Elongase inhibition and inhibition of geranylgeranyl pyrophosphate cyclisation enzymes, part of the gibberellin pathway
76
Q

Acid amide (Group 15) Symptoms

A

No emergence of susceptible weeds (mostly grasses)

Crops may be injured (cold, wet conditions; high application rate; improper placement)

Sorghum is sensitive to injury

Symptoms Include

Drawstring effect on broadleaf crop leaves

  • Also known as heart-shaped leaves

May have buggy whipping on corn

77
Q

Acid amide damage to Soybean

A
78
Q

Acetamide Damage to Corn

A
79
Q

Flufenacet (Define, Axiom)

A

Applied Preplant, PPI, Pre

Used in corn, soybean, wheat, sunflower

In corn and soybean mixed with metribuzin anad sold as AXIOM

Maybe applied up to 14 days before planting, 10 gpa carrier minimum

Used for grass and small seeded broadleaf control

Mode of Action is similar to acetochlor and metolachlor

  • Stops very long chain fatty acid synthesis, so membranes are disrupted
80
Q

Outlook - dimethamid

A

Used as preemergence or early postemergence (to the crop) but preemergences to weeds

Can be impregnated on dry fertilizer

Grass control and also some broadleaf control

  • amaranth
  • purslane
  • ragweed
81
Q

Pyroxasulfone (Zidua)

A

Used in corn and soybean

  • 1-3.5 oz /ac depending on soil type
  • Needs 1/2 inch of rain to active herbicide
  • Minimum carrier volume is 5 gpa

Can be fall applied, early preplant, ppi, pre or early post

Grasses and Sedges

82
Q

Dinitroanilines (WSSA Group 3)

Root Inhibitors

A

Trifluralin

Pendimethalin

83
Q

Dinitroaniline Herbicides (WSSA Group 3)

A

Root Inhibitors

Used a dye intermediates

All highly colored (orange, yellow)

Some have fungicidal activity

Taken up by germinating seedlings

84
Q

Dinitroaniline Family (WSSA Group 3)

A

Soil Applied Herbicide

Pendimethalin

  • Applied pre to corn → DO NOT incorporate

Treflan

  • If applied to corn, apply after corn is 8” tall and incorporate
  • DO NOT apply preplant or preemergence as injury can be severe
85
Q

Site of Action of Dinitroaniline Herbicides

A

binds to a-tubulin

  • Mutations at certain points in this protein do not allow for binding and result in a resistant plant
86
Q

Mode of Action Dinitroaniline Herbicides

A

Stops microtubules from assembling

87
Q

Dinitroaniline Herbicide Symptoms

A

Stunted Plants

Roots Short and Thick

88
Q

Adsorption and Translocation

A

Adsorbed by roots and shoots

Vapors can be adsorbed and kill plant

Concentrates in

  • Areas high in lipid and proteins
  • If very hihg lipid content, binds herbicde and no injury
89
Q

Effects on Growth and Development

A

Roots

  • Inhibits lateral and secondary roots
  • Swelling of root tips and cell enlarge

Shoots → Dicots

  • Decreased elongation, stunting
  • Leathery appearance of cotyledons
  • May be very dark green due to increasd chlorophyll
90
Q

Bleaching Herbicides

A

Inhibit 4 HPPD (3 Families) (WSSA Group 27)

Isoxazole → isoxaflutole (Balance); pyrasulfotole (Huskie)

Triketone → mesotrione (Callisto)

Pyrazolone → topramezone (Impact)

Inhibit DOXP Synthase (WSSA Group 13)

Isoxazolidinone Family → Clomazone (Command)

91
Q

Isoxaflutole (Balance Flexx)

A

Used pre or early preplant

Corn, Sugar Cane

Use for broadleaf weeds - excellent control of velvetleaf, control of ragweed, pigweed and some grasses (foxtails, barnyard grass)

92
Q

HPPD Inhibitors (Group 27)

Site of Action

A

Inhibits p-hydroxyphenyl pryuvate dioxygenase (HPPD)

93
Q

HPPD Inhibitors (Group 27)

Mode of Action

A

Stops plastoquinone biosynthesis which leads to inhibition of cartenoid synthesis

94
Q

What are Carotenoids

A

Constituents (tetraterpenoid orangic molecules) of the plants that add pigment (color) to the leaf

95
Q

What do Carotenoids do

A

Harvest Energy (i.e. Chlorophyll-photosynthesis)

  • Taking in the light energy & splitting water (ATP)

Protect the leaf from free radicles and oxidative stress

(xanthophylls and carotenes)

96
Q

Balance Flexx (Group 27)

A

Plants are bleached white

Tolerance of plants is due to rapid metabolism of the herbicide

(herbicide is broken into smaller molecules)

Degraded in soil by chemical and microbial means

Some problems with carryover seen in the cool Midwestern soils and leaching

97
Q

Balance Flexx Injury Symptoms

A

White Tissue (happens first)

Poor Emergence

Stunted Plants

Growing point dies

98
Q

Mesotrione (Callisto)

A

Used pre or post in corn

Used for control of Broadleaf weeds, cocklebur, velvetleaf, lambsquarters and some grasses

½ Life in Soil → 5 to 15 days

Same site and mode of action as Balance Flexx

  • Inhibits HPPD, carotenoid biosynthesis, plants are bleached
99
Q

Soil Applied Herbicides - Bleaching Type (Group 13)

Site of Action

A

DOXP Synthase (1-deoxy-D-xylulose-5-phosphate synthatase) that is a key component of isoprenoid synthesis

  • Different site of action than Balance Flexx adn Callisto
100
Q

Soil Applied Herbicides - Bleaching Type (Group 13)

Mode of Action

A

Similar to HPPD herbicides; stops carotenoid synthesis (pigment inhibitor)

  • Same symptoms as HPPD herbicides
  • Decreased carotenoid synthesis and bleached plants
101
Q

Clomazone (Command) Group 13

A

Used in soybean and processing pumpkings (ornamental pumpkings are sensitive)

Soybean not injured the plant metabolizes the herbicide

Controls annual grasses and some broadleaf weeds such as velvetleaf

Problems with drift due to volatization problems from wet or moist soils

102
Q

Post Emergent Applications

More Problems with Drift and Aerial Transport

A

Wind Speed

  • Higher speed, more drift

Inversion Conditions

  • Inversion more movement close to ground

Distance to the nontarget area

  • Further the distance to offset areas (large buffer zone) less risk of contamination

Droplet size

Smaller droplets - further drift

103
Q

Herbicide Uptake in the Foliage Depends on

A

Spray Timing (plant size/cover)

Formulation and Additives

Application Equipment (droplet size)

Plant properties (hairs, smooth, waxy)

Time to rain (rainfastness)

104
Q

Foliar Uptake of Herbicides

A

Uptake more difficult than through root

Factors affection foliar sorption

Retention

  • Dependent on carrier

Water “falls” off leaf - lack of wetting and spreading

Granules - Bounce off

105
Q

To Help Retian Herbicide on the Leaf

Use Oils or Surfactants

A

Help water spread and adhere to leaf

Reduce surface water tension

Allow closer contact of the herbicide with the leaf surface

Help minimize runoff (help water stick to the leaf)

106
Q

Foliar Retention

A

Dependent on Drying Time

  • If dries too quickly get residues than will not enter plant
  • If the herbicide does not dry quickly enough may get washed of by rainfall
107
Q

Barriers to Herbicide Absorption by the Leaf

A

Cuticle

Cell Wall

Plasmalemma

108
Q

Herbicide Movement through the Cuticle

A

By diffusion (passive process from high to low concentration)

Moves through

  • Intermolecular Spaces
  • Pectin Spaces (if water soluble)
  • Embedded Waxes (if nonpolar)

Depends on the Chemistry of the Herbicide

Nonpolar Molecules (like EC formulations)

Can easily move through wax but dont move through water well

Polar Molecules (like amine formulations)

Cannot move through wax but once in the leaf can move in polar (pectin or water filled spaces

109
Q

Bariers to Herbicide Absorption by the Leaf

Cell Wall

A

Made up of Cellulose Strands

Interspaces fill with water

Water soluble herbicides penetrate the cell water easier than EC type herbicides

Movement in the cell wall is by diffusion

110
Q

Barriers to Herbicide Absorption by the Leaf

Plasmalemma

A

Outer membrane of the living cell that encloses cytoplasm

For most herbicides penetration into the cell is by active transport cell has to expend energy

If the herbicide does not get through the plasmalemma and into the cell - usually is ineffective

111
Q

Soil and Foliar Applied Herbicides

A

PPO Inhibitors (Group 14)

Photosynthetic Inhibitors → Triazines (Group 5)

Meristem Inhibitors (ALS Enzyme Inhibitors) → IMI and SU (Group 2)

112
Q

Inhibition of protoporphyrinogen oxidase herbicides

(PPO or Protox Inhibitors) Group 14

Mode of Action

A

Cell Membrane Disruption

113
Q

Inhibition of protoporphyrinogen oxidase herbicides

(PPO or Protox Inhibitors) Group 14

Site of Action

A

Inhibiton of protoporphyrinogen oxidase (Protox or PPO Inhibitors)

114
Q

Saflufenacil (Kixor) - Mechanism of Action 14

A

Sharpen (other applied post)

PPO is an enzyme of chlorophyll and heme biosynthesis

Inhibition of PPO leads to accumulation of a chlorophyll precursor (PPIX)

PPIX then absorbs light and causes single oxgen to form

Leads to membrane breakdown via lipid peroxidation

115
Q

Saflufenacil (Kixor)

A

Used for broadleaf weeds (pigweed, waterhemp, wild buckwheat)

Applied at 2 oz/ac in coarse (sandy) soils up to 3 oz/ac in fine (clay) soils

Tank-mixed with many herbicides

116
Q

Sulfonylurea Herbicides

A

Active at low rates

  • 1/3 to ½ oz per acre (do not overapply)

Specific Herbicide Dictates

  • Crop (corn, soybean, wheat, sugarbeet)
  • Weed Spectrum (some best on broadleaves, some control grasses and broadleaf weeds)
117
Q

Resistant Weed Problems

A

Resistant weed populations built up in as little as 2 cycles of use

Some weeds including kochia and prickly lettuce which were very well controlled after one application showed resistance after 2 or 3 applications

Use some of ALS type herbicide once every 48 months

118
Q

Carryover Problems

A

Carryover (even if applied at ½ oz rate) to sensitive crops several years after application

Longer carryover if soil pH is 8 or greater

Example

Red River Valley North Dakota

119
Q

Clorsulfuron Uses

A

Used for broadleaf weed control in wheat, barlet

Applied pre or post up to 2”

Problems with carryover, resistant weeds

Active at low rates

120
Q

Clorsulfuron Soil Activity

A

½ life 4 to 6 weed if pH < 7

½ life up to 3 years > 7

  • In high pH soils, problems with rotational crops such as sugar beets, sunflowers, lentils, chlorsulfuron at <1 ppb can cause problems

Breakdown is through hydrolysis at urea group and occurs much faster in low pH (7 or lower) soils

Not bound to soil - leaching and carryover problems

121
Q

Uses of Classic

A

Annual broadleaf control in soybean

Used pre or pst

Used at higher rate than Glean (.5 to .75 oz/ac)

Antagonism if applied with post grass herbicide

122
Q

Imazaquin (Scepter)

A

Used pre and post for broadleaf control in soybean

Use rate about 2 oz a.e./ac

½ Life

  • Long persistence in some environments
  • 1 year restriction on corn following application
123
Q

Imazethapyr - Pursuit

A

Used in legume crops for broadleaf and grass control at 4 to 6 oz rate

  • PPI
  • Pre
  • Post

Clearfield corn

Selected for resistance (nonGMO) and allows for Pursuit/Lightning to be used for control

Clearfield Rice/Canola/Sunflowers

124
Q

Imazethapyr - Pursuit

A

Used for common cocklebur, wild buckwheat, NonALS kochia, Lambsquarters, barnyardgrass, foxtails

½ life 4 months but can be longer

IMI resistant corn (Clearfield or Lightning) developed for that reason

Problems with resistant weeds and cross resistnace to SU herbicides

125
Q

Cloransulam (FirstRate) Uses

A

Used in soybean

Pre or Early Post

Used for broadleaf weed control - ragweed (common and giant), marestail, velvetleaf

Can be mixed with Roundup in RR soybean and other broadleaf and grass herbicides

Use rates .3 oz product/ac - post and .6-.75 oz product/ac pre

126
Q

Flumetsulan (Python)

A

Broadleaf control in corn and soybean

Only applied preemergence (preplant, ppi or pre)

Restrictions on some rotational crops

  • Sweet corn and sunflower - 18 months
  • 26 months cannola, sugar beets
127
Q

Foliar Applied Herbicides - Act like the Growth Regulator AUXIN

Group 4

A

Phenoxy (Aromatic carboxylic) acids (2,4-D; MCPA; 2,4-DB)

Benzoic Acids (Banvel, Clarity)

Picolinic Acids or Pyidines (Tordon, Milestone, Quelex halauxifen for wheat)

128
Q

What is Auxin

A

Naturally occuring plant growth hormone (in form of IAA)

  • Move from site of production to site of aciton
129
Q

Effects on Plant Mechanims

A

Increased respiration due to uncoupling of oxidative phosphorylation

(ATP is no longer produced from ADP in the mitochondria)

Decreased photosynthesis

In plant roots inhibits

  • Elongation of cells (plants have short stubby roots)
  • Decreased water uptake by roots
  • Leads to decreased transpiration (leaves get hot)
  • Stomatal closure (no carbon dioxide enters)
  • Even lower photosynthesis
130
Q

Translocation of All Auxin Herbicides

A

Translocated (moved in the plant) in the symplast (living tissue of the plant; moved in the phloem)

Moves to actively growing shoot and root tips

  • Shoots elongate, get epinasty (twisting and bending of stems due to ethylene production)
  • Vascular tissue destroyed due to unchecked cell division
  • Roots stop growing, get stubby roots
  • If applied when flower initials are forming will cause infertility problems or malformed flowers
131
Q

Selectivity of Auxin Herbicides

A

Selective Herbicides (does not control all weed types)

Control broadleaves weeds the best

  • Although poor control of weeds in Polygonum (smartweed) family

Grasses

  • May be killed if applied at seedling stage
  • Injury occurs if applied at a susceptible stage (tillering and boot of cereals)

2,4-D was the first high potency herbicide (use rate 1 to 4 lb/ac)

132
Q

Uses of 2,4-D

A

Used to control

Broadleaf Weeds in

  • Corn
  • Wheat
  • Pastures
  • Noncropland

Will kill or injure grasses if appliked at critical times

Tank-mix partner with many herbicides

133
Q

Visual Effects of 2,4-D

A

Epinasty

  • Bending of stems due to differentinal growth rates of elongating regions

Thickening of stems and leaves

Cupping and Twisting of stem

Brace root proliferation (corn plants)

Timing is key on grass plants to avoid injury (malformed roots, sterile flowers)

134
Q

Dicamba Uses

A

Broadleaf control in grass (grain, corn)

  • does not control mustard

Pre emergence applications can control some grasses

Drift and Volatility Problems

  • Soybean very sensitive to dicamba
  • Injury can occur at rates 50 x lower than 2,4-D

If applied too late to corn, cracking and brittle stems

135
Q

Dicamba Herbicidal Activity

A

Absorbed by Foliage (some root uptake)

Translocated in phloems (some in xylem)

Accumulates in meristems

Can be exuded into soil and taken up by other plants

Acts like 2,4-D (alters nucleic acid synthesis, etc.)

Tolerant plants metabolize dicamba rapidly

136
Q

Dicamba Soil Activity

A

Not adsorbed by soil

Can leach readily into and through root zone

Can be a problem if need to replant less tolerant crop

137
Q

Picolinic Acids

A

Act like Auxin

Highly toxic - 100 times more active than 2,4-D

Used for broadleaf weeds in grass, pasture, range, forest

Adsorbed through roots and foliage

Damage looks like 2,4-D

138
Q

Picolinic Formulation

A

Acid not water soluble so derivatized to:

  • Na Salt
  • Isopropyl amine salt

Premixed only with

  • 2,4-D
139
Q

Picolinic Uses

A

Broadleaf weed control in grainland, fallow, noncrop, forest, range, pasture

  • Does not control mustards
  • Do not rotate to broadleaf crops

Translocated mostly symplastically

Plant growth reponse similar to 2,4-D

Not metabolized in plants

140
Q

Clopyralid (Stinger)

A

Known for Canada thistle control

Also used for other broadleaf weed control in

  • Sugar beets
  • Corn
  • Wheat, Barley, Oats
  • Rangeland, Pasture, Noncropland, CRP

Readily translocated in the phloem

141
Q

Auxin Inhibitor - Distinct

Mode of Action

A

Inhibits polar transport of IAA

142
Q

Auxin Inhibitor - Distinct

Site of Action

A

Abnormal accumulation of IAA which causes imbalances in shoots and roots and inhibits growth

143
Q

Auxin Inhibitors - Distinct

Symptoms

A

Sensitive broadleaf weeds exhibit rapid and severe plant hormonal effects (e.g. epinasty) after application of Distinct

Symptoms are visible within hours

Plant death usually occurs within a few days

Corn tolerant becasue of rapid metabolism

144
Q

Symplastically Translocated

Herbicides that look like Amino Acids

A

Glyphosate (Roundup)

Glufosinate (Liberty)

145
Q

Glyphosate Site of Action

A

Enol pyruvyl shikimic acid phosphatase (EPSP) enzyme

146
Q

Glyphosate Mode of Action

A

Inhibits aromatic amino acid synthesis

Amino acids not formed

  • tyrosine
  • phenylalnine
  • tryptophane

This leads to problems with protein synthesis

147
Q

Glyphosate Soil Activity

A

Very strong adsorptoin to soil

  • Binds with Fe, Ca, Al
  • Compounds not taken up unless in solution

Very little leaching

No carryover

Microbial degradation is major means of degradation in soil

148
Q

Glyphosate Herbicide Activity

A

Absorbed by foliage

Translocated to meristems and root buds in the phloem

Visual Effects

  • Sometimes deep purpling (wild buckwheat, corn)

~ Stunting

~ Chlorosis (yellowing of tissue)

~ Wilting

~ Tissue Necrosis (dead tissue)

  • Seen after

~ 5 to 15 days depending on annual/perennial

149
Q

Problems with Glyphosate Application

A

Do not combine with

  • Wettable powders or dry flowable (binds irreversibly to the clay particles)
  • Hard or dirty water (binds with iron, calcium and soil)

Maybe washed off by rain and have no activity

  • Some formulations are better sorbed and have more rainfastness than others
  • Use with surfactants and at times fertilizers to increase uptake (Use AMS not UAN)
150
Q

Glufosinate

A

Amino acid Herbicide

Not water soluble - formulated as an ammonium salt (described as a.e.)

Nonselective Herbicide

  • Kills grasses and broadleaf weeds
  • Used post emergence only
  • No soil activity
  • Works best when the growing point of corn is emerged from soil (30” corn)

Liberty and Ignite are not easily taken up

151
Q

Glufosinate Site of Action

A

Glutamine synthase an enzyme that converts glutamate + ammonia to glutamine

152
Q

Glufosinate Mode of Action

A

When glutamine synthase is stopped toxic accumulations of ammonia are found in plant tissue

153
Q

Glufosinate Symptoms

A

Chlorsis (yellowing of tissue) and Wilting

3 to 5 days after application

Necrosis (dead tissue)

1 to 2 weeks

154
Q

Lipid Synthesis Inhibitors (ACCase Enzyme Inhibitors)

A

Aryloxyphenoxies (‘fops’, ‘props’ and ‘dops’)

Cyclohexanediones (‘dims’)

Pinoxaden (‘dens’)

155
Q

Aryloxyphenoxy Site of Action

A

Blocks the ACCase (acetyl CoA carboxylase) enzyme

156
Q

Aryloxyphenoxy Mode of Action

A

Stops acetyle CoA from going to malonyl CoA, the first step of fatty acid synthesis; inhibition of long chain fatty acid synthesis

Long Chain Fatty Acids needed for cell membranes

  • No membranes, no cell integrity
  • No new growth
  • Plant death
157
Q

Aryloxyphenoxy Symptoms

A

Grass Herbicides

Symptoms

  • Root and shoot growth slow soon after application (seen as stunting)
  • Purpling of Steam
  • ‘Mushy’ growing point
158
Q

Diclofop

A

Used for post-emergence grass control (wild oat, foxtail, crabgrass) in barley and wheat

Applied when susceptible grass is in the 1 to 4 leaf stage

Controls downy brome if applied ppi

Need Good Coverage

Inhibits Shoot Growth

159
Q

Diclofop Symptoms

A

Slow to Develop

Chlorosis and Stunting of Plant

Degrades quickly

½ life → 10 to 30 days

160
Q

Fluazifop

A

Post Emergence Grass Control

  • Volunteer Corn
  • Quackgrass

Absorbed by foliage and translocated

Inhibits ACCase activity

161
Q

Fluazifop Symptoms

A

Symptoms

  • Stunting
  • Chlorosis
  • Necrosis
  • Decayed growing point

Symptoms slow to develop

Low soil mobility

½ Life → less than 1 week

162
Q

Sethoxydim (Poast)

A

Used for post emergence annual grass control in alfalfa, soybean and sunflower

Increased uptake when mixed with crop oil

ACCase Inhibitor

½ Life → 2 to 13 days

163
Q

Foliar Applied Contact Herbicides

A

Selective (only kill broadleaf) Photosynthetic Inhibitor

  • Bentazon (Basagran) → Broadleaf (Group 6)
  • Bromoxynil (Buctril) → Broafleaf (Group 5)

Selective (kill grass only)

Difenzoquat (Group 26, site unknown)

Selective (kills broadleaf and grasses, not crops)

PPO Inhibitors → Group 14

Nonselective (kills all plants)

Paraquat → Group 22

164
Q

Bentazon Site of Action

A

Photosystem II in chlorophyll of plant - site B

165
Q

Bentazon Mode of Action

A

Inhibits electron transport in Photosytem II

  • Binds to an amino acid in the protein bound plastiquinone enzyme and does not allow electron transport to continue (stopping photosynthesis)
166
Q

Bentazon Symptoms

A

Chlorosis

  • If not good coverage, yellow spotting

Necrosis

Wilting

Stunting

Tolerant crops may show these symptoms form slight to moderate (depending on variety)

167
Q

Bentazon Soil Activity

A

Very water soluble but not leached due to binding with soil

Soil persistence 3 to 5 months but not active cause

  • Tightly bound
  • Does not translocate well to the leaves of the plants (site of action)
168
Q

Bromoxynil Site of Action

A

Photosystem II (same as bentazon)

169
Q

Bromoxynil Uses

A

Appliked Post to:

  • Wheat
  • Barley
  • Oats

For seedling broadleaf control

Best when weeds are small, < 4 leaf stage

Controls

  • Wild buckwheat
  • Annual smartweed

These are weeds that 2,4-D does not control well

170
Q

Bromoxynil Mode of Action

A

Inhibits photosynthesis by stopping electron flow in PSII so no reducing power is generated in photosynthesis

  • Secondary effect is lipid peroxidation which causes holes in membranes, loss of cell integrity follwed by loss of cell function
171
Q

Bromoxynil Symptoms

A

Leaf Chlorosis (due to lipid peroxidation)

Leaf spotting if poor coverage

Necrosis

172
Q

Diphenyl ethers Site of Action

A

Inhibits carotene biosynthesis (protoporyhyringen)

(Protox or PPO)

173
Q

Diphenyl ethers Mode of Action

A

Oxidation of membranes and cell constituents (breaks down membranes) because singlet Oxygen builds up

  • carotene buffers against singlet O formation
174
Q

Diphenyl ethers - Symptoms

A

Water Soaking

Wilting

Foliage burn

175
Q

Aciflurofen Uses

A

Early postemergence broadleaf and small control in soybean

Excellent control of

  • Pigweed
  • Mustard
  • Black Nightshade

Poor control of large seeded weeds (sunflower)

Contact Herbicide - need excellent coverage

176
Q

Paraquat (Group 22)

A

Nonselective Contact Herbicide

Used in lots of crops to dry down (i.e potatoes)

Used to dessicate weeds at the end of the season prior to harvest

Used as burndown in spring

Does not translocate - poor control of perennials

177
Q

Paraquat Symptoms

A

Plant dessication

Rapid wilting due to disruption of membranes and water loss of cells

Cocklebur (mature and drought stressed) are tolerant to paraquat

178
Q

Paraquat Mode of Action

A

A free radical is formed using paraquat and keeps reoxidizing to paraquat

  • reoxidation results in Hydrogen peroxide (H2O2) production which destroys cell membrane
179
Q

Paraquat Site of Action

A

Photosystem I in chlorophyll the paraquat molecule acts as a free radical and scavenges electrons from photosynthesis and also respiration

180
Q

What is Herbicide Resistance

A

The inherited ability of a plant to survive and reprouce following exposure to a dose of herbicide that is lethal to the wild plant type

181
Q

Tolerance

A

Ability of a plant to survive and reproduce after herbicide treatment

182
Q

Cross Resistance

A

Plants that are resistant to several herbicides in a similar chemical group with a similar mode of action

183
Q

Multipe Resistance

A

Plant is resistant to herbicides that are chemically unrelated and have different mode of actions

184
Q

Factors that Influence Resistance Development

A

Over reliance/exclusive reliance on a single herbicide (or herbicide mode of action) for weed control

  • Single site of action increases problems

(ALS, ACCase, glyphosate, PPO, PSII, all ahve single site of action)

An increase in the application frequency of a particular herbicide

185
Q

Management to Prevent Resistant Weeds

A

Use integrated weed managment techniques

Prevention is the best method

Diverse program is needed

Tank mix at least 2 chemicals with different sites of action

Then:

  • Rotate Culivation Techniques
186
Q

Rotate

A

Use herbicides with short-term soil activity

Use optimum doses to prevent weed escape

Use cultural managment to prevent weed seed spread

Tank mix different sites of action

It is recommended not to use herbicides with the same site of action more than once every 3 years

187
Q

Ask at Least 6 W’s

A

Which weeds

What method of control

  • May not alwasy choose an herbicide

Where present

What mode of action or combination

  • Whats been used in the past

What stage of plant growth (when to apply)
- Choose the right timing

What rate

Weeds (6 decks)

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