Herbicide Classification

1
Herbicide Classification

• Herbicides are classified according to timing and
  method of application and chemistry.
• Select a proper herbicide based on weed
  sensitivity as well as turfgrass tolerance, and
  also when and how you want to control the weed
  population.

2
Herbicide Classification

• Foliar Absorbed Herbicides
• Absorption of the active ingredient occurs in
  leaves.
• Postemergence (POST) control only
• Examples glyphosate, 2,4-D, dicamba
• Root Absorbed Herbicides
• Absorption of the active ingredient occurs in
  roots.
• Preemergence (PRE) or sometimes POST control
• Examples DNA crabgrass herbicides, atrazine

3
Herbicide Classification

• Selective vs. Nonselective Herbicides
• Selective herbicides control or suppress certain
  plants without negatively affecting the growth of
  other plants.
• Selectivity may be due to differential
  absorption, translocation or physical
  (morphological) differences between species.

4
Herbicide Classification

• Selective vs. Nonselective Herbicides
• Selective herbicides may be detoxified in plants
  or just not converted into its active
  ingredients.
• Examples 2,4-D, mecoprop, dicamba control many
  broadleaf weeds but many turfgrasses are
  tolerant. PRE crabgrass herbicides are safe on
  many turfgrass species also.

5
Herbicide Classification

• Selective vs. Nonselective Herbicides
• Nonselective herbicides control plants regardless
  of species.
• Examples Glyphosate, glufosinate and paraquat
  are nonselective, foliar absorbed herbicides.
• (Note glyphosate is selective to certain turf
  species at low rates)

6
Herbicide Classification

• Contact vs. Systemic Herbicides
• Contact herbicides kill only the portion of green
  tissue that is contacted. Therefore, uniform
  spray coverage and particle size are essential
  for adequate control. (the entire plant must be
  sprayed)
• Example If a drop of paraquat (a nonselective,
  contact herbicide) were placed on a leaf tip,
  only the leaf tip would show injury symptoms.

7
Coverage with Granular vs Spray
8
(No Transcript)
9
Herbicide Classification

• Contact vs. Systemic Herbicides
• Contact herbicides do not kill perennial
  underground structures such as rhizomes, tubers
  and bulbs. Repeat applications to regrowth may
  eventually drain the plants underground
  resources, but it is better to try to control
  perennial weeds with systemic herbicides.
• Use contact herbicides on annual weeds.

10
Herbicide Classification

• Contact vs. Systemic Herbicides
• Systemic herbicides are extensively translocated
  in a plants vascular system from point of
  absorption (leaf or root) to sites of action.
• Example If a drop of glyphosate (nonselective,
  systemic herbicide) were placed on a leaf tip,
  the entire plant would express injury symptoms
  due to translocation throughout the plant.

11
Herbicide Classification

• Contact vs. Systemic Herbicides
• Systemic herbicides are transported throughout
  the vascular system along with nutrients, water
  and organic materials necessary for plant growth.
• Systemic herbicides require days to weeks for
  total control. (herbicide must travel throughout
  plant)
• Systemic herbicides are more effective on
  perennial weeds than contact herbicides.

12
Herbicide Classification

• Contact vs. Systemic Herbicides
• Contact herbicide examples
• MSMA for POST grass control
• Bentazon for POST yellow nutsedge control
• Paraquat for nonselective weed control

13
Herbicide Classification

• Contact vs. Systemic Herbicides
• Systemic herbicide examples
• Glyphosate and glufosinate for nonselective weed
  control
• 2,4-D, mecoprop, dicamba for broadleaf weed
  control
• Atrazine and simazine for annual bluegrass and
  broadleaf weed control

14
Herbicide Classification

• Herbicide Timings
• Herbicides can also be characterized as
• Preplant
• Preemergence
• Postemergence

15
Herbicide Classification

• Herbicide Timings
• Preplant herbicides (soil fumigants) are used in
  areas where a new turf stand is to be
  established. They are nonselective herbicides
  that kill desirable and undesirable plants!
• Soil fumigants kill seeds.

16
Herbicide Classification

• Herbicide Timings
• Preplant herbicide examples include
• Methyl bromide (to be completely banned in 2005
  because it is an ozone depleter)
• Metam-sodium
• Dazomet

17
Herbicide Classification

• Herbicide Timings
• PRE herbicides should be applied and activated
  prior to weed seed germination (either annual or
  perennial).
• PRE herbicides form a thin barrier at or right
  below the soil surface. Emerging seedlings
  contact the treated zone, absorb the herbicide,
  then die.
• PRE herbicides in turf are selective herbicides.

18
Weed Control With Preemergence Herbicides
Herbicides do not prevent weeds from germinating,
they kill weeds as they grow through the
herbicide treated zone.
19
Weed Control With Preemergence Herbicides
Large gaps in herbicide barriers result in weed
escapes.
20
Herbicide Classification

• Herbicide Timings
• Weeds that have already emerged before
  application or activation are not affected by PRE
  herbicides because their primary growing point
  has escaped treatment.
• PRE herbicides must be activated with
  approximately 0.5 inch of irrigation or rainfall.

21
Herbicide Classification

• Herbicide Timings
• PRE herbicides are relatively immobile,
  persistent and nonvolatile in soils. However, if
  left on the soil surface for an extended period
  of time without activation by water, these
  herbicides can volatilize or photodecompose.
• PRE herbicides do not control perennial weeds
  emerging from vegetative structures.

22
Herbicide Classification

• Herbicide Timings
• PRE herbicides (especially crabgrass and
  goosegrass herbicides) are very effective as
  granular applications.
• Particle sizes are uniform and small enough to
  ensure adequate soil coverage as long as your
  sprayer is properly calibrated and youre
  applying the correct amount!!!

23
Herbicide Classification

• Herbicide Timings
• PRE herbicides DO NOT kill seeds. They dont
  keep seeds from germinating. They kill seedlings
  as they germinate!
• PRE herbicides kill weeds before they are
  visible. This lack of dead and dying weeds is
  more aesthetically pleasing.

24
Herbicide Classification

• Herbicide Timings
• POST herbicides are applied directly to the
  emerged weed, and are usually more effective on
  seedlings. Plants have two growth stages,
  vegetative (more easily killed when rapidly
  growing) and reproductive.
• POST herbicides CAN be used on grass and
  broadleaf weeds, but MUST be used on sedge and
  kyllinga species, wild garlic, and many other
  perennial weeds. (Yellow nutsedge is an
  exception metolachlor provides PRE control).

25
Herbicide Classification

• Herbicide Timings
• POST herbicides usually require multiple
  applications for adequate control. They can be
  foliar or root absorbed, selective or
  nonselective, contact or systemic.
• Example 2,4-D is a POST, selective, systemic,
  foliar absorbed herbicide.

26
Herbicide Classification

• Herbicide Timings
• POST herbicides are more effective when applied
  as liquid formulations rather than granular
  formulations (liquids stick to the weeds).
• If granular products are chosen, apply to wet
  foliage so the herbicide will stick to the weeds
  and not roll onto the soil where they are
  ineffective.

27
Herbicide Classification

• Herbicide Timings
• POST herbicides are more effective when
• Applied to actively growing weeds
• Temperature range from 60 to 85 degrees
• Good soil moisture
• Applied BEFORE mowing
• Mowing is delayed 1-2 days after application

28
Herbicide Classification

• Herbicide Timings
• POST herbicides must penetrate a waxy leaf
  cuticle to get inside of the plant. When plants
  are actively growing, the cuticle is thinner
  allowing for easier penetration.
• When plants are drought-stressed, the cuticle
  becomes thicker to conserve plant moisture and
  herbicide penetration is more difficult.

29
Herbicide Classification

• Herbicide Timings
• POST herbicides usually should be avoided when
  temperatures exceed 90 degrees. The weeds could
  be drought-stressed and also the herbicide could
  become volatile and drift to nontargeted
  sensitive plants.
• Example 2,4-D injures tomatoes, cotton, tobacco.

30
Herbicide Classification

• Herbicide Timings
• Delay mowing for several days prior to a POST
  application to allow for more available foliage
  for herbicide absorption and to ensure that the
  weeds are actively growing.
• Delay mowing for several days after a POST
  application to allow for herbicide translocation
  throughout the plant.

31
Herbicide Classification

• Herbicide Timings
• Do not apply POST herbicides in the rain or
  irrigate immediately after application.
  Depending on the individual label, herbicides can
  be rain-fast (inside the plant) in as little as
  one hour or as long as 12 hours. If a POST
  herbicide gets washed off to the soil, it becomes
  ineffective.

32
Herbicide Classification

• Herbicide Timings
• Herbicide retention on a leaf is affected by
• Leaf size
• Leaf shape
• Leaf surface area
• Leaf angle

33
Herbicide Classification

• Herbicide Timings
• Good herbicide retention on a leaf occurs when
• Leaf size is LARGE
• Leaf shape is WIDE
• Leaf surface area is NON-WAXY
• Leaf angle is HORIZONTAL (FLAT)

34
Herbicide Classification

• Herbicide Timings
• Poor herbicide retention on a leaf occurs when
• Leaf size is SMALL
• Leaf shape is NARROW
• Leaf surface area is WAXY
• Leaf angle is UPRIGHT

35
Herbicide Classification

• Herbicide Timings
• Wild garlic and nutsedge species are examples of
  weeds that have narrow, waxy, upright leaves.
  Many herbicide particles tend to miss the plants
  entirely, or bounce or slide off the leaves.
• For POST herbicides to be effective on these
  types of weeds, spray adjuvants are needed.

36
Herbicide Classification

• Herbicide Timings
• Adjuvants are chemicals added to a pesticide
  formulation or tank-mix to improve mixing and
  application, or enhance pesticide performance.
• Check the herbicide label to determine if spray
  adjuvants are needed.

37
Herbicide Classification

• Herbicide Timings
• Spray adjuvants include
• Surfactants
• Methylated seed oils
• Crop oil concentrates

38
Herbicide Classification

• Herbicide Timings
• Surfactants consist of several classes of
  chemicals that reduce the interfacial tension
  between water and solids (plant material) or
  other liquids.

39
Herbicide Classification

• Herbicide Timings
• Classes of surfactants
• Wetting Agents used to increase the wetting
  capacity of water (make water wetter)
• Spreaders allow pesticides to form a uniform
  layer or coating over the treated surface
• Stickers cause pesticides to adhere to plant
  foliage and reduce spray runoff or washoff

40
Herbicide Classification

• Herbicide Timings
• Types of surfactants
• Anionic negatively charged, readily leach from
  soil
• Cationic positively charged, binds
  electrostatically to soil causing waterproofing
• Nonionic no charge, best type of surfactant to
  use

41
Herbicide Classification

• Herbicide Labels
• It is important to read and understand the label
  of any pesticides that you use, not just
  herbicides!!! For example
• PRE and POST herbicides generally should not be
  applied to newly seeded, sodded or sprigged
  turfgrass until it becomes well established.

42
Herbicide Classification

• Herbicide Labels
• Immature turfgrass seedlings can be affected by
  supposedly tolerant herbicides. Tolerance
  ultimately depends on root growth. This and
  other important information will be stated in the
  label. Individual labels will give their
  definition as to what is an established turfgrass.

43
Herbicide Classification

• Herbicide Labels
• Some PRE crabgrass and goosegrass herbicide
  labels state that applications should not be made
  to turfgrass seeded the previous fall.
• Examples benefin, oryzalin, benefin
  trifluralin

44

• Trimec Classic POST Broadleaf Herbicide
• Fescue seed can be sown 3 to 4 weeks after
  application
• Do not apply to newly seeded turf until 2nd or
  3rd mowing
• Confront POST Broadleaf Herbicide
• Do not reseed until 3 weeks after application
• Newly seeded turf should be mowed 2 to 3 times
  before application
• Millennium Ultra POST Broadleaf Herbicide
• Do not apply to newly seeded turf until well
  established