Herbicide Absorption: Foliar - Lecture Slides | PLNT 4070, Study notes of Agricultural engineering

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Herbicide Absorption: Foliar

Weed Science & Technology

PLNT 4070/

November 10, 2008

Plant Foliar Surfaces

Cuticular membrane is a major barrier to

penetration of foliar applied pesticides

• Cuticle plays a role in spray contact and retention as well as penetration

Much more difficult for a pesticide to enter

the plant through the foliage than the root

• All above ground plant parts are covered by a cuticle

Cuticle Composition & Structure

Cuticle thickness and composition

influenced by:

• age of plant
• environment (temperature, humidity, moisture, light) - Field bindweed: Non-irrigated Irrigated g/100 leaves 5.4 11 mg wax/g leaf 1.5 0.

Cuticle Composition & Structure

Epicuticular waxes

• Mixture of long chain alkanes, alcohols, ketones, esters, and fatty acids
• (^) Lipophilic (non-polar)
• Predominant chain length 21 to 37 C units

Embedded waxes

• Contain lesser quantities of hydrocarbons
• Greater proportion of polar constituents

Cuticle Composition & Structure

Pectin

• Pectin strands located either at cutin cell wall interface or are interspersed in the cutin layer
• (^) They are the most hydrophilic component of the cuticle

Absorption

Movement of material into plant from an

external surface

Influenced by:

• Contact & retention
• Penetration

Contact & Retention

Factors that influence herbicide contact and

retention on the leaf surface:

• Special structures
  • trichomes
  • stomata
  • veins
  • bladder hairs

Contact & Retention

Factors that influence herbicide contact and retention on the leaf surface:

• Leaf morphology
  • angle
  • shape
  • width

Contact & Retention

Ramsdale & Messersmith (2001) demonstrated CHEAL retained only 25% as much spray solution as AMARE Redroot Pigweed Common Lambsquarters

Contact & Retention

Factors that influence herbicide contact and

retention on the leaf surface:

• Environment
  • temperature
  • humidity
  • light
  • wind
• Cuticle
  • thickness
  • type of wax
  • wax structure

Penetration

Involves:

• Penetration through the cuticle
• Penetration through cell walls
• Penetration through the plasmalema
• Release into cytoplasm

Cuticular Membrane Penetration

Two routes of entry:

• Lipid soluble
• Water soluble

Affected by:

• Formulation
• pH
• Particle size
• Cuticle thickness
• Environment

Plasmalema Penetration

Plasmalema composed of lipids or

lipoproteins

• Minor barrier to penetration
• Two routes:
  • Active
    • Energy required
  • Passive
    • Difusion
    • Gradient differences