Fungicides

1
Chapter 13

• Fungicides

2
Introduction

• Plant Pathology
• Irish potato famine
• Phytophthora infestans
• Downy mildew of grapes
• French wine industry

3
1st Generation Inorganic Fungicides

• Professor Millardet
• Bordeaux mixture
• Copper sulfate
• Calcium hydroxide
• Other copper sulfate mixtures
• Currently replaced with copper-based compounds

4
1st Generation Inorganic Fungicides

• Bordeaux mix on grape vines
• Note bluish color to the leaves

5
1st Generation Inorganic Fungicides

• Fungicides before 1960
• Protectants
• Only work outside plant tissue\
• Inorganic fungicides
• Fungitoxic
• Phytotoxic

6
1st Generation Inorganic Fungicides

• Washed off easily reapplication needed
• Mercurous chloride
• Heavy metal (Hg) compounds
• Residues causedacute and chronic toxicity to
  animals

7
1st Generation Inorganic Fungicides

• Long-term exposure ? severe brain damage
• LD50 1 5 mg/kg

8
2nd Generation Organic Fungicides

• Organo-mercurial fungicides
• Retained persistent fungitoxicity
• Less poisonous to animals
• Organo-tin fungicides
• often relatively phytoxic
• Toxic to animals
• LD50 108 mg/kg

9
2nd Generation Organic Fungicides

• Phenols
• Disinfectants general biocides
• Wood preservatives
• Orchard floor (ground) disinfectants, killing
  overwintering saprobes

10
2nd Generation Organic Fungicides

• Dithiocarbamates
• Organic, protectant fungicides
• Low toxicity
• LD50 400 up to 8000mg/kg
• Ethylene thiourea causes teratological effects
  (malformed offspring) with LD50 of 10mg/kg

11
2nd Generation Organic Fungicides

• Quinones
• Protectant fungicides
• Most effective against apple scab
• Chloranil effectiveness
• 750,000 investment ? 19 million return in pea
  yield in 1951

12
2nd Generation Organic Fungicides

• Oats on left sprayed with Zineb
• Oats on right untreated
• Note lodging (falling over) from crown rust
  disease

13
3rd Generation Systemic Fungicides

• Benzimidizoles (1960s)
• Benomyl
• Applied externally to plant
• Move inside plant and kill fungi there
• Apoplastic fungicide accumulates between cell
  walls, not in cells
• Cannot move down to roots from leaves

14
3rd Generation Systemic Fungicides

• Applied at base of stem, it could move upward in
  xylem to leaves
• Resistance developed two years after introduction
• Selective only for fungi except basidiomycetes

15
3rd Generation Systemic Fungicides

• Benomyl, a systemic fungicide

16
3rd Generation Systemic Fungicides

• Sterol-inhibitors
• Prevent biosynthesis of ergosterol
• Ergosterol major component of fungal cell
  membranes
• Fungal growth retarded with a reduction in
  ergosterol