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Fungicides and Nematicides. Stephen J. Toth, Jr. Wayne G. Buhler Department of Entomology Department of Horticultural Science North Carolina State University North Carolina State University. Photograph from Jack Bailey.

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Fungicides and Nematicides

Stephen J. Toth, Jr. Wayne G. Buhler

Department of Entomology Department of Horticultural Science

North Carolina State University North Carolina State University

Photograph from Jack Bailey.

plant disease agents

Brown necrotic lesions on potato foliage caused by air pollution (ozone)

Plant Disease Agents
  • Living organisms - including fungi, bacteria, viruses and nematodes
  • Nonliving agents - including unbalanced soil fertility, toxic chemicals, air pollution, frost, drought, sunburn, wind and hail

Photograph by Gerald Holmes.

identifying plant diseases
Identifying Plant Diseases
  • Symptom - reaction of the host plant to the living organism or nonliving agent (e.g., leaf spots, wilting, galls on roots)

Alternaria blotch on apple

Crown galls on peach

Photographs provided by Turner Sutton.

identifying plant diseases4
Identifying Plant Diseases
  • Sign - physical evidence of the presence of disease agent (e.g., mold or fungal spores, bacterial ooze)

Green mold on orange (Penicillium)

Bacterial ooze on crabapple (fire blight)

Photographs provided by Turner Sutton.

  • Organisms that lack chlorophyll and obtain their food by living on other organisms
  • Reproduce by spores (aids in identification)
  • Attack crops above and below soil surface
  • Spread by wind, rain, insects, birds, soil, machinery and contaminated seed

Blue mold (apple) fungal spores and fruiting structures of cherry powdery mildew. Scanning electron micro-graphs by Alan Jones.

  • Microscopic, one-celled organisms that reproduce by dividing in half
  • Identified by plant symptoms or by signs of the bacteria
  • Spread by infected seed, humans, insects, birds, contaminated rainwater, irrigation water and equipment

Wildfire bacterium of tobacco (Pseudomonas tabaci)

Photograph provided by NCSU

Plant Pathology Department.

  • Too small to be seen with ordinary microscope
  • Cannot complete their life cycle independently
  • Transmitted by insects, infected plants, fungi, nematodes, etc.
  • No pesticides available to control viruses; control by using disease-free or resistant plants and cultural methods (e.g., crop rotation)

Scanning electron micrograph of tobacco mosaic virus

Photograph provided by NCSU

Plant Pathology Department.

history of fungicide use
History of Fungicide Use
  • Prior to 1882: disease control with elemental sulfur and copper
  • From 1882 to 1934: disease control based on organo-metallics (fixed or organo-copper)
  • 1934: modern era of organic fungicides began with the dithiocarbamates (i.e., thiram)
  • 1943: EBDC fungicides introduced, greatly improved fungicidal activity
history of fungicide use9
History of Fungicide Use
  • Before mid-1960s: fungicides were protectives, used at pounds per acre
  • Mid-1960s to 1980s: fungicides introduced with systemic and/or curative effects, used at pounds per acre
  • 1980s to 1990s: sterol-inhibiting fungicides were introduced which are systemic fungicides with both protective and curative activities, used at ounces per acre
types of fungicides
Types of Fungicides
  • Protective (preventative): application prevents the establishment of an infection
  • Curative: application interrupts the development of an established infection before visible symptoms
  • Eradicant: application interrupts further development of an established infection having visible symptoms
  • Residual: remains on surface of the leaf and provides protection
  • Systemic: movement of fungicide inside the plant (locally or throughout the plant)
classes of fungicides inorganics
Classes of Fungicides: Inorganics
  • Inorganics are protective (preventative) fungicides
  • Sulfur: one of oldest fungicides used, about 8 million pounds used in 1990 in U. S.; works as a general growth inhibitor; advantages include cheap cost and ease of application (dusts); disadvantages include limited spectrum of activity (best on mildews), must be applied frequently at a high rate and phytotoxic at high temperatures
  • Copper: phytotoxic to plants in elemental form (use uncommon)
classes of fungicides copper
Classes of Fungicides: Copper
  • Copper is bound to organic and inorganic molecules in fixed-type coppers, less toxic to plants
  • Broad spectrum poison; useful as fungicides and bactericides; protective (preventative) fungicides
  • Bordeaux mixture (copper sulfate and hydrated lime), copper sulfate, copper hydroxide and other copper compounds
classes of fungicides organics
Classes of Fungicides: Organics
  • Organics are protective (preventative) fungicides
  • Broad spectrum control, multi-site activity
  • Represent 60-70% of fungicides used
  • Dithiocarbamates: thiram
  • Ethylenebisdithiocarbamates (EBDCs): manozeb, maneb and zineb
  • Captan: one of the most widely used fungicides worldwide, broad spectrum control
  • Chlorothalonil (Bravo, Daconil 2787): widely used, ornamentals and turf
classes of fungicides systemics
Classes of Fungicides: Systemics
  • Systemic and/or curative activities
  • Benomyl (Benlate): broad spectrum, widely used
  • Thiophanate-methyl (Topsin-M): broad spectrum, turf and fruit
  • Iprodione (Chipco 26019, Rovral): broad spectrum, turf and ornamentals
  • Metalaxyl: seed treatments (Apron), field and vegetable crops (Ridomil), and turf and ornamentals (Subdue); narrow spectrum of activity, effective against certain soil-borne diseases
classes of fungicides systemics15
Classes of Fungicides: Systemics
  • Sterol inhibitors: large group of fungicides, widely used, broad spectrum of activity, has both protective and curative activity; include imazalil (Fungaflor), triforine (Funginex), fenarimol (Rubigan), mycobutanil (Nova), propiconazole (Tilt) and triadimefon (Bayleton)
classes of fungicides fumigants
Classes of Fungicides: Fumigants
  • Highly volatile chemicals that have fungicidal activity; include methyl bromide (controls fungi, nematodes, insects and weeds) and chloropicrin

Photograph from USDA/ARS.

classes of fungicides antibiotics
Classes of Fungicides: Antibiotics
  • Antibiotics are substances produced by microorganisms which inhibit growth of plant diseases in very dilute concentrations
  • Streptomycin (Agri-Mycin): used as dust, spray and seed treatment, mostly for bacterial diseases
  • Small, usually microscopic, roundworms
  • Nematodes parasitic to plants have a stylet (hollow feeding spear)
  • Feed on plant roots, stems, leaves and flowers
  • Above-ground symptoms include stunting, yellowing, loss of vigor and general decline of plants

Nematodes under light microscope. Photograph provided by Tom Melton.

Damage to peanuts by sting nematodes. Photograph from NCSU Plant Pathology Dept.


Root knot nematode damage on okra

Photographs from NCSU Plant Disease and Insect Clinic.

classes of nematicides fumigants
Classes of Nematicides: Fumigants
  • Exert toxic action as a gas
  • Methyl bromide: used since 1941; potent biocide; soil-fumigant that controls nematodes, fungi, insects and weeds
  • Chloropicrin: used at the end of World War I; now used as warning agent (2%) with methyl bromide (98%); mixed with 1,3-dichloropropene (Telone C-17)
  • Others: 1,3-dichloropropene (Telone) and vapam (Busan)
classes of nematicides non fumigants
Classes of Nematicides: Non-fumigants
  • Less phytotoxic than fumigants
  • Extremely toxic to humans
  • Most are granular formulations, easier to apply
  • Organophosphates: inhibit acetylcholinesterase, paralyze and kill nematodes; include disulfoton (Disyston), ethoprop (Mocap) and fenamiphos (Nemacur)
  • Carbamates: inhibit acetylcholinesterase, paralyze and kill nematodes; include aldicarb (Temik), carbofuran (Furadan) and oxamyl (Vydate)
  • Ware, G. W. 1994. The Pesticide Book. 4th edition. Thomson Publications, Fresno, California. pp. 79-82, 139-153.