Presentation on theme: "Fungicides and Nematicides Photograph from Jack Bailey. Stephen J. Toth, Jr.Wayne G. Buhler Department of EntomologyDepartment of Horticultural ScienceNorth."— Presentation transcript:
Fungicides and Nematicides Photograph from Jack Bailey. Stephen J. Toth, Jr.Wayne G. Buhler Department of EntomologyDepartment of Horticultural ScienceNorth Carolina State University
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 Brown necrotic lesions on potato foliage caused by air pollution (ozone) Photograph by Gerald Holmes.
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 Diseases Sign - physical evidence of the presence of disease agent (e.g., mold or fungal spores, bacterial ooze) Bacterial ooze on crabapple (fire blight) Green mold on orange (Penicillium) Photographs provided by Turner Sutton.
Fungi 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.
Bacteria 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.
Viruses 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 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 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 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 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 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 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 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: 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 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 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
Nematodes 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.
Nematodes Root knot nematode damage on okra Photographs from NCSU Plant Disease and Insect Clinic.
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 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)
Reference Ware, G. W. 1994. The Pesticide Book. 4th edition. Thomson Publications, Fresno, California. pp. 79-82, 139-153.