\m 25 8 93 2 1 'Characteristics of Plant Disease' \m 26 9 6 2 2 'Introduction' \m 75 31 37 3 2 'What is a Plant Disease?' \m 89 36 69 3 2 'What Causes Plant Disease?' \m 162 71 44 4 2 'How Are Living Agents That Cause Plant Diseases Dispersed?' \m 189 81 86 5 2 'How Do Pathogens Enter a Plant?' \m 215 92 103 5 2 'What is Necessary for Plant Disease to Occur?' \m 227 96 120 5 2 'How Can These Agents Cause Disease?' \m 241 102 62 6 2 'How Do We Control Plant Diseases?' \m 346 152 50 8 1 'Submitting Samples to the Florida Plant Disease Clinic' \m 388 171 82 9 2 'Guidelines for Submitting Samples' \m 522 216 45 12 1 'Active Plant Pathologists in Florida' \t'September 1987' 'I-' \a Dr. Tom Kucharek, Extension Plant Pathologist \a \a GENERAL PLANT PATHOLOGY Dr. Tom Kucharek, Extension Plant Pathologist GENERAL PLANT PATHOLOGY \h 1 'Characteristics of Plant Disease' \h 2 'Introduction' CHARACTERISTICS OF PLANT DISEASE Introduction Plant diseases continue to have identifiable impacts. The southern corn leaf blight epidemic of 1970 cost Florida growers at least $5,000,000. Blue mold, a long forgotten disease of tobacco in the plant bed, suddenly became epidemic in the field during 1979 in the U.S.A. and Canada. Continued epidemics occurred in 1980 and 1983. Controls for these diseases have been effective but expensive. Many Irish descendants in this country are here because a disease called potato late blight starved their forefathers out of Ireland in the mid 1800's. Soybean stem canker was epidemic in 1983. Virus diseases have caused total destruction of watermelon and squash plantings. Recently, tomato spotted wilt virus has been found in Florida on tomatoes, peanuts, tobacco and gladiolus. The citrus industry in Florida was tasked in the early 1900's and again recently by citrus canker, a disease caused by a bacterium. Stringent quarantines and the eradication of millions of citrus trees were used for control of citrus canker. Other diseases that are typically less newsworthy than the above-mentioned diseases occur commonly. Diseases such as peanut leafspot, bacterial spot of tomatoes and peppers, blackrot of cabbage, pythium root rots of turf grasses and rhizoctonia stem rots are but a few diseases that occur each year in Florida. Control of these diseases is achievable when growers use production techniques that are proven to be effective and within the economical limitations of the crop. With ornamental and forest trees successful curtailment of plant diseases has been limited. This appears to be related to the minimum value placed on the crop and the difficulty in establishing extensive interagency and public cooperation to minimize disease spread at an early date. Successes are over- shadowed by ravaging epidemics that denude our environment of majestic flora. The American chestnut tree, for practical purposes, been eliminated from this country because of a fungus disease called chestnut blight. At the present time, the dreaded Dutch elm disease continues to scourge the country. Lethal yellowing of coconut palms has changed the "tree line" of south Florida. Control of plant diseases requires extensive efforts in some situations and minor adjustments in other situations. Dr. E. C. Stakman wrote decades ago that, "plant diseases are shifty enemies." Those of us that recognize the practical implications of this statement must direct our plant disease control strategy by using a common understanding and language. The science of plant pathology is charged with the opportunity to reduce the impact from plant diseases. \b\v \v \v \h 2 'What is a Plant Disease?' What is a Plant Disease? A plant is diseased when its chemistry or structure has been submitted to an abnormal, sustained alteration. This definition, although vague, is useable. It tells us that a leaf pulled off a tree is not a disease but instead an injury because the alteration is not continuous. A fungus, bacterium or virus, on the other hand, enters a plant and continues to deprive the plant of nourishment or continuously alters normal functions of the plant. The lack of a nutrient over a period of time likewise causes a continuous dysfunction resulting in undesirable symptoms. \h 2 'What Causes Plant Disease?' What Causes Plant Disease? Plant diseases are caused by either non-living or living agents. Non-living agents include low temperatures, high temperatures, atmospheric impurities, mineral deficiencies, mineral excesses, or possibly other causes. The living agents that cause plant diseases are fungi, bacteria, a few higher plants, nematodes, algae, viruses, mycoplasmas, and viroids. FUNGI are plants that lack chlorophyll, stems, leaves, and roots. Their vegetative body is made up of microscopic, tubular structures called hyphae or amoeboid structures called plasmodia. Fungi are further characterized by the production of microscopic "seeds" called spores. A spore of Helminthosporium maydis, the causal agent of southern corn leaf blight, is approximately 1/250 of an inch long. Fungi produce different types of spores. Some spores are suitable for wind or water dissemination while others have thick walls, thereby being adapted for survival in soil or other concealed places for many years. Some spores serve as carriers of genetic traits for sexual reproduction. Many fungi can live as saprophytes in the soil or decaying plant litter as well as being parasitic. Fungi that can grow saprophytically on old crop debris and soil usually can be grown as a culture on a growth medium in the laboratory. Some fungi, however, such as rusts, downy mildews and powdery mildews, are obligate parasites, that is, they normally grow only in a plant. Certain rusts have been cultured in a laboratory. Some fungi produce microscopic or macroscopic modified hyphal aggregates called sclerotia which serve as survival structures. BACTERIA are microscopic, one-celled organisms which increase by division of cells. Some bacteria, under favorable conditions, can divide every 20 minutes. In 24 hours this could result in 300 billion new individuals. A typical bacterium is 1/12,500 of an inch long. Bacteria can be grown as cultures in a laboratory. Bacteria survive on host plants, susceptible weeds, and organic debris in soil. Within the last 15 years a group of bacteria that are limited to xylem tissues of plants were identified as causing plant diseases. At first they were thought to be rickettsia and then called rickettsia-like bacteria, but now they are considered to be xylem limited bacteria. They tend to be smaller than other bacteria causing plant diseases and some are culturable in the laboratory. They are transmitted by leafhoppers and can be graft transmitted. Pierces disease of grape and phony peach are caused by xylem limited bacteria. \bVIRUSES are particles made up of a nucleic acid core and a protein coat. No cellular structure is present although some may be enclosed by a membrane. Viruses reproduce in living cells of susceptible host plants. Virus particles are not visible with light microscopes; an electron microscope is used to reveal their structure. A typical tobacco mosaic virus particle is 1/80,000 of an inch long. Viruses are obligate parasites. VIROIDS are low molecular weight nucleic acids that have been associated with certain plant diseases. Viroids are similar to a virus but lack a protein encapsulation. Viroids causing plant diseases contain RNA only and, therefore, are the smallest known infectious agents causing plant diseases. Avocado sunblotch, citrus exocortis, and chrysanthemum stunt are either caused by or associated with viroids. ALGAE resemble fungi in size and structure but differ primarily by the presence of chlorophyll in algae and the absence of chlorophyll in fungi. Algae have unicellular, colonial, and filamentous species. A few are parasitic on plants grown in subtropical or tropical environments. Tropical fruit trees such as mango, avocado, and citrus are infected by red algae. MYCOPLASMA have a cellular-like structure (elementary body) without a true cell wall. They contain protein, DNA, RNA, and enzymes. The elementary bodies vary in shape and size; some are 1/2,500 of an inch long and others are 1/10 that size. Also, mycoplasma are sensitive to heat and some antibiotics. Many plant diseases, previously thought to be caused by viruses, transmitted by leafhoppers and in the "yellows" group, are now known to be caused by mycoplasmas, not viruses. Corn stunt spiroplasma is a mycoplasmal disease. \h 2 'How Are Living Agents That Cause Plant Diseases Dispersed?' How Are Living Agents That Cause Plant Diseases Dispersed? FUNGI have hyphae or plasmodia which grow on or in the soil or within host tissue. Fungi also have spores which may be spread by wind, insects, rain, or irrigation water. Some spores have flagella (tails) which allow them to swim in farm ponds, rain water, dew, or soil moisture. Fungi also spread when infected plants (including seed) are moved from one location to another. Similarly, fungi may be carried on tractor or maintenance implements, or people working within the planting. BACTERIA are spread by insects, irrigation water, rain, movement of infected plants, seeds, seed pieces, grafting, and farm equipment. VIRUSES are spread by mechanical rubbing of one infected plant on another, insects, fungi, nematodes, transporting of infected plants from one location to another, seeds, seed pieces, grafting, dodder, farm equipment, and man's hands. Each virus may be spread by certain methods; for example, many legume viruses are spread by seed and aphids but not by fungi or nematodes. MYCOPLASMA are dispersed by leafhoppers or moving infected plants. VIROIDS are spread by implements, pruning tools, or other mechanical devices. \b\v \v \v \h 2 'How Do Pathogens Enter a Plant?' How Do Pathogens Enter a Plant? FUNGUS spores germinate, form a germ tube, and then from the germ tube an infection peg is formed which penetrates directly through the cuticle or stomata of a leaf. Infection of roots and stems occurs either by germ tubes formed from spores or hyphae that penetrate the tissue. Fungi can also infect plant parts when wounds are made by harvesting, farm implements, hail, wind, blowing sand, insects, nematodes, or other fungi. BACTERIA enter plants through wounds or natural plant openings such as stomata, lenticels, or hydathodes. When plant tissue is gorged with water, bacterial ingress into plant tissue increases. VIRUSES can enter a plant through wounds. Also, aphids transmit many of the viruses that occur in Florida. Other insect-types are known to transmit viruses. Tomato spotted wilt virus is vectored by thrips. When an insect feeds on a plant, the virus passes from the insect into the plant or the insect acquires the virus from the plant. Some nematodes transmit viruses by piercing the root which can result in the passing of the virus particle from the nematode into the host plant. Corky ringspot virus in potato is transmitted by certain nematodes. Fungi are vectors for certain viruses. Soilborne wheat mosaic virus is transmitted by a soil-inhabiting root fungus. \h 2 'What is Necessary for Plant Disease to Occur?' What is Necessary for Plant Disease to Occur? A susceptible plant, an agent causing the disease, and a suitable environment are all necessary for disease to occur. For example, fungi that cause leafspots need a susceptible host, moist conditions on the leaves, and favorable temperatures so that spores will germinate. Many root rotting fungi need a susceptible host coupled with high soil moisture or a soil pH favorable for fungus growth. \h 2 'How Can These Agents Cause Disease?' How Can These Agents Cause Disease? Disease is caused by the agent impairing necessary functions of the plants. Some diseases block water conducting vessels in the plant which results in a wilted condition similar to drought. Root rots destroy the roots that absorb water and nutrients from the soil. Leaf spotting diseases reduce photosynthesis in the plant which results in less food manufactured by the plant. Seeds, seed pieces, fruits, and flowers may be destroyed by rots or blights. Diseases of this type reduce the reproductive ability of a plant, and in the case of ornamentals, the disease is unsightly. \b\v \v \v \h 2 'How Do We Control Plant Diseases?' How Do We Control Plant Diseases? The most important point in controlling a plant disease is choosing the best control method or series of control methods for a given situation. The best control method for disease on one type of a plant may not be the best method for another disease on the same or different plant species. Also, the use of more than one control measure (systems control) is often needed. We try to control a plant disease by finding that part of the life cycle of a living pathogen that will succumb to available control methods and utilize the control methods early in relation to pathogen propagation. Once the pathogen increases in numbers, usually accompanied by an increase in disease, disease control becomes difficult. Most plant disease control methods are preventative. Some eradicative techniques are available but should not be relied upon for consistent control. Diseases caused by non-living agents are often controlled by simply adding fertilizer, avoiding excess amounts of fertilizer, controlling an air pollution source, or protecting plants from the adversities of the weather. Plants affected by non-living agents are often more susceptible to living agents. Diseases caused by living agents are controlled by different methods. For some diseases, resistant varieties are the best means of control. The use of resistant varieties is not new. Rust resistance in wheat was in use at the very beginning of this century. Since that time, resistance to many diseases has been found and used. New tomato varieties in Florida were bred for mechanical harvesting and resistance to Fusarium wilt, gray leaf spot, and other disorders. Eradication and exclusion have been effective for controlling several diseases. Exclusion of disease is one of the purposes of quarantines. For example, some orchid diseases have been stopped from entering this country by the quarantine service. Lettuce mosaic virus has been controlled by indexing seed lots; those seed lots which contain virus-contaminated seed cannot be planted in Florida. Citrus canker in Florida was controlled in the early 1900's by both exclusion and eradication. Eradication of disease may be done by other means also. For example, we can attempt to eradicate or reduce a disease by removing other species of plants that are also hosts of the disease. These plants may be weeds or alternate hosts. Alternate hosts support part of the life cycle of the organism causing disease. Roguing and destroying diseased plants of the species we are growing can also be used in controlling plant disease. Surgery of plants can be used to control plant diseases. For example, a bacterial disease of woody plants called fire blight can be reduced by remov- ing and destroying infected branches. Sanitation around propagating beds, greenhouses, and fields is an excellent control measure. Routinely clean and disinfest potting benches, soil bins, and greenhouse benches. Disinfest tools and equipment, especially if they have been used in areas with diseased plants or general debris. After using tractors and implements in a field known to have a soilborne disease \bsuch as black shank of tobacco, steam sterilize implements or at least wash off the soil from the tires and implements before using that tractor in other fields. This practice reduces the possibility of carrying the fungus to a healthy field. Using a tractor in the non-infested field first is a good idea. Destroy old plant debris as it can harbor diseases. Wash your hands and forearms thoroughly after handling diseased plants. Crop rotation is another method whereby we can reduce disease incidence. Crop rotation is done by alternating a given crop with non-susceptible crops. For example, peanuts planted in a field the year after soybeans were grown or vice versa is a poor rotation as both are susceptible to southern stem rot caused by Sclerotium rolfsii. In general, grass crops rotated with non-grass crops is a good rotation plan. However, the rotation of two non-grass crops like cotton and peanuts may be best because root knot nematodes that infect peanuts will not infect cotton. Crop rotation is of little value for controlling obligate parasites that produce wind blown spores such as rusts, downy mildew, and powdery mildews. Double cropping within a one-year period is not considered as crop rotation. The selection of disease-free stock is another good control measure. This includes not only healthy ornamental plants but also healthy transplants for such crops as tobacco, tomatoes, peppers, strawberries, and fruit trees. The difference between profit and an economic set-back may depend on attaining healthy stock. Disease-free seed follows this same principle of control. Viral and bacterial diseases of peas and beans can be minimized if the buyer insists on purchasing seed produced in the western parts of the United States. Lettuce mosaic virus has been effectively controlled by growers and regulatory personnel cooperating in seed-indexing programs. Control of insects and nematodes often reduce disease when a disease causing organism is partly or wholly dependent upon these organisms. Insects and nematodes not only act as vectors, carriers of disease, but also their damage can provide an entrance point for disease-causing organisms. Weed control is beneficial for disease control; weeds can harbor inoculum, interfere with spray deposition, reduce plant vigor, and reduce aeration within crop canopies. Finally, timely applications of chemicals are used to control many plant diseases. The most important consideration when spraying fungicides is to have the fungicide on the plant before infection takes place; most fungicides are protectants not eradicants. Recently, therapeutic fungicides have been developed. Use chemicals with non-chemical control methods to maximize efficacy of chemicals. USE FUNGICIDES WITH CAUTION NOT FEAR. READ THE ENTIRE LABEL AND FOLLOW THE DIRECTIONS. USE ONLY APPROVED FUNGICIDES ON A GIVEN CROP. STORE FUNGICIDES IN A COOL DRY PLACE. STORE AND TRANSPORT FUNGICIDES IN SUCH A MANNER THAT CHILDREN OR UNAUTHORIZED PERSONS ARE DENIED ACCESS. \b\v \v \v \v \h 1 'Submitting Samples to the Florida Plant Disease Clinic' SUBMITTING SAMPLES TO THE FLORIDA PLANT DISEASE CLINIC (FPDC) AND INTERPRETATION OF RESULTS When a plant sample is received at the Florida Plant Disease Clinic (FPDC), it is given a number and recorded. Each sample is processed on an individual and first come, first serve basis. Diagnostic protocol begins with a visual observation of symptoms to determine what further clinical procedures, if any, are needed to associate pathogens with the dysfunction. Some samples can be diagnosed visually or with a microscope without culturing. Some samples must be re-moistened for a period of time to encourage signs of pathogens. Some samples are dissected and placed on various culture media to determine what pertinent organisms might be present. The interval of time necessary to associate pathogens with a dysfunction varies; but currently, most samples are processed through the laboratory in seven days or less. Certain samples must be submitted through more time consuming procedures, and the "turn around time" is longer. A fast turn around time, by itself, is not indicative of a diagnostician's prowess. We are aware of the urgency in responding to the county agent as early diagnosis coupled with early initiation of plant disease control procedures is a sound principle. Results are sent to the county agent who submitted the sample or who is responsible for the sample should the sample be submitted out of protocol. University researchers who submit samples receive the results directly and such is available to county extension staff at their request. University Extension Specialists who submit samples should fill out the diagnostic form, like everyone else, and indicate from where the sample originated so that the sample can be processed. Results from the FPDC demonstrate an association of symptoms and signs with dysfunctions. A cause-effect relationship is not intended for all samples. Recipients of our results should be cognizant of other variables that might also be associated with the dysfunction at hand. The response you receive about a sample may or may not include control information. Often the control for the disease may be lengthy and complex. Many Plant Protection Pointers, fact sheets plus the Plant Disease Control Guide contain the necessary control information. \b\v \v \v \h 2 'Guidelines for Submitting Samples' Guidelines for Submitting Samples In order to facilitate better diagnosis, the following guidelines should be utilized by those who submit samples: Adequate Samples: If a client brings an inadequate (dried, mush, etc.) sample to the county agent, the county agent should tell the client that should the FPDC receive such, it will be discarded and answered as an inadequate sample. Collecting Pertinent Information About a Specific Situation: Complete the form. Diagnosis of plant diseases is done with laboratory facilities coupled with pertinent information about the history and distribution of the problem. This information should include the kind and variety of plant, prevalence of problem, severity of problem, location (garden, backyard, commercial planting, greenhouse, etc.), cropping history, fertilization, pest control measures, etc. County agents are encouraged to present their evaluations about the problem. Often the grower is hesitant to give information about his practices for fear of embarassment; but, if he is informed that time and money can be saved, this important information may be relinquished. Sample Aquisition: Annual row crops (vegetable and agronomic) (1) Dig the entire plant from the soil. Also, see no. 7 in this section regarding large samples. (2) Shake off or wash off the soil from the root system. This reduces post- age rates and secretary burn out. Also, we do not test soil for the presence or absence of pathogens. Results of such soil tests are unreliable. (3) Wrap entire root system in wet newspaper, toweling, etc. Place wrapped root system within a plastic bag and secure with a rubber band, twister, etc. (4) Place plant with wrapped root system into a paper or plastic bag. Use a paper bag if soft rotted tissue is evident. (5) Send plants that are partially diseased, not those that are totally decomposed. Sending plants displaying various symptoms is advantageous. (6) Where fruit symptoms seem to be of concern by the grower, no root or shoot system need be sent unless those plant parts are also displaying abnormal symptoms. (7) Where the disorder is clearly a leaf spot disease on large samples, submit leaves attached to part of the stem and wrap cut part of stem in wet wrap as described above for root system. \b\v \v \v Woody ornamental and fruit tree branch diebacks (1) Grower should prune out and destroy dead branches. It is not necessary to send a sample of dieback unless it reoccurs after pruning dead wood. We can always isolate fungi from dead wood. Use disease control programs for the crop at hand. (See Plant Protection Pointer No. 21) (2) Submit dieback samples if dieback reoccurs making sure that some water or fertilizer relationship is not the origin of the problem. Also, submit a portion of the root system from the plant in question and the lower stem if it can be acquired. (3) Cankers from tree and shrub specimens should include branch tips with leaves and 3-5 branches 1/4 to 1/2 inch in diameter and at least 6 to 8 inches long. Turf Samples Turf samples should include a 3 to 5 inch diameter sod piece with some soil clinging to the root system. The depth of the plug need not be more than 3 to 4 inches. Dried and fried turf samples will not be processed. Acquire samples displaying intermediate symptoms. Fruit Samples Fruit samples should be submitted according to row crop guidelines if from a vegetable crop. Fruit that display wet rot and foul aromas should not be sent. Instead, locate early symptoms of this disorder and submit fruit with early symptoms. Fruits with a disorder may also have the same problem with different symptoms on leaves and branches. Submit suspect foliage and branch tissue with the fruit. Often such foliage and branch tissue will be above or near the fruit. Fruit and tuber samples should be individually wrapped in newspaper. Miscellaneous (1) Large leaves with leaf spots may be placed in plastic bags for shipment. (2) Tobacco leaves sent to the clinic for virus analysis have arrived in good condition when slightly moistened, pressed together, and placed in a plastic bag. Pepper, tomato, and other specimens for virus analysis should include entire plant packed as mentioned in Annual Row Crops (Vegetables and Agronomic Crops) above. (3) REFRIGERATE THE SAMPLES OVERNIGHT if you cannot send them until the next day. Pack in a container which is strong enough to withstand crushing in transit. \b\v \v \v Important reminders (1) A special note is needed for samples (especially tobacco and vegetables) where a virus disease is suspected. Our techniques require fresh specimens; dried up specimens cannot be diagnosed for virus. Also, leaves or plants of such specimens sent to the clinic should include young and old leaves. (2) REMEMBER, WHEN YOU MAKE PHONE CALLS INQUIRING ABOUT A SAMPLE YOU SENT, WE MUST TAKE TIME AWAY FROM OUR WORK FLOW. ALL WE MAY BE ABLE TO OFFER IS A PARTIAL ANSWER AT THAT TIME. PARTIAL ANSWERS HAVE BEEN MISLEADING TO GROWERS WHEN THE FINAL RESULT HAD MORE PERTINENT INFORMATION. (3) GOOD QUALITY SPECIMENS ARE REQUIRED FOR DIAGNOSIS! \b\v \v \v \v \h 1 'Active Plant Pathologists in Florida' ACTIVE PUBLIC PLANT PATHOLOGISTS IN FLORIDA S. A. Alfieri Division of Plant Industry Gainesville Ed Barnard Division of Plant Industry Gainesville Jerry Bartz Plant Pathology Department Gainesville Richard Berger Plant Pathology Department Gainesville George Blakeslee School of Forestry Gainesville Ron Brlansky Citrus Research and Education Center Lake Alfred Carlos Blasquez Citrus Research and Education Center Lake Alfred G. Eldon Brown Citrus Research and Education Center Lake Alfred Larry Brown Division of Plant Industry Gainesville Raghavan Charudattan Plant Pathology Department Gainesville Ann Chase Agricultural Research and Education Center Apopka Jim Crall Agricultural Research and Education Center Leesburg \b\v Lawrence Datnoff (Extension Appointment) Everglades Research and Education Center Belle Glade Mike Davis Ft. Lauderdale Research and Education Center Ft. Lauderdale Jack Dean United States Department of Agriculture Canal Point Kenneth S. Derrick Citrus Research and Education Center Lake Alfred Art Englehard Gulf Coast Research and Education Center Bradenton Ed Freeman (Extension Appointment) Plant Pathology Department Gainesville Bill French Agricultural Research and Education Center Monticello Dean W. Gabriel Plant Pathology Department Gainesville Steve Garnsey United States Department of Agriculture Orlando Tim R. Gottwald United States Department of Agriculture Orlando Nigel A. Harrison Ft. Lauderdale Research and Education Center Ft. Lauderdale Ernest Hiebert Plant Pathology Department Gainesville Don Hopkins Agricultural Research and Education Center Leesburg Charles Howard Agricultural Research and Education Center Dover \b\v Jeff Jones Gulf Coast Research and Education Center Bradenton John P. Jones Gulf Coast Research and Education Center Bradenton Monica Juhnke (Extension Appointment) Ft. Lauderdale Research and Education Center Ft. Lauderdale Jim Kimbrough (Extension Appointment) Plant Pathology Department Gainesville Harold C. Kistler Plant Pathology Department Gainesville Tom Kucharek (Extension Appointment) Plant Pathology Department Gainesville Richard Lee Citrus Research and Education Center Lake Alfred David Loschke Plant Pathology Department Gainesville H.H. Luke United States Department of Agriculture Gainesville Frank Martin Plant Pathology Department Gainesville R.T. McMillan Tropical Research and Education Center Homestead Jack McRitchie Division of Plant Industry Gainesville John Miller Division of Plant Industry Gainesville Dave Mitchell Plant Pathology Department Gainesville \b\v Mike Moss Tropical Research and Education Center Homestead Stan Nemec United States Department of Agriculture Orlando Charles Niblett (Extension Appointment) Plant Pathology Department Gainesville Randy C. Ploetz Tropical Research and Education Center Homestead Kenneth Pohronezny (Extension Appointment) Tropical Research and Education Center Homestead Daryl Pring United States Department of Agriculture Gainesville Dan Purcifull Plant Pathology Department Gainesville L. Hank Purdy Plant Pathology Department Gainesville Richard Raid (Extension Appointment) Everglades Research and Education Center Belle Glade Dan Roberts Plant Pathology Department Gainesville Norm C. Schenck Plant Pathology Department Gainesville Robert Schmidt School of Forestry Gainesville Tim Schubert Division of Plant Industry Gainesville Fred Shokes North Florida Research and Education Center Quincy \b\v Gary W. Simone (Extension Appointment) Plant Pathology Department Gainesville Ron Sonoda Agricultural Research and Education Center Ft. Pierce Don Spalding United States Department of Agriculture Miami Bob Stall Plant Pathology Department Gainesville Jim Strandberg Agricultural Research and Education Center Sanford James Tammen Progress Center Gainesville L. W. Timmer Citrus Research and Education Center Lake Alfred Roger Webb (Extension Appointment) School of Forestry Gainesville D. Pete Weingartner Agricultural Research and Education Center Hastings Jack Whiteside Citrus Research and Education Center Lake Alfred Bill Zettler Plant Pathology Department Gainesville Retired: R.S. Mullin Case Weilberg Bob Marlatt Al Cook Howard Miller Ernie Ducharme Phares Decker R.W. Hanks Carter Seymour Bob Magie Mortimer Cohen H.H. Luke John Darby Al Feldman