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Copyright 2005, Board of Trustees, University
Gulf Coast Research
and Education Center
5007 60th St. E., Bradenton, Florida 34203-9324
W Institute of Food and Agricultural Sciences
..- University of Florida
F s ,
GULF COAST RESEARCH & EDUCATION CENTER
IFAS, UNIVERSITY OF FLORIDA
5007 60th Street East
Bradenton, FL 34203
Bradenton GCREC Research Report BRA1991-24 December
IDM INTEGRATED DISEASE MANAGEMENT
FOR THE GREENHOUSE GROWER
Arthur W. Engelhard1
Ornamental plant production is an intensive and complex type of agriculture
that is prone to use many pesticides (which have their well-publicized
"problems"). An integrated disease management (control) system has many
individual components and only one is pesticides. It functions most efficiently
when the maximum number of input factors is integrated into the total production
system. The components and their roles in disease management and the state of
the art of each is discussed herein.
Plant diseases and biological control. Plant diseases are caused by
microorganisms such as fungi, bacteria, viruses, viroids, mycoplasma-like
organisms (MLO's), etc. There are millions of microorganisms in nature (soil,
air, water); most of them are "good guys," and a few are "bad guys" or pathogens.
The many non-pathogens help keep plant pathogens "in check" most of the time.
Many investigators around the world are looking for biological control
agents, i.e., for specific microorganisms that can be used to economically and
efficiently control plant pathogens and/or diseases. Currently, no products for
broad scale disease control are available for general use in the U.S. However,
researchers at a USDA laboratory found a fungus called Gliocladium virens. The
fungus, when incorporated into the soil, reportedly has activity against
soilborne organisms such as Pythium and Rhizoctonia. It was registered by the
EPA in 1990. A product is being developed jointly by W. R. Grace & Company and
Grace-Sierra Company. If highly effective, the product would solve some of our
most common soilborne disease problems in greenhouses without using chemicals.
The product reportedly will be test marketed in 1992.
Another type of biological control that is gaining momentum is in the area
of special media mixes and composts that have disease (soilborne) control
properties based on the activities of microorganisms. Dr. Harry Hoitink of The
Ohio State University, OARDC, Wooster, OH 44691, has successfully developed mixes
with disease control properties.
1Professor and Plant Pathologist
Although biological control agents for diseases (except crown gall) are
not available, we certainly have many non-chemical control practices that
are equally available to the low budget operation as well as the intensively
managed operation outfitted with the latest computer controlled equipment.
Some of the practices are simple operations or common sense procedures that
often are overlooked.
Soap, water, disinfectant. Using soap and warm water is an excellent
way to reduce contamination on the hands and the potential spread of
pathogens to plants. Washing facilities and disinfectants should be readily
available in strategic locations, and their use be mandatory in potting,
manual seeding and transplant rooms. Signs to remind employees to clean up
should be displayed conspicuously.
Employees should wash hands before starting to work. They could have
worked in their home gardens and could then introduce pathogens into the
work environment. Also, wash after eating, as common pathogens can be on
food items such as tomatoes, cucumbers, peppers, squash and carrots. Do not
use tobacco products, as tobacco can harbor viruses.
Footbaths and equipment baths. Footbaths at strategic locations such
at the entrance to tissue culture labs, propagation houses, stock areas and
ebb and flow systems can help reduce the carrying of soil particles
containing pathogens. Shallow baths for tractors also serve the same
Disposal of diseased plants. We can be our own worst enemy. We
introduce pathogens, spread them around with our work activities, and,
finally, distribute the pathogens around the operation by our diseased plant
disposal methods if we drop leaves, soil, fungi, and bacteria all the way
from the greenhouse to the dumpster. Place diseased plants in plastic bags
at the production site.
SSanitation. Keep the greenhouse as free of pathogens as if it were a
hospital room. Sanitize benches, watering tubes and systems, tools, trays,
pots, and walls. Walks should be of concrete so they can be washed and
sanitized, and not of wood or soil where pathogens can grow and multiply.
Do not allow weeds and algae to grow under and on the benches as they can
Walls of packing houses and cold storage, tables and floors. Certain
microorganisms, especially Botrytis, Alternaria, "molds," and some bacteria
are saprophytic and will grow on many substrates, including walls and wood
in benches and flats. Non-plant surfaces and walls can be sanitized by
spraying with a low volume sprayer.
Inadvertent introduction of diseased plant material. Do not carry
diseased plants, seeds or other propagules into the greenhouse. If this
happens, the tray, the bench, the soil, and the worker are probably all
contaminated and the human element can be an efficient vector for disease.
The worker could have a pathogen on his or her hands and clothes. Always
examine carefully plant material for problems (diseases, also insects and
mites) at a separate location before taking the plants into the greenhouse
or production area. Seeds which harbor pathogens should be treated with
chemicals, bleach, or steam. Careful exclusion of a pathogen prevents a
Rubber gloves and aprons. Pathogens are easily carried on the hands
and under the fingernails (even nematodes). Disposable rubber gloves are
available by the box and can be worn while transplanting, potting, removing
diseased plants, pruning, and in taking cuttings. Sanitizing the hands is
more effective and safer when rubber gloves are worn.
Communication. Signs, group meetings and person to person directions
are important operating procedures. Some suggestions for signs follow:
Wash hands before transplanting, pruning, or seeding
Keep feet off benches and beds
Do not sit on benches
Do not sit or walk on soil mix
Hang up hoses to prevent contamination from water and soilborne
Wash hands after eating (several common pathogens are on tomatoes,
lettuce, cucumbers, squash)
No smoking or other use of tobacco. Tobacco products carry plant
Scouting. Closely examine crops one to three times per week, depending
on the crop and the history of problems. This early warning system helps
identify problems in early stages of development. Control is easier and
losses are reduced through early detection.
Identify the problem accurately. Always identify a problem accurately
and then treat the cause. If we apply chemicals for a misdiagnosed problem,
we can make the problem worse, or depending on the history of treatments, we
can, create a phytotoxicity problem or at the least spend dollars without
benefit'and also potentially harm the environment. High tech kits are
available for identifying Pythium, Phytophthora, and Rhizoctonia pathogens
and others. Some viruses also can be identified using commercial kits.
However, whatever the method of identification, a certain amount of
technical knowledge and information is required. For a persistent,
difficult or complex problem, consult people with technical competency. I
have seen plants with wilting leaves, decay in the crown, and some root rot.
The symptoms resembled diseases caused by Phytophthora, Pythium or
Rhizoctonia (depending on the extent of "infection") but the primary culprit
was fungus gnats, which, incidentally, can spread Pythium.
Cultivar resistance. The use of resistant cultivars is an excellent
disease control method. Drop very disease susceptible cultivars from the
production schedule and, as much as possible, grow those that are resistant.
We recently grew many garden and pot varieties of chrysanthemums and found
that many are resistant to Ascochyta blight and probably would need few or
no foliage sprays for this fungous disease. Knowledgeable growers usually
know their problem cultivars and act accordingly.
Cultural controls. Allow adequate plant spacing so the foliage will
dry rapidly (fungus spores usually need a film of water to germinate and
start disease), use irrigation systems that do not wet the foliage and use
soil mixes with adequate drainage which is not conducive to soilborne
disease development. Also grow plants on raised benches or supports to
protect them from potential contamination from the ground.
Nutrition. Plants should be grown using the best recommended
fertilization practices for the particular crop. Plants that are growing
under less than an optimum nutritional state are more prone to develop
chlorosis and necrosis in leaves and thus, are subject to attack by weak
pathogens or ones that can readily colonize senescent tissues. Botrytis,
Alternaria, Stemphylium, and Colletotrichum, are in the latter category.
Some diseases, such as Fusarium wilt, are less severe when grown at a high
pH (6.5-7.0) than low (5.0-6.0) and, with a nitrate source of nitrogen
(calcium or potassium nitrate) rather than ammonia (ammonium sulfate,
ammonium nitrate). The lime (pH)-nitrate-chemotherapeutant drench system
developed at the University of Florida, Gulf Coast Research and Education
Center, Bradenton, has provided excellent control of Fusarium wilt (Fusarium
oxysporum) on such plants as chrysanthemum, aster, tomato, and probably
would be effective on other crops affected with Fusarium wilt.
High-tech environmental monitoring. Certain diseases caused by fungi
and bacteria, for example the fungus Botrytis cinerea, are dependent on a
water film or free water for spore germination and infection. Equipment can
be installed in greenhouses that monitors environmental factors such as
temperature, humidity and horizontal air flow. Watering, ventilating,
heating and cooling can be synchronized with environmental parameters not
conducive to disease development. Computer controlling these critical
parameters can make disease management more accurate. There are obviously
more technical and local details involved such as local climate, greenhouse
orientation, cloudiness, sunshine, snow, rain, shading, specific crops and
location in the country. Conditions obviously are different in New
Hampshire than in Florida or Ohio or Holland, but progress and success in
disease control are available now, and should be utilized, especially in the
larger, sophisticated operations.
Chemical control. The judicious use and proper application of
fungicides provides an important method of disease control. Foliage
fungicides that are known to provide good disease control are only as good
as the spray coverage. Seldom does spraying over-the-top give disease
control. Moisture is usually more adequate on the lower leaf surface for
pathogen development so good disease control is obtained only with good
spray coverage on both the lower and upper leaf surfaces. Also, soil
drenches with fungicides should only be applied to moist soil as channeling
through a part of the soil may occur when dry soils are drenched. Spraying
soil fungicides on the foliage for the control of Pythium and Phytophthora
root rots needs more research to clearly demonstrate efficacy.
We have used tank-mix combinations for foliage diseases very
successfully since 1974 when our research indicated one-half the labelled
rate of each fungicide in the tank-mix gave control equal to or better than
the full rate of each component. We have added new combinations as new
materials became available. Advantages of the mixtures are that the
spectrum of biological activity is increased with two types of chemicals in
the mix, potential phytotoxicity of a material is reduced because it is used
at half-rate, and the potential for selecting resistant strains of a
pathogen is reduced because of the presence of the second chemical.
Probability of selecting for resistance is further reduced when the tank-
mixes are alternated.
Listed below are some of the tank-mixes that have been used
successfully. Labels should be consulted to determine proper use in a given
area and crop.
benomyl and captain
benomyl and chlorothalonil 2787
benomyl and mancozeb
iprodione 26019 and captain
iprodione 26019 and chlorothalonil 2787
iprodione 26019 and mancozeb
propiconazol and captain 50W
propiconazol and chlorothalonil 2787
propiconazol and mancozeb
Benomyl, one of the most important and useful fungicides we have ever
had, is included even though it has been withdrawn from the ornamentals
market. It is to be hoped that the product will be available again someday.
The Gulf Coast Research and Education Center
The Gulf Coast Research and Education Center is
a unit of the Institute of Food and Agricultural Sci-
ences, University of Florida. The Research Center
originated in the fall of 1925 as the Tomato
Disease Laboratory with the primary objective of
developing control procedures for an epidemic out-
break of nailhead spot of tomato. Research was ex-
panded in subsequent years to include study of sev-
eral other tomato diseases.
In 1937, new research facilities were established
in the town of Manatee, and the Center scope was
enlarged to include horticultural, entomological, and
soil science studies of several vegetable crops. The
ornamental program was a natural addition to the
Center's responsibilities because of the emerging in-
dustry in the area in the early 1940's.
The Center's current location was established in
1965 where a comprehensive research and extension
program on vegetable crops and ornamental plants is
conducted. Three state extension specialists posi-
tions, 16 state research scientists, and two grant
supported scientists from various disciplines of
training participate in all phases of vegetable and
ornamental horticultural programs. This interdisci-
plinary team approach, combining several research
disciplines and a wide range of industry and faculty
contacts, often is more productive than could be ac-
complished with limited investments in independent
The Center's primary mission is to develop new
and expand existing knowledge and technology, and
to disseminate new scientific knowledge in Florida, so
that agriculture remains efficient and economically
The secondary mission of the Center is to assist
the Cooperative Extension Service, IFAS campus
departments, in which Center faculty hold appropri-
ate liaison appointments, and other research centers
in extension, educational training, and cooperative
research programs for the benefit of Florida's pro-
ducers, students, and citizens.
Program areas of emphasis include: (1) genetics,
breeding, and variety development and evaluation;
(2) biological, chemical, and mechanical pest manage-
ment in entomology, plant pathology, nematology,
bacteriology, virology, and weed science; (3) produc-
tion efficiency, culture, management, and counteract-
ing environmental stress; (4) water management and
natural resource protection; (5) post-harvest physiol-
ogy, harvesting, handling and food quality of horti-
cultural crops; (6) technical support and assistance to
the Florida Cooperative Extension Service; and (7)
advancement offundamental knowledge of disciplines
represented by faculty and (8) directing graduate
student training and teaching special undergraduate
l The Institute of Food and Agricultural Sciences,
University of Florida.
L A statewide organization dedicated to teaching,
research and extension.
D Faculty located in Gainesville and at 13 research
and education centers, 67 county extension
offices and four demonstration units throughout
SA partnership in food and agriculture, and natural
and renewable resource research and education,
funded by state, federal and local government,
and by gifts and grants from individuals, founda-
tions, government and industry.
0 An organization whose mission is:
Educating students in the food, agricultural,
and related sciences and natural resources.
Strengthening Florida's diverse food and
agricultural industry and its environment
Enhancing for all Floridians, the application
of research and knowledge to improve the
quality of life statewide through IFAS exten-