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Group Title: Research Report - University of Florida Agricultural Research and Education Center ; BRA1982-21
Title: Poinsettia diseases and their control
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Title: Poinsettia diseases and their control
Series Title: Research Report - University of Florida Agricultural Research and Education Center ; BRA1982-21
Physical Description: Book
Language: English
Creator: Engelhard, Arthur W.
Publisher: Agricultural Research & Education Center, IFAS, University of Florida
Publication Date: 1982
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HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida





Agricultural Research & Education Center
IFAS, University of Florida
5007-GOth Street East
Dradenton, Florida 33508-9324
Bradenton AREC Research Report BRA1982-21 November 1982

POINSETTIA DISEASES AND THEIR CONTROL

Arthur W. Engelhard1
PAGE
PLANT DISEASE 2
DISEASE MANAGEMENT 2
FUNDAMENTALS OF PLANT DISEASE CONTROL 3
Prevention Protection 3
Envi ronmental Control 3
Chemical Control 3
Sanitation 4
Eradication 5
Exclusion 5
Resistance 5
DISEASES CAUSED BY FUNGI 5
Phytophthora Crown and Stem Rot (Phytophthora parasitica) 5
Pythium Root and Stem Rot (Pythium spp.) 6
Rhizoctonia Root and Stem Rot (Rhizoctonia solani) 6
Botrytis Blight or Gray Hold (Botrytis cinerea) 6
Scab (Sphaceloma poinsettia) 6
Black Root Rot (Thielaviopsis basicola) 7
Rhizopus Rot (Rhizopus sp.) 7
Minor Fungus Diseases 7
DISEASES CAUSED BY BACTERIA 7
Bacterial Canker or Blight (Corynebacterium flaccumfaciens pv..
poinsettia) 7
Bacterial Leaf Spot (Xanthomonas campestris pv. poinsettiicola) 8
Bacterial Soft Rot (Erwinia carotovora pv. carotovora) 8
Greasy Canker (Pseudomonas viridaflava) 8
Crown Gall (Agrobacterium tumefaciens) 9
DISEASES CAUSED BY VIRUSES 9
Poinsettia Mosaic Virus and Poinsettia Cryptic Virus 9
DISEASES CAUSED BY NEMATODES AND ALGAE 9
Root Knot Nematode (Meloidogyne spp.) 9
Algal Blight (Cephaleuras sp.) 9
SELECTED REFERENCES 9
TABLES
Table 1 Disinfectants and treatments for pots, benches,
equipment and media 11
Table 2 Fungicides that control soilborne diseases of Poinsettia 12
Table 3 Fungicides that control foliage and flower diseases of
Poinsettia 13
1Professor of Plant Pathology





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POINSETTIA DISEASES AND THEIR CONTROL
Much of peninsular Florida has a mild, subtropical climate In which poinsettia
pot plants are produced commercially outdoors, in semi-covered structures, and in
greenhouses for the Christmas season. Poinsettias also are grown in south Florida
as outdoor landscape plants.
The commercial poinsettia production season generally begins around May when
cuttings are obtained from specialist-propagators who concentrate on producing
healthy plant material. The cuttings are grown into stock plants from which further
cuttings are taken. Other growers purchase plant material unrootedd, callused, or
rooted cuttings) that will be grown and sold as flowering plants for the Christmas
season. The production period includes the hot, rainy, summer months (June to
October), followed by cooler, dry months from October through December. The plants,
therefore, are exposed to a wide range of environmental conditions and consequently,
to a wide range of pathogens endemically destructive in the prevailing climate.
Because of this maximum potential for host exposure and pathogen development pro-
ducers must practice the best principles of sanitation, disease prevention, and
total disease control to produce high quality plants.
PLANT DISEASE
Plant disease can be caused by a variety of pathogenic organisms which can be
classed as fungi, bacteria, viruses and nematodes and also by lesser known types
including richettsias, mycoplasma-like organisms and viroids. Another classification
scheme includes the physiological diseases which include nutritional excesses,
deficiencies, and imbalances. ::
Plant nutrition is important in the overall plant diesease.management program.
The course of disease development may be affected by level of nutrition. Also,
symptoms on plants subjected to nutritional excesses, ,deficiencies or imbalances
may overlap those caused by pathogens. A total disease management program requires
that plants should be grown under an optimal nutritional regime.
Disease develops when a susceptible part of a plant (host) and a pathogen come
together in an environment favorable for the pathogen to infect the plant. A
disease-damaged plant cannot be restored to its original condition.. Rotted roots
are gone; only new ones.grow. Holes in leaves do not'fill in."' Diseased plant
parts rarely are restored to their original :growth and vigor by control: measures.
Disease control after diseased plants are present generally is a matter of preven-
ting additional plant damage and preventing new infections. Obviously, the best
procedure is to prevent pathogens from being introduced or from becoming established
in the nursery.
DISEASE MANAGEMENT
Disease control is obtained by integrating into the overall management plan
certain procedures and practices which eliminate or reduce the chances of intro-
ducing pathogens into the operation and which keep the damages and losses to a
minimum should plant disease develop. An important aspect of the disease manage-
ment program is to scout (observe) regularly the crops to detect at an early
stage any plant problems that may be developing. After detecting disease, accurate
diagnosis at an early stage is extremely important, so the best control procedures
can be initiated against the target pathogen.
Following are the fundamentals or basics of plant.disease control.






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FUNDAMENTALS OF PLANT DISEASE CONTROL
PREVENTIONN PROTECTION
Environmental. When a pathogen and susceptible host are together, a disease
develops only when the environment in the greenhouse, outdoors or in the soil meets
the necessary requirements for penetration, infection and disease development. For
example, black root rot (Thielaviopsis) is favored by temperatures in the 60's,
by excessively wet soil andby high soil. pH. This disease is not a serious problem
in Florida because of our high temperatures and acid growing media. Gray mold
disease (BotXtis) is a constant problem especially when bracts and flowers are
developing. It develops under conditions of high relative humidity and moisture.
Greenhouse operators can use their ventilating and heating systems to control
relative humidity and temperature. Water condensation occurs on leaves as the
temperature drops and the relative humidity rises after sundown (warm air has the
capacity to hold more water than cold air). To avoid this, greenhouse operators
open the vents and turn on exhaust fans to make one exchange of air. This removes
moisture-laden air and reduces the relative humidity in the greenhouse below the
condensation point. Enough heat needs to be added to maintain the inside temperature
above the outside temperature. Pythium root rot can be reduced by keeping the
soil moisture adequate:but low, as opposed to excessively wet.. Overhead watering
encourages and/or spreads foliar diseases by maintaining excessive moisture on the
leaves and flowers (most spores need free water to develop). If there are no
suitable alternatives to overhead watering, every effort should be made to water
early in the day so the leaves dry rapidly. Creating an unfavorable environment
for the pathogen and.minimizing the potential for introducing the pathogen are
excel lent management'tools for controlling disease.
Chemical control. One of the fundamental principals of plant disease control
is to prevent disease. If pathogens are never introduced, theoretically, no
disease develops. However, in spite of man's best efforts, nature does prevail at
times. For such occurrences, preventive soil and foliage pesticide (drench, spray,
dust and fumigation) programs are used. These are minimal programs designed to have
disease control' chemicals constantly present at susceptible sites (leaves, roots,
etc.) so if a pathogen is inadvertently introduced, control is effected. For
example, because of the everpresent threat of having Pythium, Phytophthora or
Rhizoctonia damage, the plants should be drenched wit effective chemicals at
potting time and at appropriate intervals thereafter, if necessary. If scouting
the crop reveals no disease, future applications may not be needed. Similarly,
foliage spray applications are made during critical periods to control pathogens
"in season". The spray must be applied to give uniform and complete coverage of
foliar parts. If an airborne spore lands on the sprayed leaf, germination is
inhibited and no disease develops. The fungicide acts as a protectant, preventing
infection from occurring. Obviously, to be successful, such a program must be
started before disease occurs. Such programs utilize lower rates and less frequent
applications than those used to "catch up" after a serious disease outbreak occurs.
Chemicals are one of the best tools available for disease control. However,
they always should be used in concert with other disease control methods in an
overall disease management program. If sanitation procedures or soil sterilization
and/or pasteurization, for example, are not used and much disease develops, then
even an overuse of chemicals cannot be expected to create miracle disease control.
Damage is permanent. Plants usually do not regain what they lost to disease, nor
can the dollar loss be recouped. Therefore the grower should practice preventive
disease control.
If disease occurs, it is absolutely necessary to diagnose accurately the








problem, preferably before fungicidal therapy is attempted. No single fungicide
will control all diseases. Some are specific in their control of only one disease,
while others have broader spectrums of activity. Accurate diagnosis is important
so the best control with the "most muscle" can be used. Accurate diagnosis can
save much time and money because some diseases cannot be chemically controlled.
Occasionally the use of the wrong chemical or procedure could aggravate the problem,
or an infectious disease may not even be at fault. .
Fungicides to be used for disease control are listed in Tables 2 and 3.
Labels should be read carefully before chemicals are used. It is the user's
responsibility to follow the labeled instructions.
Sanitation. Old plant parts, trash piles and weeds provide food sources where
plant pathogens can grow and produce inoculum to infect other plants. A constant
clean-up program should be in force all the time in the greenhouse or production
areas. Sanitation and subsequent disease control involve common sense measures
that we often forget to apply. Hoze nozzles should be kept off the ground to
prevent contamination and spread of plant pathogens through watering systems. Hands
should be washed with soap and water before working with plants or handling steri-
lized potting soil or clean stock. Also, hands should be washed and rinsed in
disinfectant after handling diseased plants. Feet should be kept off benches
and dirty hands and fingers should:be kept out of soil in pots. Trash piles where
inoculum can be produced and then blown or washed away or be carried by insects
to plants should not exist.
The majority of diseases of floricultural plants in greenhouses are caused by
soilborne plant pathogens. Growers often inadvertently introduce soilborne plant
pathogens into pathogen-free soil. This results in serious plant losses. The
following steps are suggested to prevent this problem:
1) Do not dump sterilized soil on dirty floors or potting benches or into
non-sterilized benches, flats, pots or other containers. Disinfect floors
or potting benches or put down new plastic sheeting or even clean, unused
newspapers. Disinfect benches, flats, pots and other containers before
using.
2) Do not handle sterilized soil with dirty hands, shovels, trowels and other
equipment, especially in the morning (an employee might have worked in
his garden before work). Wash hands first. Use only disinfected shovels
or trowels, etc.
3) Do not walk or.sit on sterilized soil or stand on benches of sterilized
soil.
4) Do not put disease-free planting material and disinfected pots and flats
on dirty surfaces. Place them on clean, disinfected surfaces or on unused
newspaper or plastic.
5) Do not set plants grown out of doors into sterilized soil devoid of
microorganisms. A low level of a pathogen kept in check out of doors by
competing harmless microorganisms could grow unchecked and be destructive
in sterile soil.
6) Keep the nozzle-end of water hoses off the floor and out of contact with
soil at all times.


7) Sterilize automatic watering tubing and pipes between crops.








Eradication. Eradication refers to eliminating a pathogen(s) that has gotten
into a production system. The ideal time to eradicate a pathogen that was intro-
duced the previous season is in the period between seasons. In Florida, poinsettia
plants should not be held to the following season because of the likelihood of
carrying over pathogenic organisms. Bacterial canker once was of common occurrence
years ago when growers maintained stock year-round. Scab was prevalent when
poinsettias were planted in the vicinity as outdoor landscape plants. Crown-of-
thorns plants should be eradicated from the vicinity as a bacterial disease the
plant carries also infects poinsettias. The off-season also is the time to
eradicate poinsettia pathogens from spaghetti tubing and other water systems, flats
and benches by flushing and/or dipping with a disinfectant. Organic debris should
be cleaned up, hauled away and buried. Start a new season with clean, pathogen-
free facilities.
During the season, plants that are obviously diseased should be removed
promptly and buried or hauled away. Such plants serve as inoculum sources for
other plants. One leaf spot may harbor thousands of spores or millions of
bacteria.
Exclusion. Simply stated, exclusion means do not bring in disease organisms
on plants, flats, soil, clothes, people (on dirty hands, shoes, etc.), tractors,
cars, etc. Most importantly buy certified, disease-free cuttings and plants.
Soil mixes should be pasteurized or sterilized, and flats, pots, tools, water
systems, trays, etc. should be steamed or chemically sterilized-before use. If you
look at a neighbor's plant problem, do not return to your operation because bacteria,
viruses, nematodes or fungi might.be carried on clothes, hands or tires. Go home,
shower, change clothes and come back the next day.
Resistance. The experienced grower quickly observes that certain cultivars
are more resistant to a disease than others. The grower should capitalize on this
characteristic whenever possible. Any management techniques, such as grouping
together susceptible cultivars that would need extra control procedures or placing
resistant cultivars in disease-prone locations-should be used.
DISEASES CAUSED BY FUNGI
Phytophthora Crown and Stem Rot (Phytophthora parasitica): Phytophthora
parasitica attacks all parts of the poinsettia plant. Gray, wet lesions develop
at the soil line or on stems. The necrosis and decay occurs under optimum moisture
(rain, dew, overhead watering) and high temperature conditions. As disease
progresses, the affected stem or entire plant wilts and dies. A stem canker forms
under less optimum conditions. The pith cavity turns brown and discoloration in
both the pith and vascular area may extend above and below the visible canker. Leaf
symptoms may start as small, tan, 1 mm diameter spots which may enlarge progressive-
ly to encompass a large part of the entire leaf. The necrotic leaf spots do not
form well-defined, lesions. They frequently develop on the leaf margins where a
leaf touches the soil. Affected parts of leaves may dry and curl. Chlorotic
areas which are not distinct halos usually occur adjacent to necrotic tissue.
This disease can be very severe. All plants in a section of a range may be
killed if effective control procedures are not used. Plants both in greenhouse and
outdoor production areas in peninsular Florida are affected. Phytophthora crown
and stem rot is caused by a water mold as is Pythium root and stem rot. The section
on the latter disease should be consulted for additional control procedures.






-6-


Pythium Root and Stem Rot (Pythium spp.). Pythium spp. are water molds.and
are most destructive in poorly drained, excessively wet soils. They become worse
during rainy periods when temperatures are 25oC (770F) or higher. Pythium commonly
causes a wet decay of roots, stems, cuttings and young plants. Under severe
disease conditions, plants are killed. Under milder conditions, Pythium is a good
root pruner. Small roots slough off (the outer part-of the root can be skimmed
off leaving the inner core or stele) and are killed, resulting in reduced growth,
yellowing of leaves, and partial defoliation of lower parts of the plant.
Pythium spp. can be expected to be in all, soils outdoors. Therefore, plants
always should be kept high enough off the ground or the soil covered with a mulch
so that splashing water from rains, watering operations, etc. will not come-in
contact with pots. Also, hoses, pot watering tubes and other equipment that come
in contact with potted plants should not be allowed to touch the ground. Feet of
personnel should not be placed on benches and hands should be washed before hand-
ling or touching plants. Since other fungal diseases caused by Rhizoctonia solani
and Phythopthora parasitica, and the bacterial diseases caused by Xanthomonas
campestris pv. poinsettcoa, Corynebacterium flaccumfaciens pv. poinsettia, and
Erwinia spp. can be similarly destructive, the same sanitary procedures should be
followed for them.
Rhizoctonia Root and Stem Rot (Rhizoctonia solani). Rhizoctonia is a
fungal pathogen that has its greatest Impact in the early stages of production
(propagation and recently transplanted plants). It causes decay of cuttings
under mist. On young plants symptoms range from necrotic lesions on roots and
stems to severe rot and death of the host. Brown to black, sunken, constricted
stem lesions (cankers) develop just below the soil line and in the crown area on
older plants. Lower leaves on affected plants may become chlorotic and fall off.
Infected plants display varying degrees of retarded growth. Under severe disease
conditions, leaves and terminals may become infected.
Botrytis Blight or Gray Mold (Botrytis cinerea). This diseases is one of the
most destructive diseases of poinsettias and many other floral and vegetable plants
in Florida. The pathogen is extremely aggressive and adaptive under optimal
environmental conditions. It can actively attack flowers and leaves, especially
damaged ones. Botrytis is an excellent saprophyte, which means it grows on dead
and dying organic matter. No matter where it grows, masses of gray spores,
quickly numbering in the millions, are produced. The spores are airborne. Leaves
damaged in any way, whether mechanically or by nutritional or cultural reasons,
are quickly colonized by the Botrytis fungus. The. true flowers are colonized as
soon as they mature. Important preventive procedures include removal of dead,
dying and injured plant tissue, allowing adequate plant spacing to provide good
aeration and drying of the foliage, and -cleaning up all organic debris lying about.
Greenhouse ventilation procedures as outlined on page 5 also assist in the control
of Botrytis blight.
Scab (Sphaceloma poinsettiae. This disease occurs on outdoor landscape
plants and on commercially produced potted plants. It also has been seen in wild
Euphorbias. It was considered a limiting factor in poinsettia production in
Florida into the late 1960's. Not carrying over stock plants and starting with
disease free cuttings has contributed significantly to the control of this disease.
Untreated, infected plants in gardens usually die within two years. They are a
serious source of inoculum when close to commercial production sites.
Numerous circular to elongate raised lesions from 1 to 10 mm long develop on
the stems. Coalescing lesions cause them to appear longer. The lesions have tan
centers and may be surrounded by a red or purple margin. Stem lesions may become






so numerous or they may continue to develop until they encircle the stem and kill
the branch. Heavily infected branches are stimulated to extended growth. An
infected branch on a pot plant may be twice as long as other branches, presumably
due to a gibberellin-like effect. Leaves are small on affected branches and fall
before they are mature. The elongated, thin stems are a specific diagnostic
symptom for this disease.
Brown to dark brown round to angular spots up to 4 mm diameter develop on
leaves. Initially chlorotic spots 1-2 mm diameter develop on the upper leaf
surface. As a chlorotic spot enlarges, a tan center which may have a thin, dark
margin develops. Some of the dark spots while no larger than 3 mm diameter develop
a concave surface. On other spots the adjacent leaf surface develops a puckered,
irregular or blister-like contour. Chlorotic halos around the spots are 1-2 mm wide
but when leaf spots become abundant, the entire leaf becomes chlorotic and falls
off. Large necrotic areas develop at the terminal lobe or leaf margins. Elongate,
tan lesions develop on petioles and leaf veins.
Conidia, produced in depressed centers of old lesions, are splashed about by
water. Infected plants should be removed and either hauled off, buried or burned.
Poinsettia plants should not be carried over to the following season.

Black Root Rot (Thielaviopsis basicola). This fungus causes black, rotted
lesions on the roots and, under severe conditions, lesions and longitudinal cracks .
develop at the base of the stem. Leaf spots may develop also:.on the undersides of.
lower leaves. Infected plants show varying degrees of stunting, low vigor, chlo-
rosis, and defoliation of lower leaves. The disease is favored by temperatures in
the 60's and by excessively wet soil. Soil acidity, pH of 5.5 or lower, inhibits'~
the disease.
Rhizopus Rot (Rhizopus sp.). Poinsettia plants growing under high humidity,
high temperatures (7-32 or 80-900F) and poor aeration-are:subject to a soft,
wet rot of..the foliage and stems caused by Rhizopus. This fungus seems to be an
opportunistic organism that attacks physiologically old plants that are growing
under certain unfavorable conditions. Also, cuttings in propagation during hot
weather are attacked, especially when they are placed too close together.
Conceivably, this fungus could attack boxed and sleeved plants held too long in
transit. Improving 'environmental conditions for the plants., such as lowering the
temperature and humidity, should control this relatively uncommon but potentially
destructive disease. -
Minor Fungus Diseases.- Other fungal pathogens have been reported on poinset-
tias but none are known to be a common problem'in Florida. Cylindrocladium spp.
can cause severe rot in propagation benches, and Cercospora,-Botryosphaeria,
Colletotrichum, Uromyses (rust) cause leaf spots. Rootand stem rots and cankers
may be caused by Sclerotinia, Phymatotrichum, Fusarium, Botryosphaeria and
C itocybe.

DISEASES CAUSED BY BACTERIA
Bacterial Canker or Blight (Corynebacterium flaccumfaciens pv. poinsettiae.
The predominant feature of this disease is the black streak that develops in
stems, usually starting'at the apex and extending downward but usually not to the
soil line on living plants. The streaks also may extend to the petioles and leaf
veins. Affected leaves may fall. The streaks may appear water-soaked in wet ,.
weather on outdoor grown plants. When the disease is present in stock plants,
infected cuttings may die in the rooting bed or they may root but die after
transplanting. The development of stem cankers and stem dieback frequently occurs





-8-


on growing plants. Lateral branches may develop on survivors, especially when
the environment is dry. If plants are kept dry under cover or there is no rain or
water on outdoor grown pot plants, new growth may continue to develop, producing
some saleable plants. Roots are not affected. Brown spots surrounded by a
chlorotic ring develop on leaves and bacterial exudate may be present on the under-
side of such leaves. Affected stems may crack causing an open lesion from which
bacteria may ooze. This pathogen is commonly carried over on infected stock plants.
Control depends on using disease-free plants, not carrying over stock plants,
and keeping the foliage dry. Any plants suspected of being infected should be
placed in a poly bag, removed and buried. Hands should be washed with soap and
water and disinfected with alcohol or other disinfectant before poinsettia plants
are handled again.
Bacterial Leaf Spot (Xanthomonas campestris pv. poinsettiicola). This disease
occurs frequently on poinsettia plantsin Florida. It affects only the leaves,
producing dull gray to brown, water soaked lesions. The leaf spots turn dark brown
with age, are several mm in diameter, develop a yellow halo and can be seen on both
upper and lower leaf surfaces. Severe leaf spotting results in leaf abscission.
This pathogen is the same one that causes a leaf spot of crown-of-thorns (Euphorbia
milii) so the latter plant should not be maintained or grown in the vicinity of
commrcially produced poinsettia plants. Agristrep@ and copper-maneb sprays
successfully prevented this disease in research experiments but only when applied
as preventive sprays before infection took place, but not after infection occurred.
Bacterial Soft Rot (Erwinia carotovora pv. carotovora). This disease was
reported to cause severe losses in several north central states but apparently has
not become a serious problem in Florida. Bacterial soft rot is a problem during
\propagation. Unrooted and rooted cuttings undergo a soft decay, resulting in
completely macerated plants. The disease is particularly severe under warm
(23-30oC or 75-86VF), moist conditions. It may be introduced on infected
cuttings. The disease also can be severe in the final two weeks of plant produc-
tion, especially when plants are forced under high temperatures. Affected plants
wilt, stems darken, and leaves become water soaked. Necrotic streaks can be seen in
the vascular tissue in the crown. Within 48 hours a soft decay of leaves, stems
and petioles occurs resulting in total loss of the plant. Strains of the pathogen
have attacked chrysanthemums, shasta daisy, Aglonaema ictum, Syngonium podophyllum
and dahlia. Strict sanitation practices, discarding diseased plants, controlling
temperature and humidity below optimum for the disease and not growing plants too
soft and succulent will help control this disease.
Greasy Canker (Pseudomonas viridaflava). This disease produces a stem canker,
leaf spot, and bract and bud blight. It has been reported in California where it
has persisted in greenhouse poinsettia culture since it was first found in 1979.
The poinsettia strain also causes typical disease symptoms in the known hosts for
this pathogen of tomato, cauliflower and pumpkin. Disease is severe in the 27-32 C
(80-90 F) range.
Stem cankers develop primarily where pruning wounds are made on the stems.
They'have an oily or greasy appearance and are not characterized by a soft rot.
Older, dry cankers are light tan to brown with a papery texture. Water soaked
lei'ons with halos occur on the leaves.
Necrotic areas develop rapidly on bracts and buds dehisce. Bacterial ooze is
associated with blemished areas on bracts.
Sanitation during pruning, roguing disease plants, and maintaining low
relative humidity help control spread.







Crown Gall (Agrobacterium tumefaciens). Crown gall is a bacterial disease
that occurs on many vegetative and woody plants. The main symptom is the develop-
ment of round galls or swellings near the base of the stems. Stunting of growth
can occur. Diseased plants should be destroyed or burned. Proper sanitation and
cultural practices to prevent further spread on equipment, tools, hands, etc., are
essential to help control this disease.
DISEASES CAUSED BY VIRUSES

Viruses. Poinsettia plants that have distorted or curly leaves and bracts,
bracts that fail to color normally, bracts that remain small, straplike or fanshaped.
or leaves with a mosaic or mottled appearance may be infected with a virus. Poin-
settia mosaic virus and pionsettia cryptic virus have been described on poinsettia
plants. Since there is no control for a virus disease, infected plants should be
removed carefully, placed in a poly bag, and buried. Strict sanitation and cultural
practices should be employed to prevent spread of the disease. Individuals hand-
ling plants with symptoms should wash their hands thoroughly with soap and water.
Purchasing disease-free plant material is a good safeguard against virus diseases.
Do not propagate from virus infected plants.
DISEASES CAUSED BY NEMATODES AND ALGAE

Root Knot Nematode (Meloidogyne spp.). Knots or small gall-like growths on
the roots are the primary symptom of the disease. Affected plants may be weak and
unthrifty. Occurrence of this disease in pot plants indicates contaminated soil or
soil mix ingredients were used and incomplete control was obtained when the mix was
sterilized or pasteurized. Using disease-free plant material and sterilized or
pasteurized soil mix prevents the disease.
Algal Blight (Cephaleuras sp.). A leaf disease caused by a pathogenic green a
alga, Cephaleuras sp., occurs on cuttings under mist propagation. The alga grows
on both leaf surfaces and can induce chlorosis and weakening of leaves, and perhaps
even defoliation if development continues. The disease is favored by the high
moisture conditions under mist and usually stops after plants are potted and foliage
is kept dry. Copper sprays may be helpful if the disease becomes destructive to
plants under propagation. It usually ceases to develop after plants are potted
and foliage is kept dry.
SELECTED REFERENCES

1. Engelhard, A. W., and R. C. Ploetz. 1979. Phytophthora crown and stem rot,
an important new disease of poinsettia (Euphorbia pulcherrima). Proc. Fla.
State Hort. Soc. 92:348-350.
2. Fulton, Robert W., and Jeanette L. Fulton. 1980. Characterization of a
tymo-like virus common in poinsettia. Phytopathology 70:321-324.

3. Hoitink, H. A. J., and G. C. Daft. 1972. Bacterial stem rot of poinsettia,
a new disease caused by Erwinia carotovora var. chrysanthemi, Plant Dis.
Reptr. 56:480-484.

4. Koenig, Renate, and D. E. Lesemann, 1980. Two isometric viruses in poin-
settias. Plant Dis. 64:782-784.

5. McFadden, A., and D. B. Creager. 1960. Recent occurrence of bacterial blight
of poinsettia in Florida. Plant Dis. Reptr. 44:568-571.





-10-



6. McFadden, A., and H. R. Morey. 1962. Bacterial leaf spot disease of
poinsettia in Florida. Plant Dis. Reptr. 46:551-554.

7. Miller, J. WV., and C. P. Seymour. 1972. A comparative study of Corynebacterium
poinsettia and Xanthomonas poinsettiaecola on poinsettia and crown-of-thorns.
Proc. Fla. State Hort. Soc. 85:344-347.


8. Ruehle, G. D. 1941. Poinsettia scab caused by Sphaceloma.
31:947-948.


Phytopathology


9. Starr, Mortimer P., and P. P. Pirone. 1942. Phytomonas poinsettia n. sp.
the cause of bacterial disease of poinsettia. Phytopathology 32:1076-1081.


10. Suslow, T. V., and A. H. McCain.
Pseudomonas viridiflava. Plant


1981. Greasy canker of poinsettia caused by
Dis. 65:513-514.








Table 1. Disinfectants and treatments for pots, benches, equipment and media.
Chemical Controls Rate Method
Steam Fungi, bacteria, nematodes, 180F for 30 minutes. Cover glats, clay pots, benches and steam
soil insects, and weed seeds 160 F for pasteurizing at 180 F for 30 minutes.
soil Plastic may be damaged
Aerated steam Same as above 140-160F for 30 min.
for soil

Household bleach Some fungi and bacteria. Not 1:10 dilution (0.525%) Drench empty benches, flats, tables, tools,
(5.25% sodium effective against Fusarium, add 9 parts H20 to 1 etc. Soak clean pots for 30 minutes. A
hypochlorite), Verticillium, Cylindrocladium part bleach, new solution should be made up for each
CloroxV lot of pots treated. Automatic watering
system tubing should be flushed with water
before reuse. Caution, corrosive to metal.


Formaldehyde
(Formalin)


Fungi and bacteria, including
Cylindrocladium, Fusarium,
Pythium, Rhizoctonia,
Thielaviopsis, Vericillium,
aXanthomonas.


1 part Formalin in 50
parts H20


Drench empty benches, tables, potting tools,
etc. Caution applicator should wear
proper respirator. Use in well ventilated
location.


Physan 20 Bacteria, fungi, viruses, 1 oz/3 gal water Use on flats, pots and benches
algae, mildew (on walls, etc).
Not effective against nematodes
or weeds.
Hyamine Fungi and bacteria. Good 1 fluid oz/10 gal Rate for porous surface
algacide. Not effective 1 fluid oz/20 gal Rate for hard surface. More effective
against nematodes or weeds. in alkaline pH water.
LF-10 Fungi and bacteria. Not effec- 6 oz/5 gal (1:106) Only limited activity against some
tive against Fusarium,7Verti- important plant pathogens.
cillium, Thielaviopsis, Cylin-
drocladium, Pythium, Xanthomonas
pelargonii, and resistant or
resting bodies of some fungi.






Table 2. Fungicides that control soilborne diseases of Poinsettia.
Cier.ical and Rate Use
formulation Controls 100 gal 1 gal Greenhouse Field INotes
Erenches 2
rencl Rhizoctonia 1 lb. 4.5 g X X 1-2 pt./ft2 for benches and field.
(Lenlate 50% UP) Cylindrocladium Pot plants 6-8 oz/6" pot. Add
Fusarium recommended quantities of diazoben
Thielaviopsis or ethazol if Pythium or
Sclerotinia Phytophthora control are desired.

ciazoben Pythium 4-8 oz (pots) X Apply pt./6" pot. Apply 100 gal/
(Lesan 3;% UJP) Phytophthora 12-24 oz (outdoors) X 400 ft for benches. Use the higher
rate for outdoors. IHake one appli-
cation only outside. Chemical is
light sensitive so use immediately.
Where Rhizoctonia control is also
desired, add recommended quantities
Sof PCNB or benomyl.

ethazol + tniophanatt Rhizoctonia 6-12 oz X X Apply at 1 qt/ft for bench and field.
vrethyl Pythium For pots apply sufficient amount to
(Banrot 40% UP) Thielaviopsis wet the soil, such as pt./6" pot.
Phytophthora Irrigate immediately with the
Fusarium volume of the fungicidal drench. Do
not apply with fertilizers or
pesticides.

ethazol Pythium X X Apply to 400 ft2 and add additional
(Truban 30% iHP) Phytophthora 3-10 oz water at one half fungicide rate.
Truban 25% EC) 4-b liquid oz In pots use about pt./6" pot.
Terrazole 35% WP) Nix 5 oz 5G/yd3 of soil medium.
(Truban 5G)
retalaxyl Pythium 0.5 2.0 fluid oz X X Apply to 40Q-500 ft2 of bed area or
(Subdue 2E) Phytophthora 1-2 pts./ft Do not apply more
often than every 6 weeks.
FPN 75% HP Rhizoctonia 13.3 oz 3.b g X Use 300 gal H, /1000 ft2. Add


(Terraclor 75W)


Sclerotinia
Sclerotium


recommended quantities of diazoben
or ethazol if Pythium and Phyto-
phthora control are desire also.










Table 3. Fungicides that control foliage and flower diseases of Poinsettia.

Chemi cal and Rate Use
forr:ulation Controls 100 gal 1 gal Greenhouse Field Notes
Foliar Sprays

benonyl Botrytis Ib. or X X Systemic benoriyl should be tank
(Benlate 5UP) Scab 227 g 2.3 g mixed with another effective fungi-
cide because of widespread resis-
tance to Botrytis.

captain Scab 2 lb. X X Not effective against bacterial
(Captan 50 wP; Botrytis 908 g 9.1 g disease.
Orthocide 50WP) Fungus leaf spots


Scab
Botrytis
Fungus leaf


1-2 lb.
681 to
spots 908 g


therral dust
(Exothermi Terril


Botrytis
20%)


smoke generator -
see label


3.5 oz/1000 ft


Thiophanate methyl Botrytis 1.5 Ib. or X X
+ r~ancozeb Scab 681 g
(Zyban 75 HP) Fungus leaf spots

vinclozalin Botrytis 1-1 lb. X X Repeat every 10 to 14 days. Does
(Ornalin 5) UP) Sclerotinia 454 to 6.8 to not control scab.
681 g 10.2 g


mancozeb


6.8 to
9.1 g




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