leaf, stem, and bract blight caused by Botrytis cinerea (Strider and Jones,

1985). However, in 1992, another foliar fungal disease called powdery
mildew

(PM) caused by Oidium spp. was a problem for many poinsettia growers, especially

those in the northern United States and Canada. White, talcum-like powdery

mildew colonies up to approximately 1/2″ in diameter occurred on either
the upper

or lower leaf and/or bract surfaces. In many cases, PM detection was delayed

because colonies were primarily on undersides of lower leaves. Therefore,
many

growers did not become aware of PM infection until late in production when
the

bracts were infected and the losses siqificant (personal observation, M.

Daughtrey and M. Hausbeck). Customer
dissatisfaction (retail shops and

consumers) also occurred when poinsettias
developed PM after leaving the

production greenhouse.
Growers that detected PM early in production reported successful

elimination of the disease by removing infected leaves and applying fungicides.

Similarly, sanitation and fungicide application have long been integral

components of Botrytis disease management. Unfortunately, fungicides that
are

commonly used against B. cinerea do not control PM on poinsettia. The fungicides

ornalin, Chipco 26019, and Exotherm Termil are frequently used to control

Botrytis blight, but none of these materials is recommended for control
of PM.

At least 20 poinsettia growers responding to a survey on PM had used

Bayleton/Strike, Cleary’s 3336/Domain/Fungo Fla, Zyban, or Phyton 27 in
1992,

with at least 60% of those growers reporting efficacy (Hall, 1993).
Controlling disease caused by B. cinerea and oidium spp. through

modification of the greenhouse environment would allow more precise disease

management than traditional control methods provide. However, since the

environmental requirements for these two fungi are different, the individual

thresholds must be incorporated together in order to provide control for
both

Botrytis and PM. Conidia of B. cinerea require
free moisture in order to

germinate. In contrast, preliminary information on PM on poinsettia
indicates

that at 25C only 80% relative humidity (RH) is required for 70% conidial

germination (Hausbeck, unpublished data).
In order to produce a cost-effective, high quality poinsettia, integrated

disease management strategies including sanitation, fungicide application,
and

environmental manipulation must be established for the control of Botrytis
blight

and PM.
LITERATURE REVIEW – Powdery Mildew. The first observation of PM on poinsettias

in the United States is reported to have occurred in Pennsylvania and the
Pacific

Northwest in 1990. Poinsettia growers in Mexico reported PM on poinsettia
during

1988 and 1989 and growers in Puerto Rico have also observed PM. In April
1992,

a few growers from the Midwest, South, and East Coast reported PM (Daughtrey
and

Hall, 1992). Reports of PM were more common in the fall of 1992 (M. Hausbeck
and

M. Daughtrey, personal observations). Differences in
susceptibility were not

noted among cultivars.
Since PM is a relatively new disease on poinsettia, the specific causal

agent is unidentified. The fungi that cause PM diseases are obligate parasites.

Although PM diseases occur on many hosts, the individual species of PM
are very

host specific. Accordingly, the PM that occurs on poinsettia
has not been

transferred to other crops (Daughtrey and Hall, 1992)
In general, the occurrence, distribution, and severity of a powdery mildew

infection are affected primarily by temperature, relative humidity, light,
and

wind (Coyier, 1985). Condia germinate on the leaf surface
and produce germ

tubes, followed by the production of haustoria which penetrate the host’s

epidermis. Mycelium develops within 24-48 hours, with maturation
of conidia

occurring in as little as 72 hours under optimum environmental conditions.

Secondary inoculum production frequently occurs after a minimum of 5-7
days

following inoculation (Coyier, 1985).
Preliminary observations of the PM

affecting poinsettia indicate that at 20C, 70% of the conidia germinate
when

held at relative humidity > 80% (Hausbeck, unpublished data). Observations
in

the field on cucurbit crops indicate that PM has the potential to “explode”
once

established at a low level. In a 1992 research trial,
incidence of cucurbit

leaves infected with PM increased from 10% to 70% within a week’s time
under

favorable environmental conditions. In contrast, the epidemic was halted
in the

portion of the field where fungicides were applied when disease was first
noted

(Hausbeck, unpublished data).
Few fungicides are labeled for control of powdery mildew on poinsettias.

The following are labeled for control of powdery mildew and list poinsettias
on

their label: Phyton 27, Cleary’s 3336 F/Cleary’s 3336
WP/Domain Fl/Fungo

Flo/SysTec 1998, Terraguard, and Zyban.
A number of systemic fungicides

effective for PM control on other crops are not available to poinsettia
growers.
Botrytis Blight. Botrytis cinerea is a serious disease of poinsettias.

it causes considerable damage on the stems and foliage during propagation
and

throughout the growing season, and, most importantly, may attack bracts
during

the critical flowering period.
Free moisture and temperature are of primary importance for B. cinerea

conidial germination and subsequent infection, although conidia can be
very

tolerant of drying (Good and Zathureczky, 1967). When free moisture is
present,

conidia of B. cinerea germinate within 60 minutes of inoculation at the
optimum

temperature of 20C. Four hours after inoculation, 40%
of the conidia have

germinated and by 6 hours, 77% of the conidia have germinated (Hausbeck,

unpublished data).
In a commercial greenhouse, conidial “showers” were typically associated

with grower activity including irrigation, spraying of pesticides, and
harvesting

of cuttings (Hausbeck and Pennypacker, 1991).
The occurrence of conidial

“showers” during and immediately after harvesting of cuttings
is an important

consideration in disease management because new infection courts are made

available in the form of wounded stems at the same time that concentrations
of

airborne conidia are large. Further, cuttings removed from the stock plants
are

frequently exposed to large concentrations of airborne conidia that may
influence

disease occurrence during propagation.
In order to protect plants, fungicides that are effective against B.

cinerea are used repeatedly. Continuous use of systemic fungicides has
resulted

in the selection of resistance in B. cinerea populations to benomyl (Benlate)
and

vinclozolin (Ornalin, Curalan) (Moorman and Lease, 1992) . modification
of the

environment in a commercial greenhouse has been a successful control tool
in a

commercial greenhouse to reduce B. cinerea inoculum and blight. Environmental

modification could be used in conjunction with a disease prediction system
to

reduce sole dependency on fungicides (Hausbeck, 1993).

OBJECTIVES AND POTENTIAL BENEFITS – As the greenhouse industry moves toward
the

21st century, growers must face increased regulation and concern for the

environment that will result in increased costs in production and narrow
the

profit margin. Only through the production of cost-effective,
high quality

produce delivered in the quantities wanted and at the time it is wanted
will the

industry remain viable. In addition to these challenges, poinsettia growers
are

in the unique position of managing a “new” disease called PM.
This disease

appears to have the potential to negatively impact the poinsettia industry

through reduction of plant quality and/or increased fungicide costs. However,

in the rush to learn about powdery mildew, the longtime nemesis of poinsettia

(Botrytis blight) must not be forgotten. Rather, the inclusion of B. cinerea
in

this project will benefit all greenhouse floral crops that are infected
by

Botrytis blight. Therefore, the following objectives have been defined.
1. Develop a scouting program for management of PM and Botrytis blight.
2. Develop an effective fungicide spray program for PM and Botrytis blight.
a.)

Identify fungicides effective against the foliar blights of poinsettia
that may

safely be used on foliage and/or bracts. b.) Determine the appropriate
timing

of fungicide applications during the disease cycles. c.) Determine an effective

fungicide rotation to prevent occurrence and build-up of resistance. d.)
Provide

efficacy and phytoxicity data necessary to support a full or special registration

of effective fungicides that are not currently labeled for control of foliar

blights on poinsettia.
3. Investigate the epidemiology of PM. a.) Determine the level and duration
of

temperature and RH necessary for conidia of PM to germinate, infect, and

sporulate on poinsettia tissue. b.) Investigate the ability of the fungus
to

remain latent in host tissue. c.) Investigate the efficacy of heat treatments

in eliminating active and latent infections.
4. Incorporate the known epidemiological data on B. cinerea with that determined

for PM into an integrated disease management system that utilizes sanitation,

fungicide applications, and environmental manipulation to reduce disease

incidence and severity.
5. Develop a grower guide entitled “Foliar Disease Management for Poinsettias”.

MATERIALS AND METHODS
1. Develop a scouting program and guide for PM and Botrytis
blight. The

following Pilot Scouting Program will be trialed with grower cooperators
in New

York, Texas, and Michigan. The protocol to be used is patterned after that
used

for scouting whitefly (Ferrentino, 1992) and will include the following:
A). PRE-CROP ACTIVITIES
Gather background information on scheduled crop and previous diseases and

determine which areas are to be scouted.
Map the greenhouse range and indicate poinsettia growing areas.
B). SCOUTING PHASE I: Before Any Powdery Mildew/Botrytis Blight Has Been

Detected.
Upon arrival of poinsettias, scouts will examine 1/10 of the cuttings prior
to

potting.
• After plants are potted, scout the crop weekly.
• For each plant monitored, examine four fully-expanded leaves in the lower

and middle canopy levels (a total of 8 leaves) .
C). SCOUTING PHASE II: once Powdery Mildew/Botrytis Blight Has Been Detected.
Put a colored flag into the first 10 pots where PM or Botrytis blight is

detected. Alert grower immediately so that treatment may begin.
Advise the

grower to carefully remove (and bag) all infested leaves prior to fungicide

application.
Record any additional plants detected with PM or Botrytis blight during
the

season. The grower should use the scouting data to identify
areas where leaf

removal is important.
* All control practices should be noted by grower.
2. Develop a safe and effective fungicide spray program for
PM and Botrytis

blight. Collect efficacy and phytotoxicity data necessary to support a
full or

special registration of needed fungicides.
Researchers in Michigan, New York, and Texas will trial fungicides for
their

efficacy in controlling PM and Botrytis blight on poinsettia, including:
Baking

Soda, Bayleton/Strike, Chipco 26019, Cleary’s 3336/Domain/Fungo Flo, Daconil,

Dithane T/O, Eagle, Milban, Oil/Sunspray, Ornalin, Phyton 27, Pipron, Protect

T/O, Zyban, Rubigan, Soap ( Mycogen’s 1446), Sulfur, Terraquard, Triforine,
and

Zineb. Dip treatments will also be investigated.
3. Investigate the epidemiology of PM. a.) Determine the level and duration
of

temperature and relative humidity (RH) necessary for conidia of PM to germinate,

infect, and sporulate on poinsettia tissue. Leaf discs will be inoculated
with

conidia from actively sporulating PM colonies on infected poinsettia leaves.
The

inoculated leaf discs will then be placed on pads of water agar on top
of

aluminum mesh within individual RH chambers. RH levels to be examined include

45% through 95% at 10% increments. The varying RH levels
will be maintained

through the use of salt solutions prepared by dissolving the appropriate
salt in

boiling water to saturation. The RH chambers will be placed in an incubator
at

15, 20, or 25C for a minimum of 24 hours. Following incubation, the leaf
discs

will be fixed in FAA, cleared in 7O% ethanol and stained in 1% aqueous
trypan

blue. Conidial germination and infection into the host tissue will be determined

by viewing the conidia under a compound microscope (100x) . A minimum of
100

conidia will be observed. Germination rate
at the optimum environmental

conditions (as determined above) will be determined by incubating inoculated
leaf

discs for 2, 4, 8, 12, 16, 24 hours and counting germinated conidia as
described

previously. Studies of the environmental conditions necessary for sporulation

will be investigated using whole plants that will be inoculated and maintained

under optimum conditions for germination and infection. Following the incubation

period, plants will be moved to a growth chamber set at 15, 20, or 25C
at levels

of RH of 60, 70, 80, or 90%. The time to colony appearance will be noted
and

leaf discs removed, prepared as described previously, and the newly-formed

conidia counted. b.) Investigate the ability of the fungus to remain latent
in
host tissue. Poinsettias will be inoculated and incubated in a growth chamber

under a regime favorable for germination and infection (as determined by
previous

experiments). Following incubation, cuttings will be removed and maintained
in

a growth chamber under conditions that are unfavorable for colony development
for

1, 4, and 8 weeks. Plants will then be returned to the environmental conditions

that are known (based on previous studies) to prompt PM development. The
time

to colony formation will be noted. Histological
studies will be pursued it

results from the described study indicate additional information could
be

obtained through those methods. c.) Investigate the efficacy of heat treatments

in eliminating active and latent infections. Cuttings
will be inoculated and

incubated under conditions favorable for germination and infection. Cuttings

will then exposed be temperatures of 28, 32, or 40C for 2, 7, or 14 days.

Following the exposure to the temperature regime, cuttings will be placed
under

environmental conditions favorable for PM.
4. Incorporate the known epidemiological data on B. cinerea with that determined

for PM into an integrated disease management system that utilizes sanitation,

fungicide applications, and environmental manipulation to reduce disease

incidence and severity. This objective seeks to bring
together all of the

information generated by this study and previous studies into a comprehensive

strategy for controlling PM and Botrytis.
5. Develop a guide entitled “Foliar Disease Management for Poinsettiasn.

As significant information is gathered, a guide for growers and handlers
of

poinsettias will be developed and will cover identification, scouting,
fungicide

application, and environmental manipulation for the control of PM and Botrytis

blight.

LITERATURE CITED
Coyier, D. L. 1985. Powdery mildews. In: Diseases of Floral Crops – Vol.
I,

Praeger Publishers Division, Westport, Connecticut, D.L. Strider, editor.

pp. 103-140.
Daughtrey, M., and J. Hall. 1992. Powdery mildew – A new threat to your

poinsettia crop. GrowerTalks, September, pp.23-31.
Ferrentino, Gerard W. 1992. Pest Monitoring: The basis of any IPM Program.

Proceedings for the 8th Conference of Insect and Disease Management on

Ornamentals, SAF, Alexandria, VA, pp. 37-41.
Good, H.M., and Zathureczky, P.G.M. 1967. Effects of drying on the
viability

of germinated spores of Botrytis cinerea. Phytopathology 57:719-722.
Hall, J. 1993. Powdery mildew. 65th International Floriculture Industry
Short

Course. Cincinnati, Ohio.
Hausbeck, M.K. 1993. Biological Control and Environmental Manipulation
for

Control of Botrytis. Proceedings for the 9th Conference of Insect and

Disease Management on Ornamentals, SAF, Alexandria, VA, pp. 73-79.
Hausbeck, M.K., and S.P. Pennypacker. 1991. Influence of grower activity
and

disease incidence on concentrations of airborne conidia of Botrytis cinerea

among geranium stock plants. Plant Dis. 75:798-603.
Moorman, G., and R. Lease. 1992. Benzimidazole- and Dicarboximide-Resistant

Botrytis cinerea from Pennsylvania Greenhouses. Plant Dis. 76:477-480.
Strider, D.L., and R.K. Jones. 1985. Poinsettias. In: Diseases of Floral
Crops

- Vol. II, Praeger Publishers Division, Westport, Connecticut, D.L.

Strider, editor. pp. 351-404.

BUDGET – The following budget is proposed:
Greenhouse Supplies:
6,000

Includes growing media, containers,

fertilizer, photographic costs, and development

of educational materials for growers.

Travel:
7,000

To coordinate IPM implementation and to

collaborate with researchers involved in this

project.

Growth and Dew Chamber Usage and Supplies
1,800

($50/unit/month x 3 units)

Salaries

* Experienced greenhouse scouts for New York,
4,500

Michigan, and Texas

(1 scout/state, 150 hours @ $10/hr)

* Graduate Student Stipend
15,000

* Undergraduate Research Assistant
5,200

($5.00/hr x 20 hrs/wk x 52 wks)

* Research Technician (1/4 time)
7,200
TOTAL
46,700

QUALIFICATIONS OF RESEARCHERS
Dr. Mary Hausbeck is an Assistant Professor and Extension Plant Pathologist
at

Michigan State University. Her current responsibilities at MSU include

greenhouse crops. She has completed studies on the crown and root rot of

geraniums caused by Pythium ultimum documenting etiology, symptomatology,

fungicide efficacy, and cultivar resistance. She has also provided information

essential to the development of environmental manipulation of B. cinerea.
She

has, also published research on TSWV/INSV on greenhouse crops. In addition,
she

routinely screens fungicides for efficacy against foliar and root rot pathogens

on a wide range of crops.
Ms. Margery Daughtrey is a Senior Extension Associate with the Department
of

Plant Pathology, Cornell University and conducts a reseach and extension
program

on diseases of ornamental plants. She has conducted numerous powdery mildew

control trials on annuals, woody, and herbaceous perennials and greenhouse

poinsettias, testing conventional fungicides as well as horticultural oil
and

sodium/potassium bicarbonate formulations. Ms. Daughtrey has assisted in
the

development of the NY Greenhouse IPM program, which has successfully developed

and executed improved management strategies for greenhouse and sweetpotato

whiteflies on poinsettias.
Dr. Larry Barnes is an Associate Professor and Extension Plant Pathologist
at

Texas A & M University. Dr. Barnes received his B.S. degree in microbiology
and

his M.S. degree in plant physiology from Texas Tech University. He received
his

Ph.D. in plant pathology from Texas A & M University. Dr. Barnes is
responsible

for supervision and operation of the Texas Plant Disease Diagnostic Laboratory

as well as plant pathology extension educational programs in greenhouse
and

nursery crops.