Integrating Control of Botrytis and Powdery Mildew in a Greenhouse Crop 1996 Proposal
Daughtrey (Cornell University), and Larry Barnes (Texas A&M University)
Executive Summary
Poinsettia growers are in the unique position of managing a “new” follar
disease- Traditionally, Botrytis blight has been the primary follar disease
of poinsettia. However, powdery mildew (PM) (Oidium sp.) continues to be
a problem for many poinsettia growers, especially those in the northern
U. S. and Canada. PM detection can be delayed because the white, talcum-like
colonies can occur on undersides of lower leaves. Also, the ability of
the fungus to be latent and therefore exhibit no symptoms is not understood.
PM has the potential to negatively impact the poinsettia industry through
reduction of plant quality and/or increased fungicide costs.
A disease management program that addresses both PM and Botrytis must
be developed. The inclusion of B. cinerea in this project will benefit
all Greenhouse floral crops that are infected by Botrytis blight. The following
objectives have been defined:
1) Develop a PM spray program for stock plants and cuttings;
2) Investigate the environmental effects on PM infection latency, and
disease development,
3) Integrate B. cinerea and PM data for a comprehensive disease management
system,
4) Develop a grower guide entitled “Foliar Disease Management for Poinsettias”.
Significant progress on has been achieved and includes:
• Development of a PM spray program for poinsettia finishing and postharvest,
• Twelve poinsettia cultivars have been evaluated for susceptibility
to PM.
• A PM management program including scouting, removal of infected leaves,
and fungicide applications has been successfully used in a commercial poinsettia
crop. The influence of DIF growing regimes on Botrytis has been determined.
INTRODUCTION -
The primary foliar disease of poinsettia has traditionally been leaf,
stem, and bract blight caused by Botrytis cinerea (Strider and Jones. 1985).
However, another foliar fungal disease called powdery mildew (PM) (Oidium
sp.) continues to be a problem for poinsettia growers. especially those
in the northern U.S. and Canada. White, talcum-like powdery mildew colonies
up to approximately 1/2″ in diameter occur on either the upper or lower
leaf and/or bract surfaces. The first goal of this research was to eliminate
PM from the finishing and postharvest phases of poinsettia production.
PM could escape detection until late in production when bracts became infected
and the losses significant because PM colonies were initially occurring
on undersides of lower leaves.
The development of PM after poinsettias had left the production greenhouse
resulted in customer dissatisfaction (retail shops and consumers). A PM
management program emphasizing early disease detection via scouting, removal
of infected leaves. and appropriate fungicide selection and timing is now
available to growers involved in the finishing and postharvest phases of
poinsettia production. The next phase of research will pursue the elimination
of PM from the stock plant and cutting phases of production. The ability
of PM to be latent and exhibit no symptoms or signs is not understood.
However, understanding this component of PM biologic is critical to the
production of disease free poinsettia propagules. Since the environmental
requirements for Botrytis and PM are different, the individual thresholds
for each fungus must be integrated to provide control for both Botrytis
and PM. B. cinerea conidia require free moisture in order to germinate.
In contrast, free moisture is not necessary for PM to germinate. In order
to produce a cost-effective, high quality poinsettia, integrated disease
management strategies including sanitation, fungicide application, and
environmental manipulation must be established to control Botrytis blight
and PM.
LITERATURE REVIEW - The first observation of PM on poinsettias
in the United States is reported to have occurred in Pennsylvania and the
Pacific Northwest in 1990. Growers in Mexico reported PM on poinsettia
during 1988 and 1989 and growers in Puerto Rico have also obsessed PM.
In April 1992, growers from the Midwest, South, and East Coast reported
PM (Daughtrey and Hall, 1992: Daughtrey and Macksel, 1994b). PM occurrences
continue to be reported in the U.S. and Canada (M. Hausbeck and M. Daughtrey,
personal observations). Since PM is a relative new disease on poinsettia,
the specific causal agent is unidentified. PM species are host specific
and 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 PM infection are affected primarily by temperature, relative
humidity (RH), light, and wind (Covier, 1985). Conidia germinate on the
leaf surface and produce germ tubes, followed by the production of haustoria
which penetrate the host’s epidermis. Maximum germination of conidia of
PM on poinsettia is 72, 61, and 42% at 25, 20, and 15 C, respectively when
RH is 85% (Hausbeck and Kalishek, 1994).
Observations in the field on cucurbit crops indicate that PM has the
potential to “explode” once established at a low level. 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). Botrytis cinerea is a serious
disease of poinsettias, causing considerable damage on the stems, foliage,
and bracts. 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 20 C. Four hours after inoculation,
40% of the conidia have germinated and by 6 hours, 77% of the conidia have
germinated (Hausbeck, unpublished data). Botrytis conidial “showers” are
typically associated with grower activity (Hausbeck and Penitypacker, 1991).
The occurrence of conidial “showers” during and immediately after harvesting
of cuttings is important in disease management. Cuttings removed from the
stock plants may be 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 systematic fungicides has resulted in the selection of
resistance in greenhouse B. cinerea populations (Moorman and Lease, 1992).
Environmental modification in a commercial greenhouse has been a successful
control tool 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 - The following have been completed:
1. Development of a PM scouting program. A weekly scouting program was
implemented among stock plants and cuttings in a commercial greenhouse
range that had just been discovered to have poinsettias infected with PM.
One out of every 30 plants were selected at random using a zig-zag pattern.
Plants with PM were flagged and infected leaves (typically 2-5) removed
and placed in plastic bags. Cultivars where PM was detected were scouted
at a 1 to 10 ratio. On the first observation, 36% of one cultivar was infected
with PM. The fungicides chosen and applied by the grower included an application
of Phyton 27 (1.5 oz/10 gallons) and an application of Terraguard 5OW a
week later. Within 6 weeks of the initial scouting date, PM could not be
detected and did not reappear during the course of crop production (Hausbeck
et al., 1994a,b).
2. Development of a PM spray program for finishing and postharvest phases
of poinsettia produciton. Fungicide sprays were initiated after the first
appearance of PM colonies on bracts. While growers would want to avoid
a situation where PM has progressed to the bracts, this system works well
to determine fungicide efficacy. In a 1994 MSU study, PM was best controlled
by Chipco 26019 WDG 50 WG (1.0 or 2.0 lb/100 gal) or the higher rates of
Terraguard 5OW (16-4-4 or 16-8-8 oz/100 gal for the first, second, and
third applications) or Cleary’s 3336 WP 5OWP (1.5 lb/100 gal, two applications).
There was no difference between Chipco 26019 rates (1.0 vs 2.0 lb/100 gal).
Likewise, the lower rates of Terraguard 5OW (16-4-4 oz/100 gal) were as
effective as higher rates of Terraguard 5OW (16-8-8 oz/100 gal).
However, lowering the Terraguard 5OW rates further to 8-4-4 oz/100 gal
was not equally effective as the higher rates. Although the best fungicide
treatments evaluated in this trial would be unacceptable in controlling
PM on bracts, these treatments would be highly effective on poinsettias
not in color. A weak link in managing PM is the inability to protect bracts
in the finishing or postharvest production phase. To evaluate the length
of time fungicides can provide protection against PM, plants were maintained
for 56 days beyond the last fungicide application in a greenhouse full
of severely infected poinsettias. In this study, 42 days appeared to be
the longest duration of control available beyond the last fungicide application.
No PM colonies were active 42 days after higher rates of Terraguard 5OW
(16-4-4 oz or 16-8-8 oz/100 gal., a total of 3 sprays) were applied following
disease detection.
When healthy plants were treated with Terraguard 5OW (4 or 8 oz/ 100
gal, a total of 4 applications) prior to exposure to PM, protection lasted
for 42 days. Good control was also obtained 42 days after the last application
when Chipco 260195 WG ( 1 or 2 lb/ 100 gal) or the lower rate of Terraguard
5OW (8-4-4 oz) was used after PM detection. When a low rate of Terraguard
5OW (2.0 oz/ 100 gal, a total of 4 sprays) was applied prior to exposure
to PM, good control was obtained for 42 days (Hausbeck, 1995). All fungicides
included in the 1995/96 MSU total effectively limited the number of leaves
infected with PM compared to the untreated plants. By the first assessment
date, an average of 17 leaves per untreated control plant was infected
with PM. Disease pressure was significant in this trial, with the untreated
plants having an average of 63 infected leaves per plant by the last assessment
date.
Several fungicides limited the incidence of PM to <5 leaves per plant
and included the high (4.0 oz/100 gal) rate of Strike 25DF, the low (4.0
oz/100 gal) and high (8.0 oz/100 gal) rates of Pipron 8LC applied weekly,
Rubigan EC, and the low (4.0 oz/100 gal) and high (8.0 oz/100 gal) rates
of Terraguard 5OW. Treatments resulting in a minimum average of 15 infected
leaves per plant included the low (0.15 lb/100 gal) rate of BAS49OF 5ODF,
the low (24.0 oz/100 gal) and high (128.0 oz/ 100 gal) rates of LABS 114
30AS, X-77, Stylet Oil, and RH-3866 4OW. The ability of fungicides to provide
continued protection is currently being evaluated. A similar study is ongoing
at Cornell Univ.
3. Screen poinsettia cultivars for resistance to PM. Multiple-stem poinsettias
with mature bracts representing 12 cultivars were inoculated with PM. Cultivars
with red bracts (Freedom Red, Red Sails, V-14 Glory, Supjibi Red) had significantly
more bracts infected (>91.2%) than the cultivars with pink (V-14 Pink,
Hot Pink) (85%). white (Topwhite, V-14 White, V-17 Angelika White) (53-96%,
or variegated bracts (Jingle Bells 3, Pink Peppermint, V-17 Angelika Marble)
(53-79%) (Celio and Hausbeck, 1994). This experiment has been repeated.
4. Evaluate the impact of temperature (15-25C) and RH (35-95%) on PM
conidia. Effects of temperature (temp.) and relative humidity (RH) on germination,
appressorium formation, and shriveling of conidia were studied on Freedeom
Red leaf discs in l5, 20, and 25 C growth chambers. RH levels included
95, 85, 75, 65, 55, 45, 35%. Maximum germination of conidia was 72, 61,
and 42% at 25, 20, and 15 C, respectively, when RH was 85%. Appressorium
formation was not significantly affected by temperature or RH with >89%
of the germinated conidia forming appressona. Shriveling of conidia was
least (6%) at 25 C and 95% RH; greatest (39%) at 20 C and 35% RH (Hausbeck
and Kalishek, 1994). 5. Evaluate the impact of environmental manipulation
on B. cinerea. The influence of DIF on the susceptibility of poinsettia
bracts to Botrytis was investigated using the following day/night temperature
regimes: 16/16, 16/19, 16/22, 19/19, 19/16, 19/22, 22/22, 22/16, and 22/19.
When poinsettias were grown under the same average temperature prior to
inoculuation, DIF (16/21, 19/19, 22/16) did not impact subsequent disease
development. Susceptibility did appear to be increased by increasing average
temperatures from 16 to 22 (Pritchard, et al., 1995).
OBJECTIVES AND POTENTIAL BENEFITS - The following are proposed:
1. Develop an effective PM spray program for stock plant and cutting
production.
2. Investigate the epidemiology of PM. a.) Investigate the ability of
the fungus to remain latent in host tissue. b.) Investigate the efficacy
of heat treatments in eliminating active and latent infections.
3. 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.
4. Develop a grower guide entitled “Foliar Disease Management for Poinsettias”.
MATERIALS AND METHODS -
1. Develop an effective PM spray program for stock plant and cutting
production.
a.) Efficacy of fungicides applied to healthy stock plants in protecting
harvested cuttings from subsequent exposure to PM. Stock plants will be
treated with fungicides at 7, 14, or 30-day intervals or untreated. Cuttings
will be removed weekly and propagated in a greenhouse eniviromnent containing
poinsettias with sporulating PM colonies. Disease incidence and severity
will be recorded to assess fungicide efficacy.
b.) Efficacy of fungicides applied to stock plants exposed to PM to
provide curative effects to cuttings throughout propagation. Stock plants
growing in a greenhouse with poinsettias with sporulating PM colonies will
be treated with fungicides at 7, 14, or 1-day intervals or unspraved. Cuttings
will be removed weekly and propagated in a PM-free environment. Disease
incidence and severity will be recorded to assess fungicide efficacy.
2. Investigation of the epidemiology of PM: Progress to Date: Peak corudial
concentrations (PCCs) were not associated with grower activity in two MSU
research greenhouses (GH2g, GH11a). Atmospheric conidial concentrations
(ACCs) were highest in both greenhouses between the hours 1000 and 1700
and appeared to be associated with increases in temp. and VPD. GH2g had
significantly higher ACCs throughout the study than did GH11a. During May
maximum temps in GH11a were >= 30C on seven days while temps in GH2g were
>= 30C only once. ACCs in GH11a declined following the period of high temps.
GH2g reached max temps of 30 C in mid-June, after which ACCs also declined.
Trap plants in GH2g developed colonies an average of 2 days sooner than
those in GH11a. In GH2g, after a minimum of 6 days at temps > 10 C. PM
colonies were no longer observed on trap plants although small numbers
of ACCs were still observed. These data suggest that at high temperatures
(>30C), conidia are not readily produced and those conidia that are produced
during may not be viable (Shaw and Hausbeck, 1995).
Research Proposed: PM sporulation will be investigated using inoculated
plants maintained under optimum conditions for conidial germination and
infection. Following the incubation period, plants will be moved to a (15-25C)
growth chamber at 60-90% RH. The time to colony appearance will be noted
and leaf discs removed, fixed, and the newly-formed conidia counted. To
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 bv 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 including
scanning electron microscopy will be pursued if results from the described
study indicate additional information could be obtained through those methods.
To 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 40 C 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 strategic for controlling PM and Botrytis. Progress to
Date: A weather-driven conidial release predictor developed for use for
Botrytis blight on onions in the field was used to time protectant fungicide
sprays for control of Botrytis leaf blight on a greenhouse crop in a commercial
operation. A computerized automated field weather station (Envirocaster)
was used. Plots receiving weekly sprays of chlorothalonil (Daconil 2787)
or predictor-time sprays were not significantly different based on visual
disease ratings although both plots had lowered disease ratings in comparison
to the unsprayed control plots. Since the humidity was high, an equal number
of sprays was applied for plots receiving weekly or predictor-timed sprays.
Research Proposed: The experiment described above will be duplicated in
commercial greenhouses with grower cooperators.
5. Develop a guide entitled “Foliar Disease Management for Poinsettias”.
Significant information has been gathered smce the start of this project.
A guide for growers and handlers of poinsettias can now be developed and
will cover identification, scouting, fungicide application, and environmental
manipulation for the control of PM and Botrytis.
LITERATURE CITED
Ceho, G.J.. and M.K. Hausbeck. 1994. Influence of temperature and relative
hurnidity on germination of conidia of Oidium sp. on poinsettia. Phytopathology
84:108-5 (abstract).
Covier, D. L. 1985. Powdery mildews. In: Diseases of Floral Crops -
Vol. 1. Praeger Publishers Division. Westport. Connecticut. D.L. Strider.
editor. pp. 103 - 140.
Daughtrey, M., and J. Hall. 1992. Powderv nuldew - A new threat to your
poinsettia crop. GrowerTalks. September, pp. 23-31.
Daughtrey, M., and M. Macksel. 1994a. Efficacy of fungicides for control
of powdery mildew disease of poinsettia, 1992. Fungicide and Nematicide
Tests 49:373.
Daughtrey, M. and M.T. Macksel. 1994b. Occurrence and control of powdery
mildew in U.S. Greenhouses. (Abstr.) Phytopath.
Good, H.M.. and Zathureczky, P.G.M. 1967. Effects of drying on the viability
of germinated spores of Botrytis cinerca. Phytopathology 57:719-722.
Hausbeck, M.K. 1993. Biological Control and Environmental Manipulation
for Control of Bottytis. Proceedings for the 9th Conference of Insect and
Disease Management on Ornamentals. SAF. Alexandria. VA, pp. 73-79.
Hausbeck, M.K, 1995. More mileage from Poinsettia fungicides. Greenhouse
Grower 13(10): 42-45.
Hausbeck, M.K., and J. Kalishek. 1994. Influence of temperature and
relative humidity on germination of conidia of Oidium spp. on poinsettia.
Phytopathology 84:1085 (abstract).
Hausbeck, M.K., J. Kalishek. M. Daughtrey, and L. Barnes. 1994. Keep
the colonies at bay (part 1). Greenhouse Grower 8:45-48.
Hausbeck, M.K., J. Kalishek, M. Dauehtrey, and L. Barnes. 1994. Keep
the colonies at bay (part 2). Greenhouse Grower (9:88-92).
Hausbeck, M.K. and J.J. Kusmer. 1995. Evaluation of curative fungicides
for the control of powdery mildew of poinsettia. 1993. 50:397.
Hausbeck, M.K. and J.J. Kusmer. 1991. Evaluation of preventative fungicides
for the control of powdery mildew of poinsettia. 1993. 50:398.
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. 75:798-803.
Moorman, G., and R. Lease. 1992. Benzimidazole- and Dicarbomoxide-Resistant
Botrytis cinerea from Pennsylvania Greenhouses. Plant Dis. 76:477-480.
Pritchard, P.M., M.K. Hausbeck, and R.D. Heins. 1995. Influence of day/night
temperatures on the susceptibility of poinsettias to Botrytis cinerea.
Phytopathology 85:1171 (abstract).
Shaw, B. and M.K. Hausbeck. 1995. Epidemiology of powdery mildew in
poinsettia. Phytopathology 85:1170 (abstract).
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. 151-404.
BUDGET
Greenhouse Supplies: 4,000
Includes growing media, containers, fertilizer, photographic costs,
and development of educational materials for growers.
Undergraduate hourly assistance ($1,500/researcher) 4,500
Growth and Dew Chamber Usage and Supplies 1,800 ($50/unit/month x 3
units)
Salaries * Graduate Student Stipend (1/2 time) 15,000 *
1/4 Research Technician including fringes 10,000
TOTAL COST OF PROJECT $35,300
Chemical Industry Contribution 10,000
Paul Ecke Ranch Support 7,500
AMOUNT REQESTED FROM AFE $17,800
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 research
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.
