Integrating Control of Botrytis and Powdery Mildew in a Greenhouse Crop Final Report
Integrating Control of Botrytis, Powdery Mildew, and Downy Mildew in Flower
Crops
M.K.
Hausbeck, Michigan State University; M. Daughtrey,
Cornell
University; and L. Barnes, Texas A&M University
INDUSTRY
NEEDS:
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Commercial flower growers must face increasing pesticide regulations
while adopting environmentally-sound practices which may increase production
costs and decrease profits. In
addition to these challenges, growers of flower crops must manage a host of
potentially devastating diseases including powdery mildew (PM), downy mildew
(DM) and Botrytis.
PM is a continuing problem for poinsettia growers, especially those in
the northern U.S. and Canada, and it was considered a “new” disease in the
U.S. in the early 1990s (Daughtrey
and Hall, 1992). The fungus which
causes the disease is currently referred to as Oidium
sp. since the information necessary to classify it further is lacking.
More information is needed on the effect of environment on the
infection and progression of PM. However,
understanding this component of PM biology is critical to the production of
disease-free poinsettia cuttings. Information
learned regarding PM on poinsettia will be helpful in understanding PM on
other crops, such as gerbera and rose, which continue to offer significant
challenges to growers. New
fungicides are needed for a PM management program for roses because the PM
fungus has likely developed resistance to fungicides currently relied upon.
While much is known about the general biology of Botrytis
cinerea, this fungus continues to cause significant losses at all stages
of production. 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).
Botrytis conidial “showers” are typically associated with grower
activity (Hausbeck and Pennypacker, 1991), and those occurring during and
immediately after harvesting are important in disease management.
In order to protect plants, fungicides that are effective against B.
cinerea are used repeatedly, and continuous use of systemic fungicides has
resulted in the selection of resistance in greenhouse
Environmental modification in a commercial greenhouse has been a
successful control tool to reduce Botrytis blight has
traditionally been the primary foliar disease of poinsettia causing leaf,
stem, and bract blight (Strider and Jones, 1985).
Botrytis also frequently causes storage blights of cut flowers.
When cut roses are stored under high humidity, petal spotting caused by
Botrytis may progress rapidly and blight the entire flower head.
Gerbera flower blight can be a limiting factor in production, with
symptoms often occurring during storage or transport and shipment, when
temperature fluctuations result in high humidity and condensation on flowers
(Salinas and Verhoeff, 1995).
Tthere is little information regarding DM on floriculture crops even
though this disease continues to negatively impact certain sectors of the
floriculture industry. DM of
roses (caused by Peronospora sparsa)
results in plant stunting and foliar chlorosis.
DM (caused by Peronospora
antirrhini) is a devastating disease on cultivated snapdragons, especially
on seedlings raised in humid conditions.
DM causes yellowing of leaves and stunting of plants, and the fungus
may also infect the growing points of established plants (Nelson and Strider,
1985). In general, sporulation of
Peronospora spp. requires high
humidity or dew and temperatures of 4-7 to 22-25 (Yarwood, 1943).
There is little information regarding the influence of environment and
stages of the DM fungus infection cycle.
Knowledge of the environmental effects on the establishment and
progression of specific diseases would allow growers to manipulate their
greenhouse environments to best avoid disease development.
The judicious use and rotation of fungicides with different modes of
action, the use of biocontrols, and optimizing the interval between
applications would help avoid development of fungicide resistance in the
fungus while providing disease control in an efficient manner.< ![if !supportEmptyParas]>
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PROJECT
OBJECTIVES:
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1.< ![endif]>
Conduct fungicide trials
using registered and experimental fungicides and biocontrol agents in both the
greenhouse and the field to:
-
control PM in gerbera, rose, and poinsettia stock plants
and cuttings;
-
control Botrytis in postharvest roses; and
-
control DM in
snapdragon.
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2. Work to support additional
registrations for needed fungicides on flower crops.
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Survey and meet with
snapdragon producers to explore options for cultural management of DM and
initiate research regarding the source of DM epidemics in snapdragon.
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Research the environmental
and cultural factors affecting disease development (epidemiology) of Botrytis,
DM, and PM.
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Develop grower recommendations for integrated control of Botrytis
(rose, poinsettia), PM (gerbera, rose, poinsettia) and DM (snapdragon).< ![if !supportEmptyParas]>
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RESEARCH
CONDUCTED:
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1.
Conduct fungicide trials using registered and experimental fungicides
and biocontrol agents in both the greenhouse and the field to:
-
control PM in gerbera, rose, and poinsettia stock plants and
cuttings;
-
control Botrytis in postharvest roses; and
-
control DM in
snapdragon.
-
Over the course
of this grant, there have been two trials for PM on gerbera, 14 trials for PM
on rose, six trials testing fungicides on PM on poinsettia, two trials for
Botrytis on cut roses, and one trial for DM on snapdragon.
PM on gerbera
Eight fungicides
and 15 treatments were investigated for their ability to control PM on
gerbera. The systemic fungicides,
Systhane (applied at 14-day [14d] or 21d intervals) and Terraguard (4 or 8 oz
at 7d), provided complete PM control throughout the course of the trial.
Strike (1 vs. 2 oz, 30d) failed to provide adequate PM control beyond
21d after application at either rate. Triact
(0.5%) and ZeroTol (1%), contact, surface-active products, provided generally
good PM control at 7d intervals. Soluble
Silicate provided fair-to-good control at 2000 ppm, however, it left
noticeable residue on the plants.
Five fungicides (Pipron,
Terraguard, Strike, and Systhane) applied at 10d intervals were compared for
their ability to control PM on gerbera.PM on roses
A 1996 study at MSU
compared BAS 114 UBF (Milsana), BAS 490/Cygnus and the industry standard
Strike. All treatments were
effective compared to the untreated control.
BAS 490/Cygnus (0.2 lb) was significantly more effective than other
treatments in reducing incidence and severity of PM.
BAS 114 UBF (0.5 or 1%) was similar to Strike in disease control.
2.)
BAS 490/Cygnus (0.2 lb, 7d) was compared to Rubigan (6 oz, 7d) in New
York in 1996. By the end of the
experiment, both products had significantly decreased the percentage of leaves
with PM (0 to 0.8%) compared to the controls (84.6%) for cv. Red Sunblaze.
3.)
Terraguard (4 oz) at 7d and 14d intervals was compared to Latron (1 pt)
at 7d intervals at New York in 1997. Terraguard
at 7d intervals resulted in significantly better control of PM throughout the
experiment.
4.)
A 1997 trial at New York compared eKsPunge and/or Latron B-1956 with
Terraguard. All treatments
significantly reduced foliar PM compared to the untreated control.
EksPunge was significantly more effective at 7d than 14d intervals.
5.)
Another study at New York in 1997 compared monopotassium phosphate
product (eKsPunge) with and without spreader-sticker to Terraguard (Daughtrey
and Macksel, 1997b). Treatments
of Latron, eKsPunge + Latron, and Terraguard at 7d intervals provided
significant reduction of disease, but the level of control was acceptable only
with the Terraguard treatment. Terraguard
7d was superior to the other treatments
6.)
An experimental fungicide (WAC-72) was compared to Cleary’s 3336 and
Pipron + Latron B-1956 (Daughtrey and Macksel, 1997c).
At the final rating, the most effective treatments were Pipron (8oz) +
Latron B-1956 and the combination of these
two materials with Cleary’s 3336 (16 oz).
A new fungicide
(Recover FL) was compared with Pipron, Strike, and Terraguard.
All fungicides significantly limited PM on foliage and flowers compared
with the untreated control. Pipron,
Strike, and the high (300 ppm) rate of Recover were especially effective in
limiting the number of flowers infected (<0.3%) (unpublished data; Hausbeck
et al., 1997).
8.) Both
fungicides significantly limited PM on flowers and foliage in comparison to
the untreated control. There was
no significant difference between type of fungicide used or length of
treatment interval (7d vs. 14d).
9.)
All fungicides significantly limited PM on foliage compared with the
untreated control. Cleary’s 3336
WP + Pipron LC + Clearspray T/O, Cleary’s 3336 WP, and Cleary’s 3336 WP +
Clearspray T/O significantly limited the number of flowers with PM compared
with the untreated control.
10.)
In a study at Cornell (1998/99), a trial comparing WAC-72 (recently
registered as ‘First Step’), Kaligreen, Pipron, and a baking soda +
horticultural spray oil “home remedy” preparation (not legal for
commercial greenhouse use) was conducted.
All of the products provided equally good control in all treatments.
Few, if any, colonies were visible on the bicarbonate-treated plants.
11.)
In a second study conducted at Cornell (1998/99), 7d treatments at all
rates of WAC-72 tested provided excellent control, as did the Pipron sprays.
PM was reduced, but less effectively, by combinations of thiophanate-methyl
and either Pipron or WAC-72 applied on a 14d basis.
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12.)
A trial comparing varying rates and application intervals of Heritage
against Strike, an industry standard was conducted at MSU in 1998.
Although there were no significant differences, trends noted. Strike
and the untreated control had higher percentages of foliage and flowers
infected than Heritage at both rates (4 and 8 oz), regardless of being applied
at 7, 14 or 21d intervals.
13.)
A trial in 1999 (similar to the 1998 study) at MSU compared various
rates and application intervals of Heritage against Strike, an industry
standard. Again, there were no
significant differences among treatments; however, Strike limited disease on
the foliage compared to the untreated control.
Heritage (4 or 8 oz) provided foliar PM control comparable to the
Strike standard when applied every 7 or 14d.
14.)
A second study at MSU in 1999 compared Cygnus alone or in combination
with Latron B-1956, Latron alone, Strike + Latron, Heritage, BAS 114 UBF (Milsana),
and Systhane. Cygnus (0.1 or 0.2
lb, 7 or 14d) and Systhane (5 oz, 14d) held PM to <5% on foliage. (0.1
or 0.2 lb) + 2 oz Latron B-1956 (7 or 14d), and Systhane resulted in a rating
of <1.0 (where 0=no PM) for PM on foliage and on flowers.
Heritage (2 oz, 14d) also had a rating of <1.0 on flowers only.
PM on poinsettia
All treatments significantly reduced the number of PM colonies on
leaves and bracts compared to the untreated control.
Terraguard (8 oz) and Pipron (8 oz) + Latron (0.06%) resulted in no
colonies on the bracts, while Strike (4 oz) resulted in no colonies on the
leaves.
In a study
conducted in New York (Daughtrey and Macksel, 1997a), all treatments gave
significant control of PM on leaves compared to the untreated control.
Weekly sprays with eKsPunge + Latron or Latron alone gave significant
control of foliage, but were ineffective on bracts.
On bracts, the best control (no colonies) was seen in Terraguard
treatments. A strobilurin
fungicide, BAS 490/Cygnus, was also tested at 14d intervals and provided
control of PM on bracts that was statistically similar to Terraguard, although
a few scattered colonies were visible. Weekly
treatments with the experimental fungicides AC-72 and WAC-73 was also
effecttive at controlling disease on bracts although leaf and bract tip burn
was observed.
A 1997/98 trial at
MSU compared 0.2 lb BAS 490 + 2 fl oz Latron B-1956 (7 or 14d), Systhane (4, 8
or 12 oz, 14d), Strike (2 oz) + Latron (7 or 14d), Pipron (4 fl oz, 14d),
Terraguard (4 oz, 14d), WAC-72 (2.5 or 5 lb, 7 or 14d) and Cleary’s 3336 (1
lb) + Latron B-1956 (14d) for control of PM on poinsettia.
At the last observation date, all treatments were significantly better
than the untreated control with the exception of WAC-72 (2.5 lb, 14d).
Only the high rate of WAC-72 (5 lb) at 7d intervals resulted in
phytotoxicity.
4.)
A second study in 1997/98 at MSU compared Phyton-27 at varying rates
alone or in combination with Latron B-1956 (1 fl oz) at 7d intervals against
the industry standard Strike (4 oz, 14d) for control of PM on poinsettia.
Phyton-27, regardless of rate or whether a spreader-sticker was added,
showed significantly more disease than Strike for percentage of infected
leaves and bracts and for infection severity; it was comparable to the
untreated inoculated control on all observation dates.
5.)
Sixteen materials, including strobilurins, industry standards and
alternative chemistry products applied at at 7 or 14d intervals, were tested
in New York in 1998 (Daughtrey, et al., 1999).
All treatments significantly reduced PM severity on bracts and leaves
in comparison to the untreated control. No
PM colonies were detected on plants treated with the sterol biosynthesis
inhibitors (SBI) Strike, Terraguard and Systhane (all 14d); or Pipron,
eKsPunge (MKP), or Terraguard alternated with eKsPunge (all 7d).
Other materials tested which significantly suppressed disease were
Cleary’s 3336, BAS 114 UBF (Milsana, extract of giant knotweed), ZeroTol 27%
(hydrogen dioxide), Phyton-27, and WAC-72 (bicarbonate) (all 7d), and the
strobilurins, Cygnus, CGA 279, and Heritage (all 14d).
Spray residue on plants treated with eKsPunge and Cleary’s 3336 (7d)
was unacceptable; treatments alternating between Cleary’s 3336 and WAC-72
showed less residue.
6.)
Michigan’s 1998-99 fungicide trial included all products tested in
New York plus 10 additional materials. The
area under the disease progress curve (AUDPC) was used as a means of
summarizing the number of PM colonies occurring on the bracts over time.
Cleary’s 3336 + Latron B-1956 failed to provide control significantly
better than the untreated control. Applying
a low rate (2 oz) of Heritage at a 14d interval was similar to using a higher
rate (3 oz) at a 21d interval. Also,
using a higher rate (3.2 oz) of Cygnus at a longer interval was no different
than using a lower rate (1.6 oz) every 7d.
While there were no significant differences in the XDE-795 (quinoxyfen)
rates tested, the lowest rate (5 ppm) had more disease than the higher rates
tested. Similarly, there were no
significant differences among the CGA 279 rates tested although the lowest
rate (0.5 oz) had the most disease. Both
rates of Systhane completely prevented the development of disease.
While Cleary’s 3336 + Latron B-1956 did not effectively control PM,
alternating this application with WAC-72 was effective.
A number of treatments provided a significant level of protection 60d
after the last fungicide application and included the following: Heritage (2
oz, 14d), Cygnus, XDE-795, CGA 279 (1 and 2 oz), and Systhane.
Systhane applications completely prevented PM development even 60d
after the last fungicide application. PM
development on the leaves was negligible, and not reported.
Botrytis on cut roses
Eight shipments of
three cultivars (pink ‘Dolores,’ dark red ‘Royalty,’ red ‘Kardinal’)
of long-stemmed cut roses were received at MSU with the buds wrapped in
cellophane and stems packed with ice. The
treatments were postharvest flower dips of l lb/100 gal of Decree, 12.5 oz/100
gal of Phyton-27, and the untreated control.
Roses were inoculated with Botrytis
spores or misted with water. ‘Royalty’
seemed to be the most susceptible cultivar.
When averaged across shipments, an application of Phyton-27 to
uninoculated roses resulted in significantly more healthy roses than the
untreated control.
In a second set of
experiments at MSU, red ‘Robina’ roses were treated by either dipping or
spraying the flower to runoff. Roses
were misted with Botrytis spores and
later rated for disease development. All
controls became blighted. Ornalin
FL effectively limited Botrytis blight with 16.7% healthy roses in experiment
1 and 25% healthy roses in Experiment 2, but left a slight residue on the
flowers in both experiments. Timsen
40WP (experiment 1) was the only other treatment with healthy flowers; it had
33.3% healthy roses 3d after inoculation, but all showed some sign of
infection after 5d. All
treatments delayed the development of blighting in Experiment 1.
In Experiment 2, several treatments resulted in substantially less
blighting than the untreated control and included WAC-73, ESC11 (Pseudomonas
syringae), ESC10 (P. syringae),
and Ornalin FL. TopShield (Gliocladium catenulatum) in
Experiment 1 left heavy residues on the flowers and did not provide control.
DM on snapdragon
Experimental
materials, ¬ìExp 1,¬î ¬ìExp 2,¬î and ¬ìExp 3″ were tested at Cornell
for their ability to prevent DM on snapdragons.
Only one yellow spotted plant (3%) with sporulating DM was noted in the
Exp 1 (higher rate) treatment and only 3 spotted plants (10%) in the lower
rate treatment. Plants treated
with Exp 2 also were well protected, showing only 1 spotted plant (3%).
None of the Exp 3-treated plants showed yellow spotting, while 30% of
the plants treated with Protect T/O and 73% of the plants treated with Banol
developed yellow lesions. Protect
T/O acts as a protectant whereas the experimental materials are at least
locally systemic.
Exp 2 and the higher rate of Exp 1 gave the best results overall, since
suppressing sporulation is important for managing an epidemic.
2.
Work to support additional registrations for needed fungicides on
flower crops. At the time
this grant was initiated, the fungicide Strike 25WDG was the only industrial
standard available for the control of PM on poinsettia.
During the course of this grant, based on the results of
fungicide trials, the following products have been registered for use
on poinsettia: Systhane, Terraguard, Phyton-27, Pipron, Cleary’s 3336.
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3.
Survey and meet with snapdragon producers to explore options for
cultural management of DM and initiate research regarding the source of DM
epidemics in snapdragon. Researchers
visited with producers and cut flower growers to assess current cultural
management strategies. A spore
monitoring project was initiated with a grower cooperator and is ongoing.< ![if !supportEmptyParas]>
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4. Research the environmental and cultural
factors affecting disease development (PM on poinsettia
A
scanning electron microscope (SEM) was used to determine that PM conidia began
to germinate within 2 hours of landing on a poinsettia leaf at 20 C (85% RH).
Conidial germination peaked at 76% within 36 hours after inoculation.
Within 24 and 48 hours after inoculation, 32.5 and 51.0%, respectively,
of germinated conidia had the structures (appressorium and haustorium)
necessary to infect the plant leaf. Using
SEM, unique morphological features of the powdery mildew fungus were observed
including an arced basal cell and thin ridges on the subterminal cells of some
conidiophores (Celio and Hausbeck, 1998).
Conidial germination was reduced, and development of secondary germ
tubes and haustoria was severely limited when incubation temperatures were 30
C (Celio and Hausbeck, 1998).
Microscopy studies of the infection process were conducted in relative
humidity (RH) chambers (35-92% RH) at 15, 20 and 25C, in which leaf disks cv.
Freedom Red) were incubated for 48 hours (Byrne and Hausbeck, 1998).
All aspects of the infection process were limited at 15C.
Infection rates were highest at 20C under 35-50% RH.
The highest temperature evaluated, 25C, favored maximum germ tube
elongation and development of secondary germ tubes and appressoria. The effect of
temperature on sporulation was quantified using leaf disks placed on agar
disks and incubated in petri dishes for 14d at 15 or 20C (Byrne and Hausbeck,
1999). The number of
conidiophores and length of conidial chains on the leaf disks were recorded. Sporulation was
initiated 9d after inoculation. Maximum
conidial chain lengths were 4 and 7 conidia at 15 and 20C, respectively.
The percentage of conidiophores bearing no conidia were 33 and 15%, at
15 and 20C, respectively.
DM on snapdragon and rose
A Burkhard spore trap and weather-monitoring equipment were placed on
site at two commercial grower cooperators.
One grower is a producer of cut snapdragons and the other a producer of
potted roses. Rainfall, relative
humidity, temperature, leaf wetness, wind velocity, and direction were
monitored with average values recorded hourly.
The trials were conducted from December through April, and analysis of
the data is ongoing. Spores of
the DM fungus were detected in the atmosphere just prior to the grower report
of the first DM occurrence in field snapdragons.
It was noted that spore release of the DM fungus typically occurred in
mid-morning during a time when the relative humidity decreased and the wind
speed increased. This followed a
dew period occurring the previous evening that likely provided the necessary
conditions for the spores to develop. Similar
information is currently being generated regarding the DM fungus that affects
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5.
Develop grower recommendations
for integrated control of Botrytis (rose, poinsettia), PM (gerbera, rose,
poinsettia) and DM (snapdragon).
Development
of a PM spray program for finishing and postharvest phases of poinsettia
production
Based on the
fungicide trials that were conducted during the course of this grant, the
following products completely prevented development of PM colonies on
poinsettia: Terraguard and Pipron + Latron for bracts and Strike for leaves
(trial 1); Terraguard (trial 2); Strike, Terraguard, Systhane, Pipron,
eKsPunge, Terraguard alternated with eKsPunge (trial 5); Systhane (trial 6).
Good control of PM was achieved with the following products:
WAC-72 (leaf/bract tip burn observed), WAC-73 (leaf/bract tip burn
observed), Cygnus (trial 2); Strike (trial 4); Cleary’s 3336, BAS 114 UBF
(dark spots observed), ZeroTol (white spots observed), Phyton-27, WAC-72,
Cygnus, CGA 279, Heritage (trial 5); Cleary’s 3336 alternated with WAC-72,
Cygnus, XDE–795, CGA 279 (trial 6). These
products give growers alternatives to systemic fungicides (Systhane,
Terraguard, Strike) in the management of this disease.
Further development and registration of the experimental fungicides
listed here will increase the alternatives available to growers.
Development of a PM spray program for the stock plant and cutting
phases of poinsettia production
Studies
were initiated to determine whether an application of a systemic fungicide to
a stock plant could provide protection to the cuttings that would subsequently
be removed from that plant. Stock
plants were given a single treatment with Terraguard or Systhane eight days
before cuttings were taken. After
the cuttings were removed from the stock plant, they were inoculated with
powdery mildew conidia and maintained in an environment conducive to disease
development. The Terraguard
treatment suppressed PM development for approximately 29 days.
The Systhane spray controlled PM infection for 55 days.
In another study, when cuttings were removed two months following
fungicide application they became as diseased by PM as cuttings from stock
plants receiving no fungicide sprays (Unpublished data; Byrne and Hausbeck,
1998). Fungicide trial 5 found
that Systhane completely prevented PM development even 60d after the last
application, and the following products gave a significant level of protection
60d after application: Heritage (s oz, 14d), Cygnus, XDE-795, CGA 279 (1 and 2
oz).
Screen poinsettia cultivars for resistance to 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; Celio
and Hausbeck, 1997).
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BENEFITS
TO INDUSTRY:
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1. Conduct fungicide trials using
registered and experimental fungicides and biocontrol agents in both the
greenhouse and the field to:
-
control PM in gerbera, rose, and poinsettia stock plants and cuttings;
-
control Botrytis in postharvest roses; and
-
control DM in snapdragon.
PM on gerbera
Several
novel fungicides, Triact, Soluble Silicate, ZeroTol, showed promise as new and
alternative tools to systemic fungicides for PM management.
PM on roses
New
fungicides are needed for the industry because the PM fungus has likely
developed resistance to currently relied upon fungicides.
A biocontrol (Recover), strobilurins (Cygnus, Heritage) and alternative
chemistries (BAS 114 UBF, eKsPunge, Kaligreen, WAC-72), were investigated for
their usefulness in a PM management program for roses.
Research studies will help to identify new fungicides that offer
promise for commercial development and use, which will offer growers
additional tools to manage fungicide resistance of PM.
PM on poinsettia
The
registered SBI fungicides (Strike, Systhane, Terraguard) are currently
providing excellent PM control. However,
considering the history of other PMs developing resistance to this group of
fungicides, resistance management programs must be developed and im0plemented
now to delay the development of resistance.
This project has identified a number of new products with different
modes of action that can be used reliably in a management program.
Further, this research has identified products that provide PM
protection for up to 60d following the last application.
Botrytis on rose
In
our studies, blighting of rose petals was the most severe symptom caused by
Botrytis. The industry standard
Ornalin FL consistently limited blighting caused by Botrytis in both
experiments. The commercially
available Phyton-27 is also effective in limiting Botrytis blight.
Based on our results and using blighting as a primary criterion, the
following products should be pursued in additional Botrytis trials:
alternative chemistry products Timsen 40WP and WAC-73, and the biocontrol
ESC10.
DM on snapdragon
Further
product development and registration of experimental materials, Exp1, Exp2 and
Exp 3, should yield some superior new DM controls for snapdragon.
2.
Work to support additional registrations for needed fungicides on
flower crops. Growers need a
variety of products and biocontrols available for disease control to allow
rotation of fungicides used which would avoid development of resistance in the
pathogen causing the disease.
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3.
Survey and meet with snapdragon producers to explore options for
cultural management of DM and initiate research regarding the source of downy
mildew epidemics in snapdragon. A
better understanding of DM and an evaluation of whether cultivars differ in
their susceptibility to this disease will be crucial in development of an
effective management program.< ![if !supportEmptyParas]> < ![endif]>
4.
Research the environmental and cultural factors affecting disease
development (epidemiology) and delayed symptom expression (latency) of
Botrytis, DM, and.PM on poinsettia
Information
from our research may further the progress in accurately classifying the PM
fungus and therefore increase our knowledge regarding host range and origin of
this pathogen.
Temperature manipulation may be a useful tool in managing PM on
poinsettia. For example, it would
be advisable for growers to drop the greenhouse temperatures temporarily
immediately following detection of PM to discourage rapid reproduction of the
fungus. Slowing down the ability
of the fungus to reproduce via temperature manipulation can greatly increase
the efficacy of fungicide control programs and reduce losses due to reduced
plant quality.
High temperature eradicative treatments might be feasible when
vegetative growth is desired such as during stock plant production or
following rooting of cuttings. In
may be advantageous for rooted cuttings to be exposed to a high eradicative
treatment since the plant size is small, requiring treatment of a much smaller
area than if treating larger stock plants.
While these treatments would not be helpful in a situation where
reinoculation is possible, it may be helpful in situations where propagators
are interested in treating rooted cuttings prior to shipment to insure the
poinsettia cuttings are free of powdery mildew.
Though it is unlikely that heat treatments can be used alone, there may
be the potential to incorporate temperature manipulation with scouting and
fungicide applications to further reduce growers’ powdery mildew management
costs.
DM on snapdragon
Currently,
there is little information regarding the environmental factors that trigger a
DM epidemic. Knowledge of the
environmental factors that are favorable for DM development could alert
growers that sprays need to be initiated or intensified to avert or limit a
disease epidemic.
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5.
Develop grower recommendations for integrated control of Botrytis
(rose, poinsettia), PM (gerbera, rose, poinsettia) and DM (snapdragon).
A PM management program for all susceptible flower crops
emphasizes early disease detection via weekly scouting (especially important
when the environment favors disease development), removal of infected leaves
or plants in bags to contain spores, and appropriate fungicide selection and
timing of fungicide applications.
A PM management program for poinsettia: Poinsettias are
susceptible to PM regardless of bract color.
Since cultivars with red bracts are particularly susceptible to PM,
additional attention should be paid to red-bracted poinsettias when scouting.
While cultivars with white bracts are less susceptible to PM, it is
worth noting that detection of PM in a commercial setting may be delayed due
to low visibility of PM on white bracts.
Effective fungicides have been identified that have systemic properties
and offer superior control of PM. Timely
applications of products tested in our studies have been the key for many
growers in turning around a PM epidemic and ensuring that PM colonies do not
reappear after leaving the greenhouse.
Propagators using Terraguard or Systhane on stock plants can anticipate
an extended period of protection for those cuttings removed from the stock
plant soon after fungicide application. As
a result, fungicide applications to cuttings could be delayed from one to two
months depending on the fungicide used. This
strategy would save unnecessary fungicide expense.
Studies indicate that high (30 C) temperature eradicative treatments
might be helpful in situations where propagators are interested in treating
rooted cuttings prior to shipment to insure the poinsettia cuttings are free
of PM.
A PM management program for rose: Trials carried out during the
course of this grant showed that while none of the fungicides completely
prevented PM on roses, there are products which significantly decreased the
disease, and they should be used in conjunction with scouting, and removal of
infected leaves where feasible.
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FUTURE
RESEARCH NEEDED AND FUTURE BENEFITS TO INDUSTRY:
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Epidemiology and management of PM:
a.)
Observe and quantify the effects of RH and temperature on the
sporulation of PM on poinsettia leaf tissue.
b.)
Determine the long-term effects of a high temperature treatment on the
infection process of PM of poinsettia.
c.)
Investigate the longevity of latent PM infections on poinsettia.
d.)
Determine the factor(s) prompting the release of conidia into the
greenhouse atmosphere.
e.)
Determine the efficacy of standard fungicides, biocontrol agents,
naturally-derived fungicides and novel fungicides in controlling PM on
poinsettia, gerbera, and rose. f.)
Determine which gerbera cultivars are especially susceptible to PM.
Epidemiology and management of
DM:
a.)
Determine the environmental factors that are conducive to disease and
prompt release of sporangia. This
system would be useful where DM occurs annually, alerting growers when the
environment is favorable for DM thereby prompting fungicide applications.
b.)
Determine which snapdragon varieties are especially susceptible to DM.
c.)
Determine the efficacy of standard and novel fungicides in controlling
DM on snapdragons and roses.
Epidemiology and management of
Botrytis:
a.)
Determine which cut rose varieties are especially susceptible to
Botrytis.
b.)
Determine the efficacy of standard fungicides, biocontrol agents,
naturally-derived fungicides and novel fungicides in controlling Botrytis on
cut roses.
Test a Botrytis
forecaster developed for other crops for its suitability for use in
floriculture.
Future Benefits to Industry:
Knowledge of the environmental effects on the establishment and
progression of specific diseases would allow growers to manipulate their
greenhouse environments to best avoid disease development.
Knowing the susceptibility of popular cultivars to specific diseases
would allow growers to either select varieties that offer some disease
resistance or know that susceptible varieties need to be closely monitored for
appearance of disease.ADDENDUM
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Literature
Cited:
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Byrne,
J.M., and Hausbeck, M.K. 1998.
Influence of temperature and relative humidity on infection processes
and sporulation of Oidium sp. on poinsettia foliage.Byrne,
J.M., and Hausbeck, M.K. 1999.
The effect of temperature on sporulation of
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Celio,
G.J., and Hausbeck, M.K. 1994.
Susceptibility of poinsettia cultivars to Phytopathology
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Celio,
G.J., and Hausbeck, M.K. 1997.
Evaluation of poinsettia cultivars for susceptibility to powdery
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G.J., and Hausbeck, M.K.. 1998.
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Daughtrey,
M., Byrne, J.M., and Hausbeck, M.K. 1999.
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The First International Powdery Mildew Conference, Aug. 29-Sept. 3,
Avignon, France.
Daughtrey,
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Powdery mildew - A new threat to your poinsettia crop.
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Long Island Horticultural Research Laboratory Annual Report p. 17.
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Daughtrey,
M., and Macksel, M. 1997c.
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M.K., and Pennypacker, S.P. 1991.Botrytis
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P.E., and Strider, D.L. 1985.
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Strider, D.L., ed.Salinas,
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D.L., and Jones, R.K. 1985.
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