Integrating Control of Botrytis and Powdery Mildew in a Greenhouse Crop Progress Report –December 1994
Date 12/19/94
Title of Project Integrating Control of Botrytis and Powdery Mildew in a Greenhouse Crop
Institution where work is being conducted Michigan State, Cornell, Texas A&M
Amount of Endowment Grant $ 30,000
Covering Period 1/1/94 to 12/31/94
Anticipated Date of Project Completion/Final Report 12/31/95
Individual(s) Conducting Project:
(List Project Leader First)
Mary Hausbeck - Title Assistant Prof.
Telephone Number 517-355-4534
Margery Daughtrey - Title Senior Ext. Assoc.
Larry Barnes - Title Associate Prof.
Integrating Control of Botrytis and Powdery Mildew in a Greenhouse Crop
M. Hausbeck, M. Daughtrey, and L. Barnes
Michigan State University, Cornell University, and Texas A&M University
- A. Project Objectives:
- Poinsettia growers are in the unique position of managing
a “new” disease called powdery mildew (PM) along with longtime nemesis of
poinsettia (Botrytis blight). The following objectives have been defined:
greenhouse range for the detection of Botrytis blight. Plants being grown for
retail sale were scouted weekly. One out of every 30 plants was observed.
Plants were selected at random using a zig-zag pattern between benches. The
bottom leaves and senescent leaves that had dropped into the pot were observed.
If sporulating Botrytis was discovered, plants were flagged and infected leaves
were removed and placed in plastic bags to prevent further spread of the fungus.
Typically, on each infected plant, one senescent leaf that had fallen onto the
soil surface had sporulating Botrytis present. For our research purposes, the
cultivars where Botrytis was detected were scouted again at a 1:10 ratio to
better determine the incidence of disease. Fungicide applications were based on
weekly scouting results. Greenhouse environmental conditions including
temperature, relative humidity, and leaf wetness were monitored. This program
prompted one application of Termil whereas typically the grower would have
applied a minimum of 4 weekly applications. There was no loss in plant quality
as a result of increased disease due to the reduced applications of fungicide.
bracts, ability to prevent infection, ability to eradicate a pre-existing
infection, and a long treatment interval. We’re also looking for chemicals that
suppress PM fungus sporulation, since blocking spore production prevents the
spread of an epidemic.
Phyton 27 and Terraguard, both labeled for application to poinsettias and for PM
control, were effective in our trials. Chipco 26019 was also effective; it is
labeled for use on poinsettias, but not for powdery mildew control. Strike and
the numbered pesticides MYX4020, UBI40771 EXPI0307A and EXP10452A may be
beneficial in managing PM, but are not currently labeled for poinsettia use. One
additional active ingredient, thiophanate methyl (found in Domain, Cleary’s 3336
and Zyban) is effective against PM on poinsettia.
27 and MYX 4020 alternated, or the experimental UB14077 gave strong mildew
suppression: on average, fewer than two colonies developed per leaf. Powdery
mildew colonies were first observed October 12 on control plants, leaves. The
number of colonies in untreated checks tripled between October 12 and December
23. The MYX 4020 treatment occasionally caused injury to leaves.
although none entirely eliminated PM colony development on bracts. In additional
trials in New York and Michigan, biweekly Terraguard post-infection treatments
also suppressed disease. Strike and the experimentals EXP10452A and 10307A
suppressed sporulation after a single fungicide application. Chipco 26019
suppressed sporulation only after two applications; however, Chipco 26019’s
ability to suppress PM is exciting, since this material also control Botrytis.
Residue was noted on bracts in all treatments. Some minor leaf or bract necrosis
was apparent in plants treated with the higher rate of Chipco 26019 and
EXP10452A, but the lower rates tested were just as effective against PM as the
higher, injurious rates.
colonization on leaves. By December 23, Strike and Terraguard treated plants
showed almost no detectable mildew. An assessment of bract infection on February
3, seven weeks after the last treatment showed impressive suppression of colony
development on bracts. This extended period of bract protection is encouraging,
since in the absence of fungal suppression, PM will continue to develop.
Fungicides for Powdery Mildew On Poinsettias
Margery Daughtrey and Mary K. Hausbeck
- Fungicides - they’re invaluabletools to manage powdery mildew
when they’re used in combination with
monitoring, roguing diseased plants and manipulating the
environment. If growers are overly
reliant on one or just a few active
ingredients, powdery mildew fungi
can develop resistance. Because of this
long-range threat, the ideal solution
would be to increase the diversity of
fungicides registered for powdery
mildew control.
- How effective are fungicides - registered and not registered - in
- Research Findings
- In our studies powdery mildew
- Strike and the numbered pesticides
controlling powdery mildew? In New York
and Michigan we’re conducting studies to test fungicide effectiveness
against powdery mildew on poinsettias. Key attributes include: safety to
poinsettia leaves and bracts, ability to
prevent infection, ability to eradicate a
pre-existing infection, and a long treatment interval. We’re also looking for
chemicals that suppress powdery
mildew fungus sporulation, since
blocking spore production prevents
the spread of an epidemic.
built up rapidly on untreated poinsettias. Phyton 27 and Terraguard, both
labeled for application to poinsettias
and for powdery mildew control, were
effective in our trials. Chipco 26019
was also effective, it is labeled for use
on poinsettias, but not for powdery
mildew control.
MYX4020, UB14077, EXP1007A and
EXP10452A may be beneficial in man.
aging powdery mildew, but are not
currently labeled for poinsettia use.
One additional active ingredient, thiophanate methyl (found in Domain,
Cleary’s 3336 and Zyban) is effective
against powdery mildew on poinsettia
based on 1992 trials.
| Fungicides Effective Against Powdery | |||
| Mildew on Poinsettia | |||
| Trade name | Common name | Rate(s) tested | Spray interval |
| *Phyton 27 | coppersulfate | 13oz/100gal | 7-day |
| 21.36FC | – pentahydrate | 50oz/100gal | 7-day |
| *Chipco 26019 | iprodione | 16oz/100gal | 14-day |
| 50WG | 32oz/100gal | 14-day | |
| *Domain 46.2F | thiophanate-methyl | 10oz/100gal | 7-day |
| Strike 25 DF | triadimefon | 2oz/100gal | 14-day |
| *Terraguard 50W | triflumizole | 4oz/100gal | 14-day |
| 8oz/100gal | 14-day | ||
| *Materials not registered as pesticides were excluded from this table | |||
| Only products with an asterisk are Environmental Protection Agency-reg- | |||
| istered for use on poinsettias. Consult with your local cooperative exten- | |||
| sion service to determine what products are registered in your state. | |||
- All of the post-infection treatments
gave significant disease suppression,
although none entirely
eliminated mildew colony development
on bracts. In additional trials
in New York and Michigan, biweekly
Terraguard post-infection treatments
also suppressed disease.
Strike and the experimentats
EXP1 0452A and 10307A suppressed
sporulation after a single fungicide
application. Chipco 26019 suppressed sporulation only offer two
applications, however, Chipco
26019’s ability to suppress powdery
mildew is exciting, since this material also controls Botrytis, another
important poinsettia pathogen.
Residue was noted on bracts in all
treatments. Some minor leaf or
bract necrosis was apparent In
plants treated with the higher rate
of Chipco 26019 and EXP10452A,
but the lower rates tested were just
as effective against mildew as the
higher, injurious rates.
Michigan State University. Powdery
mildew conidia were supplied
once, on October 29. Fungicides
were applied until runoff on
November 9 and 23. Plants were
rated on a scale of 0 to 10 (0=no
bract infection; the rating of 10 was
assigned to plants with more than
five bracts infected and three or
more of the bracts nearly covered
with powdery mildew sporulation).
The experiment was replicated six
times using one Freedom poinsettia
for each treatment in a completely
randomized design.
applied biweekly markedly
reduced the mildew colonization
on leaves. By December 23, Strike
and Terraguard treated plants
showed almost no detectable
mildew. An assessment of bract
Infection on February 3, seven
weeks after the last treatment
(data not shown), showed impressive
suppression of colony development
on bracts. This extended period
of bract protection is encouraging,
since in the absence of fungal
suppression, powdery mildew will
continue to develop on bracts in a
retail or home setting.
Cornell University’s Long Island
Horticultural Research Lab.
Powdery mildew conidia were present
continuously beginning
September 16. On September 8,
and weekly or biweekly thereafter,
fungicides were applied until
runoff. Powdery mildew colonles
were counted on the upper three
leaf pairs of each poinsettia plant.
The experiment was replicated five
times using three V-14 Glory poinsettias
for each treatment in a
completely randomized design.
