Integrating Control of Botrytis and Powdery Mildew in a Greenhouse Crop Progress Reports –September 1994
Date 8/29/94
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 12/31/97
Individual(s) Conducting Project:
(List Project Leader First)
Mary K. Hausbeck - Title Assistant Professor
Telephone Number 517-355-4534
Margery Daughtrey - Title Senior Extension Assoc.
Larry Barnes - Title Associate Professor
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 the longtime nemesis of
poinsettia (Botrytis blight). The following objectives have been defined:
A scouting program was implemented in a commercial
greenhouse range that had just been discovered to have poinsettias infected with
PM. Stock plants and cuttings were scouted weekly. One out of every 30 plants
was observed. Plants were selected at random using a zig-zag pattern between
benches. Both the top and bottom surfaces of four older, mature leaves were
observed. If PM 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, two to five leaves had PM colonies present.
For our research purposes, the cultivars where PM 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. The fungicide used was
chosen and applied by the greenhouse staff. Greenhouse environmental conditions
including temperature, relative humidity, and leaf wetness were monitored. on
the first observation, 36% of one poinsettia 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 50W a week later. Within
six weeks of the initial scouting date, PM could not be detected and did not
reappear during the course of crop production.
that Domain, Strike, Terraguard, Phyton 27, Sunspray + baking soda combinations,
insecticidal soap, Chipco 26019, and UBI4077 may be of benefit in managing
powdery mildew on poinsettia.
temperature and relative humidity (RH) on germination, appressorium formation,
and shriveling of conidia were studied in 15, 20, and 25′C growth chambers.
Conidia were incubated in sealed containers for 24 hr on 9-mm-diameter leaf discs
cut from mature leaves of poinsettia ‘Freedom’. The discs were placed on 2.5 x
1.25 cm pieces of water agar on screening over saturated salt solutions that
provided 95, 85, 75, 65, 55, 45, 35% RH. A minimum of 100 conidia on each of
three leaf discs were observed and each experiment was conducted three times.
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
appressoria. Shriveling of conidia was least (6%) at 25′C and 95% RH; greatest
(39%) at 20′C and 35% RH.
for PM into an integrated disease management system that utilizes sanitation,
fungicide applications, and environmental manipulation to reduce disease
incidence and severity.
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 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.
