Greenhouse
Project > Botrytis Blight of Greenhouse Crops
The Plant Disease Diagnostic Laboratory
Prepared by Dr. Robert L. Wick, Department of Microbiology,
Room 111, Fernald Hall, University of Massachusetts Amherst, MA 01003.
Tel. (413) 545-1045 Fax (413) 545-2532.
Revised February 19, 1998
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Botrytis
on Poinsettia leaf, with spores
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Introduction
Botrytis blight is one of the most common fungus diseases of greenhouse
crops. The disease is often referred to as gray-mold because it produces
a crop of gray fuzzy-appearing spores on the surface of infected tissues.
A variety of plants including ornamentals, vegetables and herbs are susceptible.
Management of environmental conditions, sound cultural practices, and
fungicides will control this disease.
Symptoms and Life History
Depending on the host and environmental conditions, Botrytis can
cause leaf and flower blight, fruit rot, cankers, damping off and root
rot. Plants may be attacked at any stage but new tender growth, freshly
injured tissues and aging or dead tissues are preferred. Spores are produced
in abundance on lesions as well as on plant debris left on benches, the
greenhouse floor and cull piles. Spores are easily disseminated by air
currents and splashing water. Given the common occurrence of Botrytis
in greenhouses and the relative ease in which it can propagate itself,
greenhouse managers must avoid conditions that are conducive to disease
development.
Like other fungi, Botrytis has a specific range of temperature
and relative humidity that is necessary for spore germination, infection
and disease development. In general terms, germination of spores and infection
of the host is dependant on a film of moisture for 8 to 12 hours, relative
humidity 93% or greater, and temperatures between 55 - 75 F. Botrytis
blight is more prevalent in the spring and fall months. Regulation of
temperature, humidity and leaf wetness duration can prevent disease development.
Disease Management
An integrated approach is desirable for the successful management of Botrytis
blight. Control weeds, and remove plant debris between crop cycles and
during production. Space plants to allow for good air circulation and
reduction of humidity within the canopy.
Reduce humidity. Reduction of humidity by heating and
ventilating is relatively inexpensive compared to the loss of revenue that
can result from Botrytis blight and other plant diseases. Warm air holds
considerably more moisture than cool air. In the evening, as warm air becomes
cooler, the relative humidity (RH) rises until water vapor begins to form
a film of moisture on surfaces (dew formation). This film of moisture is
essential for Botrytis (and other fungal pathogens) to germinate
and cause infection. To prevent excessive humidity and dew formation, turn
on the heat and open the vents. The warm humid air is ventilated to the
outside as the cooler outside air is drawn into the greenhouse. As the incoming
air is heated up, (even if it is saturated) the RH drops significantly.
This air exchange should only take 5 or 10 minutes. The energy necessary
to run fans and to provide heat is not significant. Under some conditions,
this cycle may have to be repeated several times during the evening. The
process can be simplified by installing timing devices.
Moving air, even in a closed greenhouse, helps to reduce moisture on
plant surfaces. Horizontal air-flow, as described in the Connecticut
Greenhouse Newsletter No. 125, produces more uniform temperatures
and reduces the pr obability that cool spots in the greenhouse will develop
a condensation problem. This publication is available through the University
of Connecticut, Cooperative Extension. Humidity can also be reduced by
watering in the morning when it is cool so that rising temperatures absorb
moisture.
Table 1. Fungicides for the control of Botrytis (see key
to symbols below).
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Botran
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Chipco 26019
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Daconil 2787
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Fore
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Exotherm Termil
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Ornalin
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Phyton
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Zyban
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African Violet
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---
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e
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---
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R
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R
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R
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R
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---
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Begonia
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---
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e
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R
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R
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R3
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R
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R
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R
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Carnation
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---
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R
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R
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R
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R3
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R
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R
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R
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Chrysanthemum
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R
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R
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R
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R
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R
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R
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R
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R
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Cyclamen
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---
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R
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---
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---
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R
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R
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R
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---
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Easter Lily
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---
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R
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R
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R
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R
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R
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---
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---
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Fuchsia
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---
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e
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---
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R
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R
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R
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---
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---
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Geranium
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R
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R
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R
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R
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R
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R
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R
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R
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Gloxinia
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---
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R
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---
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---
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R
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---
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---
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---
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Hydrangea
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R
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R
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R
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R
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R
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R
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---
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---
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Impatiens
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---
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R1
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---
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---
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R3
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R
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R
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R
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Lisianthus
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---
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e
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---
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---
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---
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---
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---
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---
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Poinsettia
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---
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R
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R2
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R
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R3
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R2
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R
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R
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Primula
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---
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e
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---
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---
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---
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R
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R
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R
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Rose
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R
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R
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R
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R
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R
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R4
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R
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R
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Snapdragons
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---
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R
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---
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R
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R
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R
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R
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R
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Statice
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---
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R
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R
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---
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---
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R
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---
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---
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Tomato
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R
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---
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---
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---
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R
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---
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---
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---
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Tulip
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---
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R
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R
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R
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---
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R
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---
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---
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Key to Symbols in Table
R = Registered for use on this crop.
--- = Not registered for use on this crop.
e = The fungicide has broad crop clearance but this host does not appear
on the label; use experimentally before applying to the entire crop.
1 Do not use Chipco 26019 as a drench for impatiens.
2 Phytotoxicity may occur to bracts.
3 Do not use Exotherm Termil on this crop when plants are flowering.
4 Ornalin is registered for rose bud wood in storage.
Links to Further Resources on the Web
Ohio
State Extension's Plant Pathology Fact Sheet on Botrytis Gray Mold
in Greenhouse Floral Crops.
Selected IPM Articles
2001
Annual Report
IPM Scouting and Decision
Making
Western Flower Thrips: Biology And Control
Fungus Gnats and Shore Flies
A Grower's Guide to Using Biological
Control for Silverleaf Whitefly on Poinsettias in the N.E. United States
Pointsettia - IPM Guidelines
Pest Management for Herbs
Pest Management for Vegetable
Bedding Plants
Botrytis Blight of Greenhouse Crops
Managing Weeds in Your Greenhouse
Natural Enemies for Greenhouse Pests
Part I: How to Use Living
Organisms for Pest Control
Part II: Parasites and Predators
Part III: Selection
and Buying of Natural Enemies Species
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