Biology & Disease Cycle of Grey Mould (Botrytis cinerea)
Grey mould (Botrytis cinerea) can be a serious problem on greenhouse
tomatoes under cool and wet (high humidity) conditions. In British Columbia, the
fungus can cause serious damage to greenhouse tomato in early spring and late
fall. B. cinerea is a cosmopolitan fungus that has a wide host range,
including tomato, pepper and lettuce. The fungus can infect almost all parts of
a plant, including stem, leaf, petiole, peduncle and fruit. Stem infection through
leaf-pruning scars and peduncles (fruit stem) often leads to stem canker, the
most destructive stage of the disease causing substantial crop losses.
Grey mould thrives under cool, wet conditions and often establishes on dying
tissues. It produces masses of dry spores called conidia that are air-borne.
Spores are readily dispersed by wind (air currents), over-head irrigation or
sprays, tools (particularly pruning shears & knives), machinery and workers. An
epidemic situation can happen from air-borne spores that can infect soft
tissues, cut-wounds and blossoms when moisture is present.
||Figure 1. Botrytis infection on tomato (var. 'Bizarr') stem,
showing brownish-grey, dry lesion and girdling of the stem. Masses of
grey colour Botrytis spores can be seen on the surface.
The most common and damaging infections take place through leaf-scars
during de-leafing operation. Botrytis spores can remain dormant for
10 to 12 weeks within leaf scars made at pruning. Such spores can be triggered
to germinate by low light, plant stress or shift in fruit load. Spores germinate
and penetrate the plant surface within 5 to 8 hours on wet/moist plant surfaces
at the optimum temperature of 15-20°C. A new
infection can produce visible symptoms and masses of spores (conidia) within a
few days, thus a multiple cycles of infection can be expected in a given growing
Botrytis can survive/overwinter as mycelia and/or sclerotia in the
soil, on plant debris, and on perennial plants and weeds for several months or
|Figure 2. Botrytis infection on tomato (var. 'Bizarr') stem and
fruit peduncle. Infected tissues turn brownish-grey and masses of grey
Botrytis spores can be seen on the surface.
||Figure 3. Tomato (var. 'Bizarr') leaf infected with Botrytis
showing brownish-grey discolouration and withering.
Management of Botrytis
PREVENTION (Steps to be taken before the onset of disease):
- Follow overall biosecurity procedures: Enforce strict biosecurity
& phytosanitary requirements as appropriate for your greenhouse operation.
- Prevent initial infection and introduction of Botrytis into
greenhouse: Enforce general year-around sanitation practices and
thorough year-end clean up (thoroughly disinfect greenhouse physical
structures, machinery and tools between crops).
- Grow resistant/tolerant varieties if any: Avoid growing tomato
varieties that are highly susceptible to Botrytis. Choosing a
resistant if not a tolerant variety will reduce disease severity and build
up of spores during critical infection period.
- Adopt good cultural practices: Remember! Cool & wet conditions
are ideal for Botrytis outbreaks and high humidity (>80%) is highly
conducive for disease development. To avoid this, leave adequate spacing
between plants, increase air circulation by removing lower leaves from
overly shaded areas. Maintain adequate heat and ventilation, particularly in
the nights where temperature can be expected to drop significantly. Monitor
the moisture level in the greenhouse. Avoid over-head irrigation. Avoid
spray operations in the late afternoons and on cloudy days; spray operation
in the morning hours is highly recommended. Any water-based irrigation or
spray operations must be done in the morning hours and on sunny days to
minimize prolonged wetness on plant surfaces. Avoid puddling of water on the
surfaces of greenhouse production sites.
- Scouting and early detection of Botrytis infection:
Periodically and closely monitor for Botrytis disease symptoms,
especially in the spring and fall seasons. Follow a strict and structured
fungicide spray program (see below) and cultural practices to prevent the
spread and severity of the disease.
ERADICATION / MANAGEMENT:
- Follow strict sanitation and cultural practices as outlined under
- Most importantly, eliminate or minimize the inoculum (spore) load &
sources of inoculum in the greenhouse:
- Remove heavily infected plants from the bay. When doing so, if possible,
wrap the infected plant tissues with a wet paper towel/newspaper (use soap
water or KleenGrow®, previously Chemprocide) to prevent spores from dislodging into the air.
- Cover cull/trash piles of infected plants with a plastic sheet and take immediately to
a far site for deep-burial or incineration. Consider the greenhouse
location and the wind direction when choosing a plant refuse dump-site.
- Treat the Botrytis lesions on stems at a very early stage –
scrape off the epidermal layer of the tissue and immediately apply an
appropriate fungicide paste (Ferbam, see below).
- Severe lesions cannot be treated, as
described in step (3), since they have already damaged the vascular
system; for such lesions, cover the lesions with disinfectant-treated
paper towels/newspaper to reduce spore dispersal.
- Apply Botran at 7-day intervals or as required to infected lower
stems up to 60 cm from the ground.
- Treat the tarped-flow periodically with an appropriate disinfect.
- De-leafing operation and worker sanitation practices: One of the
primary sources of Botrytis infection is via leaf-cut wounds, which often
result in severe stem canker. Pruning is recommended in the early afternoon
since it will allow leaf-cut wounds to dry quickly. Treat pruning shears and
knives with disinfectant after pruning each plant. Use a couple of pruners
alternatively; this will give sufficient time to disinfect a pruner (dip
pruning shears/knives in either 70% ethanol or 0.1-0.2% KleenGrow for a
minimum of 2 min). The second factor is handling of infected plants and
de-leafing of plants by the workers. Use hand-sanitizers as frequently as
possible, particularly when de-leafing.
- Follow a scheduled fungicide spray program: Begin using fungicides at the very first sign of symptoms or when the conditions are favourable for disease development. Expected results may not be achieved with any good fungicide program if the disease pressure is high. Use a combination of chemical- and bio-fungicides (Table 1); choose from different chemical groups for maximum efficacy for Botrytis control and to prevent the pathogen from developing resistance to a specific chemical.
- Decree and Botran are restricted to 3 applications and Pristine and Scala to 1
application per crop cycle. Since Botrytis can be expected to cause damage in
spring and fall use Pristine and Scala wisely, alternating witih other chemicals in spring and fall.
- Use the biological
fungicides Prestop and Rhapsody preventatively, before the onset of disease or when disease pressure is low. Biological fungicides may not give expected results when applied at high disease pressure.
- To prevent resistance development in the pathogen to a fungicide,
- Never apply a fungicide below recommended rate
- Use fungicide at the highest recommended rate
- Do not apply the same fungicide repeatedly. Rotate
fungicides from different chemical groups.
Table 1. A summary of registered fungicides and label information (Please
adhere to product label instructions when using each chemical).
||Chemical / biocontrol agent
||Mode of Action
||use preventatively; do not exceed 3 applications per crop cycle; apply at 7 day intervals; spray the stem of the plant from ground level to a height of 45 to 60 cm
|Decree 50 WDG
||use preventatively; do not exceed 3 applications per year; apply at 7-10 day intervals; treated tomatoes CANNOT be used for processing
|Ferbam 76 WDG
use preventatively before onset of disease or at first sign of symptoms; apply every 3-4 weeks
||boscalid + pyraclostrobin
||7 & 11
||preventative, locally systemic
||do not exceed 1 application per crop cycle, use in rotation with other fungicides at 7-14 day intervals
||Bacillus subtilis QST 713
|| use preventatively before onset of disease or at first sign of symptoms; apply at 7-10 day intervals
||use preventatively; no residue tolerance for export to USA
||preventative, locally systemic
||use preventatively; do not exceed 1 application per crop cycle; use in rotation with other fungicides at 7-10 day intervals
||use preventatively before onset of disease or at first sign of symptoms. Caution: toxic to bees & beneficial insects
1REI - re-entry interval indicated on label
2PHI - pre-harvest interval
NC - not classified
Dr. Siva Sabaratnam
Abbotsford Agriculture Centre
British Columbia Ministry of Agriculture