Botrytis (grey mildew) waste factor number 1 in Rosa
When discussing post-harvest problems, research of various sources has shown that the fungus Botrytis cinerea (grey mildew) is the most common reason for flower waste. Botrytis gets its necessary food out of living and dead flowers and plants and will have a very damaging effect on them.
The infection and expansion
The infection starts with minuscule fungi spores. These spread via air and land on the plant. To be able to germinate moisture (water, i.e. condensation droplets) is needed. At first, Botrytis infection can be recognized as white spots on the petals. Gradually these spots expand and become brown and clearly visible. From that time on, the process of expansion cannot be stopped any more; the effect is so dramatic that the affected flower(s) must be thrown away, to avoid further infection. Atlow temperatures ( ± 5°C) the germination evolves slower than at higher temperatures (± 20°C).
Storage
The way to control damage as much as possible, is to hinder the germination of spores. This can be achieved by avoiding condensation.Which means: avoid temperature fluctuations. Store flowers at low temperatures (± 5°C) and keep doors closed as long as possible. A problem for retail is that the infection often starts early in the chain; at grower or wholesale level. That is why it is important to be very anxious about the first signs of Botrytis infection when buying flowers. These can be noticed as little white/brown spots on the petals, the so-called ‘pocks’.Flowers with this kind of infection should not be sold/bought. In addition: do not keep the flowers sleeved too long, because otherwise the humidity between the buds increases to the level of saturation, with condensation as a result, when temperatures fluctuate.
Hygiene, the key solution
Finally it is important to work as hygienically as possible, this means:
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Cleaning up remains of plants and flowers
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Daily cleaning of tables, scissors and knives
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Remove affected flowers immediately.
Botrytis can affect a lot of flowers, and some varieties more than others, i.e. Rosa ‘Grand Prix’ is very susceptible to Botrytis.Most problems occur with Rosa, Gerbera, Chrysanthemum and Eustoma (Lisianthus). To make it even more complicated, the Botrytis infection varies very much from one grower to the next and from season to season!
 
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Botrytis, the number one enemy of flowers, especially Rosa.
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TIPS
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Infection with Botrytis often happens early in the chain
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Pay attention to the presence of ‘pocks’ when buying flowers
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When experiencing continuing Botrytis infections, buy your flowers from a different grower
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Assure a relative humidity of 90-95% in cold stores for daily storage of flowers
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Avoid considerable temperature fluctuations
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Get the flowers out of the sleeve as soon as possible and into the water
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Work hygienically.
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