Why grey mould shows up "right now"

Botrytis is not random: cool air, high humidity, poor ventilation and dead flower/leaf debris together bring it on. Prevention is almost entirely the first three.

It establishes on dead tissue — spent flowers, old leaves, wounds — then spreads through humid air. Cleaning up beats spraying, and comes first.

The four conditions it likes

• Cool temperatures (typically cool, humid stretches and seasons).
• High humidity with a water film sitting on leaves or fruit.
• Poor airflow, dense plants, low light.
• Spent flowers, old leaves and infected fruit left around — the entry points.

Four things to do before any spray

• Clear debris: remove spent flowers, old leaves and infected fruit and take them out of the growing area.
• Control humidity: water in the morning, never in the evening; ventilate so leaves do not stay wet.
• Thin the canopy: open it up so light and air get in.
• Avoid wounds: prune on a dry, sunny day and keep wounds dry that day.

If it is already there

• Clean first, then treat: remove what is clearly infected before spraying.
• At first symptoms, spray at the label rate — products differ a lot; never double it.
• Do not use the same product twice in a row; alternate to slow resistance.
• Keep ventilating after spraying: spraying without drying the air usually fails.

An easily missed detail

On crops where you hand-pollinate or dip flowers (tomatoes, for example), petals and stigmas left on the young fruit are a favourite entry point. Removing the spent petals and stigmas 7–15 days after treatment — when the fruit is about 10–20 mm across — clearly cuts the number of infection points.

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