Most obvious in dank weather when it causes flower spotting. Mid
and deep blue varieties are particularly susceptible being disfigured by white
spots. Certain white varieties readily show brown spots, but others are more
resistant. This very common and widespread disease is often a secondary
infection on Fusarium or on physical damage and then appears in the form of a
grey fluffy mould which can spread to kill the plant.
Difficult to control chemically, but
fortunately the most aggressive strains are not the most resistant to
treatment. Generally speaking, an improvement in ambient conditions will
produce the most favourable results. The disease likes mild damp conditions
with stagnant air, and consequently is discouraged by air movement, a buoyant
atmosphere, and high or low temperatures.
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