Answer: Sunpatiens require lots of air circulation all around. If they are crowded, the soil is moist and the humidity is high (from water evaporation or from relative humidity), they can develop a fungal disease called Botrytis. Yours sound as though they might be over-crowded if they are interplanted with vinca. Sadly, your plants may be showing symptoms of gray mold (botrytis). If so, there's not much you can do to help them regain their health.
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