“To my knowledge coleus downy mildew hasn’t been seen regularly in a few years, but we’ve had reports of outbreaks last season and again this season so it’s a good time to become refamiliarized with its symptoms and signs.
Symptoms include leaf spots, which can vary in appearance from small necrotic spots, often angular in appearance, to larger necrotic patches. On some cultivars the spots appear diffuse or faded, or like groups of speckles. Other symptoms can include stunt, leaf twisting or curling, and leaf drop in extreme cases. On leaf undersides you can see fuzzy sporulation, grayish in color. Sometimes the sporulation is easy to observe, but other times it can be difficult to see or may not be present – the lack of sporulation does not necessarily mean that downy mildew is not the culprit.
Both seed and vegetative types are susceptible. There is a wide range of susceptibility and resistance among coleus cultivars – from varieties that show conspicuous leaf symptoms and leaf drop to cultivars that show minimal or no symptoms even under conditions with high disease pressure. Make note of the cultivars on which you see issues and those that you don’t, and in the future avoid the ones you’ve had problems with.”
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