The Q&A Archives: White Dusty Substance on Rosemary

Question: I moved my potted rosemary plants indoors for the cold weather. I notice that new growth is totally covered in a white dusty substance which does not rub off. Are the plants diseased? And if not, can the new rosemary growth be eaten/used in cooking? Diane Mix East Haven, CT

Answer: I think that the white substance you see on the new growth is normal. As the leaves mature, their appearance will probably change. If you examine mature leaves, you will see tiny white hairs on the undersides of the leaves This should be very similar to the substance you've observed on the new leaves. The only other explanation is that the your plant is suffering from powdery mildew.....but you would see that on mature leaves as well as immature leaves.

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