Rosemary leaf spotting
We recently moved several potted herb plants to a new house. In their previous location, they had received insufficient sun and water, and the pictured rosemary plant was among them. We assumed that the wilt and leaf spotting was wholly due to this and that pruning and improved conditions would help. However, upon planting a new rosemary plant with it, the younger plant has begun showing the same spotting. The larger rosemary will be removed and discarded and the smaller repotted, but are there additional organic controls that should be used?
Clackamas County Oregon
Thank you for your question. There are two diseases that are known to infect rosemary, both fungal and both related to soil moisture. These are native to dry regions, and require little water or nutrients to thrive. You can read about the diseases here: https://pnwhandbooks.org/plantdisease/host-and-disease-descriptions?title=Rosemary+ Once the soil is infected, it will cause similar problems for any healthy new plant. Rather than use treatments, dispose of the plants and potting soil, use a new container and uncontaminated soil, and do not water it so much. Good luck!