09/29/2026
MSPC manages the Bush Park Adopt-a-Rosebed program. Many of our adopters have asked how to deal with black spot. Joe McNally, the park's Natural Infrastructure Specialist, talks us through it in this video. If too many leaves are infected, you should treat with a spray rather than pull leaves off. The spray can be 1 teaspoon baking soda, a few drops of dishwashing liquid in one quart of water. The entire leaf needs to be sprayed. Any fallen leaves (even the old dried ones) should be picked up because they still carry active fungal spores that will stay in the soil to infect plants later. We've seen some evidence of powdery mildew. The same procedure applies. All leaves can be put in city composting. Your home compost may not get hot enough to kill the fungus. And while you are picking up leaves, pull mulch away from the stems. It tends to migrate right up to the plant but should be at least 3" away from the base of the plant (aka the crown)