Black Spot on Knock Out Roses

Asked September 4, 2013, 11:32 AM EDT

By the pictures on this site our Knock Out Roses have "Black Spot." What needs to be done to treat this? (Picture number 2 on this site) www1.extension.umn.edu/garden/ask/

Cleburne County Alabama

1 Response

Black spot is easily treated, but it is important to keep the diseased leaves that have fallen picked up and disposed of. Don't leave them under the plant because they contain the spores of the fungi and will reinfect your plant when water or rain bounces off of the leaves, carrying the fungi spores and depositing them where they land.

Also, create a good air flow around the plants, so the moisture will not stay around the plant. Fungi love moist, still air to grow. Prune the inside branches that are touching and crossing. This will help air flow.

A good fungicide will help also. Daconil or Rose Pride both have a fungicide. Both are systemic, which means the roots and leaves take up the poison and bring it into the plant. This will protect the leaves that do not have the fungus and kill the spores that do attack the other parts of the plant. It is easier also, because you don't have to completely cover the plant for complete protection, as in topical fungicides.

Here is a link for more reading if you wanted to know more.
http://www.aces.edu/timelyinfo/PlantPathology/2010/April/TI2010.pdf

Good luck.