black spot on roses

Asked May 5, 2019, 11:01 AM EDT

I’ve used sprays and systemic rose food that are supposed to combat black spot. Nothing works. Any suggestions?

Washington County Oregon

1 Response

Black spot is a very common disease on roses grown in the northwest. The best strategy is to choose a rose known to have tolerance to black spot. Unfortunately, no rose is completely black spot.

Limiting black spot relies on several cultural strategies:
- Avoid dense plantings and shaded areas.
- Avoid overhead watering that keeps plants wet for extended period of time. The idea is to water early enough in the day that the leaves are dry completely prior to night fall.

In general, new spring growth is most susceptible to black spot.
1) The goal of applying a spray is to protect the leaves before they are infected.
2) Removing and discarding infested leaves may help limit new infections.
3) Regularly collect and discard all fallen leaves.
4) Sprays are unlikely to succeed unless the above cultural controls are in place.

Sprays which can be used by home gardeners include these:
Bonide Fung-onil Multi-purpose Fungicide;
Ferti lome Liquid Systemic Fungicide II;
Hi-Yield Captan 50 W Fungicide;
Infuse Systemic Disease Control;
Ortho MAX Garden Disease Control; and
Spectracide Immunox.

I'm unfamiliar with an effective "systemic rose food."