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Regular Contributor
Posts: 193
Registered: ‎03-10-2010

Black Spot on knockout

One of my knockouts has black spot on most of the canes all the way down. They haven't leafed out yet but are starting to just a bit. Where I live, we had tons of rain last summer and fall so it's probably from too much moisture. Do I need to cut the canes completely down, pull the rose out, or can I treat the black spot with something? Thanks in advance!

Respected Contributor
Posts: 2,142
Registered: ‎07-27-2015

Re: Black Spot on knockout

[ Edited ]

@Violet Fields wrote:

One of my knockouts has black spot on most of the canes all the way down. They haven't leafed out yet but are starting to just a bit. Where I live, we had tons of rain last summer and fall so it's probably from too much moisture. Do I need to cut the canes completely down, pull the rose out, or can I treat the black spot with something? Thanks in advance!


@Violet Fields I placed a link to a page about knockouts. There is a section that talks about diseases and pests. Hopefully, there is something that can help you with your plants.

 

https://www.knockoutroses.com/faqs

Honored Contributor
Posts: 15,439
Registered: ‎03-09-2010

Re: Black Spot on knockout

[ Edited ]

First thing I would do is prune any crossing or branches smaller than the diameter of a pencil from the center working your way outward. Since there are no leaves on it now, you can get a better idea of where to prune and also remove any winter damage such as any blackened or browned canes. Cut back to where you see green in the center of the cane. Pruning in the center of a rose improves air circulation.

 

Try to water in the AM (4 AM) if using automatic sprinklers and water deeply instead of short bursts of water. The leaves will be able to dry out once the sun emerges. If you water in the evening, the leaves do not get a chance to dry out and it sets up a cycle to encourage fungal growth. Mulch around the rose to prevent fungal spores from splashing up on the plant. 

 

Blackspot:

 

Image result for blackspot

Many times its lack of air circulation plus this rain you have had that sets up the cycle for any blackspo or other fungal disease.

 

Blackspot is usually a group of irregularly shaped black spots. Anthractnose is another fungal disease that has a circular edge with a tan to white center. Usually the plant contains this anthractnose by dropping out the center of the fungal area so it looks like a hole was made by something.

 

Anthractnose:

 

Image result for rose anthracnose

☼The best place to seek God is in a garden. You can dig for him there. GBShaw☼
Honored Contributor
Posts: 8,667
Registered: ‎03-15-2014

Re: Black Spot on knockout

I don't grow roses but I thought the thing about knock-outs is that they're resistant to most or all diseases, hence their popularity.  I see them all over the place around here.

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Posts: 13,878
Registered: ‎03-09-2010

Re: Black Spot on knockout


@ValuSkr wrote:

I don't grow roses but I thought the thing about knock-outs is that they're resistant to most or all diseases, hence their popularity.  I see them all over the place around here.


They're disease resistant, but not immune. You still want to take the normal precautions to avoid problems. Normal precautions include removing infected materials (old fallen leaves for example) from around the plant. Trash them instead of composting them. Any old mulch left from last year in the area might be best removed also and replaced with fresh. Give the plants good air circulation to let them dry out. Water very early in the day, or at ground level, so the foliage can dry out. You can also spray it with a rose spray to limit disease/insect issues if you're not adverse to the use of chemicals. 

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Regular Contributor
Posts: 193
Registered: ‎03-10-2010

Re: Black Spot on knockout


@GAQShopr53 wrote:

@Violet Fields wrote:

One of my knockouts has black spot on most of the canes all the way down. They haven't leafed out yet but are starting to just a bit. Where I live, we had tons of rain last summer and fall so it's probably from too much moisture. Do I need to cut the canes completely down, pull the rose out, or can I treat the black spot with something? Thanks in advance!


@Violet Fields I placed a link to a page about knockouts. There is a section that talks about diseases and pests. Hopefully, there is something that can help you with your plants.

 

https://www.knockoutroses.com/faqs


Thanks for the link! I checked it out and it has really helpful info.

Regular Contributor
Posts: 193
Registered: ‎03-10-2010

Re: Black Spot on knockout

@JustJazzmom  Thanks for the detailed information! Very helpful!

Regular Contributor
Posts: 193
Registered: ‎03-10-2010

Re: Black Spot on knockout

Thank you all for your replies. Last summer wasn't kind of my plants at all - humid, rainy, and cloudy so much of the time. They never got a chance to dry out. I'll have to make sure I prune in the middle of the plant to improve air circulation.