Black Spot On Roses: Treatment & Prevention

It can happen to anyone… your rose species and bushes are beautiful and blooming like crazy. You spend your days admiring their beauty and then all of the sudden you see it…. the dreaded black spot on all your rose varieties that can take your entire home garden of roses down if not treated.

It happened to me this year. I spent days admiring the fact that my 3 year old rose bush the kids gave me from Mother’s day a few years back was finally happy with its home and was showing off daily.

It was producing so many blooms I could barely keep up with the deadheading once they were spent. that’s when i saw the black spot – at first I tried to say it was the excessive rain we were getting and after a few says I could no longer deny it, it was in fact black spot.

I figured this was a good time to share with you what it is, what is does, and how to treat & prevent black spot on roses.

Roses are generally hardy plants that aren’t difficult to grow. However, they can still be prone to diseases that wreak havoc in your otherwise beautifully blooming rose garden.

Let’s get to the bottom of this plague on our rose bushes.

What is Black Spot?

Black spot is a fungal disease that specifically affects roses. It is caused by diplocarpon rosae, a fungus that develops as black spot on the leaf surfaces of roses.

The black spot disease causes the entire leaf on your beautiful roses to turn yellow with black dark spots and black lesions (of course) and the drop off of the fallen leaves makes your rose bush look just awful.

Furthermore, the development of the disease can also seriously weaken rose plants. The black spot fungus is a common disease during hot, humid conditions, or a humid environment such as rainy summers and hot days with cool, damp nights.

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When foliage of rose bushes and plants lose their diseased leaves due to circular black spots, they are unable to collect and store energy for the winter and to grow well in the spring. This results in weaker growth and reduced and fewer blooms.

The fungus diplocarpon rosae can also infect young rose canes. It causes dark purple or black blisters on canes while flowers may show some red spotting.

When plants are infected, they set fewer flower buds and no upper and lower leaves. These plants also become more susceptible to other problems.

How to Prevent Black Spot

The thing you need to remember about black spot of rose is that it is easier to prevent than to cure. This is because existing fungal spores can remain in the soil and overwinter on lower and upper leaves as well as stems. When favorable conditions arise, they can germinate and start destroying your rose garden.

It’s important to give your rose plants ideal growing conditions to make them less susceptible to problems. Plant roses in a sunny location that can get full sun with well-draining soil. Avoid cramming too many in an area to allow for good air circulation. When watering them avoid getting the entire plant leaves wet.

Since old and new spores can also be transferred and spread through water droplets, it’s best to spread thick layer of mulch on rose garden beds. Mulch can prevent water from splashing up from the soil to the rose’s leaves.

Black Spot Treatments

If your rose bushes are infected by black spot, there are still measures you can take to save your precious blooms. 

First, you can prune infected leaves of roses especially when you do your dormant pruning in early spring. Prune out canes that are showing signs of infection. This will help stop the spread of black spot from the infected leaves.

Be sure to prune up to 8 inches below the site of infection and make sure to do it in dry weather conditions. Don’t forget to disinfect your pruning shears between cuts using a 10% bleach solution or rubbing alcohol to prevent the spread of spores containing this common fungal disease.

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Be sure to bag up the diseased canes and old and new leaves tightly so as not to infect other areas of your garden and have a spread of the disease. Don’t add these clippings to any compost either as the black spot spores can spread new infections from there, too.

Second, you can use topical sprays to treat and prevent this common fungal diseases from invading your roses. Some ideas include:

• Mixing 1 teaspoon baking soda and 1 teaspoon of liquid soap in 1 quart of warm water. This preventive spray can be applied to lower and upper leaf surface.
• Insecticidal soaps with added fungicides
• Using 100% cold pressed neem oil as an organic fungicide and pesticide. Avoid applying neem oil within two weeks of using sulfur-based products
• Spreading sulfur powder in your garden beds to control fungal diseases and insect pests.

Preventing black spot is the best approach. But, if you see the leaf spots don’t panic, act quickly and you can save your beautiful rose garden.

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