By Stan V. Griep
American Rose Society Certified Consulting Rosarian – Rocky Mountain District
A common rose disease is known as black spot (Diplocarpon rosae). The name is very appropriate, as this fungal disease forms black spots all over the foliage of rose bushes. If left unchecked, it can cause a rose bush to totally defoliate. Let’s look at how to get rid of black spot on roses with proper roses black spot treatments.
How to Control Black Spot on Roses
Once your rose bush gets attacked by the black spot fungus, its markings are there to stay until the marked leaves fall off and a new leaf is generated. The fungus that causes the black spots can be killed and not do any further damage to the foliage but the marks will remain for some time. In my rose beds, a rose named Angel Face (floribunda) was a black spot magnet! If I did not spray her when her leaves first started to form in early spring, she would most certainly get the black spot.
My fungicidal spraying program for the last several years to prevent black spot in roses has been as follows:
In the early spring when the leaf buds on the rose bushes first start to push out the little leaves, I spray all the rose bushes with a black spot treatment fungicide called Banner Maxx or a product called Honor Guard (a generic form of Banner Maxx). After three weeks and then at three week intervals, all rose bushes are sprayed with a product called Green Cure until the last spraying of the season. The last spraying of the season is done with Banner Maxx or Honor Guard again.
Should the dreaded roses black spot get ahead of you in the rose beds, a product called Mancozeb fungicide will stop black spot on rose bushes in its tracks. I found out about this great product a few years ago when rose black spot got ahead of me and the rose Angel Face was well under attack. The Mancozeb does leave a yellowish powder on all of the foliage, but that is part of how it works. This product is applied every 7 to 10 days for three sprayings. After the third spraying, the normal spraying program may continue. The black spot fungus should be dead, but remember the black spots on the rose leaves will not disappear.
The Mancozeb product may be mixed with another fungicide called Immunox and then applied to the rose bushes to lessen the amount of yellowish powder left on the foliage. Both are added to the spray tank as if they were the only product in the tank mix. I have personally used both of these application methods and both worked very well.
Preventing Black Spot on Rose Bushes
Keeping the rose bushes thinned well at pruning and deadheading times will help the airflow through the bush, thus also helping to prevent black spot on roses and other fungal disease outbreaks.
With any of the fungal diseases, an ounce of prevention truly is worth a pound or more of cure! Either having a routine spraying program or keeping a close eye on your rose bushes is a priority. The sooner roses black spot treatment starts, the easier it is to gain control of it. I like to use the Green Cure as my main fungicidal spraying product, as it is earth friendly and does the job it needs to do.