Question of the Week – Number 1: May 23, 2019 – Black Spot of Roses
“Why are all the leaves on my rose developing black spots, turning yellow and then falling off?”
The leaf spot known simply as “black spot” of roses has been well known to rose growers for all of history. It’s far more serious in the warm, humid weather of spring and fall. It abates somewhat in summer’s hot, dry weather.
Some varieties of roses are far more susceptible to black spot than others. From that beginning, Dr. Steve George of the Texas AgriLife Extension began an exhaustive comparative study 25 or more years ago in which hundreds of rose varieties were grown and evaluated side by side at a large number of test sites in both Texas and across America.
As it became obvious that some of the varieties were far more resistant to black spot than others the tests were refined and the best of the best were identified as EarthKind® Roses.
If you have a plant that is, unfortunately, not one of the EarthKind® Rose selections, you’ll need to apply an approved fungicide weekly in spring and fall. Plant your roses in raised beds in areas with good air circulation.
Note: As you’re growing roses, keep your eyes open at the same time for the serious rose rosette virus. It is a fatal disease for which we have no effective preventive technique, nor do we have a control once a plant is infected. See the information I have archived at my website.