I am sorry for this delayed reply to your gardening question. The spring rush has brought a deluge of questions and we are working hard to catch up!
Black spot of roses is caused by a fungus. It is a major problem on roses across the country. The best way to manage it is to plant resistant varieties. There are several fungicides registered for use on roses that will control black spot, but regular spraying is required to maintain control on susceptible varieties.
Fungicides don't cure old black spot infections, they just keep new ones from forming. In time the old infected leaves fall off and are replaced by new foliage that the sprays will protect from infection. Most varieties however, must be sprayed on a regular basis to prevent black spot infections from becoming severe. In severe cases it can even cause defoliation of the plant. There are many fungicide products labeled for black spot on roses. Among the less toxic, natural options are: Soap-Shield (a soap spray containing copper), and Green Cure (contains potassium bicarbonate). There are several other synthetic options for controlling the disease. Your County Extension Office can assist by recommending other specific products.
There are several varieties that are naturally resistant. Here's a few for you to consider:
'Carefree Beauty', 'Knock Out', 'Belinda's Dream', 'Nearly Wild', and 'Old Blush'.
Thanks for the question. Best wishes for a wonderful gardening season. Please stop in again soon!
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