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 fungus of rose is everywhere. If you have roses, you will have some black spot. There are varieties that are resistant and seldom get black spot. When they do it is usually not a significant problem and seldom if ever requires a spray. Cultural conditions can make black spot a rampant problem or a minor nuisance. Overcrowding, poor air circulation, and frequent wetting of the foliage all predispose plants to black spot 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 Remedy (contains sodium bicarbonate or "baking soda"). There are also several synthetic products on the market which are very effective against blackspot. Visit your Home Depot garden center and look for products labeled for this disease. Follow label instruction for application rate and frequency.
Thanks for the question. Best wishes for a wonderful gardening season. Please stop in again soon!
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