Spray Roses BEFORE They Get Disease
Rose Foliage is very beautiful this time of year. It is dark green streaked with the red of fresh new growth. There are no ugly spots or discoloration.
That will soon change as black spot, mildew and rust spores are deposited on those fresh new leaves. Then the black spots, yellow discoloration, powdery mildew residue and rust pustules will begin appearing. Plants will begin dropping damaged leaves.
The first thing you can do to reduce rose diseases is to remove and clean up all the old leaves. If you look closely in the lower part of the plants you will see old leaves with black spots still hanging on some plants. The spots on those old leaves are producing the spores to infect the new growth.
My favorite pesticide for roses is Neem Oil. This organic compound is an extract from the Neem Tree which grows in Australia. It prevents all three of the major rose diseases mentioned above. It also kills aphids and most other insects which attack roses. It is not long lasting. It needs to be applied at least once every two weeks. Neem oil is usually only available in full service nurseries and garden stores.
There are also many other chemical fungicides available for controlling rose diseases. Most fungicides protect only uninfected leaves. Propiconazole, Myclobutanil and Tebuconazole are all systemics which will stop disease progression in already infected leaves. You will have to check ingredient labels to find these compounds. For more information check under pest control on my web site: naturalpruningnw.comlink text
But aren’t there some rose varieties which are resistant to these diseases? Sadly there are very few. Heirloom Roses (heirloomroses.com)link text has developed several disease resistant varieties. The most disease resistant roses I know are the Floral Carpet varieties. These are landscape or ground cover roses which do not have flowers suitable for cutting.