April through October, spray monthly (or only when needed) with the modified Cornell University organic spray (see formula below) to control black spot, powdery mildew, spider mites, and aphids.
Modified Cornell Formula: Mix into one gallon of water, in the order listed:
2 tbsp. of ultrafine horticultural oil (such as Sunspray™ oil)
1 heaping tbsp. of baking soda
1 tbsp. of fish oil/seaweed emulsion
3-5 drops of Superthrive®
1 tbsp. of mild dishwashing soap (such as Palmolive green -- but see note below)
[Note: Labels on newer containers of Sunspray™ oil indicate that it now contains an emulsifier. In that case, the dishwashing soap can be omitted.]
Mix well and spray with a pump-up sprayer late in the evening, after first watering your roses thoroughly and spraying them with the hose to scare off some, most, or all of the beneficial insects.
DON'T ADD VINEGAR. NEVER USE ANY TYPE OF FISH OIL/SEAWEED PRODUCT CONTAINING SULFUR WITH A HORTICULTURAL OIL SPRAY. AND NEVER MIX A CHLOROTHALONIL FUNGICIDE (e.g. Daconil™ or Fung-onil™) WITH HORTICULTURAL OIL OR USE THEM ON ANY PLANT WITHIN 10 DAYS OF EACH OTHER.
For black spot control, it is important that you spray all of the plant's wood, as well as the foliage. It has been found that the black spot spores reside in lesions in the canes and that they attack, not only the foliage, but also the canes and prickles.
Used with permission from the Field Report
Entered by Kaye
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