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November 15, 2005
Blackspot
Diplocarpon rosae
Blackspot on the roses in the shade. What to do? Fungicide.
How can we tell which is least toxic? The Environmental Protection Agency has come up with three categories of toxicity: DANGER, WARNING, or CAUTION.
Toxicity is based on the le thal dose 50 or LD50 for a pesticide. The LD50 is the amount of a chemical that will kill 50% of the subjects exposed to it. Thus, the lower the LD50 for a chemical, the more toxic the chemical is. ...
Pesticides that carry the word DANGER on their container are the most toxic. The LD50 of these pesticides can be less than 7 drops of a liquid or less than 50 mg/kg of a solid. These pesticides may also be labeled DANGER because of their ability to cause irreversible damage to the eye or skin.
Among the newer fungicides, Compass (blackspot), Immunox (myclobutanil) (powdery mildew) and Remedy (potassium carbonate; powdery mildew) are all CAUTION-labeled pesticides. Perhaps the newest and most innovative CAUTION-labeled fungicide is harpin protein marketed as Messenger by Eden Bioscience. When sprayed on the rose bush, the protein stimulates the rose’s own defense systems to help protect against fungal infections and to enhance growth.
Posted by Sue at November 15, 2005 10:03 PM