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How to treat and prevent black spot on roses Black spot is a fungal disease The fungus develops as black spots on the leaves, eventually causing the leaves to turn yellow and drop. Besides looking unsightly, it can seriously weaken the rose plant. Black spot on roses thrives during cool, wet weather. Read on for information on treatments for black spots on roses. Black spot will appear as somewhat circular black spots on the leaves. It usually occurs on the upper sides of the leaves, but it can also develop on the lower sides. The outer edges of the black circles are jagged or feathered and usually surrounded by a yellow ring. Spots usually start on the lower leaves and move upwards. They can appear as early as when the leaves first develop. These points can be enlarged and eventually merged. Affected leaves often fall off the plants, and if not controlled, the entire plant may fall. 2 Leaf loss reduces the plant's ability to photosynthesize food, weakening the bush and causing a decline in rose production. The fungus can also infect young canes, causing dark purple or black blisters on the canes, and even the flowers may show some red spots. The fungal spores that cause black spot to germinate in the spring are dispersed by rainwater splashes and watering, as well as by wind, which also carries the spores. If not managed, your roses will continue to get black spots. If you experience an exceptionally hot summer in July and August, high temperatures can limit future spore development. Existing spores overwinter on infected fallen leaves and stems, waiting for favorable conditions. Spores germinate in the spring and must be continuously moist for seven hours before germination occurs Roses prefer a sunny spot with well-draining soil and regular, weekly watering. Plant roses in a spot where they get morning sun, which helps to dry the moisture from the leaves. All-day sun is best. Avoid wetting the leaves when watering. There's not much you can do about the rain, but avoid overhead sprinklers and direct the water directly to the plant's roots. Cut off the roses with the black spot. Remove all infected leaves and always do a thorough cleaning every fall. Remove and discard any remaining leaves when pruning dormant roses in late winter/early spring Cut off any canes that show signs of infection. Make sure to clean up fallen leaves as well and dispose of them properly. Apply a thick layer of mulch around the base of the plant. Mulch prevents the soil from splashing onto the plant, and if spores are present in the soil, this will help prevent the spread of black spot on roses. Consider using a dormant spray during the winter to suppress overwintering spores. Bordeaux mixture : This is a fungicide containing copper sulfate and hydrated lime. It can be used as a powder or mixed with water and sprayed. Bordeaux mixture also repels some insect pests, but it can burn the leaves of plants. It is usually used as a preventative in the spring before the plants fall. Insecticidal soaps with added fungicide: You can use an organic fungicide, which is often sulfur added to regular insecticidal soap. The soap coats the leaves and helps the fungicide attach to the plant. Neem Oil : Neem is an organic fungicide and pesticide, obtained from the seeds of the neem tree. It gets into the plant's system, so you don't have to worry about coating everything or reapplying after a rain. Sulfur: Sulfur prevents fungal diseases. It is also used to control several insect pests. Sulfur comes as a finely ground powder. If you prefer to spray it, look for one that is labeled wet so it will mix with water. WARNING Sulfur can be mildly toxic to humans and other animals You can use milk and baking soda. 1 liter of milk 2 liters of water 1 tablespoon of baking soda 3 drops of povidone iodine. Spray with this solution every 7 to 10 days. It also offers some protection against powdery mildew Hydrogen peroxide: There are reports that spraying a mixture of 1 tablespoon of hydrogen peroxide (3 percent concentration) and 1 cup of water works on blackheads as well. Roses least resistant to black spot include hybrid tea roses, grandifloras and miniature roses. Most hardy roses include hybrid floribundas, shrubs and climbers.