Black spot, or diplocarpon rosae, is one of the most dreaded diseases of roses. Hence our study on black spots on roses with baking soda. Black spots form on the leaves and stems, causing them to yellow and fall off. A severe infection can lead to complete defoliation of the plant. Adopting a regular schedule for applying fungicide sprays can significantly reduce the extent and damage that the fungus can cause to your roses. You don’t need to buy expensive potions from the garden center. Just mix one of these tried-and-true recipes from ingredients you may have on hand at home.
1 tsp baking soda 1 tbsp dormant horticultural or vegetable oil 1 tsp insecticidal soap or dish soap 1 tsp water 1 gallon of water 1 pitcher with a lid for mixing and storing 1 liter spray bottle
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Cornell University conducted research years ago on the use of common baking soda as a fungicide. They found that adding oil is essential for the effectiveness of the recipe. Several other versions of the original recipe add a bit of dish soap or insecticidal soap to help the solution adhere to the leaves and to help control harmful insects. If you want to keep the recipe organic, use dish soap instead of insecticidal soap.
Milk Black Spot Spray
1 cup of milk, any type 2 cups of water 1 pint spray bottle
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Milk is a popular home remedy for black spots on roses, but modern testing has proven its effectiveness against fungi. The downside of using it is that it can become smelly when applied too thickly due to the decomposition of the fats in the milk.
Black Spot Spray with Mouthwash
1 tsp vegetable oil 1 tsp water 1 tsp apple cider vinegar 1 tsp unflavored antiseptic mouthwash, such as Listerine 1 tsp liquid dish soap 1 ½ tsp baking soda 1 quart spray bottle
Mouthwash is formulated to inhibit the growth of bacteria and fungi in the mouth. Combined with other known fungicides like baking soda and vinegar, it becomes a powerful weapon in your arsenal against black spots.
Instructions for preparing the recipes and applying fungicide sprays against black spots
Mix all the ingredients in the gallon-sized pitcher and close the lid. Shake vigorously until the ingredients are well combined. Pour enough of the gallon jug mixture into the spray bottle to fill it. Spray the roses weekly in the morning, thoroughly wetting them with the spray.
Tips for combating black spots on roses
Water the roses well a day or two before treatment. Start spraying in the spring, at the time of the first leaf emergence, and continue until frost. Reapply after rain. Avoid spraying in the heat of the day or at night. Remove and destroy leaves or stems that show black spots. Purchase disease-resistant rose varieties. Do not let the plants become overcrowded. Reduced air circulation encourages the formation of black spots. Keep them pruned and trimmed for optimal air circulation.