QUESTION: There is a fair bit of black spot on my roses, and I have lost the recipe for a baking soda spray to control the disease.
ANSWER: The baking soda spray, developed at Cornell University, helps to control the spread of both black spot and powdery mildew on roses. Remove infected leaves before spraying and apply the spray to both upper and under sides of the leaves, as well as the stems.
The original spray combines five ml (one teaspoon) each baking soda and horticultural oil in one litre of water. Shake the mixture well before and during the spraying.
Refinements to the spray include the addition of five ml insecticidal soap to help the solution adhere and cling longer to the plant. To foliar feed the plants and enhance their disease resistance, adding 10 ml of liquid seaweed fertilizer to the mix will be helpful.
Alternating the baking soda spray with a sulphur spray may help to increase the effectiveness of both. Apply sprays every 10 days as needed. Make sure the plants are well-watered before spraying them, and apply the spray in the evening, never during warm, sunny days.
-- Postmedia News
