These are a variety of diseases that can be caused by bacteria, viruses or fungi. Injuries to the plant by nematodes can also perpetuate leaf spot disease. It can affect a variety of trees, shrubs and vegetable. Leaves and stems usually display circular brown spots with purplish to dark brown borders.
A neem oil spray or one made with baking soda can be effective in treating this disease. A baking soda spray is made by adding together 1 tablespoon of baking soda, 2 1/2 tablespoons of vegetable oil and 1 tablespoon of a mild soap to 3 litres of water.