Fungus And Insecticide Treatments. Plants infected with fungi also may have insects creating the problem. For example, fungi such as sooty mold usually occur when insects such as aphids or scale are present secreting honeydew.
The gardener needs to treat both problems by using a fungicide and an insecticide because each product on its own will not treat both problems. Using a separate sprayer for each product is the most effective and safest way of application, but sometimes mixing the two is possible