Back to List of Contents . Disease fungi parasitize food crops and they exhibit distinctive symptoms like downy mildew and powdery mildew that create pale patches on the leaves of the plant. Rusts can be identified by their rusty color on the leaves. Leaf spot causes round, yellow spots on the leaves that darken over time. Virus are spread by insect carriers especially aphids, leafhoppers, mealybugs, and whiteflies.
Viral diseases damage the plant by destroying the chlorophyll in cells, causing yellowing of leaves.
Symptoms of viral diseases include lower than normal yields and poor fruit or vegetable quality. Back to List of Contents . Organic growing practices utilize soil amendments, fertilizers and growth promoters as supplements to the maintenance of heightened biological activity and delivery of nutrients to plants. Botanicals are of interest to those concerned with pest management for a variety of health and environmental reasons. They can be accepted in the organic market where synthetic pesticides are not allowed.