Fungi
The fungi that most people are familiar with are mushrooms - some edible,some poisonous.
These strange parasitic organisms are never green,have no leaves or flowers, and in place of roots have a mass of white threads.
A few fungi grow on tree trunks.
Most appear to be growing in the soil but are, in fact, growing on plant remains in the soil.
Not being green, fungi cannot photosynthesize so they depend on the food developed by other plants.
Many fungi that grow on leaves, fruits, and stems are so small that they are invisible without a microscope.
Fungi damage plant tissues by producing toxins,enzymes,or growth-regulating substances that alter or destroy plant tissues.
Farmers see only the diseases that fungi cause, or sometimes a powdery mat that covers the diseased parts.
Fungal disease is not easy to identify.
The signs yellowing, wilting and withering-are similar to those produced by frost, poor nutrition, nematodes, bacteria or other factors.
Many different types of chemicals called fongicides, have been developed to kill fungi that cause plant diseases.