The fungi give the pea plant nitrogen and the pea plant gives the fungi sugars, which are carbohydrates. However, sometimes the relationship between plant and fungi is detrimental to the health of the plant. Anthracnose Rusts May is a critical time for many fungal diseases because cool weather and lots of moisture, conditions commonly found in May, are essential for most fungi spores to germinate. When a spore germinates it produces a tube that enters the plant, either through natural openings in the plant or by the tube actually puncturing the plant. Once inside the plant, the fungus grows throughout the plant, taking the carbohydrates it needs from the plant.
Some fungi also produce poisons that kill the plant cells.
Frequently we do not notice any symptoms of the disease until several months after the spore has germinated and the fungus has entered the plant. When a fungus enters a plant and causes the plant to have symptoms it is causing a disturbance in the way the plant grows. Therefore we refer to the fungus as a disease. I don't advocate spraying every plant in your yard with fungicide in May. However, if you have certain plants in your garden that are prone to fungal infections every year I would recommend putting a little fungicide on them now.