Home Is Where Your Trees Are

Fungi

Fungi, the chief vegetable parasites, have symptoms, life cycles, and remedies quite different from the insect pests. They become active about the same time in spring, for the most part, but most of them reproduce and attack far oftener than the insects. In some, new crops of spores can ripen just a few days apart and require only a spell of damp warmth to trigger a fresh outburst. When the outbursts occur, the spores literally explode from the fruiting fungus bodies and are air-borne for long distances. They thrust their mycelia into healthy parts of trees, from leaves to roots, as well as entering lesions to attack exposed tissues. Because of their virulence and the tininess of their infesting particles, fungicidal spraying is to be thought of as fumigating, to kill germs. If they could be controlled as well as liquids or dusts in the open air, gases would make the best fungicides, to penetrate and permeate as the spores do. Many fungicides are formulated so that they give off gases on the trees and are hence most effective on still days.

Symptoms of fungoid infestation can be schematized as follows:

Below the fungi on plant life's ladder, bacteria and viruses cause diseases by what might be called simple infection. Crown gall in the rose family (apple, pear, cherry, almond, etc.) and in many other trees is caused by a bacterium which, entering a lesion, causes overgrowth of woody cells, resulting in rough swellings, sometimes huge, usually on the tree's base or roots but also well aloft in poplar and willow. One of the few ailments suffered by sassafras is an incurable virus called yellows, which bunches the twigs, blanches and dwarfs the leaves.