Elms, cultivated as ornamental shade trees, frequently fall victim to a fungal ailment known as Dutch elm disease. The Dutch elm fungus, principally carried by two species of beetles, causes the tree to lose most of its leaves and eventually die. Diseased trees can sometimes be treated by the injection of a fungicide into the bark; however, in advanced cases, the trees must be cut down and burned in order to dispose of the fungus-contaminated wood.

Michael Leach/Oxford Scientific Films Tree with Dutch Elm Disease," Microsoft® Encarta® 96 Encyclopedia. © 1993-1995 Microsoft Corporation.

Galls are swellings formed on living plants in response to insect or bacterial parasites. The gall, or cecidium, is formed when chemicals secreted by the invading parasite stimulate swelling or rapid growth of plant tissues into an enlarged, thickened covering around the site of infection or parasitic invasion. Galls come in many shapes depending on the type of invading parasite, and although they may occur at any location on a plant, their formation is common in areas of active plant growth.

Avril Ramage/Oxford Scientific Films Oak Apple Gall," Microsoft® Encarta® 96 Encyclopedia. © 1993-1995 Microsoft Corporation.

Most types of plant-related diseases are caused by fungi. The leaves of this plant have been infected by tar-spot fungus. Fungi can infect all parts of the plant including leaves, stems, flowers, roots, and fruit. The physical manifestations of fungal diseases of plants include wilting, club root, root rot, wood rot, cankers, various types of mildews, blights, lesions, and leaf spots. The effects of fungal diseases can be devastating as evidenced by the potato blight that destroyed the Irish potato harvest of 1845 and caused a widespread famine in Ireland.

Dorling Kindersley Fungal Diseases of Plants," Microsoft® Encarta® 96 Encyclopedia. © 1993-1995 Microsoft Corporation.

The calico virus of the peach is one of a number of infectious plant viruses transmitted by insects. Since the virus itself is very difficult to treat, the best method of treatment is to control the insects that carry the disease.

Kathy Merrifield/Photo Researchers, Inc. Calico Virus of the Peach," Microsoft® Encarta® 96 Encyclopedia. © 1993-1995 Microsoft Corporation.

Chemical sprays and hydroponics have enabled the farm communities to be able to meet farming demands while combating natures' diseases.

A researcher at the University of California-Davis, checks a rack used in hydroponics research. Hydroponics involves growing plants with nutrient solutions rather than soil. The plants are supported by racks or porous material such as gravel.

Lawrence Migdale/Photo Researchers, Inc. "Hydroponics," Microsoft(R) Encarta(R) 96 Encyclopedia. (c) 1993-1995 Microsoft Corporation.