The New Student's Reference Work/Blight

Blight, a diseased condition of plants, causing deadening of the stems or roots, yellowing and early falling of the leaves, or shriveling and premature decay of the fruit. In a restricted sense the word refers to a certain mildew affection of the leaves. Blight exists among plants in their wild state, and is often aggravated by cultivation. Though pre-eminently a fungous disease (see Fungi, it may appear, as often shown by the foliage turning yellow, from the roots being poorly supplied with food and air. From the standpoint of the producer, blights may be roughly classed as the rusts and smuts of grains, blights of orchard and shade trees, of small fruits and grapes and of garden products; though several or all of these sorts of plants may be attacked by fungi that are similar, botanically, or are the same thing. Often a single species of blight-producing fungus will pass through several stages of development on entirely different plants, as in the case of wheat rust. (See Æcidiomycetes.) Damage to cereals from rust and smut in the United States amounts to from $25,000,000 to $30,000,000 yearly. While rust is common, it causes damage only when cool, damp weather allows it to mature more rapidly than the grain. While the black spores (q. v.) of rust live over the winter, in the case of those orchard blights affecting the wood, only those spores survive where the dead and healthy tissues meet. Here form, in the spring, the familiar sweet masses of "gum," which attract insects and so scatter their spores. All branches showing such hold-over blight should be pruned out. Certain apple rusts pass one stage in the jelly-like masses, commonly noticed on cedar trees after spring rains, and popularly known as cedar-apples. Some typical fungous diseases are the blights, mildews, scab and rot of potatoes beet-root rot, peach-leaf curl, apple scab, rye ergot, corn smut, loose and stinking smut of wheat, wilt disease of flax and of cow-peas. Often the ground becomes infected, as in several of the above, and must be abandoned as regards the susceptible crop. Potato scab and smuts that are transmitted by the seed are prevented by treating the seed with a weak solution of 4 per cent. formaldehyde (one pint to 45 gallons of water). Blight on trees and small fruits, as well as insect pests, is fought by spraying (see Spraying Mixtures), which kills the parasite without injuring the host. The Department of Agriculture investigated a leaf-blight that ruins nursery seedlings (see Grafting), and showed by experiment on 100,000 young trees that treatment costing but 90 cents per 1,000 trees netted profits averaging $13 per 1,000, and going as high as $40. Other experiments showed that at an expense of 15 cents per fruit-bearing tree, the marketable product could be increased 25 to 50 per cent. Black rot affecting grapes was first studied by the Department, which discovered a treatment increasing the yield 20 to 80 per cent. In five years its methods were used by 50,000 grape-growers. Plant breeding (q. v.) is used to increase the power of resisting not only insects and fungi but blight induced by climatic conditions and inherent weakness which, in the case of the California raisin grape, sometimes results in a loss of a million dollars in a single year. References: Bulletins of the Department of Agriculture and of the State Experiment Stations.