Page:Popular Science Monthly Volume 78.djvu/483

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CONTROL OF PLANT DISEASES
PSM V78 D483 Interstate migration of plant diseases 1886 to 1896.png
Diagram 2. Showing Interstate Migration of some Important Diseases.

1, asparagus rust: New Jersey, 1896; South Carolina, 1897; Michigan, 1898; Illinois, 1899; Dakota, Nebraska, Texas, 1900; California, 1901. 2, fire blight: the Hudson, 1792; California, 1895-7, 3, peach yellows: Philadelphia, 1806; Ontario, Michigan, Illinois, Maine, 1886.

first encroachment in South Carolina and an agressivecampaign against it with remedies which had recently proved efficient against smuts of other cereals checked it and completely subjugated it, so that it is no longer known in the Palmetto State. The cucumber mildew, which causes blanched spots on the leaves and often entire loss of crop, has rendered unprofitable the culture of cucumbers and cantaloupes in many sections. The two grape mildews are notorious in their destructiveness and have driven vineyardists to large expense in spraying or sulphuring.

Perhaps the most striking importation is that of the potato wart. This disease causes large unsightly knotty excrescences on the potato, rendering them worthless. It was first reported in England in 1902, found its way to Newfoundland, and it is known that two consignments of Newfoundland potatoes, probably infected, were shipped last year, one to New York, one to Boston. The spread of this disease in our states is an event to be predicted with confidence, especially as many sections of the country depend upon New England for their seed potatoes.

The large increase in aggressiveness of plant diseases has been met by a campaign of increased knowledge leading to new modes of subjugation. Though a few plant diseases are mentioned in early writings, (II. Chronicles 6-28, Shakespear's King Lear, III., Sc. 4; I. Kings 8-37; Moses 28, 22), the real significance of their presence, their nature and causes may be said to have been first recognized between the