In eastern grape-growing regions, there are two other destructive grape insects widely distributed, but each noteworthy as pests only in the Appalachian region of West Virginia and neighboring states. One is the grape-curculio (Craponius inæqualis), not essentially different from the familiar curculio of the plum and cherry. This snout-beetle feeds freely on the upper surface of the leaves and the bark of fruit stems, and the female in laying eggs devours the tissues of the grapes in excavating her egg chamber. The grape-curculio is effectively destroyed by spraying with an arsenical spray in the spring as the beetles appear on the vines and before egg-laying begins.
Another insect pest of this region is the grape-vine root-borer (Memythrus polistiformis) closely allied to the peach-borer, known by all fruit-growers and the squash-vine borer known to the growers of vegetables. This borer is the larva of a moth and is a whitish grub with a brown head which, when fully grown, is about one and three-quarters inches in length. The body is slender, distinctly segmented and has a sparse covering of short, stiff hairs. These larvæ burrow into the grape-root, at first confining themselves to the softer portions of the bark, often encircling the root several times, but later bore with the grain of the wood and by the end of the season so destroy the roots as to leave only the thin membrane of the outer bark intact. This pest is difficult to deal with. The borers cannot be removed by "worming" as in the peach, and neither can the roots be protected by sprays or washes. No one variety of the grape seems more immune than another. Thorough cultivation in the months of June and July to destroy the insects while in their cocoons at the surface of the ground seems to be the only method of stopping their ravages, and this is not always effective.
Fungous Diseases of the Grape
The grape is ravaged by four or five fungous diseases in America, unless the utmost vigilance is exercised to keep the parasites in check. Happily for commercial viticulture, there are regions, as we have seen in the description of grape regions in [Chapter I], so fortunate in their freedom from fungous diseases that there is little uncertainty in grape-growing and but small expense in controlling diseases. Also modern science has discovered the life history of all the important diseases and devised fairly effective means of combating them.
All of the fungous parasites of the grape in America are indigenous, having long subsisted on wild vines. They are, therefore, all widely distributed, and as cultivation has presented to them great numbers of grape plants in continuous areas, the diseases have increased rapidly in intensity, at times have swept like wildfire through grape regions devastating and utterly ruining great areas of vines. Means, however, are now at hand in remedial and preventive treatment, which, while because of cost may not permit the grapes to be grown profitably in all parts of America, do permit their culture for home use in practically all agricultural districts in the country.
Plate XVII.—Empire State (×2/3).
Black-rot.
This is the most widely distributed and the most destructive fungous disease of the grape in the region east of the Rocky Mountains. Fortunately, it is unknown on the Pacific coast. The disease is caused by a parasitic fungus (Guignardia Bidwellii) which gains entrance to the grape plant by means of minute spores distributed chiefly by wind and rain. Black-rot passes the winter in mummied grapes, on dead tendrils or on small, dead areas on the canes. In the spring, the fungus spreads from these spots to the leaves and forms brown leaf spots about a fourth of an inch in diameter, or oblong, black spots on the shoots, leaves, petioles and tendrils. Later the disease spreads to the fruits, not usually attracting attention until the berries are at least half grown. Soon after the ravages of the fungus become apparent on the berries, the fruits turn black, shrivel and become covered with minute black pustules which contain the summer-spores. [Figure 44] shows the work of black-rot. In the winter and spring, another form called the winter- or resting-spore is produced upon these old, shriveled, mummied berries, and these carry the disease over from one season to another.