Manual of American grape-growing

by U. P. Hedrick

Fig. 43. A bunch of grapes despoiled by the grape-berry moth.

The moth passes the winter in the pupal state on leaves underneath the vine, emerging about the time grapes are blossoming. The sexes then mate and the eggs are laid on the stems, blossom clusters and newly set fruit. After reaching full growth, the caterpillars cut out a portion of the leaf from which they make a pupal case by means of silken threads, and here pupate for the second brood which emerges in late July and August. Eggs are laid at once and from these come the caterpillars which live entirely in the berry. The larvæ leave the berries about the time the fruit is ripe, form cocoons on the leaves and hibernate. The moths are small, brown in color, mottled with gray and so much the color of the grape cane that they can hardly be detected when resting on the wood.

The grape-berry moth is difficult to control but much can be done to curtail its ravages. Spraying after the fruit sets is the most effective preventive. Bordeaux mixture should be used (4–4–50) to which has been added one and one-half pounds of resin-fish-oil soap and three pounds arsenate of lead. A second application of the same spray is advisable in early August. In a small vineyard or with a slight infestation, it often pays to pick and destroy the berries infested by the spring brood. Plowing infested vineyards in late fall or early spring to bury all leaves prevents the emergence of many of the moths. To be effective, this practice must cover the leaves deeply directly under the vines and this earth must remain until after the time for the adults to emerge. Plowing under leaves is not as effective on sandy as on heavy soils, since sandy soils do not become sufficiently compact to prevent the escape of moths.

Insect pests of minor importance.

Of the 200 species of insects that feed more or less on the grape, entomologists mention several others than those described that in occasional years or localities become abundant and cause serious injury. Thus, there are several species of cut-worms which sometimes feed on the expanding buds of the young leaves of grapes. The damage of these cut-worms to the grape is greater in California than in other parts of the United States, but nevertheless they occasionally feed on the vines in eastern regions to the detriment of the crop. The most satisfactory control measure for cut-worms is the application of poisoned bait placed on the ground at the base of the vines.

In California there is a grape root-worm (Adoxus obscurus) quite distinct from the grape root-worm of eastern America which injures both the roots and the parts of the vine above ground. As in the eastern species, the best evidence of infestation of this pest is the narrow chain-like strips eaten out of the leaves, though the insect also gouges out part of the petioles, pedicels, berries and shoots and works under ground, eating the rootlets and bark of the larger roots. Infested vines show a stunted condition, the canes fail to attain a normal growth and often the vines are killed outright. As in the case of the eastern species, this root-worm is the larva of a beetle, the life history of the insect not being greatly different from that of the eastern beetle. Two methods of control are fairly effective: the adult beetles may be jarred from the vine and captured on a screen when the infestation is restricted to small areas; or the beetles may be poisoned with the arsenical spray recommended for the eastern species. Both jarring and spraying often have to be repeated as new infestations appear.

The grape leaf-folder (Desmia funeralis) is another insect pest of vineyards in California, and occasionally in the East, which works, however, only in restricted localities and in occasional years. In California, the insects are detected in a vineyard by the characteristic rolling of the leaves in which a tube rather less than the diameter of a lead pencil is formed for the home of the larvæ. The larvæ feed on the free edge of the leaf in the interior of the roll and are thus protected by the outer layers. In the East the caterpillar merely folds the edges of the leaves together. This leaf-folder hibernates as a chrysalis, coming forth in early spring to lay eggs on the vine shortly after the foliage has appeared. There are two broods in California and the northern states and three broods in the southern states. The leaf-folder is easily disposed of by spraying with an arsenical spray just after the eggs hatch and before the larva is protected by its roll of leaves.

Still another pest found throughout the United States and especially destructive in California is the hawk-moth (Pholus achemon), the larvæ of which occasionally do serious damage to small areas of vines. These larvæ are very similar to the large worms, familiar to all, which attack the tomato and tobacco. The insect hibernates in the pupal state in the ground where it may be distinguished as a large cylindrical object of dark brown color. The moths emerge about the middle of May and deposit their eggs on the leaves of the grape, upon which the larvæ when hatched immediately begin to feed. There are several species of these hawk-moths, all of which have essentially the same life history. It is not a difficult pest to control since the larvæ are easily killed with arsenical sprays; or if there are but occasional specimens they may be picked by hand. There are several species of the hawk-moth which attack the grape but this is the common one.