Manual of American grape-growing

by U. P. Hedrick

Fig. 41. First four stages of the grape leaf-hopper. (Enlarged.)

From Canada to the Gulf and from the Atlantic to the Pacific, wherever the grape is grown, the small leaf-hopper (Typhlocyba comes) infests the grape in greater or less numbers, feeding on the lower surface of the leaf. Grape-growers commonly call these insects "thrips," a name, however, which really belongs to a very different class of insects. The injury done by this pest varies greatly with the season and the locality, in some regions it being comparatively harmless and in others exceedingly destructive in seasons when it occurs in abundance. There is great variation also in individual vineyards, those near favorable hibernating places and early spring food plants often being injured seriously season after season in succession. These leaf-hoppers obtain their food by piercing the epidermis on the under side of the leaf surface and sucking the sap, and add further injury by inserting their eggs underneath the skin of the leaf. The punctures greatly decrease the starch-producing area of the leaf with the result that the vigor of the plant is lowered, and the quality of the fruit decreased.

Fig. 42. The fifth and the mature stages of the grape leaf-hopper. (Enlarged.)

The life history of the leaf-hopper is very well known. The eggs are deposited in June or early July, and hatch from June 15 to July 10 in New York, the season being earlier or later as one goes south or north. The young leaf-hoppers are wingless, the nymph stage, but reach the adult stage in late July and August, at which time many of them mate, and eggs are laid from which a second brood may develop, although usually only one full brood is produced in a season in the northern states. Figures [41] and [42] show the several life stages of the leaf-hopper. Insects which become adults in the latter part of July feed on the foliage until autumn and then seek winter quarters, passing the winter in the adult stage under fallen leaves, in dead grass or other similar protection. The hibernating place must be dry and for this reason sandy knolls are most favored by the insects. The adults emerge in the warm days of spring and then seek food first on the strawberry, then migrate to red and black raspberries or blackberries, if raspberries are not present. They remain upon these hosts until the grape leaves expand and then migrate to these to feed, lay their eggs and die.

Three methods of control are in use to prevent the ravages of the leaf-hopper: avoiding the planting of raspberries near grapes; spraying with contact insecticides; and the destruction of hibernating places. Since the leaf-hoppers feed especially on the raspberry before the leaves of the grape have expanded in the spring, avoiding planting these two plants near each other is a very effective method of control. The contact spray must touch the body of the insect and must, therefore, be applied before the nymphs develop wings. The best spray is a half pint of Black Leaf 40 to a hundred gallons of water or bordeaux mixture. It is applied to the under side of the foliage by a trailing hose or by an automatic grape leaf-hopper spray devised by F. Z. Hartzell and described in bulletin 344 of the New York Experiment Station. The destruction of hibernating places is almost as effective a method of control as spraying. All weeds and strong-stalked grasses which die in the fall and all rubbish in the vineyard should be destroyed. It is quite worth while, also, to burn leaves and rubbish in fence rows and waste places near infested vineyards in the autumn or early winter. Cover-crops which remain green during the winter do not harbor the leaf-hoppers.

The grape-berry moth.

This pest is widely distributed, attacking the grape wherever grown in North America. The insect feeds on all varieties but is especially destructive to grapes with tender skins and such as grow in compact bunches. Its work is detected usually in compact grape clusters where a number of berries are injured by a "worm." The "worm" is a dark-colored caterpillar, the larva of the grape-berry moth (Polychrosis viteana.) There are two broods of this caterpillar, the first of which feeds on the stems and external portions of the young berries, while the second attacks the berries. The loss to the fruit-grower is of two kinds, the loss of the fruit and the marring of clusters which entails the cost of picking out worthless berries. [Figure 43] shows the work of the grape-berry moth. The damage is usually greatest near woodlands since the trees cause more snow to lodge in the adjoining vineyards, this protection permitting a greater percentage of pupæ to survive.