Fig. 38. Root-worm beetle.
The presence of the adult beetles is more easily detected on the foliage than is that of the larvæ on the roots, for the feeding beetles ravenously devour the upper sides of the leaves, leaving chain-like markings, shown in [Fig. 39], their destructiveness decreasing somewhat after a few days from their first appearance. A fortnight after the beetles begin their attack on the foliage the female begins laying her eggs, to the number of 200, placing them under the rough bark of trunk and cane. These hatch in late July or August and the young grubs at once seek the roots.
Fig. 39. Injuries caused by beetles of the grape root-worm.
Two methods of control have been devised: destruction of the beetles before they lay their eggs; and destruction of the pupæ while in the ground. When the beetles are present in large numbers, many of them may be destroyed by spraying with a mixture of cheap molasses and arsenate of lead, using molasses at the rate of two gallons to a hundred gallons of water and the arsenate of lead at the rate of six pounds. This should be followed by a second spraying a week later, using bordeaux mixture (4–4–50) and three pounds of arsenate of lead. This second spray serves to repel migrating beetles from the vines. The molasses spray is ineffective unless several days of fair weather follow the spraying, as rain washes the material from the foliage. Bordeaux mixture is not easily affected by rain. In moderately infested vineyards, bordeaux mixture and arsenate are used instead of molasses and arsenate of lead, followed in about ten days with a second application of the same material.
An effective method of reducing the number of beetles is the destruction of the pupæ. This is best done by leaving a low ridge of earth under the vines at the last seasonal cultivation to remain until most of the larvæ have pupated, and then be leveled with a horse-hoe and later with a harrow. The horse-hoe and harrow crush many of the pupæ and break the cells of others to the great destruction of the pest. This latter method of control is not adequate in itself and in bad infestations both should be used. When the infestation is only moderate, this latter method is not advised, owing to the lateness of the time of horse-hoeing. It is good horticultural practice to horse-hoe the latter part of May or early June. To wait for the pupal stage of the root-worm delays the work until numerous small roots start which would be destroyed by the horse-hoe. Spraying will control a moderate infestation.
The grape-vine flea-beetle.
