CATERPILLARS.
Characteristics.
—The caterpillars which trouble the raisin grapes are confined to three or four kinds. The most common and also the most destructive are the very large larvæ of the sphinx moth. The common grapevine sphinx (Philampelus achæmon) is a large larva, incorrectly called a worm, which is, when full grown, over three inches long. The color varies from bluish green to brown, with several lighter stripes on each side. The head is truncate, and the tail is furnished with a curved horn. The pupa hibernates in the soil below the vines, and is about half the size of the full-grown caterpillar. The full-grown moth is about two inches long by two and one-half inches between the outstretched wings. The eggs are laid by the moths on the leaves of the vines. Two broods of caterpillars appear yearly under favorable conditions, or else only one brood, which generally appears in the end of July. The caterpillars grow with great rapidity, and attain their full size in a few weeks. The pupæ hibernate in the soil and hatch the following summer.
Another large grapevine caterpillar is the Deilephila striata, which is about the same size as the Achæmon. The moth has more pointed wings, with narrow stripes, and the larva is brighter colored, often yellowish green, with several colored stripes on the sides. The eggs are not laid on the vines, but on the weeds on the vacant lands outside the vineyard, especially on species of Epilobium, but also on other weeds, and they hatch and feed on them. The caterpillars feed in ordinary years only on the weeds on which they are bred, but in other years which are especially favorable to their enormous increase they migrate to the vineyards and feed on the vines at the most alarming rate. The caterpillars of both the above large moths vary in color from green to brown or violet brown, but as a rule the Deilephila is more brightly colored than the Achæmon. The former is more active and often travels in enormous numbers, when it is called the army-worm. The Achæmon is more blunt at both extremities, the head being almost truncate.
Vineyard Scene, Rosedale Colony, Kern County, July, 1890.—Three Months After Planting.
Army-worms are smaller caterpillars, about one inch or more in length, which breed on the outside weeds, and which, when feed becomes scarce, migrate to the vineyards and feed on the vines. These caterpillars are the larvæ of smaller moths of various genera such as Prodenia and others.
Cutworms are other caterpillars of moths of the genus Agrotis, which feed on the branches of the vines, especially in the night-time, and in the daytime bury themselves in the soil beneath the vine. They are generally a gray or leathery color, while the army-worms are more violet and darker.
Damages.
—The damages from these various caterpillars are sometimes very large. Some years they occur in enormous quantities, and hundreds of tons of them may then be picked from a vineyard of a hundred acres of vines. The leaves are eaten by them, and the grapes are either scalded by the sun or do not attain their sweetness and coloring. Sometimes these various caterpillars are very common and destructive for one or two years in succession, after which they disappear and do not return to trouble the vines again for many years.
Remedies.
—The great caterpillars, after they have once infested the vineyard, can be destroyed by picking. A gang of men or boys should be furnished with buckets, which are besmeared on the inside with coal-oil. The caterpillars are picked and dropped in the buckets, from which they cannot crawl out, and when the buckets are half filled they may be emptied into trenches and covered up with soil.
Many use small scissors, with which the caterpillars are cut in twain while sitting on the vines. This will do for wine grapes, which are grown higher above the ground, but will hardly be proper on the low Muscat vines, as the contents of the caterpillars are apt to soil the grapes.
I have used Buhach sprays with great success. Ten pounds of Buhach, with a hundred gallons of water, brought the caterpillars down from the vines in forty-five minutes after spraying. As some, however, recovered, it is best to kill as many as possible of those which fall to the ground by punching them with a stick. The cost of Buhach is, however, great, and the difficulty of encountering favorable weather is such that this remedy is not apt to be extensively used.
When the vineyards are threatened by the invasion of the army-worms, or by the striped Deilephila caterpillar, the best remedy consists in trenching. A narrow trench, say one foot or more wide and two feet deep, with perpendicular sides, should immediately be dug around the vineyard. If water is at hand, fill the trench with water, on which some coal-oil may be poured,—enough to cause a film on the surface. If no water can be had, a log or scantling may be continually dragged up and down the furrow or trench, so as to crush the caterpillars before they can crawl out. In many places, however, the trench alone will do the work, as the caterpillars will generally not be able to get up the other side of the trench. What few crawl up can easily be kept down by hand-picking.
If certain attractive flowers, such as honey-suckles or petunias, are planted on a small bed in the vineyard, say near the house, the moths will come to them to feed from all the surrounding neighborhood. Only one small bed should be planted on every vineyard. A boy with a butterfly net, posted at each flower bed at sundown, can catch hundreds of moths every evening, and considerably reduce their number and prevent them from breeding.