_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.
[Illustration: 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.