SUGGESTIONS FOR WIREWORM CONTROL IN CALIFORNIA i
By Roy E. Campbell, Division of Truck
Crop and Garden Insect investigations
Wireworms, the young of click beetles, are found infesting soils
and injuring crops in many parts of California. A great many materials
and methods have been used in attempts to control wireworms, but as yet
no entirely satisfactory remedy has been found.
Granular Calcium Cyanide
One method which has been used in combating wireworms under California
conditions involves fumigating the soil with granular calcium cyanide.
Fumigating the entire soil area proved too expensive. It was found, however,
that the wireworms could be concentrated into rows by planting secds which
acted as baits. By treating only these bait rows with calcium cyanide,
the quantity required per acre was reduced materially. Many seeds have
been used for these baits, but beans and wheat have been found to attract
the most wireworms. Bean growers commonly use the low-grade or refuse
beans for bait. The bait is drilled into the soil just the same as if it
were a regular crop, and therefore the soil should be in a good friable
condition and have the proper moisture content for planting. The bait crop
is planted at the same depth that the regular crop would be planted.
In from 5 to 8 days after planting the bait most of the wireworms
in any given area will have gathered in the bait rows and be feeding on the
baits. Wireworms are most active when the soil is warm, so they reach the
baits sooner in sunny, warm weather. An occasional examination of the
planted seeds in the rows will disclose when the wireworms have been at-
tracted to the baits, Granular calcium cyanide is then applied with the
same planter used for the baits, in exactly the same rows, but about 1/2 inch
below the baits. The hydrocyanic acid gas fumes given off from the calcium
_/ For further details regarding wireworms and their control see
U. S. Department of Agriculture Farmers' Bulletin 1866, Wireworms 2nd
Their Control on Irrigated Lands, by M. C. Lane.
cyanide in the soil will kill the worms in the immediate vicinity. This
material will have dissipated in about 5 days, so that planting any crop
is safe thereafter.
The most satisfactory quantity of calcium cyanide to use has Leen
determined to be 1 pound per 1,000 feet of row. The closer together the
rows are, the more wireworms will be attracted. Considering this fact,
and the quantity of cyanide required, rows spaced not more than 2 feet
apart are suggested. When the rows are 21 feet apart, this spacing requires
approximately 100 pounds of calcium cyanide per acre. When extreme care is
exercised in the application of calcium cyanide, as little as 50 pounds per
acre gives excellent results, but since this is the case only under favorable
conditions, the larger quantity is recommended. The cost per acre for
material will be approximately $15 for 100 pounds.
This method of control works best when used in the spring, just before
the regular planting season. At that time the wireworms are most active
and are readily attracted to the baits.
Sometimes a crop is planted before the grower is aware of the presence
of so many wireworms. These are attracted to the crop the same as to the
baits, and may ultimately destroy the crop. In this case the planted crop
may be considered as a bait crop and treated in the same manner as described
above. After treatment the field may then be replanted.
For crops planted in hills, such as melons or tomatoes, which may
become infested, the calcium cyanide treatment may also be used. With a
pointed stick, a hole is punched in the ground close to the plant or hill,
and a teaspoonful of calcium cyanide is poured in. The hole is then filled
up with soil and tamped gently. This treatment will also kill any plants
remaining, but replanting can be done several days later, or at the same
time if made about a foot from the hole where the calcium cyanide was
Caution: Calcium Uanide is a dangerous poison, and when exposed
to the air it yields the deadly fumigant known as hyr ic ad
This fumigant should be used only by those familiar with its poisonous
qualities and with the precautions necessary to avoid accident.
Another method of wireworm control which has proved successful under
certain conditions involves flooding the land. However, to kill wireworms
by this method it is necessary that the soil temperatures average at least
700 F. This method of control is therefore limited to the hot summer months.
The land should be diked or ridged into basins so that water can be held
on it continuously for at least 5 days. Just enough water to cover the
soil is sufficient. Under these conditions (that is, with a soil temperature
of 700 F.or more and continuous flooding for 5 days) a very large percentage
of the wireworms can be killed. However, if the soil temperature is below
700 F., the percentage of wireworms killed by this treatment will be very low
For small plots or back-yard gardens the use of baits such as carrots
or potatoes has proved successful. These are placed in the soil to a depth
ranging from 3 to 5 inches and left for several days. They are then dug up,
the wireworms collected, and the baits returned to the soil for another
collection. The wireworms collected in these baits may be destroyed by
exposing them to the air in an open can. By digging up the baits every few
days and collecting the wireworms from them, the plot of ground can be almost
freed of these pests. The closer together the baits are placed, the quicker
the wireworms will be attracted and collected. On small ploLs Lhe baits
may be placed 3 or 4 feet apart, but on large plots it may be necessary
to space the baits farther apart so that there will not be too :any of theml
to handle without excessive labor.
Two methods of wireworm control developed at the Walla Wala, Wash,
laborator-y of this Bureau, under the direction of M. C. Lane, may be appli-
cable also in California. These methods involve the use of carbon disulfide
When carbon disulfide is introduced into the soil it forms a vapor
that is heavier than air and that penetrates downward into the Ctoil to a
depth of 18 inches or more, killing all wireworms present. For bot results
the soil should be fairly moist, but not too wet to be ploved, ad the
temperature at a depth of 6 inches should be above 600 F. Areas to be
treated with carbon disulfide should first be prepared by loosening the
ground by plowing, and smoothing it lightly afterwards with a float. One
fluid ounce of carbon disulfide should be applied in the soil about 2 inches
deep and at points not over 4, inches apart in each direction. A simple
procedure is to mark off the area lengthwise and crosswise by using a marker
with teeth set at 24 inches or less. At the intersections of the marks,
holes 2 or 3 inches deep can be punched with a stick, and the carbon disul-
fide poured into the holes from a 1-ounce measure or with a device having a
valve set to admit 1 ounce at a time. After being filled with carbonn
disulfide, the holes should be covered immediately with (Thp soil 70 d
pressed down firmly with the foot.
After 2 days the chemical will have accomplished its rnaxinu' Mil) of
wireworms. In hot weather the vapor will work itself out of the :oil. but
a second deep plowing after a week will help to aerate the soil and allow
the gas to escape faster. It is reasonably safe to plant crops a week after
treatment. A 100-pound (10-gallon) drum of carbon disulfide will be suf-
ficient to treat approximately 5,000 square feet at a cost of about $8.50.
Caution: Liquid carbon -di-sulfide. evaporates very ryLdUX pcn x-
posure to air_ and the vapor is extremely inflammable and explosiv when
mixed with air in certain poportions. It -should therefore be kept in a
cool place and handled with &reat care. Do not smoke when handling it.
It must be remembered that lighted lanterns, cigars, ,-Ctes,
UNIVERSITY OF FLORIDA
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sparks from electric switches, static or frictional electricity, sparks
caused by hammering upon metal, or even hot steam ipes ma cause an expjo-
sion of carbon disulfide vapor.
Crude naphthalene in soft crystalline form, containing over 90 percent
of pure naphthalene, is most satisfactory for use against wireworms. The
best time to apply this material is when the largest numbers of wireworms
are nearest the surface and most active. Sprinkle the naphthalene by hand
or machine along the sides of the fresh furrow from top to bottom as the
field is being plowed. Immediately after the material has been plowed in,
the entire field should be disked as deeply as possible, to mix the crude
naphthalene thoroughly with the soil containing the wireworms. The disking
is very important, because the deeper and more thoroughly the naphthalene
flakes are mixed with the soil, the better will be the percentage of kill
When applied in this manner, 500 pounds of crude naphthalene must be
used per acre to obtain a satisfactory kill of wireworms. To insure an even
distribution over the entire field, the crude naphthalene should be weighed
out at the rate of 20 ounces to 109 linear feet of 12-inch furrow slice.
This material is very effective in killing wireworms in the sandier types of
soil. It is less effective in soils rich in organic matter, and it should
not be applied after heavy applications of barnyard manure or the plowing
under of a green crop. After 5 days the gas from the naphthalene will have
accomplished its greatest kill of wireworms, and seed can be planted with
little risk of injury. The cost of naphthalene is about 5 cents per pound
in California, at which rate it would cost about $25 for the material to
treat an acre.
It is important that the temperature of the soil be at least above
600 F. during the period of treatment and that the soil be in a good tillable
condition, if the best diffusion of gas is to be obtained with either carbon
disulfide or naphthalene.
Many experiments have been made by numerous investigators in different
parts of the country in an attempt to find a poisoned bait that will kill
wireworms. But unfortunately norr has been found. Although the wireworms
can be attracted to various baits, any poison added to these baits either
has not affected the wircworms or has been repellent, so that the wireworms
would not feed on the bait.
Many other materials have been used to treat the soii infested with
wireworms, but they have been ineffective or too expensive. Therefore
only the control methods listed here are recommended at this time.