LEAFLET NO. 50
SOIL INSECTS atd LEAFHOPPERS
ATTACKING SWEETPOTATOES
W. G. EDEN, L. L. HYCHE, and J. A. GRIFFIN
Department of Zoology-Entomology
ALABAMA FARMERS have har-
vested approximately 18,000 acres of
sweetpotatoes annually for the past 5
years. Average value of the crop has
been about 3 million dollars per year.
With proper use of present information
on insect control, yields can be in-
creased and the quality of sweetpota-
toes greatly improved. Experiments
on control of insects of sweetpotatoes
have been conducted for the past 5
years at the Chilton Area Horticulture
and North Alabama Horticulture sub-
stations at Clanton and Cullman, and
at the Horticulture Field, Ashford.
Recommendations given in this leaflet
are based on results from these ex-
periments.
SOIL INSECTS
Wireworms are the most important
soil insects of sweetpothtoes in Ala-
bama; however, others, such as larvae
of certain flea beetles, cause some
damage to the underground parts of
sweetpotatoes. These immature in-
sects inflict serious injury to sweet-
potatoes by feeding on the roots. Al-
though wireworms 
rarely, if ever,
cause complete crop failure, the punc-
tures made by their feeding (see photo)
mar the appearance of the sweetpota-
toes and lower their market value.
Also, the punctures afford excellent
entrances for such diseases as soil and
storage rots. These rots may result in
heavy losses of stored sweetpotatoes.
Life history. Wireworms are imma-
ture forms of click beetles or skip-
jacks. One of the more common species
found in Alabama is the Gulf wire-
worm, Conoderus amplicollis (Gyll.).
The life cycle of this insect is com-
pleted in 1 year. Adult beetles are
approximately 3/8-inch long and 1/8-
inch wide, dark brown, and velvety.
Female beetles deposit their eggs on
or near the surface of the soil during
May and June. The eggs hatch in 8 to
10 days, and the young larvae begin
feeding immediately. The larvae (wire-
worms) attain most of their growth
during the first 8 or 10 weeks of life
and are almost fully grown by the end
of November. They grow very little
during the winter, and complete their
development ir tie spri g. The larval
.00
J
Sweetpotatoes damaged by wireworms.
AGRICULTURAL EXPERIMENT
t/ie ALABAMA POLYTECHNIC
E. V. Smith, Director
STATION
INSTITUTE
Auburn, Alabama
JUNE 1956
period is approximately 10 months.
Mature larvae are about 3/4-inch long
and nearly 1/8-inch wide. They have
hard, shiny, yellowish-brown bodies
and dark brown or black heads. Pupa-
tion occurs in earthen cells in the top
layer of the soil during April, May,
and June; length of the pupal period
is approximately 8 to 10 days. Adult
beetles emerge in May and June with
a small percentage emerging in July.
Control. Results of experiments con-
ducted since 1951 show that wireworms
can be controlled by introducing in-
secticides into the soil. Of several in-
secticides tested, aldrin, dieldrin, and
heptachlor have consistently been the
most effective. These materials should
be applied prior to planting at the rate
of 2 pounds of technical insecticide per
acre. Effective control may be obtained
by applying in the row as insecticide-
fertilizer mixtures, or they may be
applied separately. The insecticides
may also be applied broadcast as
sprays, granules, or insecticide-fertili-
zer mixtures. Dusts may be used, but
some of the material will be lost by
drift. Broadcast applications should
be disked into the soil prior to planting.
Mixing insecticides with the 
transplant
water has not given as effective con-
trol as the other methods.
Aldrin, dieldrin, and heptachlor 
are
available as emulsifiable liquids, gran-
ules, and dusts. Granular formulations
are easier to use, and there is 
no loss
from drift. They are gaining 
in popu-
larity for both insecticide-fertilizer
mixtures and for broadcast 
application.
LEAFHOPPERS
There are several insects 
that cause
economic damage by 
feeding on the
foliage of sweetpotatoes, 
but leafhop-
pers are probably the 
most important.
There are many different 
kinds of
leafhoppers; the 
most important ones
on sweetpotatoes belong 
to the genus
Empoasca.
Life history. Leafhoppers overwinter
in various stages, depending on the
species. Some go through the winter
in the egg stage in stems of various
plants. A large number of species
winter in the form of full-grown in-
sects, taking shelter in and around the
crops on which they feed; a few 
pass
the winter in the partly developed or
nymphal stage. Adult females 
usually
lay their eggs in stems, buds, or leaves
of their food plants. The eggs hatch
into wingless but very active nymphs
that feed by sucking the sap. They
sometimes inject a substance that is
distinctly poisonous to plant tissue, 
and
that kills the areas around their feed-
ing punctures. They shed their skins
several times while developing from
nymphs to adults, but they do not pass
through a pupal or resting stage. Leaf-
hopper adults vary in size from 1/20-
to 1/4-inch long, and rarely reach 1/2
inch in length. The adults have wings
but use their legs to a large extent in
jumping from one part of a plant to
another. They are good jumpers 
or
hoppers as their common name implies.
The general 
outline of 
their bodies 
is
long and slender, and they vary greatly
in color.
Control. Results of experiments
show that, when leafhoppers become
numerous in sweetpotato fields, it is
highly profitable to use insecticides 
to
control them. This is particularly 
true
if other factors indicate a good 
yield
of sweetpotatoes. An example 
of how
increased yields can result from 
proper
use of insecticides is given in the 
table.
Results of Controlling Leafhoppers
on Sweetpotatoes, North Alabama
Horticulture Substation, 1955
Treatment* Yield per acre
Bushels
Untreated check 422
DDT, 5 per cent 539
TDE, 5 per cent 510
Methoxychlor, 5 per cent 516
Toxaphene, 20 per cent 514
*Dusts were applied at the rate of 30
pounds per acre on August 15, 24,
and 31, and September 10 and 20.
All of the insecticidal dusts used re-
sulted in substantial yield increases.
On the basis of this and other similar
experiments, all of these insecticides
are recommended.
Applications of insecticides should
be started when leafhoppers become
numerous. A good rule is to begin
treatments when flights of leafhoppers
are obvious as you walk through the
field. Treatments should be made at
7- to 10-day intervals as long as large
numbers of leafhoppers are evident.
These insecticides are also effective on
many other insects, such as horn-
worms. tortoise beetles, and other leaf
feeders.
RECOMMENDATIONS
1. Good control of soil insects can be
obtained by using 2 pounds per acre
of aldrin, dieldrin, or heptachlor. The
insecticides may be applied to the soil
in mixtures with fertilizer or broad-
cast and disked in before the sweet-
potatoes are transplanted.
2. Mixing insecticides with the trans-
plant water has not given as effective
control as other methods.
3. Leafhoppers can be effectively
controlled with 30 pounds per acre of
5 per cent dusts of DDT, TDE, or
methoxychlor, or 20 per cent toxa-
phene.
4. Applications of these insecticides
should be made at 7- to 10-day inter-
vals when leafhoppers are numerous.
5. These insecticides will also con-
trol other insects, such as hornworms
and tortoise beetles.
ACKNOWLEDGEMENT
The authors acknowledge the cooper-
ation and assistance of C. C. Carlton
and T. S. Morrow, superintendents of
the Chilton Area and North Alabama
Horticulture substations at Clanton and
Cullman, respectively, and R. L. Liv-
ingston, in charge of the Horticulture
Field at Ashf'ord.