Imperial Valley press., 1924-08-25
Cotton Worm Is
Serious Menace,
Is Under Control

a ldISe HuINDeT or CO0lpE,lHt -
have come into the agricultural eX-
tension service office from cotton
growers whose plaLts are being
badly attacked by small worm
that eats on the leaves. Some
growers report INJURY so severe that
their entire fields will have to be
abandoned, while other fields are
so seriously threatened by the pest
that unless the worm is controlled
in the near future, the crop will
be lost
According to Farm Advisor Z.
L. Garthwaite- the insect doing the
damage is the cotton leaf perforator,
the larvae form OF which is a small
caterpillar about rs thick as a pin
when full grown, and about one
half inch long at that stage. The
caterpillars are speckled black and
white and feed entirely on the
leaves, usually on the under side.
The larvae pupate is a small white
tunnel shaped cocoon from which
a small whitish or yellowish moth
emerges, being about 3-S of an inch
long, or about the size of a mosqui-
to. This moth does no damage at
all to the plants merely flying
around in the early morning, and
hiding on the under sides of the
lower leaves during the day. The
moth deposits eggs which hatch out
into the caterpillars. Numerous
small white webs can be seen on
the underside of the leaves. Upon
closer examination small caterpil-
lars can be seen under these webs,
where they are melting.t
The cotton leaf perforator has
been known in Imperial, Yuma and
Salt River valleys for number of
years, having spread from the
wild cotton of Arizona. The amount
of damage done by this pest is
more severe in some years than
others, but every year some dam
age is reported. The pest is norm
ally kept in check by a small wasp
which lays its egg in the larvae of
the cotton leaf perforator the egg
Matching into q caterpillar. which
feeds on the inside of the cotton
leaf perforator caterpillar and de-
strovs it. Usually these wasps are
numerous enough to keep the per-
forator under control, but in some
year when the wasp is not numer-
Gus due to climatic conditions or
because ii is held down by second
,arv parasites, the perforator IN
ereases at tremendous rate, and
does enormous damage in some cot
ton fields.
Effective Measures
Some growers are of the opinion
that the yellow alfalfa butterfly
is responsible for the damage. but !
this is not so, as that caterpillar IS
an inch in length and about q quar-
ter of an inch in diameter. So far
as can be learned no control meas
ures have been tried against this
pest. In testing various methods of
control, the farm advisor S office
found that while No. 10 nico dust
and 100 per cent calcium cyanide
dust will kill a few of the caterpil-
lars, the numbers is not great enough
to Justify the expense.
In testing arsenate of lead for !
the control Of this pest 1t was
found that effective control could
be obtained by dusting the plants !
with/a mixture consisting of one !
pound of arsenate OF lead to four
pounds of lime. Where gypsum can |
be obtained free from Jumps, 1t will |
make a good substitute for the lime |
and it costs cents per pound less.
The arsenate Of lead and lime was
mixed and applied to
the cotton plants by means of a
hand dusting machine at the rate
of 20 pounds per acre. just as
effective results were obtained by
putting the dust into cheesecloth
bags or coarse barley sacks and
shaking these over the tops and
around the sides of the plants. This
method has the advantages over the
dusting machine in that these bags
cost little or nothing and it is also
easier 10 get the material on the
terminal growth Of the plant with
the bags. Furthermore cheap labor
can handle the bags to much better
advantage than machines. Where
growers prefer spraying to dusting
a mixture of 200 gallons of water
eight pounds of arsenate of lead
and one and a half pounds of kayso
or some other spreader can be used.
The great majority of cotton field
throughout the county are net sew
erely enough damaged by the per-
forator to justify control measures.
On the other hand some fields are
being attacked so seriously that
unless control measures are adopt
ed it is doubtful whether Il crop
can be made.
As rule, as you look so you are