COOPERATIVE EXTENSION WORK IN
AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
AGRICULTURAL EXTENSION SERVICE. UNIVERSITY OF FLORIDA
FLORIDA STATE UNIVERSITY
AND UNITED STATES DEPARTMENT OF AGRICULTURE
H. G. CLAYTON, DIRECTOR
Screwworms and Their Control
By LEONARD E. SWANSON AND OLIVER F. GOEN
Veterinary Parasitologist, Agricultural Experiment Station, and Animal Husbandman,
Agricultural Extension Service
Fig. 1.-Navels of calves, particularly calves dropped late in the season,
often are infested with screwworms.
AGRICULTURAL EXTENSION SERVICE
Screwworms and Their Control
Screwworm flies, Callitroga americana (C. and P.), are para-
sites that must develop in flesh. The females are attracted to
and deposit their eggs only in fresh wounds. The screwworms
are the larvae form of this fly. This pest has been a serious
handicap to the Florida livestock industry since 1933, causing
loss of flesh and even deaths in cattle, hogs and other animals.
Very cold winters may cut down on the number of infestations.
However, the flies usually survive short cold waves. Cold will
hardly kill the larvae in wounds and pupae are protected by
leaves, dirt and other debris. Following a severe winter, cases
of screwworms are light for a short period but the pests soon
re-establish themselves upon resumption of warm weather.
All warm-blooded animals (cattle, sheep, goats, deer, swine,
horses, etc.) are hosts, with an occasional infestation in man.
Any type of open wound, such as dehorning, castration, ear
marking, nail or wire cuts, dog bites or tears, hooking by other
animals, cutting of teeth in pigs, tusk injuries and wounds
created by external parasites, especially ticks and horseflies, are
the usual sites of infestation. When calving coincides with
screwworm activity the navels of newborn animals and injuries
to the dam are the most frequent sites of infestation.
To decrease the incidence of screwworm infestations, dehorn-
ing, castration and ear marking should be done when the flies
are inactive. Cold winter mornings are usually safe times for
these operations. Tip the horns of all cattle. Keep a close watch
of corrals, chutes and fences for nails, sharp boards, poles, etc.,
and remove them when found. Do not let dogs run animals,
especially vicious dogs that have a tendency to grab the ears or
noses of these animals. Avoid all unnecessary rough handling
of animals. Cut the tusks of old boars and pull the eye teeth of
Watch animals closely for any wounds, whether they be made
by man, insect or animal, and apply a recognized screwworm
preparation to them promptly. After a preventive treatment
is applied, observe the animal daily until the wound is healed
and, if necessary, re-treat. Spray or dip all animals in a
recognized insecticide for the control of ticks. Horseflies can-
not be controlled by the use of insecticides and, unfortunately,
there is no other control for these pests. Watch all animals for
screwworm signs swellings with a watery, blood-tinged
exudate, and matted hair. Foul odors may be noted for some
distance in severe infestations. Brands and other injuries
should be watched closely.
All newborn animals should be treated immediately after
birth. Where navel ill is a problem, apply tincture of iodine to
the navel region prior to applying the screwworm preparation.
There are several good screwworm preparations on the mar-
ket to prevent infestation and to destroy the larvae after they
have become established in the wounds. Smears or liquids con-
taining pine tar oil, benzol, diphenylamine or lindane can be
used effectively when applied liberally as a preventive or treat-
ment. Smear EQ 335, containing lindane and white mineral
oil, is a very effective treatment and prevention. Other similar
preparations may be used. Usually one treatment is sufficient.
LIVES UP TO 65 DAYS
FLIES MATE PUPAL STAGE
FEMALE FLIES ATTRACTED 3 TO 14 DAYS UNDER
TO FRESH WOUNDS FAVORABLE CONDITIONS
FLY DEPOSITS EGGS PUPAL STAGE IN
IN SHINGLED BATCHES LOOSE SOIL MAY LI-
(10 TO 400 EGGS) DORMANT 2 MONTHS
EGGS ON WOUND LARVAE CRAWL OUT OF
EDGES HATCH IN WOUND IN S TO 6 DAYS.
6 TO 21 HOURS BURROW INTO LOOSE SOIL
SCREWWORM LARVAE FEED
IN CLUSTERS- HEAD DOWN
TAIL OUT OF EACH WOUND
LIFE CYCLE OF SCREWWORMS
However, if excessive bleeding occurs, several treatments may
be necessary. In treating newborn calves use caution, as re-
peated applications and extensive smearing may be dangerous.
An effective control of the pests is primarily dependent upon
close observation of all animals and immediate treatment of
Press Bulletin No. 6. August 15, 19io
Florida Experiment Station.
For many reasons inspection of nurseries has been a
rather perplexing business for many years. Almost every
$tate has a law of its own and in the interpretation and
execution of such law the official inspector, usually and
for the most part because of good reasons, further insists
upon the right of being a law to himself. Efforts have
been made at various times to secure the passage of a
national law that would give some uniformity of require-
ment and usage but because of supposed conflicts of
interest between tree sellers and tree buyers all attempts
of the kind have failed.
Realizing the standard of requirement demanded by
the purchasing public in a certificate of freedom from in-
sect and fungous pests, and the constantly increasing
danger of friction between inspectors and their constitu-
ent nurserymen as well as between the inspectors of
different states, owing to such diversity of practice, a
considerable body of state inspectors met in conference in
Chicago last January and took all steps possible to reach
a basis of uniform practice and common understanding.
With this movement I am in most hearty sympathy and
wish to give as wide publicity as possible to their pro-
ceedings. All certificates already issued or which'shall
be issued by me this yar will be found to conform to the
regulations adopted by this Society of Official Horticul-
tural Inspectors. 1 regard it as very fortunate that Dr.
Forbes' of Illinois was the prime mover in effecting this
organization as his well known reputation for care and
conservatism will bring a confidence to both public and
nurserymen, the value of which can hardly be overesti-
mated at this stage of accomplishment. It is to be hoped
that the principles which have been emphasized in the
birth of the society will continue to guide it and that its
right to general confidence will never be forfeited by in-
different regard for the rights of any of the parties at
interest. The circular sent out by Dr. Forbes is as follows:
PROCEEDINGS AND ORGANIZATION OF THE SOCIETY OF OFFICIAL
CHICAoo, January 4, 1901.
At a conference of horticultural inspectors of the
states of New York, Michigan, Indiana, Illinois, Iowa,
Kentucky and Tennessee held at the Palmer House, Chi-
cago, January 4, 1901, the general subject of the methods
and objects of nursery inspection was broadly discussed,
With special attention to certain details, in which a com-
parison of views was thought to be particularly desirable.
1. Difficulties having been made by certain state
officials with respect to the acceptance of inspection cer-
tificates from other states this subject was discussed at
length, and the opinion was unanimously expressed by
the conference, that state inspectors should accept the
inspection certificates of other states issued by authorities
.legally constituted for that purpose, as PRIMA FACIE evi-
dence of the facts therein set forth. It was not intended
by this statement to prevent or discourage a supplement-
ary inspection of certified stock if, in the judgment of
any inspector, special conditions might make this neces-
2. On comparison of the practice of different state
inspectors wide differences were found in the time during
which nursery inspections are made, due principally to
differences in local condition or business methods in
different parts of the country. After full discussion it
was decided that the period of inspection should be de-
termined in each state at the discretion of the inspector,
but it was agreed that all peach stock should be inspected
as late in the season as practicable, particularly where
the surroundings were such as to cause suspicion of the
occurrence of the San Jose scale, or where the origin of
the buds was either suspicious or .unknown. In such
cases, if the nursery was inspected early, a late supple-
mental inspection of the peach stock should be made.
3. With respect to the nursery some sections of the
stock of which is so infested or infected as to make its
sale objectionable but not in a way to damage or endanger
the remainder of the stock, the practice adopted in
Illinois was approved and recommended to all inspectors.
Under this practice a nurseryman some of whose stock is
infected, for example, with the crown gall, the remainder
of it being free, is given a certificate which reads as fol-
lows: "This is to certify that the nursery stock which
bears this certificate, grown on the nursery premises of
-------- situated ------------ has been," etc., etc.
This certificate is issued with the limitation, expressed in
writing, that it is not applicable to any of the stock to
which objection is made, and on the written promise of
the nurseryman receiving it that it shall not be so ap-
4. With respect to a form of certificate for dealers
in nursery stock who do not own nursery premises, but
wish a certificate from their own state inspector available
for their shipments, the Iowa practice was approved,
under which a dealer's certificate is issued as follows:
"This is to certify that the nursery stock for sale by
---------- of ...---------- has been inspected," etc.,
etc. Previous to issuing such a certificate the Iowa in-
spector requires a statement from the dealer, certified be-
fore a notary, showing all persons from whom said dealer
has purchased stock, and containing a promise that if
stock is afterwards purchased from other persons than
those on the certified list the inspector will be notified
forthwith and opportunity given him to inspect such
stock before sale, if so desired.
The remaining sections of these .proceedings with
their application to Florida conditions are set forth in
Section 2 which will be published to follow next week.
H. A. GossARD, Entomologist.
OW State papers please copy.
Press Bulletin No. 7.
September i, 1go0
Florida Experiment Station.
[Refer to Press Bulletin No. 6 to get the proceeding connection]
5. It appeared upon a comparison of the laws and
practices of different states, that ornamental trees,
shrubs, and vines, were generally included in the inspec-
tion, if grown for sale, and that strawberry plants were
also inspected, if held for sale, in New York, Kentucky,
Tennessee, Iowa and Michigan, but not in Indiana and
Illinois. In states having a considerable business in the
sale of cuttings, it was deemed necessary that vineyards
from which such cuttings were sold should be inspected
and certified as nurseries.
6. It was generally agreed with respect to the wooly
aphis that gradually increasing pressure should, be
brought to bear for the reduction of this insect in nurser-
ies, but that no uniform practice could be established
because of wide differences in its abundance in different
states. The New York practice of requiring the rejection
and destruction of trees sufficiently infected to show
knots on the roots was commonly approved. It was also
thought well to require insecticide treatment, with kero-
sene emulsion, of roots of nursery, trees whitened by this
insect. A similar policy of gradually increasing pressure
of requirement was also recommended with respect to the
scurfy scale, particularly in those states where it is not
now generally and uniformly distributed. It was held at
present to be unwise to require the destruction of trees
exposed to infection with crown gall but not visibly so
infected. Trees actually bearing this gall either at the
crown or on the roots were regarded as unmerchantable.
7. After full discussion 'it was voted unanimously to
organize as a society of official horticultural inspectors,
membership to be open to those officially connected with
the work of horticultural inspection in the various states
of the Union and in Canada. Prof. S. A. Forbes, of
Illinois, was elected president for one year and until the
next regular meeting thereafter. It was further voted
that the first meeting of the new society should be held
in connection with the annual convention of the Associa-
tion of Colleges and Experiment Stations to which time
the society adjourned. S. A. FORBEs, Chairman.
It should be remembered that there is no law provid-
ing for the inspectioll of Florida nurseries and only such
as request inspection, agreeing to pay all traveling ex-
penses of the inspector to and from the nursery together
with an examination fee of $5, are inspected at all. I am
usually unable to give any information concerning nurs-
eries that I have not officially inspected.
If, upon inspection, a nursery is found in good condi-
tion in every respect, a certificate similar to the following
is issued: "This is to certify that I have, on this _----
day of ,-----, 1901, personally inspected the nursery
stock of the-----------nurseries, owned and operated
by _----------, of ------_-----, Florida, and find the
same to be apparently free from all pests, scheduled and
designated as pests by Boards of Horticulture and En-
tomology and seemingly healthy in every respect.
This certificate may be used with stock not grown in
the nurseries of the aforesaid only by compliance with
the requirements of the American Society of Official Hor-
ticultural Inspectors. .(Signed) H. A. GOSSARD,
Ento. Fla. Agr'l Exp. Station."
If the stock should not all be healthy, for instance if
an acre of plums is infected with crown gall, the remain-
der. of the stock being free, an exception clause is added
immediately after the freedom and health clause, thus:
------ and seemingly healthy in every respect;
except that one acre of plums is not included in this cer-
tificate." The written promise of the nurseryman will
then be taken not to use, sell or ship said excepted stock.
The violation of such a promise will be regarded as suffi-
cient cause to forfeit further right to inspection. The
presence of any of the following pests will cause the in-
sertion of the exception clause: San Jose scale, (As-
pidiotus perniciosus), West Indian scale, (Diaspis amyg-
dali), White fly, (Aleurodes citri), Cottony Cushion
scale, (Icerya purchase), crown gall, wooly aphis, peach
rosette, peach yellows or any other insect or disease likely
to inflict serious injury to said or other stock near which
it may be planted.
An inspection certificate is not and cannot be an
absolute guarantee of freedom from pests but it is much
better than no guarantee. No certified nursery in this
state is without a fumigatorium and the fumigation work
of some of our nurseries cannot be surpassed in the world.
I always inspect not only the nursery stock but at ad-
jacent premises that might mbnace the nursery and
treatment is prescribed according to the findings. In
San Jose scale,neighborhoods all stock susceptible to the
scale is thoroughly fumigated before it is permitted to
leave the nursery grounds. The keeping of any kind of
stock for more than two years is regarded with great dis-
favor and, such stock is rigidly inspected or ordered de-
Purchasers of stock from certified nurseries are re-
quested to inform me at the earliest possible moment of
stock received by them that proves to have been diseased
at the time of purchase. It is only by the co-operation
of the nurserymen and the public with the inspector that
a high standard of goods can be maintained.
H. A. GOSSARD, Entomologist.
." State papers please copy.