from a friend...
We are plagued with this here to the North of Belize!!
White fly is totally epidemic here -- and Tomato growing is
thus no longer and option.
Unless we emulate the Mexican solution - cyanide in the root cluster.
Basically - -turning a tomato plant into a Chaya -- or Macal -- and the
white flies poison themselves when they go sucking that pant juice.
So I am googling how to control this fly!
THE WHITE-FLY OF GREENHOUSES
BY CLARENCE M. WEED AND ALBERT F. CONRADI
During recent years greenhouse crops in this and other states
have been very commonly attacked by a tiny insect which has
received the common name of white-tly. It is a member of a
small and generally little-known familly whose technical name
is Aleurodes. It accomplishes its injury by sucking the sap of
its food-plants, often appearing upon the leaves in enormous
numbers. A great variety of greenhouse crops suffer from its
depredations, although in New Hampshire cucumbers and
tomatoes growing under glass have been damaged the most.
The white-flies as a family are tropical insects. In warm
climates man}" species are abundant out of doors, but in cold
regions onh^ a few sorts appear to be able to survive from sea-
son to season, except in the shelter of the heated greenhouse.
The egg of the white-fly common in our greenhouses is a
minute oblong object slightly pointed at one end. The rounded
end is attached to the under surface of the leaf so that the egg
hangs perpendicularly downward when the leaf is horizontal.
Its length is less than 1-4 mm. or about 1-100 inch. When
first laid the eggs are slightly greenish yellow, but they soon
become darker. Just before hatching the color is a dull o:lossv
In a little less than two weeks (13 days according to our
observations) the eggs hatch into little nymphs, which move
about over the surface of the leaf for a few hours, perhaps a
day ; then they insert their tiny beaks into the succulent tissues
of the leaf and settle down, taking on the appearance of a
The little scale remains in position two weeks or longer ;
then it is a tiny flattened object, with oval outline, of a slightly
greenish-yellow color, in size about 1 mm. by 1-2 mm. Under a
48 THE WHITE-FLY OF GREENHOUSES
hand lens one can see that it is scantily clothed with minute
bristles, having a denser fringe along the margins of the body.
Finally a T-shaped rupture appears in the back skin of the
insect, and the adult white-fly emerges to continue the prop-
agation of the race.
INJURIES TO THE PLANT
The mouth parts of both the nymphs and adults of the white-
fly are formed for sucking, and the insects are injurious in both
these stages. They insert their tiny beaks into the succulent
tissues of the under surface of the leaf; the latter soon shrivels,
dies, and later falls to the ground. As the adults prefer to
oviposit upon the younger shoots the lower leaves of infested
plants die first.
Observations and experiments carried on during the past
season showed that much the most harm was caused by the
work of the nymphs. Adults kept in breeding cages with
plants lived a longer time than those without food, yet in no
case did the plants die where adults alone were present.
Some time after the leaves are infested the under surface is
covered with a sticky substance excreted by the insects. This
not only tends to close the pores of the leaf, but it supports a
black fungus which soon covers the entire under surface of
the leaf, making it appear as though it were covered with soot.
In a badly infested greenhouse the upper surface shows this
fungus, but less so than the under surface.
HIBERNATION AND BROODS
We have no evidence in our New Hampshire studies that the
white-flies can pass the winter out of doors. On those plants
that were infested in the open last summer and since brought
into the greenhouse, none of its life-history stages can be found.
The treatment given those in the greenhouses subdued their
numbers and at the approach of cold weather the few that
remained were less active. Some adults linger among the
leaves of yourg beets in the greenhouse during the colder wea-
ther, occasionally appearing on young tomato plants. Adults
captured on January 14 and put in vials containing no food
died in three days, others kept in bell jars with plants survived.
No nymphs could be found at this time, and it is probable that
REMEDIAL MEASURES 49
those few found in tlie house at this time of the year are adults
that escaped the summer treatment.
The time required for this insect to complete all its life
histor}' stages is not more than five weeks, allowing one week's
time for oviposition. It follows that an indefinite number of
broods are possible, and if left unchecked their numbers may
easily become most seriously destructive.
Although this species of white-fly is a serious pest on to-
matoes and cucumbers it is not confined to these plants, nor is
it confined to forcing houses alone. On July 18, an immense
swarm was discovered in the gardens out of doors. A careful
investigation was made to discover nymphs on as many plants
as possible. They were found on a stray potato plant and
strawberry leaves. On July 26, some were found on
currant leaves, also on the leaves of a species of Erigeron.
On July 29, some were found on goldenrod, and a little later
a nymph was found on a chrysanthemum leaf. Of course,
these were very few and in all cases on the under surface of
the leaf. Unfortunately it has not been determined whether or
not these nymphs complete their life history successfully.
Mr. W. E. Britton of the Connecticut station gives a list of
58 plants upon which he found the nymphs. It follows that
this pest has a wide range of adaptation in food plants. In
our studies we have no evidence of its establishing itself in the
open in a serious way.
Kerowater Sprays. Our experiments during the summer of
1901 showed that the adult white-flies are very easily killed by
spraying with a mechanical mixture of kerosene and water,
with 5 per cent, of kerosene. We used for this purpose a knap-
sack kerowater sprayer. When the plant on which they are
resting is disturbed these adults fly into the air, making a
miniature cloud. If those thus in the air are hit by the kero-
water spray they drop down and die. In spraying it is desir-
able to begin at the top of the plants and work down.
We used this method to advantage out of doors, the adults
being very easily destroyed even on badly infested plants.
The extent to which the kerowater spray can be employed
to destroy the nymphs will depend largely on the plant attacked.
Some greenhouse plants are very easily injured by kerosene.
50 THE WHITE-FLY OF GREENHOUSES
Our experiments showed that the nymphs are readily killed by
the kerosene spray. Doubtless kerosene emulsion could be
used to equal advantage.
Hydrocyanic Acid Gas. This was the most successful, as
well as the most satisfactory, remedy we tried. Statements
had been made that this gas could not be used to advantage
without injury to the greenhouse crops. To determine the
truth of this a considerable number of tests were made, the
results showing that the adult white-flies are very easily killed
by an exposure too short to injure the plants. The more
important of these experiments are recorded below :
On July 15, 1902, a vacant section of the greenhouse con-
taining 2,833 cubic feet of space was stocked with tomato and
squash plants and a swarm of white-flies. The gas treatment
was given at 10 a. m., the day being clear and hot. Twelve
ounces of strong sulphuric acid and 12 ounces of potassium
cyanide were added to one gallon of water in an earthenware
jar. The house was kept closed for 15 minutes, at the end of
which period the adult white-flies were dead. The plants were
uninjured, except a few leaves of a lily that had been growing
under a greenhouse bench. In later experiments it was found
that the white-flies began to fall off the plants within two min-
utes after the gas was formed.
Later, during the same day, the main section of the house
was treated. This section was filled with fruiting tomatoes
and cucumbers on which the white-flies were exceedingly
abundant and destructive. At 4:30 p. m. the gas was made
by adding 6 ounces of potassium cyanide to 1 pound of water
to which 1 pound of strong sulphuric acid had been added.
Nine minutes later the house was opened, when the earth and
floors were seen to be covered by myriads of the tiny flies that
had succumbed to the deadly gas. Apparently all the adult
flies were killed. No plants were injured.
On July 28 and August 12 this treatment was repeated with
equally successful results.
It seems evident from these experiments that the white-fly
can be controlled in greenhouses by this gas treatment. The
frequency of treatment and the number of treatments required
to subdue the pests in a badly infested house will need to be
determined by further observations.
HOW TO ESTImATE THE CUBIC SPACE IN A HOUSE 51
HOW TO FUMIGATE
Before fumigating it is necessary to know the amount of
space contained in the house ; this will enable the operator to
mix his chemicals properly. Hydrocyanic acid gas if used too
strong, or if left in the house too long, will seriously injure
the plants. It is therefore very important that the directions
for treatment be followed carefully.
The best proportion of cyanide, sulphuric acid, and water
seems to be
1 ounce cyanide of potassium,
2 ounces commercial sulphuric acid,
4 ounces water.
The water should be poured into the receiving vessel first ;
then the acid should be added ; then the cyanide as directed
more fully below. Pour the acid into the icater ; never pour
the water into the acid.
In our experiments we used 1 ounce of cyanide to 400 cubic
feet of space, and left the house closed but nine minutes. Do
not expose the jjlants to the gas longer than this.
HOW TO ESTIMATE THE CUBIC SPACE IN A HOUSE
If the house is the shape of a square or a rectangle the
cubic contents are found by multiplying the height, length, and
width. If the house has a triangular roof with two sides equal,
first find the cubic contents of the space enclosed by the walls
as directed above ; then find the area of the space enclosed by
the roof by multiplying the width of the house by the length of
the house and this result by the perpendicular distance from
the top of the walls to the gable ; divide this entire product
by 3, and add the result to that of the space enclosed by the
walls. If, however, the house is irregularly shaped the prob-
lem becomes more difficult. The cubic contents may be obtained
in two ways :
a. Divide the house into rectangles, squares, and right
angled triangles. The cubic contents of rectangles and
squares are obtained by multiplying together the three dimen-
sions ; if a right angled triangle by multiplying the two shorter
sides together and divide by 2.
h. The following method, originated by Dr. B. T. Galloway,
is quoted from Prof. W. G. Johnson's " Fumigation Methods '* :
Procure from a stationer a sheet of cross section paper con-
52 THE WHITE-FLY OF GREENHOUSES
taining squares of 1-4 aud 1-16 inches. Let the 1-4 inch
squares represent square feet. Draw on this sheet a cross
section of your house, on the scale of 1-4 inch to the foot.
Count the enclosed squares, reduce them to feet, and multiply
by the length of the house. In this manner the exact cubic
contents of any house may be easily found no matter how
irregular its dimensions.
HOW TO MAKE THE GAS
The amount of cyanide used in these experiments was at
the rate of 1 ounce of cyanide of potassium to 400 cubic feet
of greenhouse space.
Use an earthen pot ; do not use metal ; this vessel should be
large enough so that the liquid does not run over on to the
greenhouse floor. In our experiments an earthenware gallon
jar was used, and this was not any too large.
Pour the water into the vessel, add the acid ; then weigh
the cyanide, put it in a paper bag. Close the ventilators, and
firmly fasten every door of the house except the one used by
the operator. This caution should not be neglected, as the
writers have repeatedly witnessed where a person unawares
approached and entered the greenhouse when filled with
tobacco fumes. Were this to happen when the house is filled
with the hydrocyanic acid gas treatment, the result would be
serious, if not fatal. When all is ready, approach the pot
with the bag containing the cyanide ; fill the lungs with air,
hold your breath, drop in the cyanide, bag and all, and leave
the house at once, lock the last door and notice the time.
After the number of minutes required to kill the adult white-
flies are passed open the doors and give the gas plenty of time
to escape before you enter.
Hydrocyanic acid gas is very poisonous, and the house
should not be entered during treatment.
These experiments related to tomatoes and cucumbers under
glass. We do not know what effect the gas might have o?i other
plants and advise preliminary trials before it is used.
Greenhouses used for growing vegetables can often be given
a stronger treatment at times when a crop is matured and the
house is empty. At such times the gas may be generated in a
much larger quantity and left over night. It will thus be
pretty sure to kill all insects present.http://www.archive.org/stream/bulletin100newh/bulletin100newh_djvu.txt