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Aeroplane dropping poisonous powders can rapidly overcome plagues which threaten crops and trees


Aeroplane applying calcium arsenate powder to cotton plants
























COTTON PLANTS are subject to attacks from the boll weevil. This insect is particularly active after heavy rainfall, and a delay, even of hours, in the application of calcium arsenate powder may cause thousands of pounds of damage to the crops. When aeroplanes are not available the work has to be carried out with carts, fifty to seventy-five of which are required to do the work of one aeroplane.




LIFE is a constant struggle for existence between man and the insect world. Human beings and insects like the same kind of food, and so keen is the contest that an eminent authority has stated that, if our tiny foes were allowed to feed and multiply unchecked, we should be without food in two years.


Modern intensive cultivation has brought new problems to the agriculturalists, not the least of which are varieties of insect pests previously unknown. But although science has created difficulties for itself, it has at the same time provided powerful weapons against the insect invaders. Among these weapons, the aeroplane is becoming increasingly important. It strikes swiftly and surely and is proving of the utmost value where man was previously helpless.


Of the countless varieties of insects which compete with us for our essential foods and raw materials, the American cotton boll weevil is the most deadly. The damage caused to the cotton crop before the aeroplane came to the rescue amounted in some years to as much as £200,000,000. The spread of the boll weevil is a typical example of the rapidity with which insect pests can spread if not checked in time. It crossed the Rio Grande into the United States from Mexico about 1893 and now infests the whole of the cotton-growing belt. Before satisfactory methods of coping with the boll weevil were discovered, it ruined thousands of farmers, drove merchants out of business and brought failure to banking houses.


The first experiments in dusting crops from an aeroplane were made in 1921 at Dayton, Ohio, and were an instant success. These experiments were directed against the larvae of a moth known as the catalpa sphinx, which was playing havoc with the foliage of a grove of catalpa trees. The work was observed by Dr. Coad, in charge of the Cotton Boll Weevil Investigation at Tallulah, Louisiana. So greatly impressed was Dr. Coad that, with the cooperation of the United States Army Air Service, he immediately decided to attack the boll weevil.


The extensive scale on which cotton is grown, compared with the small fields in countries such as Great Britain, favours the use of the aeroplane. Yet, even in America, only 20 per cent of the cotton is grown in really large plantations, the other 80 per cent being scattered over comparatively small areas, where frequent turning and manoeuvring are necessary.


Although America was the first to use this method, the credit for its suggestion must go to Germany, where a patent covering the use of aeroplanes for such purposes was taken out in 1912. The war of 1914-18 interfered with the plan and the project was temporarily abandoned.

It was the original intention of the United States Department of Agriculture to make its tests with the boll weevil. The tests would not, however, have been particularly satisfactory, because it is not easy to measure the effectiveness of the insecticide against this particular pest.


About this time (1922) a severe infestation by the cotton leaf-worm occurred in the Southern States of America. This was a much more suitable subject, for the effect of the insecticide on this pest can be easily detected. The apparatus used had to be improvised hurriedly to meet the sudden invasion. The apparatus was therefore somewhat crude, but good results were obtained.


Many difficult problems were successfully met by the Army pilots who did the work and it became evident that, with proper organization and technique, an experienced staff and suitable machines, aeroplanes had many advantages over the ordinary method of dusting. This conclusion has since been amply confirmed and the method has now developed enormously, not only in America but also in many other parts of the world.


A considerable proportion of the vast acreage under cotton in the United States is now dusted by aeroplane. Many farmers are forced by circumstances to keep to hand-spraying or cart-spraying because they are not near enough to an aeroplane dusting company, because their plantations do not lend themselves to dusting from the air, or for other reasons.


“Sky dusting” has many advantages over the use of carts, although the first consideration of every farmer must be to decide which method is the cheaper. Dusting from carts is a job which workers in the cotton fields heartily dislike. The chief reason is that it must usually be done between six and eight o’clock at night and between the same hours in the morning, because then there is generally less wind and the plants are wet with dew. During the day the poison does not adhere to the cotton plants, but drifts away and is wasted. The conditions are unpleasant because of the flying dust and the work is arduous during the two months each year that the boll weevil is active.


1,000 Acres an Hour


The aeroplane is far less dependent than ground machinery on weather conditions. Provided a suitable landing ground for refilling is available, it is possible to fly over wet and soggy ground after heavy rain, when the weevils are specially active. This is a great advantage, for it may not be possible to use a cart for several days, during which time the weevils may do enormous damage. Another point is that the crop is not trampled down and spoilt, as it may be by mules and machinery.


Speed of operation is an important factor in favour of the aeroplane. Every day, even every hour lost after the weevils have begun their deadly work means thousands of pounds lost on a big plantation. When it is remembered that one aeroplane can do the work of from fifty to seventy-five cart dusting machines, the superiority of the aeroplane in favourable circumstances for a rapid attack needs little emphasis.


One mule-drawn cart can dust at the rate of about 30 acres a day, whereas' an aeroplane can cover from 200 to 1,000 acres in an hour, according to the size and layout of the plantations. While it is in the air, the aeroplane works much faster even than this, being able to cover seventy-five acres a minute. The comparatively small amount of dust which it can carry involves fairly frequent stoppages for refilling and this cuts down the average rate considerably.


One of the most remarkable things which were discovered when aeroplane dusting was begun was the way in which the powder adhered to the plants. For this reason a much smaller percentage of the dust is wasted than in hand-spraying or cart-spraying. As the cost of the powder is one of the biggest items in boll weevil control, there is a considerable saving. In comparison with other methods, only about half of the amount of calcium arsenate (the poison used for dusting cotton) is required for aeroplane spraying.


The reason for this greater covering power appears to be twofold. First, when the dust leaves the aeroplane, instead of spreading and drifting away, as might be thought, it is caught in a strong downward rush of air which carries it with great force on to the plants.


A SPECIAL TYPE OF AEROPLANE has been evolved for dusting small crop areas






A SPECIAL TYPE OF AEROPLANE has been evolved for dusting small crop areas. It has to be easily manoeuvrable and is therefore small. Because of this, frequent stops for refilling operations — seen in progress in this photograph — have to be made The average rate of application for the dust is about 3 lb. per acre. Aerobatic flying is sometimes necessary to cover difficult corners of fields.







Secondly, the violence of the frictional force as the powder leaves the feed hopper on the machines produces an electrical charge on the dust particles, which is neutralized by the plants. This charging of the particles is often produced when dusts or mists are forced through small openings, and is effective in making the dust adhere.


When the manufacturers of cart dusters heard of this electrical effect, they devised means of producing a charge on the dust from their own machines to improve their performance. Even with this improvement, however, the cart dusters have not the same dusting efficiency as aeroplanes.

Photographs of aeroplanes carrying out dusting operations reveal the remarkable way in which the dust keeps to a well defined path. This is due to the combined effect of the rush of air past the aircraft and the additional blast of the slipstream from the propeller. The effect of these combined forces is so great as to overcome entirely the effect of ordinary air conditions.


The body of air surrounding the aeroplane moves backward considerably faster than the machine moves forward. This air follows a hollow spiral course and, for a considerable distance behind the aeroplane, the dust whirls round and round in a direction somewhat to one side of the line of flight. Finally it stops spiralling, flattens out and comes into contact with the plants.


Dusting can be carried out from the air in conditions in which it would be impossible to use ground machines satisfactorily. A breeze blowing at ten miles an hour would render such machines useless, whereas the down-draught from a low-flying aeroplane cuts right through this atmospheric drift in the course of the work.


Tests have shown that the dust can be blown down on to the plants at almost any time of the day, provided the conditions are not abnormally bad. Conditions during the middle part of the day are rather dangerous for low-flying, however, not because of the extra wind at that time of day, but because the air is rather rough near the ground.


Scope for Flying Skill


Another difficulty about flying low at midday is that the air temperature is high enough to cause engines to overheat badly in a short time. Flying for dusting is generally confined to about seven or eight hours each day, about four hours in the early morning and about three or four hours in the late afternoon. During these periods a light breeze makes conditions ideal for the work.


There is a flying technique to be learned in aeroplane dusting. Though the work requires a reasonable amount of nerve and skill, it also provides sufficient scope for initiative and judgment to make the work interesting. With large plantations, the amount of straight up-and-down flying tends to be rather tedious, but with small areas there are often difficult areas of country to be negotiated.


In these districts an aerial photograph is often taken before dusting is begun. The mosaic map of the fields thus obtained is useful for directing operations and planning in advance the methods for each field. The order in which the fields have to be treated sometimes depends on the severity of the infestation in different places, and the method depends on the nature of the country.


The pilot must decide whether he will fly parallel to the rows or across them and whether he will fly with and against the wind or across wind. It is safer to fly low against the wind than with the wind. The aeroplane generally flies back and forth, starting at one side and finishing at the other, and covering slightly overlapping strips about 200 feet wide at each flight.


POISONOUS POWDER is contained in a hopper fitted to the aeroplane


























POISONOUS POWDER is contained in a hopper fitted to the aeroplane. In this photograph the hopper is seen in place on a small machine. For large areas of crops where long straight runs may be made and tricky flying is unnecessary, larger aircraft are used. Because of the ability of these larger aircraft to carry more powder, fewer stops for refilling have to be made.




The aircraft is manoeuvred at an altitude of from 50 to 100 feet, until the right point is reached for entering the field. The aircraft then swoops down, reaching the edge of the field at from 5 to 25 feet above the crops. The pilot then straightens out at a speed of 80 to 100 miles an hour, but does not begin releasing his poison until he is well over the boundary. The reason for this is that the dust may be shot backwards as much as 100 feet before settling on the plants.


When the aeroplane has reached the other edge of the field it is zoomed sharply upwards as the supply of dust is cut off. This manoeuvre blows the last charge of dust downwards on to the ends of the rows and so reduces wastage.


Pilots find plenty of opportunity to exercise their ingenuity and flying skill in dealing with the problems offered. Country bounded by timber, or having isolated trees or farm buildings among the plants, demands a display of aerobatics to ensure proper dusting.


There may be a plantation bounded by an irregular line of timber containing, at intervals, indentations or curved bays in which the cotton is growing. If the aeroplane flew straight past these areas the plants growing in them would be missed completely.


To dust these areas the pilot flies in a straight line nearly to the end of the indentation, banks sharply and at the same time puts the tail towards the curved opening in the timber. The slight swing of the aeroplane twists the dust cloud over and sweeps it down through the area in the indentation. The pilot then rights his machine and proceeds straight down the timber line to the next opening, which is treated in the same manner. A right-angled corner hedged in by timber is another problem requiring a nice judgment if it is to be negotiated efficiently. This can be tackled in two ways.


If the timber is not too high the aeroplane can be flown directly at the obstacle and zoomed sharply upwards so as to point the tail downwards and blow the dust into the corner of the field. When the timber is too high for this method to be used safely, the pilot again flies directly at the corner, but this time banks sharply into a climb at the critical moment. This operation also brings the aircraft into a suitable position for dusting the plants in the corner.


Attacks on Locusts


When separate houses, trees and farm buildings are scattered throughout the fields, the pilot has to use aerobatic flying. Sudden dives, twists, turns and climbs are necessary to avoid these obstacles and to place the dust where it is wanted.


Sometimes it appears almost impossible to reach the plants, but an experienced pilot generally manages to find a way. It requires nerve and skill to manoeuvre an aeroplane a few feet above the ground in a restricted space and at the same time to release the dust in the correct quantity. The men who do this work earn every penny of their pay. Much of the flying is of a monotonous kind, but when these diversions occur they add zest to the day’s work.


A special type of aeroplane has been evolved for dusting the smaller areas of crops. It must be easily manoeuvrable and therefore small. Hence it can carry only a limited amount of dust and, as the average rate of application is about 3 lb. an acre, one charge does not last long.


Monoplanes and biplanes have been used, but the biplane is the type generally preferred. It has the important advantage of giving maximum visibility.


The design is such that the pilot sits higher than normally. Thus he can see fore and aft, as well as seeing the wing tips. He sits behind the loaded hopper, which is a more favourable position than between the hopper and the engine.


Another important point in design is to keep the load over the centre of gravity of the aeroplane. Its flying characteristics are then not altered whether the hopper be full or empty. The landing gear must also be exceptionally strong.


Special precautions are taken to ensure that the dust, which is sometimes inflammable, does not come into contact with the hot exhaust gases. For this reason the exhaust gases are often led up over the top of the upper wing. Dust must be prevented from entering the carburettor. This is ensured by using an air intake on the top of the carburettor, and by filtering the petrol.


The hopper holding the dust and the discharge mechanism are designed to give, as far as possible, a constant rate of discharge and to leave the pilot free to attend to his flying. Some of the earliest attempts put more dust over the aircraft and the pilot than over the crops.


THE DESIGN OF THE HOPPER so that it gives a steady flow of powder







THE DESIGN OF THE HOPPER is such that it gives as far as possible a steady flow of powder. The powder is sucked out by air rushing through the funnel-shaped scoop below the hopper. The speed of the air through this scoop varies with the speed of the aeroplane so that the dust flow can be regulated.








In the normal design of apparatus the dust is sucked from the hopper by the air rushing through a funnel-shaped scoop placed below. The speed of the air, which may reach as much as 200 miles an hour, changes with the speed of the aeroplane and thus regulates the dust flow to suit the demand.


The aircraft used for covering the bigger areas are relatively large. They carry larger quantities of dust and can cover greater distances before refilling. The ability to manoeuvre is not so important, because the time taken in turning at the end of each row is a comparatively small proportion of the total time.


Next to the boll weevil, the locust has ruined more farmers than any other insect. In South Africa, Russia, the Philippines and other countries this terrible scourge eats its way across great tracts of land, leaving not a green thing for miles round.


Here again the aeroplane finds plenty of scope for useful work. After successful experiments, the South African Government now maintains a special fleet of aeroplanes ready to take the offensive when reports are received of heavy attacks by locusts.


Hordes of locusts breed in the reed beds of the River Kuma, in the northern Caucasus, where they are virtually inaccessible by ordinary means. Acres and acres of these beds are dusted so effectively that the poison penetrates as much as 16 feet into the dense vegetation. The pilots wait until just after sunset, when the locusts have settled down for the night, and then let loose their death-dealing dust.


Besides being used for dusting rice fields in Madagascar, tea in Java, tomatoes, peas and melons in Mexico, wheat in Canada, apples and potatoes in Great Britain, aeroplanes have become an accepted weapon for combating attacks by forest and orchard pests. The insects kill the trees by eating the leaves, but if half the leaves can be saved the trees will generally survive.


Thousands of acres of forest trees have been saved from destruction in many countries. In Canada the damage caused by the spruce budworm and by the hemlock looper has been much reduced. A big job in the State of Washington, U.S.A., in which fifty-four tons of dust were deposited, achieved the preservation of some 32,000 acres of timber at a cost of £3,000.


In Silesia, Bavaria and other parts of Germany the nun moth and the pine sawfly cause serious depredations; in Russia the oak and pine forests are also periodically infested. As many as 56,000 insects were counted in one tree, but were successfully dealt with from the air. Fruit growers have also turned to the aeroplane for help, as, for example, in the citrus groves of Palestine and California, and in the peach and cherry orchards of the north-western American States. The dusting of orchards and forests presents many interesting problems which have to be overcome to obtain the best results.


Combating Malaria


The aeroplane has sometimes to be flown with the wings almost touching the tops of the trees, while the undercarriage passes between the rows. To guide the pilot in such low flying, when all his attention is required for the job in hand, the course is marked out with streamers, and fires are often lit at the boundaries.


So far we have dealt with insects which attack plants. The mosquito attacks human beings, and malaria, the disease which follows from its bite, is one of the most widespread and deadly

diseases at present known to mankind. This is the sort of big-scale problem especially suited to the aeroplane, for it can cover big distances and invade the swampy haunts of the mosquito which cannot otherwise be reached.


The 185,000 acres of salt marsh of New Jersey are typical of the type of country where the mosquito larvae are to be found. An aeroplane can make a rapid survey of these breeding places and then proceed drastically to deal with them.


The Malarial Survey of India recently set up a Mosquito Patrol for cleaning up the mosquito plague-spot known as the Bela along the Jumna River, near Delhi. This area, which is flooded every year by the monsoon rains and by the melting of the Himalayan snows, is difficult to deal with, as it is a mass of reeds and thorn scrub. The results showed conclusively that the aeroplane could deal effectively with the mosquito peril.


If by this means man succeeds in stamping out malaria from India, Africa, Burma, Australia, Russia and the other tropical countries where it is still rampant, the aeroplane will have made a remarkable contribution to the happiness of the world.


DUSTING A CRANBERRY PLANTATION in New Jersey







DUSTING A CRANBERRY PLANTATION in New Jersey, U.S.A., with the aid of an “Autogiro” aircraft to exterminate a parasite known as the leaf fly. The cost of dusting such a crop is estimated to be as low as about a hundred and fiftieth part of the value of the crop. The backdraught of an aircraft carrying out dusting forces the dust downwards on to the crops and does not disperse it in the air.








[From Part 22, published 2 August 1938]


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“Novel Uses of the Aeroplane” on this website.

Air War on Insects