WHY
IKSECTICIDES? In the light of our present knowledge they are necessary in order to circumvent that law of nature, so inexorably enforced, which decrees that for every crop that is planted there shall be two claimants: On the one side, he who planted it and rightfully expects to gather it as the product of his labor; on the other, the many forms of insects and fungi which live upon this crop, apparently no less anxious than the grower himself to reap a harvest. The competition thus created is a fight the world over between man and pest, a contest aptly described as the greatest war of all time. It is one in which sprays in the form of solids, liquids, and gases have become the contributive weapons. For a while the advantage bid fair to go to the pests, but now, after resort to a scientifically conceived and executed campaign, man's power over those forms of life which injure his cultivated plants has never before been so great. We have gone a long way in the eradication of insects and fungous diseases since those days, generations ago, when nicotine solutions, pulverized tobacco dust, or hellebore were practically the only known means of defense. The appearance of hardier foes than the soft-bodied, chewing
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Symposium Papera presented before the Division of Agricultural and Chemical Society, Washington,
insects against which these were used made necessary the use of more energetic insecticides. As a result Paris green was introduced about 1860 to halt the eastward march of the rather vigorous and well-protected Colorado potato beetle. It was but a natural consequence of the success which attended the use of the latter in the potato fields that it in turn should be applied to the destruction of orchard pests. Following this successful venture, other forms of arsenic-containing mixtures and compounds with other elements were in time developed, each possessing some special merit as to use and effect. Concurrently there came into use the fungicides in the form of lime-sulfur, Bordeaux mixtures, etc.
... .. Removal of Poisonous Spray Residues on Fruit R. H. ROBINSON Oregon Agricultural Experiment Station, Corvallis, Ore.
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U R I S G the past half-century the need for insecticides arsenicals that a grave spray-residue problem deyeloped that and fungicides to control the ever-increasing number has caused consternation among fruit growers and health of insect pests and plant diseases has steadily grown. officials alike during the past few years. This paper will be As difficulty of control increased, the use of excessive amounts limited in scope to phases pertaining to the lead arsenate of spray material became necessary in order to obtain satis- residue on apples and pears. factory results. Kecessarily it is essential to apply many of CONDITIOPSAFFECTINGAMOUNTOF SPRAYRESIDVE these insecticides to fruit and vegetables during their gron-ing DEPOSITED period. Codling moth infestation has spread steadily until now the Most spray materials comprise one or more of the following metallic elements : aluminum, arsenic, barium, calcium, pest is found in practically all localities where apples and pears are grown. Since no effeccopper, fluorine, iron, lead, magtive substitute for lead arsenate nesium, manganese, m e r c u r y , Severe infestations of insect pests and fungous has yet been f o u n d , thorough potassium, selenium, s o d i u m , diseases have required the application of abnormal spraying with this arsenical is and zinc. Many of these are amounts of toxic sprays in order to obtain effective essential for the production of nonpoisonous to human beings. control. Since cleaning sprayed fruit by memarketable apples a n d p e a r s . Others, such as mercury, are not The number of sprays necessary, chanical means proved futile, chemical solvents applied directly to food products. h o w e v e r , d e p e n d s upon the Two of them (lead and arsenic) were tried. Dilute solutions of hydrochloric acid locality and the climatic condiare deadly poisons and, chemihave proced effective and practical. W h e n proptions of each fruit district. In cally combined, constitute one of erly used it has no deleterious effect on fruit and older districts where climatic our most widely used insectiimproves its appearance materially. Suitable conditions are favorable to codcides. It is the only insecticide ling moth d e v e l o p m e n t eight commercial washing machines have been rapidly yet discovered that will check sprays may be required to secure the ravages of the codling moth developed. s a t i s f a c t o r y control. I n the i n f e s t i n g a p p l e s and pears. During the past few years wax on apples, cooler regions and where short L i k e w i s e , this or some other modified spray schedules, and combination seasons prevail, one spray may arsenical must be used for the of lead arsenate and mineral or fish oils sprays be sufficient. The lead arsenate protection of various vegetables is usually applied a t the rate of 2 have created complications. However, the utilizafrom chewing i n s e c t s . To a pounds to 100 gallons of water. lesser degree other fruits, such tion of other soltents, such as alkalies and mixWhere very severe infestations as cherries and berries, must be tures of hydrochloric acid and kerosene emulsions, frequently occur, 3 and even 4 s p r a y e d with an a r s e n i c a l together with higher temperatures and improved pounds to the hundred are often when they become infested with washing equipmenl, have enabled the industry to used. insects, such as the cherry fruit M a n y f a c t o r s influence the overcome various dificulties as they have developed. fly. It is on account of these 616
on Insecticides Food Chemistry at, the 85th Meeting of the American D. C., March 26 to 31, 1933.
On the other side of the picture lies the fact that lead and arsenic compounds, and perhaps others, although efficient, may create serious health problems by reason of the spray residue left on the crop a t harvest time. This situation is not beyond bounds, however. I n the case of fruits these residues yield to washing by effective and practical methods, procedures which, when properly used, exert no deleterious effect on the fruit. I n fact, they are said to bring about a material improvement in the fruit. I n the case of vegetables, when the application of insecticides becomes necessary, protection to the consumer lies in the limited application thereof and in efficient methods of removal of the residue in the form of washing or stripping.
amount of lead arsenate that may remain on the fruit a t harvest time. These include variety of fruit, number of sprays applied, amount and distribution of rainfall, mechanical removal by such agents as wind and leaf contact with the fruit, location of the fruit on the tree, spreading and adhesive agents, and combinations with other sprays, such as oil emulsions. These factors contribute to a varying arsenical load. Under arid conditions where little or no rainfall occurs during the growing season, one cover spray has been found to deposit sufficient arsenic to exceed the 0.01 grain per pound tolerance. Where seven or eight sprays have been applied during the season, as much as 0.160 grain is not uncommon. In the humid sections of the country, rainfall removes appreciable amounts of the spray. It cannot, however, be relied upon to remove the residue consistently below the tolerance. CLEANING FRUIT BY WIPINGMETHODS I n 1919 the author made five analyses of samples taken from two boxes of apples. The arsenic content varied between 0.0015 and 0.028 grain per pound. In that year, also, complaints were heard from eastern cities that some fruit carried a conspicuous spray residue. Thereafter heavily spotted fruit was hand-wiped, and in several districts mechanical wiping machines were devised and used with promising results. However, after chemical analyses of hundreds of samples of fruit cleaned under various conditions, it was learned that the wiping method was not generally satisfactory for the removal of the residue below the required tolerance. Furthermore, considerable bruising and other damage was done to the fruit by this cleaning method, unless great care was taken in handling the fruit. Eventually the dry cleaning methods by wiping were discarded when the solvent washing method became available.
This situation has intensified the search for less poisonous spray materials with the result that the vegetable insecticide is again coming to the front. In pyrethrum (an exterminant of household pests since 1857), derris root (once used in a small way to control insects infesting nutmegs), and now rotenone (the active principle of derris as well as of cub6 root) may lie the answer to the objections to using inorganic insecticides. It is true that nature has given us countless insect pests, yet she has also provided foes for such pests, with the result that vegetable life is maintained on a sort of a teeter arrangement. This fortuitous scheme of things seems, however, to fall short in the sense that insect life is no respecter of man’s food crops, although of course the damage would be irreparable without this natural check on the former. Obviously a malformed, scarred, or “inhabited” piece of fruit or vegetable does not carry the sales or palate appeal of one without these blemishes, when all other factors are equal. And so, it seems, it is a situation that cannot be avoided because of a fear of eating and being poisoned-rather it is one of poisoning that one may eat. H. A. SCHUETTE, Symposium Chairman
laboratories several lots of apples were washed in nitric, hydrochloric, sulfuric, and acetic acid of varying concentrations. Effective cleaning was obtained and no injury to fruit occurred. At harvest time, however, it was not thought advisable to recommend the process as practical for newly harvested fruit until tests for injury had been made, since the wax on storage fruit might protect the apple from acid injury, while recently harvested, wax-free fruit might be badly damaged by strong mineral acids. Later, when it was learned during the 1926 harvest season a t Medford, Ore., that the wiping machines were ineffective, crude dipping tanks were devised and commercial tests made by mashing pears in 0.5 per cent hydrochloric acid. KO injury developed, the pears were clean and attractive in appearance, and the analyses showed well below the 0.01 grain per pound tolerance. Orchardists and fruit packers followed the suggestion of the experiment station chemists to give the acid treatment a fair test. As a result a large portion of the season’s crop was effectively cleaned below the 0.01-grain tolerance, and threatened disaster to the crop was averted. WASHIXGWITH HYDROCHLORIC ACID
Several years’ experience has shown that hydrochloric acid is probably the most generally satisfactory of all solvents employed. A commercial grade of 20’ BB. strength is used. Many factors influence the effectiveness of the washing process, and the treatment must be modified to fit the circumstances a t hand. Fruit harvested a t the proper time and washed immediately after picking may be effectively cleaned with a comparatively low concentration of acid. A 1.0 per cent solution is sufficiently strong to remove both arsenic and lead within the tolerance, irrespective of the arsenical load, provided no wax has formed on the fruit and no oil has been used after the early cover sprays. CLEASIXGFRUIT BY SOLVENT METIIODS Injury to fruit is uncommon when washed in acid a t norEarly in 1926 preliminary washing tests using solvent mal temperatures. Care must be taken to remove the acid were carried on both in the laboratories of this station and of as completely as possible from the surface of the fruit by a the Food, Drug, and Insecticide Administration in Philadel- clean water rinse. Where higher temperatures are required, phia. Workers in the latter laboratory washed several lots of injury to the fruit may Qccur, and great care must be exerheavily sprayed New Jersey fruit in improvised tubs. Dilute cised to limit the time under the acid sprhy and to wash the ammonium hydroxide was used as the solvent. In the Oregon latter thoroughly from the fruit with clean water. 617
