Circular No. 1 1 t . United States BURK, griculture, L. O. HOWARD, hntomologUt and Chief of Bureau. PREPARATIONS FOB WINTER FUMIGATION FOB THE < II K I s WHITE I IV. By A \\ Mnuun i and \\ W Yoni i\ I i:«>i>i i i k.n. A- :i result of investigations conducted by the Bureau of Ento- mology during t In* past three years, fumigation for the citrus white fly lias been placed upon a practical basis, and the process has been M' simplified that any citrus grower can undertake the treatment of hi.s grove without depending upon experienced fumigatora to con- duct the operations. Under present conditions fumigation is the most satisfactory and profitable method of controlling the white fly in hundreds of infested groves in the ( rulf coast cit rus-groin ing regions, and its usefulness will be extended i<> nearly all infested groves when the practical recommendations in a forthcoming bulletin on the white fly have been put into effect. The superior quality of Florida citrus fruits when grown in groves free from injury from insect pests and the awakening of progressive growers to the neces- sity for organizations for combating insect pests and for marketing the fruit point to the general adoption of the control measures to be recommended in the publication referred to. At the present time the authors would recommend fumigation for the white fly under the following circumstances : In groves isolated by a distance of at least 200 yards" from all other infested grovi in citrus groves or in citrus-growing sections where the white fly has recently appeared and is still of limited distribution, and in sections where cooperation can he secured among growers in naturally isolated groups. In many cases the owner of an extensive and valuable grove which i- isolated except for a small groveof a few acres from other infested groves can well afford to loan his equipment, or. if necessary, fumigate the neighboring grot e entirely at his own expei " Exivri' t has shown that a.- .1 rul e in i fumigation can be practiced without it.-' bung rendj migration of adulte. I *• Cir. 111—09 if much lea extent ' -» -w** EPOSITORY rather than to permit the presence of such grove to interfere with his results. Full directions concerning equipment, chemicals, and methods of procedure in fumigating for t he citrus white fly have been published in a bulletin of this Bureau." This bulletin is based upon results obtained in January and February, 1907. Extensive field experi- ments have been conducted during the last two seasons and the additional results obtained will be embodied in a supplementary report now in preparation by the authors of this circular. It is hoped that before the beginning of the next fumigating season, extending from December 1 to March 1, a publication in the Farmers' Bulletin series of this Department will be available. This bulletin will contain only such advice and directions as are of practical importance in fumigation work against the white fly, omitting the details of experiments published elsewhere as the necessary basis for establishing practical conclusions. The present circular aims to call attention to the desirability and in most cases necessity for early preparations where fumigation work is planned for the coming winter season; also to give full directions for such preparations. EQUIPMENT. TENTS. Orders for tents should be placed as soon as possible after it is decided to fumigate a grove. Tent makers do not always have on hand a sufficient quantity of desirable grades of canvas to iill large orders. Delays in filling the order may necessitate shipment by express, at a cost several times the expense of shipment by freight. The first step is the determining of the sizes of tents required. It is a more common mistake to underestimate the size of a tent required than to overestimate it. Some allowance should be made for the growth of trees, in consideration of the future use of the tents. If the trees are nearly uniform in size, the largest trees should be selected for measuring. A tape measure attached to a reel is used in meas- uring trees to determine the size of tent required. Standing a few feet from the outside branches of the tree to be measured, enough of the tape is unreeled to extend over the to]) of the tree and about half way to the ground on the other side, the free end of the tape is held in one hand and the reel is thrown over the center of the tree and unreels the tape by its own weight until it reaches the ground. Two or three attempts may be necessary in order to have the tape pass over the center of the tree. It should be borne in mind that the weight of the tent will reduce the extreme height of the tree and that " Bui. 76, Bur. Ent., U. S. Dept. Agr., Fumigation for the Citrus White Fly as adapted to Florida conditions. By A. W. Morrill. [Cir. Ill] 3 it i- therefore unnecessary for the tape to pass over the highest twigs. For large trees 6 to 8 feel should !»• added to the number of feel ovei the top of the tree, as shown bj the measurement, and for small trees ( to •'» feel ^1 1< mill !>«• added. In general, trees from 10 t" 15 feel high require tents between 32 and 14 feel in size . trees from 16 to 20 feel high require tents II to "> s feel in size; trees 21 to 25 feel IhltIi require tents 60 to 70 feel in size; and trees 25 to 30 feel high require tent-, 70 t'> 76 feel in size. In regard to the number of tents required, it is Baie to estimate thai with one tenl for each I * >< > trees the work of fumigation could be completed in ten to four- teen niL_ r lil-' work. < me cicw can handle from twentj to twenty-five small tents, l"> feet iii size and smaller, and from i • fifteen tents, 50 feet in size and larger. Much depends upon t he t rees being bo spaced as to obviate inter- ference v> ith the w oik of shifl - ing the tent-. 1 la\ ing decided upon the number and sizes of tents required, orders should be placed as soon as possible. Samples, if 8-ounce army duck .should be obtained from tent and aw ning makers w ho arc in a position to furnish the tents. The selection of 1 .'lit material is a matter of greai importance. Samples of duck can be classified roughly in regard to tightness by the general texture and b) the degr< f imperviousness to direel rays of lighl when held between the eye and the sun, or any bright light. Neither of these methods is entirely satisfactory, however, in selecting material for fumigating tents. With a simple arrangement devised by the authors for testing the tightness of material submitted to the laboratory at ( Orlando, Fla., for examination, it has been found that samples of duck vary nearly 50 percent in t heir comparative tightness. Figure 1 illustrates two extreme samples of 8-ounce duck which differ to the extent of 17 per cent in this respect. As a result of "The size of tents is expressed in terms of the <1i-i.uk •■ between parallel m the octagonal sheet of canvas of which the tenl i- compos [Clr. Ill] > -4*A> V'ig. 1.— A?\ undesirable ton durk for fui the examinations made so far, the authors strongly advise against the use of drills of any kind. The appearance of these is much more misleading than that of ducks, and it seems impossible to estimate their comparative tightness except by tests with special apparatus. Our experience up to the present time leads us to recommend closely woven duck weighing 8 ounces per yard, when 28£ or 29 inches wide, or about 10 ounces per yard when the material is 36 inches wide. The more expensive grades of cloth are not always the most nearly gastight. In the case of two leading concerns which have supplied huge orders of tents for use in Florida, the medium grades of mate- rial, as shown by the prices quoted, have been found to be superior in gas-holding qualities to either the cheapest or the most expensive of the three grades upon which prices were quoted. The form of cover which is at present almost exclusively employed is the flat octagon. Frequently those who have never seen a tent of this kind fail to realize its simplicity. A square piece of canvas woidd answer the purpose as well as the octagon, but to save material and the handling of extra cloth the corners of the square are left off. A perfectly circular cover would be more economical in respect to the amount of cloth required, but the saving would not cover the extra expense of construction in this form. For specifications tentmakers may be referred to Bulletin 76 of this bureau. In general these specifications are simply that the form is approximately octagonal, of any desired size, made of par- allel strips of goods overlapped three-eighths or one-half inch, double stitched, and all raw edges hemmed. In the case of tents 50 feet or more in size a reinforcement is desirable across the middle section near each end, as described in the bulletin referred to. It is desirable that allowances be made for shrinkage, otherwise a tent after becoming wet and later drying may not be sufficiently large to cover trees of the size for which it was intended. The following published statement by the senior author is of importance in this connection and is quoted in full: 6 Shrinkage of the goods after being thoroughly wet is an important consideration in the economical construction of fumigating tents. In order that the tents approxi- mate a regular octagon, after having been used for fumigating purposes, it is necessary either to have the goods thoroughly shrunk before cutting or to make allowance for subsequent shrinkage by cutting the strips longer. A test made with a brand of 8-ounce duck commonly used in California for fumigating tents showed that the shrink- age lengthwise of the goods amounted to 7.5 per cent and crosswise 0.9 per cent. This means that in a 50-foot tent the shrinkage would result in the full-length strips shortening 3J feet, while the tent would shrink less than inches crosswise of the si ripe. Such irregularities might be remedied by a skirt of 6i-ounce drill, but it is simpler to a For sale by the Superintendent of Documents. Government Printing Office, Washington, 1>. ('. Price. L5 cents. b l?ul. 76, Bur. Ent., U. S. Dept. Agr., pp. 17-18. [Cir. Ill] plan to have each atrip cul longer bj a given amount t"r each I per ■ enl of differ in the length wi o and i i In the i i-'- referred to ,il".\>- this differ- ence i- 6 B i"-r cent, and each i"-r cent repn u tual differen i ini hi \ t i. hi constructed in thii manner would therefore measure before -linn! feel i i' 1 feel 10J in ■ feel i in< he* lengthwi •■ •■: 'in- rtrips through the middle section, an. I 19 feel n>[. inches cro 'in- strips \n.r shrinking, the dimensions would !"■ approximately 19 feel I] inches in each direction On account of the variation in the shrinkage of different brands '>f duck it i> necessary to test the crosswise and lengthwise shrinkage in the Bample selected. This may be done by marking, with a lead pencil, lines l foot or more in length, l>'>tli crosswise and length- wise of the strip of goods. The Bample should be shrunken twice, each time wetting by submerging in water for two or three hours and drying in the sun. The amount of tin- shrinkage can then be determined by measuring the pencil lines just referred to. The marking of the tents with graduated stripes, which is a part of the process of determining dosage requirements originated by the senior author," requires less than an hour for each tent. The neces- sary preparations for this, therefore, consist in procuring suitable paint and arranging for a patch of open Geld where the tents may be spread Hat to become saturated with rain or dew, thus producing the desired shrinkage. The importance of the tents being thoroughly shrunken before the measuring for the graduations is obvious. Directions for "mildew-proofing" the tents will be given in publi- cations now in preparation and it is not necessary to include them in this connection, 'rents should be thoroughly dried in the Bun before being folded for Btorage, and in preparing them for Geld n-e they should not be exposed to rain-- or dews any more than is neces- sary to shrink as advised above. POl I - am> DBRRli k- In the Gulf States, seasoned cypress is probably the besl material available for the manufacture of poles and derricks used in shifting tents. These serve practically the same purpose, the former being used in handling tents up to 50 feel in size and the latter in handling tents 50 feet in size and larger. The po|i>> have no other attach- ment than a rope, while t he derricks each consist of a pole with a crosspiece and braces at the base and eye-bolt attachment for pulley and tackle at the small end. These poles and derricks can he pre- pared for use in a shoii time, but it is verj important that the pole- he cut and peeled h >iilc enough before they are n led for use to permit them to become well seasoned. Pole- should he carefully -elected in order to have them as straight and free from knot- as possible. While only two poles or two derricks are needed for n-e at one time, an extra supply of both should always he in readiness, 1 cit., ] (C'ir. HI] so that in case of breakage the work can be continued with little interruption. The length of the shifting poles should be about 2 feet more than the height of the average trees, and the small end should be about 1\ inches in diameter. The pples for derricks should be about 3 or 4 feet more in length than the height of the average tree, and when ready for use should be between 3 and 4 inches in diameter at the base and between 2 and 3 inches in diam- eter at the toj). The method of attaching the crosspieces and braces is described and illustrated in Bulletin 76 of this Bureau. If ordinary three-eighths or one-half inch bolts are at hand, a pair of derricks can be prepared for use in less than half an hour, and this need not there- fore be considered a necessary part of the early perparations for fumigation. Cypress poles should be seasoned in a barn or packing house, or if out of doors they should be in the shade. Straight poles, while being seasoned, should be so supported as to prevent bending or warping. If, after cutting, a pole is found to be crooked, it may perhaps be made practically straight by the proper arrangement of the supports when seasoning. GENERATORS OR CROCKS. In generating the gas earthenware crocks are used. In general, trees 5 to 8 feet high will require crocks of li gallons capacity; trees to 12 feet high, crocks of 2 gallons capacity; trees 13 to 16 feet high, crocks of 4 gallons capacity; trees 17 to 20 feet high, crocks of 4 or 5 gallons capacity; and trees 21 to 30 feet high, crocks of 5 or 6 gallons capacity. For trees up to about 18 feet in height one crock will be needed for each tent, but for larger trees two crocks should be used, dividing the dosage into two equal parts. Crocks with straight sides can be used with more cyanid for each gallon of capacity than crocks which narrow at the top, and it is to the former style rather than to the latter that the preceding statements refer. The foregoing directions should enable anyone preparing to fumi- gate to determine the actual number and sizes which will be needed. It is always advisable to have several extra crocks at hand, so that delays will be avoided in case of breakage. Crocks of more than 2 gallons capacity can not be readily obtained as a rule and frequently even the smaller sizes can not be obtained of local dealers in sufficient numbers to equip a large outfit. It is important, therefore, that orders for crocks be placed as soon as possible when preparing to fumigate. As the tops or covers are not needed, dealers should take this into consideration in quoting prices. When not purchased of local dealers and no allowance is made in the price on account of the covers of the crocks, instructions should be given not to include the covers in the shipment, in order to avoid unnecessary freight or express charges. [Cir. ill] Convenient bandies for the crocks can be made ol a large siz< wire. If properl) arranged the ends of the handle will be held in position "ii opposite sides <>f the crock, otherwise the) ma} cause considerable anno) ance. MISCELLANEOUS REQUIREMENTS Of tin* numerous articles "I minor importance which Bometimes art" not easilj obtained and should therefore be arranged for as earl) as possible are rubber gloves and glass graduates. Two or three pairs of rubber gloves should I btained For a large outfit. One pair is Deeded for the one who measures the acid and generates the gas, and one pair should be available for use bj the helper who empties the contents of the crocks after fumigating. The third pair should be on hand in case one of the pairs in use is lost or destroyed hv any means. Rubber gloves can be purchased of or ordered through electrical supph houses or electric-light companies. Black rubber gloves with cloth lining are preferable to the red rubber gloves without lining which are sometimes used. The latter are not easily removed from the hands, especially after they become wet on the inside, and are on this account very troublesome. One should avoid gloves which are so thick that a wel glass graduate can not be easily handled when wearing them. A glass graduate Of 16 ounces capacity is needed for each Outfit, and if not obtainable of local dealers one or two extra one- should be always on hand. They can be purchased through local druggists or directly of wholesale drug houses. It is important that the num- bers on the graduate be plain and easily readable. Torches are preferable to lanterns, and if possible three or four of the former should be obtained. Balance-, stoneware pitcher-, dippers, water buckets, ropes, pul- leys, and other article- can usually be obtained of local merchant-. < lll'.MM u - The chemicals required in fumigation with hydrocyanic-acid are potassium cyanid K('\ and sulphuric acid ill. so, . POTASSIUM CYANID The cyanid ordinarily used in fumigating citrus tree- is put up in 200-pound cases and costs between 21 and 23 cent- a pound in ton lots. It should be guaranteed to be 98 to 99 per cent pure. In calculating the amount of cyanid required, a tree should be selected Which represent - a- Dearly a- can he e-t imated the average -i/.e of t he trees in the grove. The distance over the top can be obtained l>\ the tape measure in the same manner as described in connection with estimating the sizes of tents required. In addition to this measure- ment the circumference of the tree should he measured with the 9 baa i a used by the authors for this i>uri*>-.- [Ctr. ill] 8 tape lino. This can be done by attaching the free end of the tape to a twig and passing around the tree, hanging the tape on the outer twigs as it is unreeled. If the grove consists of two sizes of trees, as, for example, large seedling and medium-sized budded trees, an aver- age specimen of both kinds should be measured. The amount of cyanid required for these average specimens can be determined from the dosage table given herein. The following examples illustrate the method of using the table after the distance over and the circum- ference of the tree have been obtained. Example No. Distance over tree. Circumfer- ence of tree. Amount of potassium cyanid required. 1 2 3 4 Feel. 2! 38 52 66 Feet. 40 53 72 79 Ounces. 9 26 58 96 The amount of cyanid in ounces having been obtained for the aver- age tree in the grove, this amount is multiplied by the total number of trees to be treated and divided by 16 to reduce to pounds. It is advis- able to obtain from 5 to 10 per cent more cyanid than the amount esti- mated, in order to avoid delays in case of underestimation. The cyanid, being put up in air-tight tin cases inclosed in stout wooden boxes, may be stored for months without deterioration. Excess cyanid can usually be disposed of without difficulty. SI I.l'lU'KIC ACID. Sulphuric acid can be purchased in iron drums containing about 1 ,500 pounds at about 1 f V cents a pound. One drum of acid is required for about 4 cases of cyanid. The acid should be guaranteed 66° Baume or 93 percent pure. It is advisable to have a sample tested with an acid hydrometer, an inexpensive instrument which can be obtained through any druggist. Acid should not be stored for more than two or three weeks in the drum. Unless it is to be used at once the entire contents should be emptied into carboys, the mouths of which should be closed with wooden plugs, strips of burlap, and plaster of Paris. Empty carboys can be purchased for SI. 50 or SI. 75 each, and 9 are required to contain the contents of an acid drum. Only carboys in good condition should be used, since the container is made of thin glass and breaks easily if the bottom of the wooden case becomes weakened and fails to support the contents. Great care should be used in handling the acid. Probably the quickest and safest way of emptying acid from the large drum into carboys is a method which has been used on several occasions by the authors. The drum is mounted on two heavy planks resting on the ground and is arranged so that it can be rolled forward and backward easily. At one end of [Cir. ill] the planks b |»ii aboul 3 feel deep is dug. Thia Bhould be large enough for two men to stand in and place the emptj carboj in position and lift it out when filled. A large mouthed funnel madeofsheel lead is placed in the mouth of the carboj . A piece of casl iron piping aboul 6 or 8 inches long and properly threaded is a convenience, bul not a requirement. This, if available, is Bcrewed into the opening in the drum, which i-- arranged so that the acid will pour into the funnel lead- ing to the carboj. A piece of beavj plank or other suitable lumber should be si ronglj spiked across the ends of the two plank supports of the drum to proven! its being rolled too far forward. Whenever there is n suitable platform available, <>r timber is available for making n rough one, the trouble of digging the pil can be oh\ iated. It is not / 10 9 8 X N 7 X X 6 5 5 X X M /v fSi 4 X 28-36 9 33-40 13 32-39 is 3 37-45 17 25-30 7 30-37 10^ 37-46 18 2 30-36 io'i 40-61 25 33-40 13 38-54 20^2 X 1 98-44 17 38-50 19 37-51 19 36-40 14 '1 Flo i.- Diagram of ngularly set grove In proceas of fumigation with «n on tflt of four ten tg \ \ I Merrill a«l\ isable to empty drums from railroad stations or packing-house plat- forms, as more or less acid is usually spilled. No .in,' should stand uear the carboy when the acid is being poured, and care should be taken to prevent any spattering of the ami from reaching the face. When handling acid it is always well t<> have water at hand for use in case of incident. With proper care sulphuric acid can he handled without danger of any kind. DIAGRAMS OP GROVES, AMD DOSAGE rABLES While it i^ not always necessary that diagrams of groves be made. it is always advisable as a matter of record and to prevent errors. Figures 2 and :\ illustrate methods «.f making diagrams when trees rcir. mi 10 are set in the square and in the alternate system, respectively. The figures in the squares represent the records of the trees fumigated, the two upper figures separated by a dash representing the dimen- sions of the tented tree and the lower figure the amount of cyanid given." These records are made at the time each tree is fumigated. In presenting the dosage table recommended in Bulletin 76 it was stated that the amounts of cyanid could be increased from 10 to 25 per cent with advantage under certain conditions. At the present time the authors advise for general use a table (fig. 4) representing M 9 V 8 7 6 W, 5 X X 4 42-54 24 43-62 29 3 39-47 20 40-49 21 X 41-51 23 2 42-50 23 47-60 34 40-47 20 43-48 24 ■ 32-38 13 42-50 23 i B D Fig. 3. — Diagram of grove with alternating trees; first four rows in process of fumigation with four tents. three sets of trees fumigated, the tents being moved from south to north: X, X, X, trees missing. (From Morrill.) an increase of 25 per cent over the minimum requirements previously given in tabular form. This seems desirable, owing to the wide variations in the weave of various tenting materials and to the fre- quency with which slight winds might interfere with the results. MISCELLANEOUS SUGGESTIONS. With the gradual extension of the process of fumigation in the control of the white fly in Florida and other citrus-growing sections of the Gulf coast, the value of a citrus grove will be considerably " The amount is according to the dosage table given in Bulletin 76 of this Bureau. page 68. [Cir. Ill] I] affected l>\ the difficulties in Fumigation presented bj excessive heighl of trees, closeness of planting, unevenness "l ground, and ol her conditions. The systematic treatment <>l groves i" overcome these difficulties, so that the trees ma} !>■■ easil) fumigated, will Qol onl) be of value in this respect, but will constitute a good cultural practice. Trees planted too closelj for fumigation to be practicable are too close for besl results in productiveness. Limiting the I n • i lt J • t <<( trees l>\ pruning not only lessens the expense "f fumigation, but reduces the expense of picking the fruil without reducing the quantity. MM C/RCUM^ERENCE. Off* OV£S 10,15 20 25 30,35 4045 50 52*5557* 6062*65 67' 70 72'75 77' 8062'8587» «J ,10 12 2 2 2 m 3 3 3*. 3' 3 3' 3' 12' 14 1 1 14 16 4 4 4 4 ■X 16. ie , 5 5 5 5 5 18 1 10 15 20 25 30 35 4045 50 52' 55 57* 60 62'6567' 70 72* 75 77' 8082' 85 87' X) 20 5' 5- 5* 5' 5' 20 22 24 2 22 5« 6' 6* 6' 6 7 9 2 24 6' 7-' 7- 9- 26 9 9 9' 10 II 26 |28 10 II II 12 13 13 28 10 15 20 25 30 35 4045 50,52*. 5557' 60 62' 65 67' 70 72' 75 77' 80 82' 85 87' v> 30 12 13 13 14 15 30 32 34 3 36 12 13 14 15 16 18 19 3 36 15 15 16 18 19 21 23 22*23*25 24!26*27 17 18 'l9 21 38 ,'9 20 21 23 28 38 30 35 4045 50 52-5 5 57' 60 62' 65 67' 3 72' 79 77* •r 82' 85 ad\ isable. Deadwood <>n the outer parts of the trees should l>e thoroughly removed in all cases to avoid the tearing <>f tents. Watershoots should be thoroughly removed at the same time, since about I per cent of the white fly pupa' present during the winter months survive fumigation and the resistance of the insects <>n watershool leaves is much greater than elsewhere <>n the t; [Cir. lll| 12 UNIVERSITY OF FLORIDA nun mi in 3 1262 09216 5579 If possible, the cultivating and fertilizing of groves to be fumigated should follow fumigation. It is much more difficult to handle the fumigating tents on newly cultivated ground, and the dust arising in the shifting of the tents is sometimes a matter of considerable dis- comfort to the men engaged in the work. Approved: W. M. Hays, Acting Secretary of Agriculture. Washington, D. ('.. August 10, 1909. [Cir.lll] O