? y nt Circular No 37, Second Rlvise. • \ I HON United States Department of Agriculture, BUREAU OK KNTOMOLOGY. L. O. HOWARD, KntomologUt and Chief of Burca XSJ^o*' BYDBOCYANIC-ACID (i\s FOB II HliaiiM, t.Kl.l.v " s| s vm) < oil) FRAMES j a i J-.i in l'. Woods, ' of Plant Industry i N ri: i i..\. fticitle for green] se fumigation is t" Dacco in it- rnrrr+H-^Lati^ III many instances ii is without doubt the cheapest and safest insecticide to use against aphides and ;i few other greenhouse insects. It- effectiveness, however, under the l>e-t <■< >i i< I i - tions i- not great, as it requires repeated use ;it short intervals. M r. it may cause serious injury to the plants. In the case of violet- it has been found to be of only slight value against aphides working in the bud, and while it may destroy the so-called " green aphis " when exposed, it is not effective in killing the ■•In-own aphis." On the other hand, tobacco may prove injurious to the foliage and bringing on epidemics of "spot." Tobacco is also useless against scale insects in general and mealy bugs. The desirability of -'Hue insecticide as easily used as tobacco, but more penetrating and effective and less likely to injure plant-, was apparent, and l.r, -.uue absolutely necessary in our stud} of the diseases of certain crops. Hydrocyanic-acid gas, since it- introduction by the Bureau of Ento- mology in l sst '' as a remedy against scale bisects of the orange, has proved of great value as an insecticide. I'iv\ ious t<> our experiments early in 1895, though it had been occasionally tried in greenhou hydrocyanic acid was not recommended, on account of it- injurious effects upon plant-. A- a result of a series of careful experiments we found that as a rule plants were less injured by a short exposure to a relatively large amount of L r a- than they were by a long exposure to a relatively small amount. ( )n the other hand, a strong dose for a short EXPLAKATOBl NOTE. I'll. I'.i t tll;lt :l rirelll.-ir of the ]'.ure:UI Of KlltiMi.. should be written by an expert of the Bureau of Plant Industry d Is a word splanation: Messrs. \. r. Woods and P. It. l>.T-.'tt. who prepared the I two editions Jointly, (bond it necessary, In the course <>f tlieir Investigations "f the diseases of greenhouse plants, to destroy the insects Irving upon the plants which they bad under observation. For this purpose they used hydrocyanic- acid gas and thus became by this practical experience bo well fitted to litis particular phase "f the use ,.f this Important gas that I requested thei prepare a circular on this subject This last edition has been revised by Mr. Woods :it my request, i.. O. ii" • ird, 1 32802 Clr.87 08 —1 time was the mosl effective in killing insects. Different species and varieties of plants, however, were found to vary remarkably in their power of withstanding the poison. This in many cases appeared to depend upon the open or closed condition of the breathing pores as well as upon peculiarities of the cell contents. Fumigation an hour or two after sundown, with the temperature as low a> practicable, was round to give the best results. In all cases the foliage must be per- fectly dry or it may be injured by the gas. In each case the proper amount of gas to use and the length of exposure must be determined by experiment. It is impossible at present to give a general ride ap- plicable to all plants in all stages of development. "When the condi- tions are once determined they must be strictly followed to insure the greatest success. Methods of experimenting will be described in the latter part of thi- circular. The quantity of pis in each case i^ al- ways given in terms of the potassium cyanide from which it is made, Fig. 1. — Fumigating bos. showing trays and coleus cuttings. (Original.) and on a basis of a cubic foot of space, as will be explained more in detail farther on. The cyanide, as well as the gas made from it. i> exceedingly poisonous, and both must be used with the greatest care. CROPS AND PESTS OX WHICH THE GAS HAS BEEX SUCCESSFULLY USED. Ferns. — ^ovDavalliamooreana infested with a scale insect (Chion- aspis sp.), 0.075 gram of 08 per cent potassium cyanide should be used for each cubic foot of space to be fumigated, not deducting the space occupied by the plants. Length of exposure, twenty minute-. One hundred and fifty to two hundred plants with frond- in all stages of development have been thus treated two or three time- each year for the past thirteen year- with no injury to the plants and almost complete destruction of the insect. They were treated fifty at a time in a fumigating box (fig. 1). described later. [Cir. ;:tj Adiantum cuneatum and A. ballii have been tried on p mall and were not injured by the treatment. Coleun. ''Golden Beddcr," " Verchaffeltii," " Shylock," and others. Twentj four thousand plants in pol , badlj infested with the " w bite tailed " meal} b ' ' The contained 15,587 cubic feel of I reated :it the rate of one tenth of .1 gram of 98 |"i- cent cyanide of potassium per cubic foot of space for twenty minutes, one hour after dark. Orthezia all killed and plant- not injured in the least. All other of destroying the Orthezia had I n tried without effect. Large numbers of the com- mon mealy bug were also killed by this treatment; but it was not nearly so effective as for the "white-tailed" mealy bug. All coleus cuttings made l>\ the United States Propagating Gardens for 1 1 1*- past eleven years have I n fumigated l» fore being prepared for the cutt ing bed < see liir- 1 I. D&ubh English violet . " Marie Louise," " Lady Campbell," and other-. For aphides and general fumigation fifteen-hundredths of a gram of 98 per i ent cyanide of potassium for each cubic foot of space is required. The exposure, if made according to direction-, will not hurt the plant- in any stage of growth. Since the lir-t publication of tin- circular in 1899 the '_ r a- has been used on a large scale bj com- mercial growers in fumigating violets, with the greatest success, only a few treatments during the season being required. Length of ex- posure, twentj to thirty minutes. Leaf 'ating larva?, slugs, milli- pede-, cutworms, etc., when exposed are killed as well as aphides. lied spiders, however, arc not entirely eradicated by the treatment. The foliage of single violets like ( alifornia and Princess of Wales are sometimes slightly injured by the stronger dose of gas. A weaker dose i one tenth of a gram potassium cyanide per cubic foot i should be used W hen they arc to be treated. Other plants. Other plant- on which tin" gas ha- Keen tried on a small scale indicate that it ma\ probably have quite a wide range of usefulne A'"- i. " Perle des jardins," " Mermet," and " Bride." The young growth on roses is particularly sensitive and has been more or less injured in all our experiments. 1 'I'll. ! en the I 'ith L'fain of cyanide per cubic f""t of space for twenty minutes without injury. Further experiment, however, Is neces ommended for these: Idiantum ballii; Adiantum runpatum; llornna macrorl fjaia; Inthuriumci'i/stallinum: Iralla ftlicifnlia nrium intybu* ; o/or; Crotons (in variety); Dieffenbachia i>iuii equivalent to nine-hundredths gram per cubic foot. The gas is liberated after dark and left in till next morning, when thorough ventilation is given. It largely escapes, however, during the night. The treatment is said not to injure the plants in the least. Tomatoes. — Dr. Jabez Fisher, in "American Gardening" (Oct. -J'.K 1898), reports using the gas for " white fly " (Aleyrodes vaporarioinin Westw.) on tomatoes. The gas from 1 ounce of pure cyanide of potassium for each 1,000 cubic feet, left in the house over night, killed all the insects without injury to the plants. This method has not yet proved successful with us in any case, but it should nevertheless receive careful trial by other experimenters. - CUBIC CONTENTS OF THE HOUSE. It is necessary in every case to determine with great care the cubic contents of the house, frame, or box in which the fumigation is to be made. To illustrate: Fig. -1 shows cross sections of two styles of greenhouse structures now in general use. At the left is an even span house 100 feet long, 1'2 feet wide, 2 feet on the side>. and 5 feet inches from the surface of the beds to the ridge, with a walk 1-t inches wide and 15 inches deep. To determine accurately the number of cubic feet in this or a house of similar construction : First . make a rough drawing showing a cross section of the house: second, divide the space into triangles and rectangles by drawing a line connecting the two wall plates and one from the ridge at right angles to this; mark on each its resepective length in feet and inches. Compute the number of cubic feet in each of the rectangles and triangles in accord- ance with the following method. In the even span house shown at the left the number of cubic feet of space in the walk is found by mul- Fourth Report, Dept. of Agr., New Zealand. 1S96. Pp. 141-143. ■See also Fumigation Methods, by W. <;. Johnson (Orange Judd) ; Violet Culture, by Galloway (Florist Exchange); Hemenway, II. D. — Bui. 22 n. s., Div. Ent., I". s. Dept. Agric, pp. 69-78, 1 : « « • : Chittenden, F. II.— Rid. ll. n. s.. Div. Env.. U. S. Dept. Agric, pp. 20-26, 1901 [Cir. 37 quoted]; Morrill, A. X.— Cir. 57, Bur. Ent.. U. S. Dept. Agric, pp. 5-9, 1905. [Cir. ::t] tiplying the width bj the depth by the length, thus: Multiply I fool •_' inches bj I fool •"■ inches by I"" feel ; reducing to inches we have l I inches multiplied h\ l"« inches \>\ 1,200 inches equals 252,000 cubic inches; dividing tin- result bj 1,728, the number of cubic inches con tained in a cubic foot, we have L45.83 cubic feet. The rectangle A 1) \ 100 feel equals 2,400 cubic feet. This brings us to the triangles. The rule generally given for calculating the area of a right-angle triangle is to multiply the base by the perpendicular and divide tit*.* product bj 2. The resull multiplied by 1 1 1 « - length of the house will give the number of cubic feel the triangular portion con- tains. For example, taking the triangle A (' I'.: 6 feel multiplied by 8 feel 6 inches, equals 21 feet, divided by 2 equals 10.5 feet, multi- plied by 100 fee! equals 1,050 cubic feet. The mi-cm of the triangle E C D and the cubic feet in this part of the house are determined in Fig. -. — End section of even span house nt left, same of three-quarter span h" right (Original.) the same way; or, in this case, since the triangles are equal, tin' de- sired result i- obtained by multiplying the number of cubic feet in the triangle A (' E by •_': L,050 multiplied by •_' equals 2,100 cubic feet. Thf contents of thi- house is therefore ll">. s :> pin- 2,400 pin- 2,100, equals 1,645.83 cubic feet; thi- result multiplied by the required dose per cubic foot of space will give the amount of cyanide of potassium necessary for one fumigation. Fig. •_' shows Mt the right a cross section of a three-quarter span house LOO feet long, I s feet wide, front wall 1 feet I inches, back wall 6 feet 4 inches, and 11 feet in inches to the ridge. The cubic contents of thi- house i- determined in the -Mine manner, except that the two triangles being unequal, each one will have to be calculated separately. Th»> house contains 15,050 cubic feet. It will thus !><• seen thai the cubic contents of a house or frame of any style ran be readily deter- mined by simply dividing a cross section of thf same into tin- i 82892 -Ctr.87— 4X 2 6 sary number of triangles and rectangles and calculating as demon- strated above. A simpler method of obtaining the cubic contents of a house has been described by Galloway. This consists in laying off a cross sec- tion of the house according to scale, on a piece of paper ruled in squares, each square being equal to a square foot. For example, sup- pose the squares are one-eighth of an inch to a square foot. The end- section of the house is then accurately laid off on these square-, and by counting the squares and parts of squares the number of square feet of space in the end section can be easily determined. This, mul- tiplied by the length of the house, will give the cubic contents in cubic feet. AMOUNT OF POTASSIUM CYANIDE TO USE. After the number of cubic feet in the space to be fumigated is deter- mined, the amount of cyanide required is found by multiplying the cubic contents by the dose per cubic foot. For example, if single violets are to be fumigated the dose would be one-tenth of a gram per cubic foot. A dose, therefore, for the even-span house, containing 4.i'>4Cp cubic feet, would be 4,646 multiplied by .1 equals 404.0 grants. To reduce this to ounces, divide the number of grams by 28.35 (the number of grams in an ounce avoirdupois). 464.6 divided by 28.35 equals 16.38 ounces avoirdupois. It may be necessary to reduce the fraction of ounces to grains: 437..") (the number of grain- in an ounce) multiplied by .38 equals 100 grain.-. If double violets are to be fumigated the cubic contents would be multiplied by .1">. thus: 4,646 multiplied by .15 equals 696.9 grams, divided by 28.35 equals 24.58 ounces avoirdupois. .58 ounce equals 253 grains. In the case of a small space of less than 150 cubic feet the dose in grams should first be determined, and this, if necessary, can be changed to grain- by multiplying the number of grams by 15.43 (grains in a gram), thus: 30 (cubic feet) multiplied by .15 gram- equals 4.5 grams, multiplied by 15.43 (grain- in a gram) equals 69.435 grains, or approximately 09.5 grains. The reduction to oui or grains will not be necessary if metric weight- are used, which is strongly urged. When the dose for certain plants in a given house, frame, or box is once obtained, it should be carefully recorded on the house or box thus : Contents: 1,015 cubic feet. r Ferns, .075 gram per cubic foot equals Tti.l grams. \ Violets, double, at .IT. gram per cubic foot equals lo'i.L'o grams. If a scale weighing with avoirdupois weights is used, the dose d be r< [Cir. 37] should be recorded in ounces and grain? -IIM riNG v I I M l l" ll M 10 ATE. Care should be taken i<> select a night when the houses can he ven- tilated (lir required nine without injury in the plants ami when there i- no likelihood of rain. PR] PARA [TON hi I in HOUSE FOR FUM tO v I ION. On account •>! the very poisonous nature of the gas, it is necessary to arrange a number of ventilators, the more tin- better, -<> that they rail l>e easily opened from the outside. It would he very dangerous to enter the house while it contain- the gas. All broken glass should l>e replaced and hole- stopped up; a thoroughly we1 piece of news- paper will close a crack effectually or take the place of a broken glass it' necessary. It is best not to permit the gas i" gel into lire pit- or engine room-: these should he cut oil' from the pace to be fumigated. In case of a large range of houses opening into each other, it i- best to separate them into several sections, by tacking up building paper or oiled cloth -o that each section may he fumigated separately and at different time-. Theworkmay thus be done with great ease and care. and with less danger to the plant-. Great care must he exercised to have tin- foliage of the plants to he fumigated /» fifth/ . The material- required are 98 per cent cyanide of potassium, broken into -mall lump-, besl secured in I" or •_'."> pound can- at •"><> to |<> cents a pound, and commercial sulphuric acid at :'. to I cent- a pound by the carboy. For an ordinary house or frame, good vessels for liberating the gas are U or 2 gallon earthen jars of a- -mall diameter a- possible SO as to insure the immersion of the cyanide of potassium when it i.-, dropped into the acid. On*' jar should he used to about every •!'< feci ill length of such houses a- described, in order that the gas may he quickly distributed when set \v-v. When the jar- are placed in posi- tion the next step is to arrange to lower paper bags containing the desired amount of cyanide into the jars, from the outside. This i- U'-t done by passing a cord through a hook or -crew-eve attached to the roof over each jar in such a manner that when the -trii strings are loosened from the outside the hair- of cyanide will he low- ered into their respective jar-, a- shown in Wc •">. When the strings are ready, divide the amount of cyanide to he used into part- corre- [Clr.87] 8 sponding to the number of jars. Wrap each part up in a single thickness of ordinary newspaper and put in ordinary brown paper baas, and attach the bags to the strings, as shown in fig. 3. While the jars are empty test the arrangement to see if it works satisfac- torily. After each bag is suspended in place, the other end of the string securely fastened where it can be reached from the outside, and the arrangement tested, move the suspended bags to one side so they will be out of the way while putting the water and acid in the jars. When this is done, pour into each jar an amount of water about equal to the bulk of the potassium cyanide in the bag. Eight ounces of cyanide will require about half a pint of water. The sul- phuric acid should then be poured in until steam rises from the Fig. 3. — Violet house prepared for fuiuigatiou. y Original, j water. This would require for a pint of water about a pint and a half of acid. It is not necessary, however, to measure the acid, as the evolution of steam indicates when the right amount has been poured in. Always put the water in first and then pour in the acid. As soon as this is done place the bags over their respective jars. When all is ready, go out, close the door, and carefully loosen the strings, allowing the bags to settle into the acid. While the method just de- scribed is desirable for a large house or series of houses from which exit would be difficult after dark, it is not necessary to go to the trouble of lowering the cyanide into the acid by strings in most [Clr. 37] cases. When the jars containing the water and acid are properlj placed, the cyanide in the paper sacks, as previously described, may lie -et beside the jars; then il perator, starting in « nn- end of the bouse, may carefully drop the bag into the water and acid, coming out the other end of the house. It there are i w <> sets of jara in ili ffer fiii paths, it will !'»' necessary for two operators t'» start, one in each path, working in tin' same direction, at about the same rate of speed. In this way tin' cyanide can be placed very quickly and easily in quite m large series <>! jars, taking care that no cyanide i- placed in a jar in Midi a way a- to cut oil' the exit from tin' house >>( any oper ator. Tin- method of hand dropping is now tl ne most largely used. Tlir gas will very soon be given oil' and Oil every portion of thf house. It i- colorless ami smells ami tastes like peach pit-. A little of it i- harmless, but too much will cause death. A small quan- tity will leak out of the house; avoid positions where it can be smelled. The time of exposure should lie reckoned from the lower- ing of tin' cyanide into the jar-. When the proper time has elapsed, varying lor different plants as previously stated, quickly open the ventilators from thf outside, so that the gas can escape a- rapidly as possible. It will all lif "mm' from a large house, such as described in this circular, in half or three-quarters of an hour, and the ventila- tors may then be closed, if necessary. Next morning thf material left in thf jars should be emptied into a hole ami buried. It is nothing hut sulphate of potash, sulphuric acid, ami water, having a little hydrocyanic acid gas in solution. Thf latter will soon dis- appear and thf sulphuric acid will unite with lime in thf soil, form- ing gypsum. II kflGATINO BOXES. For the purpose id' experimenting ami where only 1 few hundred plant- are to be treated, a tight box ma\ be made of 30 to 50 cubic feel capacity. The box should he a- nearly air-tight as possible, with a removable cover and a -mall door at the bottom for introducing the cyanide of potassium into the howl containing water and sulphuric aeid. a- shown in fig. 1. The wire tray- shown in tne same illustration are used in fumigal ing cuttings of coleus or other plants When desired the t ray- can he removed and pot plant- -ei in the bos and given such fumigation as desired. To prevent injury to the plant- they should be so set that the foliage tloe- not come within I s inches of the bowl near the -mall door. When the plant- are arranged the top i- put on securely and a little water i- poured into the howl, and then sulphuric acid i- added till steam i- formed. The"hecessary amount of cyanide, wrapped in a small pieee of newspaper, i- then dropped into the howl and the little I fir. :;7l 10 door quickly closed. When the desired length of time has elapsed take off the cover and open the door and retire, so as not to breathe the gas. In a few minutes the gas will have sufficiently escaped so that the plants may he taken out and other- treated in the same way. Injury (if there is any) to the plants may not -how for two or three day-, so. in the case of experimenting, conclusions should not be has- tily drawn. The box may be used in the daytime if the work is done in a cool place. For experimental purposes and treating plants on a small scale, a small greenhouse containing L,000 cubic feet, or Less, is better than a box, as the results obtained with it are more reliable and there i- less danger of injury to the foliage. CONDENSED DIRECTIONS. (1) Carefully determine the cubic content- of the house and the amount of cyanide of potassium to use. (•_') Make the house as tight as possible. (3) Arrange so that the ventilator- can he opened from the out- side. (-1) Place the jars and strings in position. 1 ( 5) After dusk attach the hags containing the cyanide to string-, as described, and find if they work correctly. ( •', ) Hang the hags to one side and put water and acid into the jar- : arrange protection and put the hags in place again. ( 7 ) When all is ready lower the hags into the jars by loosening the strings from outside. (8) After the proper exposure open the ventilators from outside, leaving them open from thirty to forty-five minute- before entering the house. (9) Next morning bury content- of the jars. (10) The foliage must be perfectly dry. CAUTION. It should be remembered that hydrocyanic-acid gas is one of the deadliest poisons known fatal to human beings and plants, as well as to insects. Greenhouses which are within 50 to 75 feet of dwelling- should not he fumigated unless the windows and doors of the latter on the side next to the greenhouse can he closed during the operation. 'If the potassium cyanide is to be dropped into the jars by band, place the package beside each jar: then a man i'm each separate group of jars should start at one end and work towards the end from which quick exit can be made. After proper exposure open ventilators, etc. [Cir. :S7] Ii is essentia] thai the exact proportion of cyanide be 1 1 -< •> 1 mi the rate designated for each cubic fool of space and thai the exposure should iint exceed the limit ascertained l>\ experiment as appropriate in the plant- to be fumigated. \ great* r trength "I gas >>r a longer exposure than specified is apl i" result in injur} i" the plant It is besl to it-'' tin- method at first experi ntall} on a small scale before attempting the fumigation of an entire greenhouse, and a pre- liminary test should always be made in case plants "l a sped variety not previously fumigated are to be treated. A | >| >t < >\ ed : .1 \ MEfl \ \ " 1 1 SON, n tm ii of .1 grit ulturt . Washington, D. ('.. March ',. /> U'l, O UNIVERSITY OF FLORIDA lllllllillWIlllllll 3 1262 09216 4523