LIBRARY STATE PLANT BOARD September 1953 E-864 United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine DUSTING STORED LOUISIANA SWEETPOTATOES TO PREVENT AN INCREASE IN SWEETPOTATO WEEVILS By C. H. Gaddis, Division of Stored Product Insect Investigations, Bureau of Entomology and Plant Quarantine, and E. A. Epps, Jr., Feed and Fertilizer Laboratory, Louisiana Department of Agricul- ture and Immigration—' In the four crop years between 1949 and 1953 an estimated 7,047,554 bushels of sweetpotatoes in storage in southwestern Louisiana were dusted to prevent a build-up of sweetpotato weevils ( Cylas formicarius elegantulus (Sum.)) during the warm spring months. Prior to 1949 the State of Louisiana required the destruction or removal of all stored sweetpotatoes within the sweetpotato weevil regulated area by April 1. This requirement was necessary to prevent a heavy emigration of weevils from the storage kilns to the nearby fields, or their widespread dissemination during the transfer of sweetpotatoes from storage kilns to packing houses or dehydrators. The application of insecticide dusts to stored sweetpotatoes kills the adult weevils as they emerge before they have an opportunity to mate and lay eggs. Therefore, during the warm spring months all adults are killed as they emerge from the stored sweetpotatoes or invade the storage from undusted stocks. This procedure gradually depletes the population until a level is reached consisting only of individuals with delayed cycles which remain within the sweetpotatoes for many months. The research that furnished the basis for this treatment, carried on from 1948 to 1950 at Lafayette, La., is reported herein. The studies included the biological evaluation of different dusts, the determination 1/ The writers acknowledge with thanks the cooperation of W. E. Anderson (since deceased), S. J. McCrory and Roy Meek of the Louisiana State Department of Agriculture; G. Z. Smith, and J. B. McDevitt of the Louisiana Agricultural Experiment Station; Herbert L. Morgan and A. H. Yeomans, of the Bureau of Entomology and Plant Quarantine; Girard & Trosclair and other shippers; and various sweetpotato weevil inspectors. ■ dues -nt of a suitable du.s Ii a , observations on on of )d for Ita practical utilization w .seen 1950 and I Exploratory Tes •ness and long* >i residues of DD'I, BHC, and chlordane emulsions; DDT suspensions; and DD'I and m- hlor dusts against the sweetpotato weevil were determined in tests using flat 1-foot squares of sweetpotato- slats. Adult weevils were con- d under an ; i'etri dish at the same spot on the square- approximately 30-day intervals. Ai hours they were removed to clean Petri dishes and held in the laboratory at room temperature for observation. The results of these tests appear in table 1. It will be noted that the dusts were the onlv forn.ulations that were 100 percent effective for 365 days. le 1 .- -Mortality of adult swe» vils confined for 2 hours on insecticide residues of various ages in the laboratory at room temperature Insecticide liliters to each test square Percent morta to residues o: when exposed ited age 2 77 106 1 A\ :■ 4 365 days DDT: 0.75 % emulsi' 15 100 99 98 - 5% suspension 100 100 100 100 - 10% dust I 100 100 100 BHC, nulsioi i 87 - ' 13.5 >0% d u ' 100 100 100 * • >nal t- potat StO: g. os am: :ice of weevil '.potatoes -3- the treated crates became infested as compared with 100 percent of those in the untreated check crates. In other tests the crates and the sweetpotatoes were treated with 10 per- cent DDT or 50 percent methoxychlor dust, and held over winter under the same storage conditions. In the spring 6 percent of the DDT-dusted sweetpotatoes showed some evidence of attack and a few of them contained one or two weevil larvae. Six percent of the rnethoxychlor-dusted sweet- potatoes showed some evidence of attack, but no larvae were found. Cage tests were then run to determine the effectiveness of 50 percent methoxychlor dust in the presence of a very heavy weevil population. Each cage held three crates of sweetpotatoes. In one cage two crates were dusted; the third crate was untreated and contained heavily infested sweetpotatoes from which weevils were in the act of emerging. An other cage held two crates of untreated sweetpotatoes and a crate of infested ones. Both lots were exposed for 24 days. All the sweetpotatoes in the check cage became very heavily infested, having an average of seven egg punctures per square inch of surface. The dusted sweetpotatoes were uninfested, although approximately 13., 000 dead adult weevils were found in the cage. Storage tests of approximately 700 bushels of sweetpotatoes were conducted in four commercial kilns. The sweetpotatoes were treated with 25 or 50 percent methoxychlor or 10 percent DDT dust with an orchard duster. Prevention of reinfestation from emerging weevils was complete except where dust coverage was inadequate. Tests were also made to compare the reinfestation in dusted sweet- potatoes by weevils originating from within the dusted stock with that by weevils originating from untreated stock. Fifty and 25 percent methoxychlor and 10 and 5 percent DDT dusts were used. One-half of the dusted sweetpotatoes were exposed to crav/ling weevils; the other half contained a few heavily infested sweetpotatoes and were isolated from outside infestation. It was found that few of the sweetpotatoes were infested where the weevils emerged from dusted stock. The infestation was much greater where the sweetpotatoes were exposed to weevils from untreated stock. This difference was apparently due to the fact that weevils emerging from dusted sweetpotatoes were killed by the poison before they were ready to lay eggs. Large-Scale Tests A large-scale experiment was set up for a further study of the possibilities of using DDT or methoxychlor dusts. This experiment was designed to determine (1) the efficiency of normal washing practices in removing the residues, (2) the relative ability of the various dusts to prevent spread of weevils to uninfested sweetpotatoes, and (3) the distri- bution of dusts when applied with an orchard duster. - 4 A 1, re divided into four equal in a sep;. , foot room. An was reser-. m each lot. One of the following formulations o: Din or met!. !or was applied to each lot: 25 percent wettal '.ders dusts. Both dusts and w« powders were included to observe possible differences in remov The i rates of sv. atoes were dusted a layer is they were placed in the storage rooms, with an orchard- type power duster with a 4-inch outlet hose. One pound of dust was used for each 10 crates. Residues following washing were determined I analysis of samples withdrawn from four locations in each lot. The relative effectiveness of the various dusts was determined by confining adult weevils on dusted sweetpotatoes selected from each lot. The distribution of the dusts was determined by chemical analysis of the dust on sweetpotatoes from selected locations, and by biological tests with adult weevils confined on samples from the same locations. Residues After Washing One-bushel samples of sweetpotatoes were withdrawn from the front and back, top center.and bottom center of each lot after the 1st, 2nd, 3d, 4th, 5th, 6th, 11th, 15th, and 20th weeks. Each sample was divided into two 5-pound subsamples, one washed and the other unwashed. The un- washed subsample was selected at random after the crate had been dumped out on the apron of a standard sweetpotato washer at a com- mercial packing shed. The remainder of the bushel was then washed, and a 5-pound subsample was selected at random and paired with the shed subsample. The samples were immediately transported I Baton R • , I. .. sidues were analyzed at the Feed and I; this analysis insecticide residues v. ived I pping 1,800-gram samples of i0 ml. o:' • SUDJ4 minutes. 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C"*"* C"*"" — ' r*™' t*"* r- c- 3 — f f, : T 00 c t- - C .* — PQ Q - — - <■ N CO ( O N IT ~ n o oo r~ CC *T T — — n — -r -: -r — • • -r — r: r: rj :- — — — -r -: — - . - EC O r- t>- • • • • co in c: O CI ft (0 n n c - •- 3 W M M CC ~ ■ - t« ■>r — in 00 X uc - ^C ■- N iO ' < N ~r N CN y~ < N CN ■ r<~ m en ^_ _ in w M :- • • • • • ■ • • • • • • • • • • -r - en -r ro i— m r- o x t^ r~ r~ CC - t- 90 Ci X CO cr: CN in r- ■ ^r N -*-* - _ s - - « Q, ~ U fit, .. u .c i : Q -. 9 E - - L U >1 7 - The washing procedure reduced the toxic residues tc a very low level. The average residue from each formulation, found after washing, was as follows: P. p. m. DDT, 25% 5.0 10% 3.8 Methoxychlor, 25% 3.8 10% 2.1 The efficiency of washing did not seem to be related to the age of the residue. The residue was fairly constant regardless of the time elapse. Relative Effectiveness of Four Dust Formulations Two series of tests were run to determine the effectiveness ci the four DDT and methoxychlor dusts in controlling weevils. In the first series the four formulations were compared. Thoroughly dusted sweetpotatoes were placed in cages, and 1.00 adult weevils were introduced into each cage. At the end of 10 days the sweetpotatoes were examined for punctures and weevil-mortality records were taken. The tests were repeated three times at about 10-day intervals with the same sweetpotatoes but a fresh lot of weevils each time. At the end of the 30-day period sweetpotatoes were examined for punctures, eggs, and larvae, and the residue was determined. The results of these tests, given in table 3, show that all the dusts except the 10 percent methoxy- chlor were capable of killing all female weevils before they were able to deposit eggs in the sweetpotatoes. Table 3. --Effectiveness of DDT and methoxychlor dusts against three lots of adult sweetpotato weevils confined consecutively for about 10 days on 15 completely dust-covered sweetpotatoes and residues found at end of the tests Dust First let Second lot Third lot Number of punc- ■ tured Number of Number of Residue, p. p.m. Dead Alive Dead Alive Dead Alive sweet- potatoes eggs larvae DDT 25% 229 219 210 1 145.0 10% 216 215 224 6 94.6 Methoxychlor 25% 206 206 223 15 165.7 10% 189 5 217 1 221 Many Many 7 111.7 -8- In the s* series • thoroughness of dust coverage at two 'orage room ttom levels in the sweet to crates we Justs were 1 and the samples : and infested in the same manner as in the previou s. From the results in table 4 it :ent that the dust coverage was very uneven. Table 4. --Range of dust deposition in the storage room and crate- shown by weevil mortality and residue analyses Dust Location in crate Location in room •iber of wee D< : sidue at end of test, p. p. :: . DDT, 25 'o Bottom Back 313 : 13.9 Front 317 Top Bac k 317 108.5 Front 322 301.1 10% Bottom Back 255 70 . >nt 286 1 . Top Back 305 • . >nt 316 .. Methoxychlor, 25 o Bottom Bac k • 19.9 >nt 298 14 • Top Ba 291 23 61.2 >nt 314 1 10 . ! • • om Bac k 98 - . Hit 22 ck 1 1 I 1 (unt: -9 - Distribution of Dust in Storage Rooms The distribution of dusts applied with a power duster to one layer of crates at a time was quite uneven. The deposits were much greater near the doorway than at the rear of the rooms, and most of the dust in each crate was on the top layer of sweetpotatoes. The chemical analyses reported in table 4 demonstrated that the dust deposits on the sweetpotatoes from the bottom layers in the crates ranged from about 14 to 47 percent of the deposits on the top layer of sweetpotatoes in the same crates. The differences in mortality of weevils confined to these dust deposits are particularly marked in the 10 percent DDT and methoxy- chlor samples. These tests emphasize that with such unequal distribution of dust a much heavier application of insecticide is needed to effect high mortality. Development of a Duster for Crated Sweetpotatoes It was evident from the storage-room tests that better distribution of dust within the crates was needed. Owing to the great amount of sweet- potatoes that would be involved if a dust treatment proved feasible, it appeared impracticable to remove them from the crates in order to obtain better coverage. Such a practice would also cause some bruising or other injury. Therefore, attempts were made to develop a duster that would be better adapted to this special purpose. Preliminary tests showed that, if a small amount of dust could be puffed, or "exploded," into a crate of sweetpotatoes, the distribution and coverage would be fairly satisfactory. A duster was designed to accom- plish this objective. It dusts one crate at a time as a line of crates is passed beneath the nozzle on a roller conveyor. About 24 grams of dust (1 pound per 20 crates) is discharged by means of compressed air into each crate when it is directly beneath the nozzle. The duster (figs. 1 and 2) consists of an upright hopper that will hold about 20 pounds of dust, a revolving disk carrying four cups each of which holds the exact dosage for one crate, an arrangement to dis- charge compressed air into the cup in dusting position, a hood that directs the dust into the crate, a tunnel to shield the crates while being dusted, and a length of roller conveyor. The dust hopper has a very gradual taper. An agitator has been provided to prevent the dust from clogging but is seldom needed. The revolving disk is designed to rotate in such manner that the cups pass beneath the hopper, where they are filled with dust. The measuring cups, or "discharge cartridges," have two half-round gates attached to the bottom by hinges. Each gate has an arm to which lead counterweights are attached. The gates are so con- structed that they normally remain closed, even when the cups are filled with dust. Appropriate handles and stops have been provided whereby revolving disk can ";lling position to the point where the dust is • be The filled cups are visible during so th. e checked. The compressed air us' ropel the dust into the crates is released pressing a trigger momentarily on . e. This air pressure opens the two gates in opposite dire< , nd the dust is "exploded" and eve- spread into the sweetpotato crate. A pressure of 100 to 125 pounds per square inch gives best results. A somewhat funnel-shaped hood has been provided to confine and direct the dust from the point at which it is re- leased into a tunnel-like enclosure through which the sweetpotato crates pass. The tunnel is approximately 8 feet long, and is large enough to mit a section of roller conveyor and sweetpotato crates to move through freely. Dust is released in the tunnel at a position directly above the third crate from the entrance. It was demonstrated that crates can be passed through the duster as fast as they can be fed onto the conveyor, or about 600 to 800 an hour (fig. 3). As many as 8,000 per day have been dusted in commercial operation. Uniform coverage has been obtained with a dosage of 4/5 ounce of 10 percent DDT per crate. This duster has been adopted for practical use, and more than 50 machines have been manufactured. 1 •• tment to Remove !)I) I :"•■■ □ ■■:• Wasl er Waste water from sweetpotato-washinp nes is normally dis- posed of through an open drain to ditch, s. H only •• million of DDT is b to fish ; possibly to Livestock and wildlife. A >f the waste water fr DD I itpota.1 ild be disposal it treatment to DD 1 . L -th bluegill and bream showed that the DDT in tl -ould be rev filtration. I • ition ti n. A , I, in addil Lon to D ta of i ■ i ■ ii ■ DDT. ■ 11 - would give adequate removal of DDT. After passage through a settling pit the waste water treated with lime was found to be free of DDT at a point 100 yards from the washer. Application of Dusting Procedure for Quarantine The results of the research described above were reviewed by officials of the Louisiana Department of Agriculture and Immigration and the Bureau of Entomology and Plant Quarantine. The 10 percent DDT dust was selected for commercial use because it was generally available, it was the cheapest of the formulations that gave satisfactory performance, and the residues were removed by the usual washing practice to a level con- sidered to present no hazard to the consumer. This consideration was later confirmed by analyses of samples of sweetpotatoes taken from 12 commercial lots after they had been washed in preparation for marketing. The DDT residues after washing ranged from 0.1 to 3.6 p. p.m. Sweetpotatoes from the same samples analyzed after boiling or baking showed no DDT in the cooked sweetpotato pulp. The Schechter-Haller colorimetric method for DDT determination was used in these analyses. On October 3, 1949, the State of Louisiana revised its quarantine regulations as follows: The deadline for the shipment of sweetpotatoes from the quarantine area of Louisiana will be extended from April 1 to May 15, provided: 1. The sweetpotatoes to be marketed after April 1 are dusted with 10 percent DDT dust before March 1 of each year. 2. The applicator used in applying the DDT dust is approved by the Department. 3. The dust must be applied under the supervision of a represent- ative of the Department or the Bureau of Entomology and Plant Quarantine. 4. The wash water from the sweetpotatoes that have been dusted with DDT must be disposed of in a manner approved by the Department. All sweetpotatoes not dusted with DDT by March 1 will have to be moved out of the quarantined area, as in previous years, by April 1. These regulations were further revised on January 26, 1950, to re- move the May 15 deadline and extend the shipping period indefinitely for all sweetpotatoes dusted with 10 percent DDT before March 1. d Dus* toes with 10 percent DD *.he n has been in pra< >ur • Is were dus 1 *he 1949-50 crop. s from tl , 00 bushels from the 1952-53 ve been made of the dusted sweetpotatoes. [1 *as _;ing from them r; : d long enough to r st swi itoes. I sweetpotatoes that had been dusted were I ed to r ie length of time that weevils m: :n in them before em- It was found that a few adults were still present after 5 months' storage at prevailing and that some remained swet es were held at 70° F. storage for 4 months. At first the di st treatment was used primarily to prolong the storage and shipping seasons. Shippers have observed the benefits derived from dusting, and during the last two seasons many of them dusted sweet- potatoes that were to be kept in storage only for short periods. In the process of culling and grading dusted and undusted potatoes it was found weevil damage was much higher in the undusted stock. The treat- • proved so effective during the first three seasons that practice, all sweetpotatoes placed in storage in the weevil-infested area in the fall of 1952 were dust< Summ. Studie.- 1948 to 1952 to explore the poss of dusting table-stock sweet I - es ill storage to pr< t< ige formicari s • .• :ntulus (Sum.)). I. sts sh hat n lues of 1 DDT or 50 pe: s up to 365 . •• dust form »nd 10 • DD I - W0 i first threi toes. 1 in kill: I] ) . . ■■ . t DDT, l.fl . . DD ■ ■ 13 - The average residues were in the same order of amount as their toxicity to weevil adults. The residues after washing did not increase with their age on the sweetpotatoes. As the distribution of dust when applied with the power duster was found unsatisfactory, a duster was developed in which compressed air was used for dust dispersion. This duster was found to give good coverage throughout the crate at a dosage of 4/5 ounce of 10 percent DDT per crate. The crates were treated one at a time at the rate of 600-800 crates per hour. This duster has been adopted for commercial use, over 50 machines now being in use. DDT contamination of waste wash water was prevented by adding lime to the waste, which caused flocculation and settling of the DDT and mud present in the water. On the basis of these tests, the Louisiana State Department of Agri- culture revised its quarantine to extend the possible storage time from April 1 to May 15, provided that the sweetpotatoes were dusted with 10 percent DDT before March 1. In a later change the storage time was extended indefinitely. This treatment has had a very beneficial effect economically. Over 7,000,000 bushels have been treated in the last four crop years, and during the last two years many shippers have been dusting all stored sweetpotatoes even if stored only for a short time. Literature Cited (1) Wichmann, A. J., Patterson, W. I., Clifford, P. A., Klein, A. K., and Claborn, H. V. 1946. The determination of DDT as spray residues on fresh fruit. Three independent methods. Assoc. Off. Agr. Chem. Jour. 29: 188-218. 3 1262 09239 6497 I- . re 1.- -Dus r appl with ssed air to crates of sweetf otatoes. A, H B, ressed-air ti C, -shaj • of the tunnel. I >m. 1» r .de of hopper with 4 disk to • ire attached the four measuring cups with cou:. : outlets. MHMMMM a ™ * •