TEXAS AGRICULTURAL EXPERIMENT STATIONS. BULLETIN NO. 93. HELSWEET POTATO BORER BY ALBERT F. CON RADI Entomologist A Hill of Sweet Potatoes Infested by the Borer. (Photo by E. C. Green) POSTOFFICE COLLEGE STATION, BRAZOS COUNTY, TEXAS- TEXAS AGRICULTURAL EXPERIMENT smnons OFFICERS. GOVERNING BOARD. (BOARD OF DIRECTORS A. AND M. COLLEGE.) K. K. LEGGETT, President - - - - Abilene T. D. ROWELL, Vice President - - - Jellerson A. liAIDUSEK - - — — - LaGrange J. hi. GREEN - - - - - Yoakum W ALTON PETEET - , - - - - Dallas R. '1‘. MILNER - - - _ - - Austin L. L. MclNNis - - - - - Bryan W. B. SEBASTIAN — - - - Stephenville STATION OFFICERS. H. H. HARRINGTON, LL. D., President of the College. J. W.CARSON - - - - - Vice-Director M. FRANCIS - - - - - Veterinarian E. KYLE - - - - - Horticulturist F. R. MARSHALL - - - - R. L. BENNETT - - - - Animal Husbandry Cotton Specialist O. M. BALL - - - - - - Botanist G. S. FRAPS - — - — — Chemist A. F. CONRADI - - - - Entomologist EDWARD C. GREEN - - - C. E. SANBORN - - - JOHN C. BURNS - - - C. O. MosER - - - - M. S. CHURCH - - - H. E. HANNA - - - - C. W. CRISLER - - - C. A. POFFENBERGER - - ~ - Miss M. H. WATKINS - - - Assistant Horticulturist C0~Qperative Entomologist Assistant Animal Husbandry Deputy lieed Inspector Deputy Feed inspector Deputy Feed Inspector Clerk Peed Control Chief Clerk btenogratuher STATE SUB-STATIONS. S. A. WASCHKA, Superintendent — — Beeville, Bee County W. S. HOTCHKISS Superintendent ~ - Troupe, Smith County NoTgr-Tlte mam statzon ts located on the grounds ofthe Agricul- tural and Mechanical College, in Brazos County. The Postoflice address is College Station. Texas, Reports and bulletins are sent five upon ap- pllCallo/l t0 the Director. THE SWEET POTEO ROOT BORER A. F. CONRADI SUMMARY From the investigations of this Department, as well as the letters re- ceived from prominent sweet pototo growers, it is apparent that the sweet potato industry of Texas is seriously threatened by the sweet potato root borer, also known as sweet potato weevil. Ever since the middle of last century Texas has been one of the most important States growing the sweet potato. The insect being of a tropical origin is most destructive in South Texas, less so in Central Texas, while sporadic outbreaks are possible during the growing season in any section of North Texas. The insect has been on record since 1798. It was reported on sweet potato as early as 1857. It was probably introduced from the West lndies. It was first reported in the United States from New Or- leans in 1875, the first report from Texas being 1890. lt is present in South Texas west as far as Comal and Cameron counties, and north as far as Milam county. Early varieties as well as potatoes planted early are more seriously in- jured than late varieties and those planted late. Shallow planted tubers are more infested than those planted deep. The weevils reach the tubers chiefly by burrowing along the vines. The full grown insect is an elongated glossy snout beetle with a black head, middle part of body and legs red, hind part dark steel blue, and about 1-4 inch long. It lays its eggs on tubers and vines. The larva, which is a white foot-less grub about 1-5 inch long, tunnels in the tuber. It pupates at the end of its tunnel. The entire life cycle is completed in the potato in about 35 days. The beetles can subsist on other plants besides sweet potatoes, prin- cipally on those plants that are closely related to the sweet potato vines, such as morning glory plants. The insect has never been observed in flight in this country. 1t has well developed wings which makes it appear that migration on the wing is possible. Rotation of sweet potato fields, combined with other methods, is of value not only from an insect standpoint but from an agricultural point of view as well. Plant as remote from last field as possible- We have not found any variety of sweet potato that is immune. Raw tubers should never be thrown out nor fed to stock without hav ing been boiled. Harrow the ground after the crop has been gathered. In spring by means of volunteer plants the over-wintering weevils may be destroyed on them. As a rule stock will eat the tubers with the exception of those badly riddled and dried up. Remnants left by stock should always be gathered and destroyed by burning. ( ) 3 Burying infested tubers is discouraged. A totally infested crop should be gathered clean, and vines and all thrown into a hot fire and burned. Tuber traps may be used to advantage if carefully manipulated. Gathering volunteer slips from tubers left in the ground from the last crop as Well as selecting home grown seed from infested farms is dangerous. Adults can be easily killed when exposed to the fumes of carbon bisulphide (high lifel at the rate of 1 pound to 1000 cu. feet of space for r 24 hours. To kill the stages in the tubers carbon bisulphide should be used at the rate of 3 pounds to 100 bushels or 1000 cu. feet of space for thirty hours. The bin should be tightly closed. All seed should be imported from non-infected sections, carefully packed to avoid danger of infestation en route. Tie vines, such as morning glories, should be kept down by grazing or otherwise, as much as possible. When this is impossible they might be poisoned in and about a potato field. Farmers should co-operate in controlling the pest. THE SWEET POTATO WEEVIL. (Cylas formicarius, Fab.) The Sweet Potato Borer, the worst of all sweet potato pests, is spread- ing over South Texas. The apprehension it is causing in the minds of sweet potato growers is well founded. The insect is terribly destructive and diflicult to control. The following extracts from a few of the letters Written to us by prominent growers will serve to illustrate the seriousness of the problem. “People in this locality have already abandoned raising the sweet po- tato for the last two or three years on account of the weevil. About one- half or more of my crop was ruined by them last year. They are moving northward 10 or 15 miles a year. I intend to get new seed which is not infested and plant a large crop again next year so that if you discover a certain remedy, please let me hear from you.” “We find the potato weevil in nearly every field in the western part of the country. On some farms they have completely eaten up the crop, in most cases while they were in the ground before digging. There are about 200 farms infested with them. I think they will be about as hard to exterminate as the boll weevil.” “I send you under separate cover some kind of a bug that is eating up our sweet potatoes. They go into the ground and eat them before they are dug. What can we do?” “Has there been any insecticide discovered that will control the sweet potato beetle? They are doing very serious damage here.” “By today’s mail I am sending you some sweet potatoes that are full of some insects which have ruined the crop in this vicinity. As far as I know they attack only the sweet potato.” “I send you today by mail some sweet potatoes that are full of some kind of insect. The potato is not fit to eat, and in the lower part of the country near the head of the bay it is impossible to raise any sweet potatoes.” “Last year I had all my sweet potatoes destroyed by the weevil, and I would like to know how to prevent it. Would it be safe to use seed saved from this crop?” ( ) 4 STATISTICAL. i With the exception of the Irish potato the sweet potato is probably the most extensively grown vegetable in the United States. In 1899 it was reported by over one-third as many farmers in the United States as the number growing Irish potatoes. While this vegetable can be grown over an extensive area of territory it is chiefly a southern crop. According’ to the Twelfth United States Census, the States of Georgia, Alabama, North Carolina, South Carolina, and Texas cultivated 52.6 per cent of the acreage of the crop of 1899. If to these States the acreages of Virginia, Mississippi, Tennessee, Louisiana, Florida, New Jersey, Kentucky, Arkan- sas, Missouri, and Illinois be added, we have an acreage of 93.1 per cent of‘ the total in 1899. Since the middle of the last centuary Texas has furnished her quota to the national production of this crop. In the Census report for 1850 we find Texas with 1,332,158 bushels, or 3.5 per cent of the National crop, ranking 9th in production. In 1860, 1,846,612 bushels or 4.4 per cent of the National crop, again ranking 9th in production. In 1870 the 2,000,- 000 mark was passed, producing 10.1 per cent of the total crop for the United States. In 1890 the Texas acreage was 52,206, ranking fourth in the United States, forming 10 per cent of the total acreage; it ranked third in production, its crop being 5,500,000 bushels, or 12.5 per cent of the national crop. In 1900 Texas ranked fifth in acreage, sixth in pro- duction, cultivating 8.1 per cent of the acreage and producing 7.8 per cent of the National crop. In 1900 her acreage was 43,561, yielding nearly 3,250,000 bushels. Qf t-he 352,190 farms of Texas in 1899 they were raised on 63,209, or an average of 7-10 acres of sweet potatoes on every farm of Texas. The yield per acre in 1879 was 74.6 bushels; in 1889, 104.9 bushels; in 1899, 75.7 bushels. In 1899 the average market price was 51c per bushel, making an average value per acre of $38.77. Rank ofStates ear/z zuit/z over 1,000,000 bus/leis ofszcfeetpotatoes, at census, 1850-1000. From bu/letiu ' 24, Division of.S‘tatz.vtics, United States Department Agr, RANK 1 1850 1860 1870 1880 1890 51900 1 . . . . . . . . ..Ga . . . . ..Ga . - . - -liN.C_...;N.C..--iN.C.--.N.C. 2 . . . . . . . . . - . . _ _ . . 3 . . . . . . . . 4 . . . . . . . . ..il\/Ii55....Mi55....iAla, ....lAla, 5 . . . . . . . . 6 . . . . . . . . .....va_ ,....sLa_ .....\5_c_....N,]_....va_,....§Miss, 3 . . . . . . . . ..La.-....Va .....lTenn Va.......N_]_....iN__] 9 . . . . . . . “TeX.....TeX...._La,_....Fla- ....Tenn,-..‘iFla, . . . . . . . . .._,Ark_1 . . . . . . . . . 11 . . . . . . . . . . . . . . . . ..Fla . . . . . . . . . . . ..La,.....Ark, ....ITenn, 12 . . . . . . . . . . . . . . . . ..Ky . . . . . . . . . . . ..Ky. Fla . . . . 13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Since 1880 Texas increased its crop from 4.4 to 7.8 per cent. We (5) have no statistical data since 1990 with regard to the quantity of crop. Considering that the larger per cent of the sweet potato crop is grown for local consumption, the present annual crop of Texas, the vast expanse of unsettled territory in the State, the rapid development of new territory, the extension of railroads into every section, as well as the prominent place given the sweet potato in Southern gardens, it becomes at once apparent that We should give due attention to insect pests that threaten this indus- try with destruction. AREAS OF INPFSTATTON. Upon examining the accompanying map we find that the sweet potato is grown over the greater area of Texas. Over one-third of the product is grown within the territory where the weevil survives the winter in all stages and which is the area in which the pest is most destructive. In determining the area of present infestation as well as the area over which the pest will spread and become destructive in the future, we are guided by our studies of the distribution of the pest as well as the behavior of the insect untler different climatic conditions. ln the accompanying map the dotted line represents the boundary of the territory where the weevil is known to occur and is destructive. In studying the temperature of South Texas we find that the pest can spread as far north as line “A” before it is seriously handicapped by Texas winters. Over this territory we find that the temperature is rarely low enough to interfere with the successful sur- vival of the winter by adult weevils, and at no time are tubers left in the soil during the winter sufficiently frozen to prevent larvae and pupae from developing into adults. As the pest spreads northward aboveline “A,” the temperature condi- tions become too severe for the adult weevils to survive, but the immature stages in tubers in the soil will pass the winter successfully. To deter- mine approximately the northern limit of this territory a series of experiments was conducted for the purpose of ascertaining the minimum temperature the weevils and their larvae were able to stand. A large number of weevils in different stages were subjected to various temperatures during varying in- tervals, the experiments being repeated each time at a lower temperature until the minimum was reached that the weevils were able to survive. In a temperature of approximately 45 degrees F., they passed into a stupor that resembled hibernation. This stupor was not fatal except after they had been exposed to a temperature as shown in the following table: TIME EX- NO. STAGE CF INSECT. POSEI) DEGREES F. 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