EP LIN teh hg ah et uyuaplenet was tphinatae as Me: ee in ag Vet vel be Sy Historic, archived document Do notassume content reflects current scientific knowledge, policies, or practices. , Contribution from:the Bureau of Plant Industry WM. A. TAYLOR, Chief Washington, D. C. PROFESSIONAL PAPER September 15, 1917 THE CONTROL OF TOBACCO WILT IN THE FLUE- CURED DISTRICT.* By W. W. GARNER, Physiologist in Charge of Tobacco Investigations, Bureau of Plant Industry; F. A. Wor, Plant Pathologist and Bacteriologist, North Carolina Agricultural Experiment Station; and EK. G. Moss, Assistant in To- bacco Investigations in the Bureau of Plant Industry and Collaborator of the North Carolina Agricultural Experiment Station. [In cooperation with the North Carolina Agricultural Experiment Station.] 2 CONTENTS. Page. Page. Importance of the disease.............:.....- 1 | Crop rotation as a basis for the control of Symptoms of tobacco wilt...........-.... .- 3 Ther wal Giese eS a ee anise i 10 “ CESTGS s.r ae is era ee eae sie Aes peter 3 Crop-rotation experiments at Creedmoor, SVSUIRY. SE gee Sei Scan pe pe ei 3 NOB Or Babe ne iOS A a ees ne a 10 IROCB SE — SOE SA ae eat Ne eo ara ee 3 Length of rotation required to reclaim Cause of the disease and its present distribu- infested: soilsie: 23.4 ie see eee 15 CAEL als ore CS ee en a 4 | Precautions to prevent the spread of the dis- Susceptibility of species and varieties of COSC UH inie Gee Race cre cence see tra aya srs ese 17 Eapaecorte the wilt. 26.35. cells. 02. Byes S UNIT a Taye ere ee WN La eI AU Cea lp nla eee 18 Relation of the physical and chemical prop- biterature cited ses 2S ers ce ee see 20 erties of the soil to the wilt..:.-......--.... 7 IMPORTANCE OF THE DISEASE. Tobacco wilt is a very serious disease in portions of the flue-cured district of Virginia and the Carolinas, the cigar-leaf district of 1This bulletin presents the results of investigations conducted jointly by the North Carolina Agricultural Experiment Station and the Bureau of Plant Industry for the pur- pose of working out practical methods for the control of tobacco wilt. The experiment station began studies to this end in 1903 and the work has been continued from that time. In 1910 cooperation with the Office of Tobacco Investigations, Bureau of Plant In- dustry, was effected, and the scope of the work was considerably extended. On behalf of the experiment station, the work has been directed successively by Dr. F. L. Stevens, Prof. H. R. Fulton, and one of the present writers. Messrs. W. G. Sackett, J. G. Hall, E. H. Cooper, R. O. Cromwell, W. C. Norton, and H. EH. Stanford, assistants at the experiment station, have actively participated in the investigations, 94919°—17 1 2 BULLETIN 562, U. S. DEPARTMENT OF AGRICULTURE. fd western Florida and southern Georgia, and in several foreign coun- tries. The disease was first brought to public attention in this country in 1903, when its occurrence in Granville County, N. C., was described in separate publications by R. E. B. McKenney (5), of the Bureau of Plant Industry of the United States Department of Agriculture, and F. L. Stevens and W. G. Sackett (10), of the North Carolina Agricultural Experiment Station. Because of the possible existence of other tobacco wilts Stevens and Sackett designated the disease in question “ Granville wilt,” from the name of the county in which it was first definitely recognized. Additional information regarding the occurrence and nature of the disease is contained in a bulletin by Erwin F. Smith (7) which appeared in 1908. It is not known when the wilt first appeared in the flue-cured dis- trict of southern Virginia and the Carolinas, but it seems to have been known to the farmers of Granville County at least as early as 1881. Asa result of extensive investigations in this country and in the Dutch East Indies and Japan, it appears to have been definitely established that a wilt of tobacco which has long existed in the latter countries is identical with the Granville wilt (8).* In this country, tobacco growers in sections where the disease is known speak of it simply as tobacco wilt, and this name is retained in the present bulletin. < Since it first came under observation in Granville County, the wilt has continued to spread, and usually when a field once be- comes infested subsequent crops of tobacco are increasingly at- tacked until a practically complete failure of the crop results. The wilt is an exceedingly destructive disease locally, and in the south- ern portion of Granville County it has caused the abandonment of tobacco culture on many farms. The disease has been most destruc- tive in the region which enjoys the reputation of producing the finest quality of flue-cured tobacco grown in the country, and the aggre- gate loss to farmers is very large, although difficult to estimate ac- curately. The loss is serious every year, although varying con- siderably, depending on seasonal conditions. The plants are killed outright and a loss of 25 to 40 per cent is not unusual, while on many fields the crop is practically a total loss. Should the disease become destructive throughout the flue-cured district it would practi- cally stop the production of this type of tobacco, the annual value of which is 30 million dollars. 1 Serial numbers in parentheses refer to ‘‘ Literature cited,” page 20. 2The disease in Sumatra appears to have been first studied by Janse (4) in 1892 and later by Van Breda de Haan (1) and Honing (2), who spoke of it as a “slime sickness.”’ According to Uyeda (11) the disease is known in Japan as stem-rot, black-leg, and wilt disease and was mentioned in a book on tobacco culture published in 1881. tle'> A hr ae Sey ig val Vig Be“ nt CONTROL OF TOBACCO WILT IN THE FLUE-CURED DISTRICT. 3 SYMPTOMS OF TOBACCO WILT. The disease affects the entire plant, leaves, stem, and roots, in a characteristic manner. It may attack plants in any stage of de- velopment, but usually symptoms first appear two to four weeks after transplanting. During the period of rapid growth which fol- lows as soon as the tobacco plants have become established after trans- planting, the number of wilted plants increases rapidly, reaching the maximum at about the usual time for topping. Under certain conditions there are exceptions to this progressive increase of wilt. LEAVES. The first decided indication of the presence of wilt is the drooping of one or more leaves of the plant. This wilting usually comes on gradually, requiring several days to become prominent, and growers familiar with the disease are often able to detect the first symptoms of _ wilting a day or two before the layman would observe anything un- usual about the plant. Affected leaves also may be somewhat distorted and wrinkled. At first there is no discoloration, but the leaves soon become pale green, especially between the larger veins, and then the leaf gradually turns yellow. Meanwhile the midrib and the veins have become limp and droop in a characteristic, umbrellalike manner, which persists even after the leaves and the stalk become brown and crisp. In some cases the leaves on one side of the plant wilt first, and sometimes only half the leaf is affected at first. STALK. In the early stages of wilt, if the tobacco stalk is cut across with a _ knife the woody portion shows a yellowish discoloration, which be- comes brownish or black as the disease progresses, especially in the lower part of the stalk. By stripping off the bark the discoloration appears as longitudinal streaks. In the advanced stages the pith also becomes affected. The inner bark also decays, and as the wet rot extends outward dry, blackened areas appear on the surface of the stalk. Pressure on discolored stalks will force out from the cut ends an opaque, dirty white ooze, very different in appearance from the normal cell sap. ROOTS. The organism causing the disease enters the plant through the roots, so that by the time the leaves begin to wilt the roots will show more or less decay. When cut across with a knife the affected roots _ inthe earlier stages will show a dark discoloration in the woody por- 4 BULLETIN 562, U.’S. DEPARTMENT OF AGRICULTURE. tion lying near the bark. This discoloration appears as longitudinal © streaks in this portion of the root, just as it does in the corresponding ; part of the stalk. In the ae stages of the disease only a few : of the roots are attacked, but eventually the whole root system is - involved, : There are other diseases of tobacco involving decay of the stalk, especially the so-called sore-shin, or sore-shank, which have been mis- — taken for the wilt, but the presence of a characteristic slimy ooze — when the stalk is cut and the black streaks in the woody portion are usually sufficient to distinguish the wilt from other diseases. In typical sore-shin, moreover, the stalk rots near the base, causing the plant to topple over. CAUSE OF THE DISEASE AND ITS PRESENT DISTRIBUTION. Tobacco wilt is caused by Bacterium solanacearum E. F. S. This | is a well-known organism, first studied by Dr. Erwin F. Smith (6), which causes a destructive rot of the tomato and Irish potato and attacks many other plants besides these and tobacco. In infected | tobacco plants the bacteria soon become so abundant in the woody vessels that these become plugged, thus cutting off the water supply of the leaves, thereby causing them to wilt. If only the vessels on one side of the plant first become clogged, then only the leaves on that side of the plant will at first wilt. Naturally, with the water supply cut off, no further development of the leaves is possible and the plant must soon die. Various theories as to the cause of tobacco wilt have been put forward by farmers, and it has been believed by many that the fertilizers used on the tobacco crop have been re- sponsible in some way for the appearance of the disease. It is true that fertilizers, cultural methods, weather conditions, and the like may influence the extent of progress of the disease, but, as already in- dicated, there is no doubt whatever that the disease is due to a specific parasite. ; | As has been stated, tobacco w a though designated by other names, - has long been known in Sumatra and Java and in Japan. In this country it was first found in Granville County, N. C., but about 10 | years ago it made its appearance in the cigar-tobacco district of Gadsden County, Fla., and Decatur County, Ga., probably having been introduced there through tobacco stems used as fertilizer which came from the wilt district of North Carolina. For a number of years the disease in Granville County was confined to the southern portion of the county lying between the Tar and Neuse Rivers. This happens to be the section enjoying the reputation of producing the — finest flue-cured tobacco grown in this country. Within this area eats gare CONTROL OF TOBACCO WILT IN THE FLUE-CURED DISTRICT. 5 the spread of the disease has been rather rapid, so that now but few farms are free from it. The disease has not spread so rapidly out- side of this section, although it has long since crossed the above- mentioned rivers. It has reached the adjoining counties of Vance, Durham, Wake, and Franklin and also has been found in Ashe, Guilford, Greene, Chatham, Davidson, and Yadkin Counties. It is quite possible that tobacco wilt also exists in other sections of the flue-cured district. Although the outward spread of this wilt is not particularly rapid, its progress is none the less certain, and once established it is exceedingly persistent and exceptionally destructive. SUSCEPTIBILITY OF SPECIES AND VARIETIES OF TOBACCO | TO THE WILT. In dealing with the problem of control the first line of attack was the search for resistant varieties of tobacco. The simplest solution, of course, would be the discovery of a resistant type in the standard native varieties used in growing flue-cured tobacco. Failing in this, the next step would be to find a resistant type among the numerous varieties used in growing other classes or kinds of tobacco which are produced in this and foreign countries. If such a resistant type could be found, it could be crossed with the native flue-cured varieties with a fair prospect of obtaining a new variety combining the re- sistant properties of the foreign with the commercial qualities of the native varieties. For several years past extensive tests have been made with nearly all available varieties, including many from foreign countries, but while some varieties have been found to be less sus- ceptible than others the resistance was not sufficient to meet practical requirements. Although the final results were negative, it seems desirable to summarize briefly the work along these lines. In making the tests the general plan has been to grow the different varieties in rows side by side on soil known to be badly diseased, including occa- sional rows of a standard native variety, so as to measure the rela- tive degree to which the different parts of the field were diseased. Records of the number of healthy plants and the number dead or _ wilted were made at intervals during the growing period, the last records being taken when the plants had reached maturity. In the first tests, made in 1904, 62 varieties or types known by distinctive varietal names were used. These included some 25 subvarieties or strains of Oronoco, several of the Pryors, White Burley, Maryland, the Broadleaf, or Seedleaf, and Havana Seed types of the northern cigar-leaf districts and domestic and imported 1 Wor further details of the tests, see Stevens, F. L. (9). 6 BULLETIN 562, U. S. DEPARTMENT OF AGRICULTURE. Cuban, Turkish, and Sumatra tobaccos. Practically ail domestic © types of tobacco were represented, but none showed a high degree — of resistance, 70 to 90 per cent of the plants succumbing to the dis- ease. Work with local flue-cured varieties has been continued up to the present. Each year seed from plants which had survived in — the previous year’s test has been planted, but no progress has been _ made in developing a resistant strain. In the tests with foreign — varieties, including varieties from South America, Mexico, Cuba, Sumatra, Turkey in Asia, Turkey in Europe, Italy, and Russia, it was found that the Sumatra, a Turkish variety from Cavala in Mace- donia, and a variety from Italy designated by Comes as Nicotiana — tabacum fruticosa showed considerable resistance to the wilt, and selections from these were grown for several years. The Sumatra and Turkish were crossed also with the local flue-cured type in an effort to develop a highly resistant commercial variety. The most striking feature of these experiments was the fact that the resistance of the above-mentioned varieties depends largely on seasonal con- ditions. Under conditions tending to produce slow growth, par- ticularly dry weather, these varieties have shown a relatively high degree of resistance, and in some years less than 10 per cent of the plants died. Under conditions favoring rapid growth, especially periods of wet weather, on the other hand, nearly all plants died. No highly resistant types were obtained from any of the hybrids. A type of imported Cuban tobacco showed a resistance of 12 per cent in 1911, 96 per cent in 1912, 78 per cent in 1913, and 46 per cent in 1914, variations apparently due to seasonal conditions. Tak- — ing the tests as a whole, the Sumatra variety has shown the highest resistance of all varieties. .In this connection it should be stated that Honing (2), working along the same lines in Sumatra, tested varieties from various parts of the world, including 30 or more American varieties, and found none more resistant than the native Deli (Sumatra). The Halladay, a type developed in Connecticut from a cross of Sumatra on Connecticut Havana, also has shown con- — siderable resistance in the present tests. Since the investigations failed to show sufficient resistance in any — of the varieties of tobacco belonging to the ordinary species grown _ in America (Nicotiana tabacum), it seemed worth while to test various other species, wild and cultivated. Tests were made with several varieties of Vicotiana rustica from Italy, Russia, China, and elsewhere, but all of these were found to be very susceptible. Other species tried were longiflora, glauca, glutinosa, langsdorfii, silvestris, affinis, and sanderae (hybrid), none of which showed higher resist-_ ance than the ordinary tobaccos. CONTROL OF TOBACCO WILT IN THE FLUE-CURED DISTRICT. 7 RELATION OF THE PHYSICAL AND CHEMICAL PROPERTIES OF THE SOIL TO THE WILT. The second line of attack in searching for a practical method of controlling the wilt was to determine whether the soil could be treated by chemical or physical methods which would destroy the organism causing the trouble or weaken its activity. In 1904 a series of field plats on infested soil at Creedmoor, N. C., was given various chemical treatments before being set to tobacco. Heavy applica- tions of powerful disinfectants, including several salts of copper, formalin, corrosive subliimate, permanganate of potash, carbolic acid, iron sulphate, and sulphur, were tried. Strong acidsand alkalis and excessive applications of potash, nitrogen, and phosphoric acid also were tested. None of the treatments gave any promise of suc- cess in practical tobacco culture. In 1910 another series of field tests with chemicals was made on a diseased field near Creedmoor, including a more extensive study of the effect of acid and alkaline conditions on the disease. The effects on the wilt of soluble forms of calcium, Magnesium, silicon, aluminum, iron, and manganese were tested, but without results, these tests being based on the assumption that the wilt is not to be feared in soils containing large amounts of clay. Various fertilizer treatments were tried, only materials tending to produce alkaline conditions being used on some plats, while on others only substances favoring an acid reaction were employed. For example, one plat received per acre 200 pounds of carbonate of potash, 600 pounds of basic slag, 250 pounds of nitrate of soda, 500 pounds of cottonseed meal, and 2,000 pounds of burned lime, while another received equivalent amounts of sulphate of potash, ‘acid phosphate, ammonium sulphate, and acid sodium sulphate. None of these treatments produced any decided effect on the amount of wilt. In the following year, in order better to control the experimental conditions, a large number of glazed-tile cylinders 24 feet long and 2 feet in diameter were set in the ground so as to leave about 3 inches projecting above the ground level. The cylinders were in- stalled at West Raleigh and at Creedmoor. The pots were filled to a depth of about a foot with bottom earth taken from the holes in which the pots were placed, after which about 8 inches of subsoil and 8 inches of topsoil from a diseased tobacco field at Creedmoor were added. All tests were made in duplicate and each cylinder contained four plants. In continuation of previous work, tests were made with mixtures of varying proportions of sandy and clay soils; with ordi- ‘nary wilt soil, to which were added separately the chief chemical con- stituents of clay; with plants grown from seeds without transplant- 8 BULLETIN 562, U. S. DEPARTMENT OF AGRICULTURE. ing, so as to avoid breaking the roots; with acid reagents and alka- line reagents; and with various chemical disinfectants. Considerable difficulty was experienced in maintaining the infection in the cylin- ders, because of their becoming excessively dry or from some other unfavorable condition, so the results were rather inconstant and un- certain. The results of tests covering three years, mixtures of sandy and clay soils being used, seemed to indicate that the wilt organism is not very active in clayey soils, but none of the chemical constituents of clays applied singly to sandy soils appeared to have any decided action on the organism. A rather extensive series of tests was made with acids and alkalis. For the former sulphuric acid, acid potas- sium sulphate, and nitric acid were used, and for the latter quicklime, calcium carbonate, potassium carbonate, sodium silicate, and sodium carbonate were employed. In most cases at least two different rates of application were made. The results of tests covering three years indicate in general that alkalis are favorable to the wilt organism, | while acids retard its development, but the results were not very constant and failed to furnish any basis for a practical remedy. De- tails of the tests are shown in part in Table I. Each cylinder should have contained four plants, but it will be noted that the stand was poor, due largely to the toxic action of the chemicals applied to the soil. Tasrte I.—Tests of tobacco plants grown in cylinders containing soil treated with acids and with alkalis at West Raleigh and Creedmoor, N. C., in 19123 and 1914. 1913.—Number of | 1914.—Number of lants. lants. Cylinder No. and P P location of test.! Soil tieatment. | Healthy. | Wilted. | Healthy.) Wilted. | 3 nares i 1A ANI NOP ee oe Acid potassium sulphate, 17 grams........| None. |-...---.-- None. | 3 11 and 13 (Creed- | Acid potassium sulphate, 85 grams...-.-.- 2 6s ee eee ee. moor). ap and A2S* 2S. oe Sulphuric acid, 1 ounce in 6 quarts of water 2 |oce Sc A AO. arte oie eae | Sulphurie acid, 2 ounces in 6 quarts of None? 12.22.5525 None. | 3 water. Spang ao nee. ACs an Nitric acid,? 1 ounce in 6 quarts of water Si) - ee ee None. 5 iPandiDise ees Lime carbonate, 600 grams.............--- del eae 1 4 4 (Creedmoor)...... |. Quicklime, 300:erams. =< 2...025-20 202. 3 | Lj 2 Se See 10 (Creedmoor), 12 | (Creedmoor). Potassium carbonate, 70 grams........--. 9 |. ek AIS eee ivand 240 Ee Zand. 122. eee Sodium carbonate, 300 grams..........-.-- Asal. . 2c S554 see ee peg: 1 Riv? eee py 7 Sodium silicate, 17 grams............-.--- 1 eee 2 2 1 Tests located at West Raleigh, except as otherwise stated. __ ; tod 2 Cylinder No. 38 received 4 ounces of nitric acid and cylinder No. 43 received no acid in 1914. In the cylinder tests with disinfectants, use was made of formalin, - potassium permanganate, chlorid of lime, atomic or superfine sul- phur, @-naphthol, Bordeaux mixture, and a number of proprietary preparations, mostly coal-tar products, many of them in varying rates of application. No decidedly beneficial results were obtained. Pid Marte CONTROL OF TOBACCO WILT IN THE FLUE-CURED DISTRICT. 9 During the four years, 1911 to 1914, inclusive, field plats at Creed- moor, N. C., consisting of single rows, were used in trials with disin- fectants. The usual fertilizing and cultural methods were followed alike on all plats. The results for 1911 and 1912 are shown in part in Table Il. The permanganate of potash and chlorid of lime were applied in the same quantities and in double the quantities recom- mended by Honing in Sumatra, the weaker solutions consisting of _ 125 grams of the chemical in 25 gallons of water. The solutions were poured into the holes in which the plants were to be set 24 hours before transplanting. ~ Taste I1.—Field experiments with tobacco plants, showing the effects of soil # disinfectants at Creedmoor, N. C., in 1911 and 1912. ;, 7 : Number of plants. P ¢ ercent- ¢ Year of ‘tests and chemicals used. Huuseiayel S04 ee Caplin, age of ‘ Wilted. | Healthy.| Wilt. 43 ‘Tests in 1911:(condition on Aug. 12): _ CUNB GN se Se BE SRE 2 con SR SI eS Sees Fe a eae ge es yn ae Seer 3 1 66.8 a Potassium spermanganate........----- Weak solution, 2 quarts per 39 4 90.7 es i Oe 29 2 93.5 i Chioridco Mime... ee Dials solution, 2 quarts per 27 3 90 bak xy rill. = CMOS oi 5 AS As Se i a ee eRe NG mera ge che ea ty Ee eR 23 3 88.5 Ss Potassium permanganate SSD Deg Eee none solution, 2 quarts per 32 2 94.1 - ill. ie CUCL eos SSCS Sec ere aN a rr yen ee Beg 25 0 100 : Clnloniavonlinn Chee ore ee Strong solution, 2 quarts per 17 1 94.4 az ill. if ‘Tests in 1912 (condition on Aug. 5): we CNG = 5 35 Sets 2s Saye i el aie are en OI a a ne ae Re 5 3M TES = “ADYOVECGWOY | Ses = stein cn a aera gS sc ates 50 gallons per acre....-....-- 27 135 43.5 4 Cheeke-2 322 sain 2h Glare aS, MR ee ee Seana ge ae te Mee 38 17 69.1 F ECOTI OT os ic Set eae ce a ge 25 gallons per acre......-.... 39 22 63.9 re Gheckie etsy FE eS OR I a EN ETRY a te A RS 35 19 64.8 “NVI RNO ass ois wa se ge, A hc Re an 100 gallons per acre........-- 40 18 69 A OTe ici ceomenn eres lisa tek AE eR abe a ae BE AAP oe ed 40 12 76.9 ¢ (CHOC CIR Se ao SEBS ES SCCM GEN Set leet ees ee ieee eae ees 26 19 57.8 - Imes, with the use of formalin, sulphuric acid, naphthol, carbolic acid, Bordeaux mixture, atomic sulphur, lime sulphur, coal tar, pine _ tar, and several proprietary disinfectants. In these tests more than _ 2 score of germicides and other chemicals were applied in various - quantities and in various ways. Since the same plat was used each year, the cumulative effect of the chemicals was detrimental to the _ growth of the tobacco. Here, as in the cylinders, it was difficult te _ secure a good stand of plants. In general, there have been no con- sistent differences in the percentages of wilt in the treated and the _ untreated rows. The results are confirmatory of the cylinder tests - and do not promise success in wilt control through the use of chemi- _ cals. In 1915 certain materials supposed to contain radium, includ- ‘: / ing Banque du Radium, carnotite, and a radioactive earth, were tried in several differing oan at Creedmoor, but without any definite _ results. 94919°—Bull. Be2 17-2 9 In 1913 and 1914 the experiments were continued along the same 10 BULLETIN 562, U. S. DEPARTMENT OF AGRICULTURE. It should be added finally that in view of the theory entertained by some that lack of drainage or aeration in the soil is a cause of wilt, experiments were made on the effects of deep plowing and subsoiling, | but the results were entirely negative. Dynamiting the soil accord- ing to methods recommended was tried, with a view to destreying any hardpan or impervious layer beneath the topsoil, but no bene- — ficial action could be noted. CROP ROTATION AS A BASIS FOR THE CONTROL OF THE WILT. It has been seen that so far as known all species and varieties of | tobacco, both wild and cultivated, are readily destroyed by the wilt, — and it is well known that other plants belonging to the same family — are seriously attacked. Obviously none of these plants should be grown on tobacco land affected with wilt. The parasite, however, is | by no means limited to solanaceous plants, and is now known to | attack members of no less than nine distinct families of the higher plants, namely, (1) Solanacez (including tobacco, Irish potato, pepper, eggplant, jimson weed, etc.), (2) Leguminose (including the peanut), (3) Balsaminacez, (4) Composite (including the com- mon ragweed), (5) Euphorbiaces, (6) Pedaliacez, (7) Tropzolacez, (8) Urticacez, and (9) Verbenacez. It is probable that further search will show that still other plants are attacked by this organism. Outside of the Solanacez the peanut and the ordinary ragweed are of special importance in the flue-cured district. In parts of the dis- ; trict peanuts are an important money crop and the ragweed (Am- — Lrosia artemisiwefolia) is extremely common on tobacco lands throughout the district. Peanuts must be avoided and the ragweed kept down if rotation of crops is to be effective in controlling the wilt. CROP-ROTATION EXPERIMENTS AT CREEDMOOR, N. C. Beginning with 1911, experiments on the effectiveness of crop rota- _ tion for the control of tobacco wilt have been conducted on a tobaeco field near Creedmoor, N. C., on which tobacco was practically a total failure in 1910. The soil in this field is the Granville coarse sandy | loam and is rather uniform throughout except for a gall spot of | several square yards on the plat designated “F” in figure 1. The — plats slope away gently on either side of the turn row, which extends _ through the center of the field. The drainage is good on all plats | except for small areas on the southern edge of plat 1 and on the © northern edge of plat 4, and there is but little chance for surface © drainage from one plat to adjoining ones. In these experiments the rotation and cropping systems included nearly all of the more important crops adapted to the section, namely,. 4 YO ACRE YO ACE SACKEL LLAT ROTATION -LAT 2 POTETION FLAT FA v4 WHEAT ANO “— eee Senge BLE ites ia (COVTINCOKSLYY (COVTINCOKSL YD (COVTIMVCOESLYY) > WALAT BLVER ANDO < PIMED GRASSES , re UA-2 TOBACCO VYAIFILT TESTS s, j Ye ACRE ROTATION FLAT FP ROTATION FEAT 4 STHALO GPUS SES) (COVTINCGOKSL YD (COVTIVGESL Fe) LINE OF CYLINOERS Fic. 1.—Plan of the experiment field at Creedmoor, N. C., showing details of the crop- ping system on each plat. Plats B, C, D, 8, and F were planted to tobacco in 1916. _ tobacco, corn, cotton, peanuts, wheat, sweet potatoes, cowpeas, mixed clovers, and grasses. Two different types of cropping were fol- lowed. In the first type a single crop or group of crops was grown continuously on the same plat. Thus, corn was grown continuously - ona quarter-acre plat for five years, with crimson clover as a winter cover crop. In the same way, peanuts and sweet potatoes were each -. grown continuously on separate plats for five years, in each case ' with rye as a winter cover crop. Wheat, followed by cowpeas cut for hay, also was grown continuously on one plat. 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