/-\ \ '■! ' < ' f Ismi.-.I Mav I, 190* U.S. DEPARTMENT OF AGRICULTURE, BUREAU OF PLANT INDUSTRY Circular tfo. 7. B. r. G \U.> 'WAY, chief of Bureau. THE FIELD TREATMENT OF TOBACCO HOOT-HOT. I.V.MAN J. BRIGGS, Physicist in Charge of Physicai Laboratory. 3U99G— OS WASHINGTON : GOVERNMENT PRINTING OFFICE : 1908 l r\+s*r\ US DEPOSITORY BUREAU OF PLANT INDUSTRY. Pathologist and Physiologist, and Chief of Bureau , Beverly T. Galloway. Pathologist and Physiologist, and Assistant Chief of Bureau, Albert F. Woods. Laboratory of Plant Pathology, Erwin F. Smith, Pathologist in Charge. In 1 1 -i ligations of Diseases of Fruits, Merton B. Waitc, Pathologist in Charge. Laboratory of Forest Pathology, Haven Metealf, Pathologist in Charge. Truck Crop Diseases and Plant Disease Survey, William A. Orton, Pathologist in Charge. Plan/ Life History Investigations, Walter T. Swingle, Physiologist in Charge. Cotton Breeding Investigations, Archibald D. Shame] and Daniel N. Shoemaker, Physiologists in Charge. Tobacco Investigations, Archibald D. Shame], Wightman \Y. Garner, and Ernest H. Mathewson, in Charge. Corn Investigations, Charles P. Hartley, Physiologist in Charge. Alkali and Drought Resistant Plant Breeding Investigations, Thomas II. Kearney, Physiologist in Charge. Soil Bacteriology and Water Purification Investigations, Karl F. Kellerman, Physiologist in Charge. Bionomic Investigations of Tropical and Subtropical Plants, Orator F. Cook, Bionomist in Charge. Drug and Poisonous Plant Investigations and Tea Culture Investigations, Rodney H. True, Physiologist in Charge. Physical Laboratory, Lyman J. Briggs, Physicist in Charge. Crop Technology and Fiber Plant Investigations, Nathan A. Cobb, Crop Technologist in Charge. Taxonomic and Range Investigations, Frederick V. Coville, Botanist in Charge. Farm Management Investigations, William J. Spillman, Agriculturist in Charge. Grain Investigations, Mark Alfred Carleton, Cerealist in Charge. Arlington Experimental Farm, Lee C. Corbett, Horticulturist in Charge. Vegetable Testing Gardens, William W. Tracy, sr., Superintendent. Sugar-Beet Investigations, Charles O. Townsend, Pathologist in Chargi Western Agricultural Extension Investigations, Carl S. Scofield, Agriculturist in Charge. Dry-Land Agriculture Investigations, E. Charming Chilcott, Agriculturist in Charge. Pomological Collections, Gustavus B. Brackett, Pomologist in Charge. Field Investigations in Pomology, William A. Taylor and G. Harold Powell, Pomologists in Charge. • • menial Gardens and Grounds, Edward M. Byrnes. Superintendent. Fori ign Seed and Plant Introduction, David Fairchild, Agricultural Explorer in Charge. Forage Crop Investigations, Charles V. Piper, Agrostologist in Charge. Seed Laboratory, Edgar Brown, Botanist in Charge. Grain Standardization, John D. Shanahan, Expert in Charge. Subtropical Laboratory and Gardi n, Miami, Fla., Ernst A. Bessey, Pathologist in Charge. Plant Introduction Garden, Chico Cal., August Mayer, Expert in Charge. South Tuns Garden, Brownsvilh 'fix.. Edward C. Green, Pomologist in Charge Farmers' Coopt rative Demonstration Work. Seaman A. Knapp, Special Agent iu Ch Seed Distribution (Directed by Chief of Bureau), Lisle Morrison, Assistant in General Charge. /./ or, .1. !■'.. Rockwell. Chit Clerk, James E Jones. [Circ. 7. | 2 CON T i: NTS Page. Nature of root-rol 5 Field treatment of root-rot.... 5 Occurrence of root-rol 6 Field experiments showing the bad effects of alkaline commercial fertilizers c.n root-rol soils 6 i rreenhouse experiments with alkaline fertilizers 7 Summarj [Circ.7.] 3 Digitized by the Internet Archive in 2013 http://archive.org/details/fieldtrOOunit B. P. I.— 373. THE FIELD TREATMENT OF TOBACCO ROOT- ROT. NATURE OF ROOT-ROT. During the past few years a disease known as root-rol has made its appearance in the tobacco fields in some districts of Kentucky, Connecticut, Ohio, and Wisconsin. This disease is now generally recognized to be due to a soil fungus {Thielavia basicola), which attacks the feeding roots of the tobacco as fast as they arc thrown out. The root-rol generally makes its first appearance in the field in spots, particularly low spots, and may later develop throughout the field. The most striking feature is the failure of the plants to make a proper growth. The diseased plants are often only 8 or 10 inches high when healthy plants set at the same time are ready to he cut. These small plants will he found to have onl\ a small hall of stubby roots, and the fungus can he seen on the blackened or brownish ends of the roots, which in the active stages of the disease have a rotted appearance. Root-rol has already been successfully checked in the seed-bed by Selby 6 with the use of formalin, and by Shamel'' through sterilization by steam. Nether of these methods can he considered practicable for treating the disease in the Held. In experiments made last year l>\ \Y. W. Gilbert and the writer, a formalin solution applied to a one-tenth acre plot of diseased land at the rati' of .".nil pounds of formalin per acre'' gave somewhat increased yields, hut not suffi- cient to justifj the expense involved. FIELD TREATMENT OF ROOT-ROT. The objeel of this circular is to give briefly the preliminary results of the writer's efforts to overcome the attacks of this fungus on the tobacco in the field by the proper use of fertilizers, with the hope Sei • by Selby, of the Ohio Agricultural Experiment Station, and by Clinton, of the Connecticut Agricultural Experiment Station. Mr. \V. W. Gilbert, of the Department of Agriculture, I as a bulletin on this subjeel in preparation. ^Circular No. 59, <>hi'> Agricultural Experiment Station, c Bulletin No 91, Bureau of Plant Industr Department of Agricultun LSOl i ins would represent a cost of about $60 per acre for the formalin alone. besides ibor. [Clrc7.] b FIELD TREATMENT OF TOBACCO ROOT-ROT. that the suggestions offered can be utilized this season by tobacco growers who have fields affected with this disease. The results of the. writer's investigations thus far indicate that the tobacco is much more severely injured by the fungus on fields where the soil has been made alkaline by the long-continued use of large amounts of lime, ashes, and fertilizers containing carbonate of potash. The remedy for diseased soils appears, then, to consist in avoiding the use of lime and in applying the necessary potash in the form of the sulphate of potash, which is a neutral salt ; and. if the field is badly diseased, in applying the phosphoric acid in the form of acid phos- phate in order to help neutralize the alkalinity of the soil. The above view as to the cause of the development of the disease in some of the tobacco fields of Connecticut is in harmony with field observations, as will appear in the following pages. OCCURRENCE OF ROOT-ROT. The fungus causing this disease is one commonly found in leaf mold and decaying organic matter, and therefore may reasonably be expected in any new land. The fact that the disease does not occur on tobacco fields until they have been in tobacco for several years indicates that the fungus may be present in the soil without attacking the tobacco. If we grant this point, then some condition which favors the development of the fungus on the tobacco roots must develop in the soil after several crops of tobacco have been grown. Root-rot in the Connecticut Valley is especially prevalent in fields on which unusually large quantities of fertilizers have been used. The development of the disease is not. however, due to too high a per- centage of soluble salts in the soil. This point was tested both in the greenhouse and in the field, and it was found that the growth of tobacco upon diseased soils was 1 tetter when a liberal quantity of neutral fertilizers was used than when smaller amounts were employed. If the root system of the tobacco is greatly reduced by the root-rot, the plants that are fertilized liberally and thus have a large amount of available plant food immediately at hand will make the best growth. Heavy fertilizing will not overcome the effects of the root- rot, however, and if alkaline fertilizers are used the growth will actu- ally be decreased, as the following experiments show: FIELD EXPERIMENTS SHOWING THE BAD EFFECTS OF ALKALINE COMMERCIAL FERTILIZERS ON ROOT-ROT SOILS. During the season of 1907 a series of fertilizer experiments were tried on two diseased fields in the Connecticut \ alley. These tests were confined mainly to fertilizers which have been extensively used in tobacco growing in Connecticut. No acid ^alt^ or ready-mixed [Circ. 7.J FIELD I IM \ I M I N I '" rOBACCO RO( ' I i 7 fertilizers were used. While none of the fertilized plots on the badly diseased fields gave yields equal to those obtained from adjacenl lie It Is free from disease, large differences in yield were obtained from the fertilized plots. In .-ill cases ii was found thai the plots on which carbonate of potash was used gave the smallest plants and the lowest yields. The use of lime with the carbonate of potash still further diminished the yield. The use of carbonate of potash and lime with cotton-seed meal and ground fish gave a yield of bu< 900 pounds per acre. This yield was 200 pounds less to the acre than when no fer- tilizer was used and was only a little more than half the yield obtained from soi f the other plots. These results indicate thai the alkaline condition of the soil resulting from the use of carbonate of potash and lime favored the development of the root-rot. GREENHOUSE EXPERIMENTS WITH ALKALINE FERTILIZERS. The ell'ert of alkaline fertilizers was tested further in a series of greenhouSe experiments made with a diseased soil from Connecti- cut. All the pots were fertilized uniformly with cotton-seed meal. To some of the pots one-half per cent of air-slaked lime was also added. This cut down the weighl of tobacco to nearly one-half (53 per cent |. Adding 2 per cent of lime decreased the weight to :;.") per cent of thai of the check plots. In soils free from root-rot. the use of 1 per cent of lime gave a better growth of tobacco than when no lime was used. This shows that the lime does not injure the tobacco directly. The application of land plaster to the dis- eased -oil iii amounts varying from one-half of 1 per cent to 2 pel- cent hail no had effects and even slightly increased the growth of tobacco. When lime was used with land plaster the weighl again decreased, averaging about in per cent of that of the checks. The use of carbonate of potash in addition to the cotton-seed meal decreased the weight of the tobacco to about so per cent of the checks in spite of the fact that additional plant food was added. The use of hydrochloric acid, on the other hand, increased the yield 1>\ about in percent, although this acid carries no plant food. The plants in the check pots in these experiments made a good growth and were not seriously injured by the root-rot. although the fungus could he seen on the roots. The root systems of the plants in all the pots to which lime or carbonate of potash was added were badly diseased. The roots of the plants grown in the soil in ■ land plaster was used showed some disease, about like that of the check pots. The roots of the plants grown in the acid-treated soil were per- fectly clean and white, and entirely free from the fungus. The soil used was originally from a badly diseased field. For a year prior to these experiments it was used for grow ing tobacco in shallow greenhouse beds provided with u r <>" = o> = 00 iO