THE DAMPING-OFF OF TOBACCO AND ITS CONTROL IN PUERTO RICO

Abstract

1. Damping-off of tobacco is a very severe disease in Pu erto Rico. 2. The disease is caused by Pythium debaryanum and Phytophthora Parasitica var. nicotianae. 3. The agents of transportation of the fungus are water currents, laborers, animals, burrowing insects, etc. 4. Leaves are infected by zoospores of Phy. Parasitica var. nicotianae but apparently not by those of P. debaryanum. 5. Environmental conditions are important factors influencing the spread and severity of the disease. The disease seems to be equally severe during all seasons provided the proper moisture relations are maintained. Organic manures seem to influence favorably the incidence of the disease. The disease is severe on thickly-sowed beds. 6. Control of damping-dff of tobacco is today one of the most serious problems with Puerto Rico tobacco growers. 7. When the disease appears in small areas only, it may be checked by drenching these with a 1-30 formaldehyde solution. 8. Soil disinfestation by means of steam or with formaldehyde does not seem to be practicable under Puerto Rican conditions. 9. Phy. Parasitica var. nicotianae is probably slightly less susceptible to the sterilizing action of formaldehyde than P. debaryanum. 10. Mercury compounds have been found injurious to tobacco seedlings, and ineffectiYe against the clamping-off pathogenes. 11. In preliminary trials two applications of Corona Copper carbonate of four grams per square foot, before seed sowing, and at the same rate a week after germination, were fairly effective. Two applications of copper carbonate in the field did not give effective control probably due to the heavy rains and to overcrowding of the seedlings. Two late applications of copper carbonate on heavily infected beds were unsuccessful. Two 4-gram applications of copper carbonate resulted in good control of the damping-off of tomato, pepper, and eggplant. 12. Copper stereate, in two applications of 4 grams each, seemed to control P. debaryanum but did not have any effect on Phy. Parasitica var. nicotianae. 13. Bayer dust and Uspulun were injurious when applied to the foliage and proved to be ineffective in the control of the disease. 14. Copper sulfate solutions (4 and 5 pounds to 50 gallons) applied at the rate of 1/2 gallon per square foot before sowing the seed were ineffective. 15. Effectiveness of copper fluosilicate is doubtful. 16. Acetic acid does not control the disease under conditions of high infection. 17. Two applications of 4-4-50 and 5-5-50 Bordeaux mixture at the rate of 1/2 gallon per square foot, one before sowing the seed and the other a week after germination, were effective in controlling damping-off. The treatment was not very successful when applied to beds in the field in which the disease had made its appearance. 18. Injury to seedlings resulted when copper carbonate was applied to a tobacco seed-bed on the site of an old bed. It was proved by experiment that the injury was not clue to dryness. Soil reaction appears to have little to do as a direct cause of the injurious action. No injurious action of formaldehyde or acetic acid was found under similar conditions. Charcoal was not effective in preventing injury from the copper compounds. Recovery from injury resulted in one case when a sodium nitrate solution was applied. It is suggested that the injurious action is connected with nitrification which would be hindered by the lasting effect of the copper treatments. 19. Continuous cultivation of infested soils for periods of six to twelve months does not eradicate the disease.