TOMATO LEAF MOLD 15 



emulsion and Yi fluid ounce of copper ox>chloride per gallon are compatible and 

 nonstaining and are recommended in England when both red spider and leaf 

 mold are present (31, 36). 



Rippel (38, 39) asserted that the spores of the fungus possess extraordinary 

 resistance to the action of chemicals and require concentrations in excess of the 

 tolerance of the host to obtain control of the disease. It is asserted that a large 

 portion of the soluble poison is absorbed by the thick wall of the spore leaving 

 none to affect the plasm. Guba (17) demonstrated the toxicity of several chem- 

 icals to the spores of the tomato leaf mold fungus and indicated the limitations 

 to their merit in greenhouse culture. The practical difficulty of obtaining adequate 

 protection of the lower surfaces of the leaves where infection occurs and the inert- 

 ness to the fungus of dry chemical residues on the leaves under conditions which 

 otherwise favor spore germination are offered as fundamental reasons for the 

 inability to control the disease with ordinary spraying and dusting materials in 

 greenhouse culture. The necessity of frequent treatments during the critical 

 season and of using fungicides which are both inert to the plant and nonstaining 

 also impose serious limitations to the use of spraying and dusting materials for 

 combating the disease. Many reports show the value of Bordeaux (17) under 

 field growing conditions. The assertion that effective fungicides for controlling 

 leaf mold are lacking is inconsistent with the evidence (6, 9, 10, 11, 17, 19, 24, 

 41, 46, 47). 



ERADICATION OF THE FUNGUS BETWEEN PLANTINGS 



The disinfestation of the greenhouse interior to destroy fungous and insect 

 pests existing outside of the soil is an important sanitary practice which obviously 

 should contribute to the control of tomato leaf mold during the succeeding plant- 

 ing. Some disinfestation of the greenhouse interior after cleaning out the vines 

 may be accomplished by treating the soil with chemicals and confining the gases 

 for two or three days after the soil treatment. However, the destruction of pests 

 before cleaning out the finished vines which harbor them is preferable to prevent 

 a reinfestation from the discarded plant material outside. Several chemicals 

 have been used for this purpose but burning sulfur fumigation has received most 

 recognition because it is economical, practical, and lethal to both insects and 

 fungi. 



