4 H. H. Whetzel and S. E. A. McCallan 



Based on its function in any given case, a fungicide acts as a protectant, 

 a disinfestant, or a disinfectant. It functions as a protectant, when applied 

 to the suscept before inoculation, that is, before the inoculum has arrived 

 in the infection court (for example, in spraying apples for scab); as a dis- 

 infestant, when applied after inoculation but before infection, that is, after 

 arrival of the inoculum but before the pathogene has established itself in 

 the suscept (for example, in treating seed wheat for stinking smut) ; as a 

 disinfectant, only when applied after infection has taken place (for example, 

 in spraying plants already affected with powdery mildews). 



Fungicides that act to control the disease when they are applied after 

 the pathogene has become associated with the suscept (that is, after inocu- 

 lation or infection), are now commonly designated as disinfectants. We 

 can speak accurately of disinfection, however, only when the fungicide acts 

 on the pathogene after it has established pathogenic relations with the 

 suscept. When the toxic action of the fungicide is exerted on the path- 

 ogene while it is merely in physical association with the suscept, as in the 

 case of many seed-infesting pathogenes, it is more nearly precise to desig- 

 nate its action as disinfestation. 



One has to consider, moreover, in this connection the whole problem of 

 terminology in the matter of fungous infestation of the soil or other non- 

 living harborers of fungous pathogenes. The almost universally used 

 expressions, " diseased soil," " sick soil," " infected soil," " inoculated 

 soil," " soil inoculation," and the like, are inaccurate and unscientific in 

 the light of our present ideas and concepts of disease phenomena. Disease 

 is an injurious physiological process, a response on the part of the suscept 

 to pathogenic irritation. Even if one includes (as one usually does) in the 

 concept of disease, the chemical reactions of the dead tissues of timber to 

 the activities of decay-inducing fungi, one certainly has no similar relation- 

 ship in mind between phytopathogenic fungi and the soils in which they 

 arc present. Strictly speaking, infection is pathogenic irritation. Only 

 living things can be infected. Soil, therefore, cannot be infected, diction- 

 aries to the contrary notwithstanding; it may only be infested or contam- 

 inated. Obviously, since soil cannot be infected or diseased in any reason- 

 able sense of these words, it cannot be " inoculated." Only living things 

 that presumably possess the power to respond to pathogenic agents, can 

 be inoculated. One can contaminate or infest a soil with pathogenes; one 

 cannot inoculate it. The extensive use of " inoculate " to designate the 

 planting of organisms on culture media is equally faulty; " planting " or 

 " seeding " is better usage. 



It follows, therefore, that one may not logically speak of " disinfecting " 

 the soil, or of a " soil disinfectant." The terms disinfestant and disinfesta- 

 tion express more nearly accurately and specifically the concepts involved. 

 The writers advocate the use of the terms disinfect and disinfectant only in 



