2 MISC. PUBLICATI0:N- 16 8, U.S. DEPT. OF AGKICULTURE 



INTRODUCTION 



The word " disease " as used in this publication means any depar- 

 ture from the normal or usual condition of fruits that renders them 

 inedible or otherwise undesirable for the use of the consumer. Under 

 such a definition, internal breakdown of apples is as truly a disease 

 as blue-mold rot or scab. Internal breakdown, however, is produced 

 by environmental factors and the life processes of the fruit itself, 

 whereas scab and blue-mold rot are produced by the action of cer- 

 tain fungi which, in this publication, are referred to as the causes 

 of the respective diseases. 



The relation of various factors, physical and otherwise, to the 

 occurrence and development of the diseases of pome fruits are set 

 forth in more or less detail in the pages that follow. It is important 

 at this point to mention some of the more important facts concerning 

 fungi (molds) that need to be kept in mind in dealing with fungous 

 diseases of fruits. 



An important characteristic of most fungi is that they produce 

 minute bodies called spores, which are a means, usually the most im- 

 portant one, by which fungi reproduce themselves and are distrib- 

 uted. Being small and light, they are easily carried by wind, rain, 

 insects, and other agencies. Spores of several kinds of fungi that 

 attack fruits are quite common on the soil surface and on all plant 

 parts aboveground. They are most important on the surface of 

 fruits, because under favorable conditions they produce fine fungous 

 threads that enter the fruit and cause disease. When fruits lie near 

 one another or touch, or when they touch the ground, the disease may- 

 be spread merely by the growth of these threads, especially of fungi 

 that make a luxuriant growth extending in all directions from the 

 spot attacked. In any case, the original source of the threads was a 

 spore or spores. 



Without spores, most fungous diseases of fruits are not likely to 

 occur to a degree great enough to be commercially significant. But 

 the spores lie inert unless moisture is present to make them germi- 

 nate. The fungus threads they produce may or may not be able to 

 enter the fruit through the unbroken skin, but are always more likely 

 to enter if skin breaks are present. Temperature, too, has a direct 

 influence on spore germination and the growth of the threads; and 

 although when fruits are ripening in the field the temperature rarely 

 goes low enough there to check either of these processes completely, 

 it may reach a point (45° to 50° F.) where it checks them so much 

 that little infection occurs; or it may go high enough (80° to 90°) so 

 that both processes are accelerated and infection occurs wherever the 

 fungus can enter. Factors that favor the development of each dis- 

 ease in transit, in storage, or on the market are discussed under the 

 appropriate headings in the body of this publication. 



Certain general suggestions can be made, however, that are worth 

 the consideration of every person concerned in the growing and 

 marketing of fruit. All fruits should be handled carefully through 

 all stages of the harvesting and marketing processes. Apples or 

 pears are not visibly ruined, like eggs, when they are dropped a foot 



