14 FUXGI AXD FUXGICIDES 



Hand Picking. — With diseases like the brown rot 

 of peaches and j^hims, plum pockets, etc., mnch may be 

 done in reducing injury by persistent hand-picking of 

 the affected parts, which, of course, should be burned 

 or buried deeply in the soil. 



Use of Non-infected Seed. — Xumerons fungous 

 diseases start from the seed. For instance, the potato 

 rot exists in seed potatoes, and so infects the new crop. 

 In such cases care should be taken to obtain seed not so 

 infected, or, when j^ossible, so to treat the seed that the 

 sj)ores are destroyed. 



Destruction of Alternating Forms. — As shown 

 on other pages, some of the rusts exist in two or more 

 forms on different host-j^lants. For instance, the apple 

 rust has one form that produces '^ cedar balls" on cedar 

 trees. The destruction of the latter will prevent the 

 development of the former. 



Use of Fungicides. — The most practicable way of 

 preventing the great majority of the fungous diseases of 

 cultivated crops is by the use of fungicides (a word 

 meaning, literally, killers of fungi). These are discussed 

 more fully under the following heading. The majority 

 of them are ai)2olied externally to plants by spraying or 

 dusting. In such cases they may act in either or both 

 of two ways : (1) By directly destroying any fungus 

 spores present at the time of application ; and (2) by 

 remainino- on the surface in a condition to destrov, either 

 before germination or during that process, any sjiores 

 that may light upon the j^lant thereafter. 



THE IMPORT AXT FUisGICTDES 



The followino- list includes the fun2:icides that have 

 proved of practical value up to the present time. It is a 

 list, however, that will probably be extended during the 

 next decade, as experiments are constantly progressing 

 to learn the fungicidal value of many other substances. 



