-4- 



yoars of laboratory tests and field experiments showed the effectiveness of 

 certain chemicals in killing or preventing the discharge of ascOBpores of 

 the scab fungus* 



"Nitrogen fertilizers, such as nitrate of soda tmd sulfate of 

 oinnonia used at 12 per cent concentration, were effective, but the 500 to 600 

 pounds required per acre for effective coverage increased the nitrogen supply 

 available to the trees beyond the optimum amount for best fruit quality, 



"Elgetol used at 2 quarts to 100 gallons reduced the primary inoculum 

 more than 95 per cent when carefully applied and resulted in improved scab 

 control. The ground treatments v:ere most effective in years of excessive rain- 

 fall, like 1943 acd 1945, and reduced the anwunt of fruit infection on trees 

 receiving a vottublo sulfur program from 20 per cent to 2 per cent." As a 

 concluding statement Dr« Pal:nitcr says "No foliage fungicide sprays should bo 

 omitted because of the ground application. It is an extra application to 

 give extra protection in scabby orchards," (The above publication is Bulletin 

 No, 714,) 



DEVELOPMENT OF ORGAI^IIC FUNGICIDES , 



In order t^ understand present day developnients in plrnt post control, 

 J. G, Horsfall of the Connecticut Agricultural Experiment Station says, "The 

 farmer must brush up on his chemistry." In a recent issue of the AIF News 

 he gives us a little insight into the procedure involved in discovering and 

 testing jrganic fiHigicidos, Foll'ov^ing is a quotation from his article; "The 

 first step in developing a new fungicide is the *Edisonirji approach; try every- 

 thing once,* We at Connecticut have tested some 6000 oompounds that way. It 

 is slow. It is laborious. It is not very productive, 



"Having discovered a fev;^ possibilities, one then examines their 

 chemical structure. Referring to his college chemistry, he vdll remember 

 that every chemical is built up if parts v.'hich fit together in a certain v;ay. 

 The chemist can draw a picture of a chemical. This is called a structural 

 formula. If thej^ sec that the structural formula for a nevf compound resembles 

 that for a known fungicide, they can be fairly certain that the new compound 

 will also be a fungicide, 



"Automobiles are built of wood, iron, copper and some other things. 

 So are houses and factories,. An aut'Snobile is a car because these ingredients 

 are put together in a certain fashion; a house differs chiefly in that the 

 materials are put together differently. Hence a fiingicide differs from a 

 foodstuff mostly because the ingredients are tied together differently, and 

 each can bo recognized because of that fact, 



"in our laboratories wo pass a novr chemical through a series of 

 screening tests. First v/o see if it vail kill a fungus in tho laboratory." "■ We 

 then find whether it will kill at a concentration economical enough to com- 

 pote with established materials. Then we expose a sprayed surface to artificial 

 rain rnd sun. If it still kills the fungus after this weathering, it is ready 



