AGRICULTURAL EXPERIMENT STATION. 107 



it would be impossible to make so much as 5 per cent, of the 

 poison stay on them. There is not sufficient surface to retain a 

 larger amount. Supposing this proportion correct, however, and 

 that the trees are sprayed twice, if there are 1,200 fruits — about 

 three barrels — to the tree, the amount of poison per fruit would be 

 less that 3-1000 (.0029) grain. 



In our calculations we have not taken into account the fact that 

 the fruit is exposed to sunshine and rain for four months before it 

 is ready for use. On considering all phases of the question we 

 are led to the conclusion that there is no reason why fruit sprayed 

 as directed should be unwholesome when mature. 



6. Wlien to Spray. In planning the work for the season, it 

 was designed to learn, if possible, the best time to spray, as well as 

 the amount of poison necessary. Owing to pressure of other 

 work, however, the instructions left by the writer were not fully 

 carried out. 



The time when the first brood commences depredations, is not 

 fully determined by entomologists ; but it certainly extends over a 

 considerable period and varies with the season. Professor Gillette 

 has shown that in some seasons, at least, and with certain varie- 

 ties, the larvae may not hatch in considerable numbers for at 

 least a month after the blossoms fall.* It would seem unnecessary, 

 in such cases, to spray at once. With man} 7 varieties, however, 

 the calyx closes soon after the blossoms fall, and later applica- 

 tions of the poison will necessarily be more or less ineffectual. 



No doubt the fact that experimenters use different varieties, 

 causes much of the difference in opinion as to the proper time to 

 spray, and the value of the later applications. In case of the 

 Duchess, the spray will be just as effective a month after the 

 blossoms fall as at an earlier date. Hence, if the larvae do not 

 appear earlier, a single application at the later date will be just as 

 effectual as two or more applications, part of which are made as 

 soon as the fruit sets. With the Baldwin, however, the conditions 

 are different. About two weeks after the blossoms fall, the lobes 

 of the calyx close, and while the eggs may have been deposited, 

 the poison applied as a spray is shut out. 



It will be seen that it is unsafe to generalize from the results 

 obtained with either class of apples. It is hoped in our work of 

 next season we shall be able to secure valuable data on this point. 



* Bulletin 7, Iowa Experiment Station. 277. 



