548 EXPERIMENT STATION RECOED. 



decided advantage in maintaining an excess of lime upon the foliage, but this 

 was best accomplished by subsequent applications and not by increasing the 

 amount in the original mixture. 



Two forms of leaf injury, the brown spotting and yellowing, are common 

 accompaniments of spraying. The brown spotting is the more common injury, 

 but not all of this is due to spraying, as similar effects are caused by frosts, 

 winds, fungi, etc. Yellowing, when it appears in an epidemic form, is the more 

 serious of the 2 diseases as the affected leaves are entirely destroyed. The 

 causes of yellowing of apple leaves are obscure, but from observations extending 

 over 5 seasons there appears to be no direct positive connection between spray- 

 ing with well-made Bordeaux mixture and the yellowing of leaves. They do 

 show, however, that improperly made mixtures may cause leaf yellowing, and 

 similar results are obtained with simple solutions of copper sulphate. Much of 

 the injury following spraying is attributed to abrasions of the epidermis made 

 by insects and to infection by fungi preceding spraying. 



Studies were made of the agencies through which copper deposited on the 

 leaves becomes soluble and the manner in which the toxic action is communi- 

 cated to the cell protoplasm. Laboratory experiments showed that the copper 

 of Bordeaux mixture remained insoluble for long periods, but field experiments 

 showed conclusively that under orchard conditions copper in small quantity 

 becomes soluble very soon after deposition, and continues to appear as long as 

 any of the mixture remains upon the leaves. The presence of lime in excess 

 does not prevent solution of the copper. There was no evidence obtained to 

 support the claim that solutions of copper occur through the agency of ger- 

 minating spores nor through secretions from the leaf surfaces. 



Experiments with solutions of copper sulphate showed that the apple scab 

 fungus was quite resistant, the spores being slightly retarded in germination in 

 solutions of 1 : 100,000, while a concentration of about 1 : 10,000 was necessary 

 to prevent germination entirely. In this stronger solution some of the common 

 molds grew quite readily. 



The healthy bark of apple trees was found to be impermeable to Bordeaux 

 mixture and to solutions of copper sulphate but copper sulphate is readily 

 absorbed through wounds and promptly kills the leaves, which then become 

 brown. Copper sulphate solutions were injected through roots and through 

 holes in the trunks of trees, and uniformly resulted in browning of the leaves. 

 The time required to give evidence of the injury varied with the strength of the 

 solution and rate of transpiration, but it is usually short, varying from 25 

 minutes to a few hours. 



The importance of rain and dew as agents causing spotting of foliage follow- 

 ing the application of Bordeaux mixture was investigated, 2 trees being sprayed, 

 after which one was protected from rain and dew and the other left exposed. 

 This experiment was repeated during 3 seasons, and in each year the exposed 

 tree was more or less injui-ed by brown spots while the trees protected from 

 rain remained free from injury. Several other experiments have shown that 

 rain tended to promote injury to foliage upon sprayed trees. 



Investigations with milk of lime and copper sulphate solution showed that it 

 was the copper in solution that was the active agent responsible for the burning 

 of the foliage. From comparisons between leaves sprayed with Bordeaux mix- 

 ture and milk of lime, with Bordeaux mixture only, and with milk of lime only 

 it would seem that the leaves on which the lime was used were distinctly larger 

 than those not receiving it, and this suggests a stimulating action on the part 

 of lime. Bordeaux mixture was found to have a decided influence upon the 

 color of the leaves. When so coated apple leaves assumed a very dark green 

 color that was retained even after the coating was almost entirely washed away, 



