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TWENTY-NINTH FRUIT-GROWERS' CONVENTION. 



characteristic blackening and scorching of leaves or "burning." In our 

 experiments this season the cause of every case of this trouble was 

 found to be some one or more of the above noted factors. This acute 

 damage can be seen plainly within a week after the application of the 

 spray, and a recognition of the accidental cause and an elimination of 

 it from subsequent operations will doubtless always prevent a repetition 

 of the trouble. 



The chronic damage to foliage is a rather more obscure and difficult 

 matter. It may be described as a chronic, cumulative arsenical poison- 

 ing of the cells of the leaves, causing them to ripen, turn yellow, and 

 the leaves to fall prematurely. Some of the orchards upon which our 

 experiments were conducted suffered very seriously from this trouble. 

 The locality is one in which poisoning is extremely liable to occur. 

 We trust that this damage may be prevented in future operations if 

 due caution is exercised. This is a point on which we intend to make 

 further studies the coming season. We know that this chronic poison- 

 ing of the foliage occurred only on those orchards where spraying was 

 done often and at short intervals of time. A study of the surrounding 

 conditions on these orchards seems to indicate that so far as the codling 

 worm is concerned as good control might have been obtained if the 

 number of sprajdngs had been fewer and the intervals between spray- 

 ings greater. Furthermore, it was noted that the orchards sprayed with 

 paris green suffered more from this chronic poisoning than was the 

 case where any other of the standard arsenicals was used. Quite 

 evidently there is necessity of careful observation in the orchards that 

 are liable to damage from burning to avoid excessive spraying. As 

 soon as the foliage shows distress in the slightest degree we have evi- 

 dence that the accumulated doses of arsenic have exceeded the necessary 

 amount for efficient protection against the codling-moth. Perhaps in 

 the regions most susceptible to chronic poisoning it will be necessary to 

 discard wholly the use of paris green and to substitute one of the less 

 dangerous arsenicals. 



Turning now from this question of possible damage to the foliage 

 which must be guarded against, we come to the consideration of control 

 obtained of the pest in question, the codling-moth. As for the effective- 

 ness of the different standard arsenicals used, there seems to be little 

 to choose between them. The paris green is not, generally speaking, 

 so satisfactory to work with as either the lead or lime arsenicals. These 

 latter are more flocculent, that is, they "stay up" better in the tank, 

 as it is expressed, than does the paris green, and a more even distribu- 

 tion of the poison is probable when they are used. While the results 

 obtained by us, when either the home-made or commercial lead arsenates 

 were used, were slightly less satisfactory than with the other arsenicals, 

 our experiments this season point to a possible great value in these 

 compounds of lead and arsenic. 



