12 



wet or varnished over in a much shorter space of time than when a 

 finer spray is used, and all of the operators that I have conversed with 

 on this subject were unanimous in their statements that the time thus 

 saved much more than compensated for the somewhat larger quantity 

 of the preparation that was required when the coarse spray was em- 

 ployed as compared with a finer spray. The evidence, therefore, 

 appears to be decidedly in favor of a rather coarse spray. 



But whatever may be the character of the preparation used, or the 

 nature of the spraying nozzle employed, the success of the operation 

 will depend very largely upon the thoroughness with which the prepa- 

 ration has been applied. In the case of small trees it is comparatively 

 easy to wet every part of them, but when the trees are 20 feet or more 

 in height and have not been properly pruned it is not only difficult but 

 quite impossible to wet every portion of them ; and, unfortunately, the 

 tendency is to use as little of the preparation upon the tree as is abso- 

 lutely necessary. On tall trees the operation of spraying is made more 

 effectual by the use of tall ladders, so that the various parts of the trees 

 can be sprayed from above as well as from below. 



It is well known among those who have had any experience in trying 

 to destroy the Eed Scale with sprays of any kind that the scale insects 

 which are located upon the fruit are less affected by the different 

 liquid preparations than those located upon the leaves or bark. 

 The reason for this appears to lie in the fact that those located upon 

 the fruit, having an abundance of food always within easy reach, are 

 more healthy and vigorous than those located upon the other parts of 

 the tree, and consequently are better prepared for resisting the destruc- 

 tive effects of the spray. That healthy, vigorous insects are capable of 

 resisting the effects of a destructive agency that has proved fatal to 

 their less vigorous comrades there can be no doubt. An instance of 

 this kind is given in my report to Professor Eiley for the year 1888, as 

 published in the Annual Eeport of this Department for that year. On 

 page 128, in speaking of the effects of arseniuretted hydrogen gas upon 

 the Fluted or Cottony-cushion Scale (Icerya purchasi, Maskell), the state- 

 ment is made that " Subsequent experiments made upon perfects 

 healthy trees and insects showed that when the gas was used strong 

 enough to have proved fatal to all of the Icerya on the neglected trees 

 it did not kill one-half of those on the vigorous trees.' 7 Owing to this 

 fact it would be advisable to refrain from irrigating and cultivating in- 

 fested orange trees for several weeks before spraying them, were it not 

 for the other fact that in the case of bearing trees such a course would 

 seriously interfere with their bearing qualities or operations. Unlike 

 deciduous fruit trees, our citrus trees do not take a rest of several months' 

 duration between the ripening of the fruit and the blossoming of the 

 trees for another crop ; only a few weeks at the most intervening between 

 these two periods in the case of orange trees, while on healthy bearing 

 lemon trees both blossoms and fruit are to be found at every season of 

 the vear. 



