No. 6. DEPARTMENT OF AGRICULTURE. 507 



Large spots may be left bare and exposed to attack, and injury may 

 be caused by excessive accumulation in a few spots. 



Only a pump capable of maintaining a high pressure should be 

 used, and for this class of work the finer nozzles are called for. The 

 liquid should be kept issuing as a fine mist — so fine that it floats in 

 the air as steam or smoke. This is impossible under a low pressure, 

 for the higher the pressure the finer will be the mist, other things be- 

 ing equal. The pressure should always, therefore, be kept at its 

 maximum, if possible between fifty and sixty pounds, never below 

 forty. With the liquid issuing as a fine mist, the nozzle should be 

 held some little distance away from the tree and the mist allowed to 

 lloat in and condense itself upon the fruit and leaves in fine globules, 

 thus completely bedewing the surfaces. 



Hence the importance of the injunctions: " Use only a fine nozzle; 

 use pressure enough to keep the liquid issuing as a fine inist^ and spray 

 only until the fruit and lea/ves are completely hedewed.'''' 



Mixtures Consisting of Simple Solutions. 



Mixtures of the second class, or diluted solutions, are somewhat 

 easier to handle, in that the problem of agitation is absent. But 

 they have to be considered from two standpoints and must be handled 

 differently, depending upon whether they are used as insecticides or 

 as fungicides, or whether for internal or external fungi. If used 

 as a preventive against one of the internal fungi, then all the precau- 

 tious regarding the maintenance of a fine mist upon the fruit must 

 be observed. Otherwise, the two evils mentioned above — the leav- 

 ing of exposed spots and the injury from excessive accumulation in 

 spots — will result. Plate V has already been cited as an example 

 of damage from the latter cause. If, on the other hand, the solution 

 is used against the sucking insects or external fungi, and therefore 

 intended to destroy by contact, a different mode of application is 

 called for. In these cases a coarser nozzle, throwing a more or less 

 direct stream is desirable. The effectiveness of the spray is often 

 increased by having it strike with some force. Here the rules men- 

 tioned above, regarding the maintenance of a fine mist, do not apply. 

 Every part of the tree should be thoroughly wetted so as to have the 

 spray come in contact with every insect and fungus spot. In this 

 case the spray has usually done its work as soon as it strikes. It is 

 not important, then, to have it remain on the trees; in fact, the re- 

 verse is often desirable. Of course, when strong solutions are used, 

 there is danger of injury from the accumulation by evaporation at 

 the lower edges of the leaves, or if the solution is allowed to run 

 down the trunks and thus saturate the ground around the root 



