508 ANNUAL REPORT OF THE Off. Doc. 



crowns. It is well, therefore to avoid waste when spraying in this 

 way, and to carry the opeiation just far enough to wet every part of 

 the trees or plants. 



Emulsions. 



The mixtures of this class are practically all used against sucking 

 insects; scales, plant lice, and the like. A large proportion of these 

 mixtures is also intended for winter use, when the trees are dormant, 

 and are, therefore, not subject to the same rules as those used when 

 the foliage is present. A more direct stream is desirable, for here, as 

 with the simple solutions used for a similar purpose, the effective- 

 ness of the spray is increased by having it strike with some force. A 

 good many of the insects of the sucking class are protected by a 

 Vv'oolly, hairy or waxy covering, which it is hardly possible to pene- 

 trate without projecting the spray against them. The writer has 

 sjjrayed the plum aphis with kerosene and water through an or- 

 dinary fine Vermorel nozzle without effect; while the same mixture 

 ]<nt on through a somewhat coarser nozzle as a direct stream proved 

 wholly effective. 



When kerosene and water or the crude oil and water are used the 

 no/zle must not be too coarse. The mixing of the oil and water is 

 accomplished at the nozzle. If the nozzle is too coarse, therefore, 

 the mixing will not be thorough. The aim in the use of this class 

 of mixtures is to secure a thin coating of oil over the tree — the 

 thinner the better. For this reason the spray miist reach and wet 

 every part. It is not necessary to maintain the separate globules 

 intact. Therefore, it is not so difficult to apply this class of sprays 

 properly. Excessive dripping must be avoided, and the mixture 

 of oil and water must not be allowed to run down the tree trunks, 

 or to accumulate in the crotches of branches. In the one case the 

 root crown may be injured; in the other the bark in the crotch may be 

 killed and thus allow the entrance of disease spores to the heart 

 wood. Spraying f*hould proceed from the top downward, holding 

 the nozzle in one place only long enough to wet that part, not until 

 the liquid begins to run down. 



