116 



hardly deterniine this point, and ordinarily will not take the trouble 

 to do so. It is, therefore, important to be able to give him the exact 

 dates between which to make the application. Some species again dis- 

 close their young over a period of three or four weeks, rendering it 

 necessary to make several applicjations within this period. This is the 

 case with the San Jose scale, and holds generally, though perhaps not 

 covering quite so long a period, with most other common scale insects. 

 With some few of these the young appear almost at once, and for these 

 a single application is sufficient. An example of this is seen in the 

 new peach scale, Diaspis lanatus, which was described in a recent 

 number of Insect Life. Ditfereut insects require different strengths, 

 and i)lants at different seasons of the year will show considerable vari- 

 ation in the strength of insecticide which may be safely applied. The 

 effect of weather conditions, rains, hot, bright sunshine, etc., can only be 

 determined by actual experimentation. To get at these various points 

 requires very considerable field experience, by observers who are will- 

 ing to note, and capable of noting intelligently, and properly interpret- 

 ing, the reasons for any outcome. 



The following notes on insecticides cover, first, some experiences in 

 the use of old and standard mixtures, and, second, experiments with 

 little-tried and some new combinations. In the first series the notes 

 refer almost solely to the kerosene mixtures and resin washes and to 

 the use of these insecticides against scale insects. The old arsenicals 

 I have not discussed to any extent, as their use is much better under- 

 stood, and has not presented the difficulties that attend the use of the 

 various washes designed particularly for the scale insects and others of 

 similar feeding habits. Among these I am more than ever impressed 

 with the sui)eriority of the emulsions of milk or soap and kerosene. 



1. NOTES ox APPLICATIONS OF THE STANDARD INSECTICIDES. 



Effect on trees and foliage. — The necessity of using very strong 

 washes for most scale insects (much stronger than needed for unpro- 

 tected insects, such as plant lice, plant bugs, beetles, and larvae) makes 

 it important to determine just how strong the apphcation can be made 

 without injury to the plant. About the 1st of May, when the foliage 

 was in the vigor of its early growth, a number of plants — peach, Japan 

 quince, elm, ])ine, and strawberry — were treated with the following 

 strengths of kerosene and whale-oil soap emulsions, made after the 

 standard formula: Diluted (1) with 2 parts of water, (2) 4 parts of 

 water, (3) 9 parts of Avater, and (4) 14 parts of water, or the emulsion 

 at :^, i, n,, and ^\ strength. The application was very thorough, and 

 the limbs and twigs were thoroughly wetted by immersion In the 

 insecticide. The treatment was made on a very bright, warm day, in 

 the early afternoon. No rain occurred for four days, after which there 

 were heavy rains. No injury whatever developed in the case of the 

 pine, strawberry, and elm with any of the strengths used. With peach 



