116 
hardly determine 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 applications 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. Different insects require different strengths, 
and plants 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 superiority of the emulsions of milk or soap and kerosene. 
1. NOTES ON 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 application 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, pine, 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 water, and (4) 14 parts of water, or the emulsion 
at i, ro, and f- b 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 
