382 INSECTS AFFECTING VEGETATION 



not reveal impurities, it will serve to indicate the proper dilution 

 in a regularly prepared mixture. The hydrometer is a glass instru- 

 ment, something like a thermometer in shape. In testing a liquid 

 the hydrometer is placed in it bulb down, and the reading is made 

 at the surface of the liquid in which it is supported. The instru- 

 ments are made in two scales, the specific gravity and the Beaume. 

 Both may be placed on the same instrument. Readings on the 

 Beaume scale are given in degrees, while the reading on the specific 

 gravity is given in decimals. The Beaume scale is easier to read and, 

 while more difficult to estimate from, in this case will serve with the 

 aid of the table given below. Hydrometers can be secured for about 

 $1.25 from Arthur H. Thomas, of Philadelphia, Pennsylvania; 

 Eimer & Amend, of New York City, and other dealers in such 

 apparatus. In securing an instrument the range on Beaume scale 

 should be to 36 and 1.000 to 1.35 on the specific gravity scale. 



TABLE FOR DILUTING CONCENTRATED SOLUTIONS. 



Density Beaume Density Specific For San Jose Scale Dilute 

 Scale. Gravity Scale. With Water At These Rates. 



35 1.3181 1 to 9 



34 1.3063 . 1 to 8V 2 



33 1.2946 1 to 8 



32 1.2831 1 to 7% 



31 1.2719 1 to 7i/ 2 



30 1.2608 1 to 7 



29 1.2500 1 to 6% 



28 1.2393 1 to 6y 2 



27 1.2288 1 to 6 



26 1.2184 1 to 5% 



(Bui. 148, Md. Agr. Exp. Sta.) 



Range of Usefulness. This wash is distinctively the remedy 

 for the San Jose scale and is particularly effective in applications to 

 the smooth-barked fruit trees such as peach, pear, and plum. In 

 the case of the apple the terminal twigs are often covered with a 

 fuzzy growth, more pronounced in some varieties than others, which 

 prevents the wash from properly coating the bark. The young from 

 scale insects which escape destruction at such points, for the reason 

 indicated or from imperfect spraying, are driven out onto the new 

 growth, or, in the case of fruit spurs, onto the fruit, so that a tree 

 on which the scale has been pretty thoroughly exterminated may 

 nevertheless present badly spotted fruit. In such cases the additional 

 use of some one of the oil sprays may be necessary. This wash is of 

 equal value against closely allied scale pests, such as Forbes's scale 

 and the West Indian peach scale, and late sprayings are quite ef- 

 fective against the scurfy scale and the oyster-shell scale. 



The spring application, just before the buds swell, has been 

 demonstrated by Prof. J. M. Aldrich to kill most of the eggs of the 

 apple aphis, and Fred Johnson, of this Bureau, has found that it is 

 equally effective in destroying the eggs of the pear-tree Psylla. It 

 is useful against other pests which hibernate about the leaf buds of 

 fruit trees, as, for example, the pear-leaf blister-mite and the silvery 



