April, ’20] 
DAVIS: GREEN JAPANESE BEETLE 
193 
(b) Soil Insecticide Operations. Soil insecticide tests using sodium 
cyanide as the insecticide begun by Mr. Goodwin in 1918 have been 
continued and the amounts and methods of application are now quite 
satisfactory, giving us a kill of 90 to 100 per cent. The equipment 
consists of 600-gallon tanks drawn by caterpillar tractors. The flow 
is by gravity through 3 inch pipe with f inch holes, 48 holes to a foot, 
and covers a strip feet wide, the flow being governed by a gate valve, 
which can be operated by the tractor driver. The rate of application 
which has been found quite effective is 165 pounds of granular sodium 
cyanide in 12,000 gallons of water per acre. The cost of the insecti¬ 
cides and labor necessary is approximately $56 per acre and is too 
expensive for general use, but for small areas and in the case of the 
green Japanese beetle for large areas where the grubs are abundant 
and where larger expenditures are permissible from the standpoint of 
controlling an insect occurring only in a comparatively small isolated 
locality. To determine the area of heavier grub infestation and the 
fields sufficiently infested to be cyanided, individual square yards in 
different parts of the field are examined. For this purpose a hazel or 
grub hoe with a thin blade is very useful. 
In cyaniding, Mr. Hadley, who had charge of the soil insecticide 
work this fall, found that three tanks and two tractors can work most 
economically. Two men drive the tractors while one remains at the 
filling station mixing cyanide and filling the extra tank. As one tank 
is emptied, it is hauled to the filling station and a filled tank taken out. 
In this way the two tractors and three men lose no time and the three 
tanks are capable of covering three acres per day, that is, each tank 
treats one acre per day applying in this time 12,000 gallons of liquid. 
The water used in this work must be obtained largely from creeks 
nearby, and is pumped by a centrifugal pump. Along roadways 
where it is not possible or desirable to block the road two stand pipes 
are used, but in a field where it is possible to haul the tanks on either 
side of a pipe only one water pipe is needed. 
The important points in applying cyanide are that the holes be suf¬ 
ficiently small to allow a uniform screen of water which will quickly 
and thoroughly penetrate the soil, that the grubs be within two inches 
of the surface and that the temperature of the soil be above 48° F. 
At the rate of 165 pounds of cyanide per acre the grass is burned, but 
is not destroyed except in spots where the liquid stands. At the rate 
of 110 pounds per acre the burning is comparatively little and while 
this strength gives a kill practically equal to the greater strength when 
conditions are optimum our observations indicate that 165 pounds gives 
an effective kill over more variable and less favorable conditions. 
4. Experiments and Investigations. Up to the present time the 
