October, '19] 



WOGLUM: DOSAGE SCHEDULE 



359 



The following experiment, which presents results typical of field 

 experience with medium sized trees badly infested with purple scale, 

 shows the comparative effectiveness of 98 per cent liquid hydrocyanic 

 acid and pot-generated gas against this insect at temperatures between 

 65° and 70° degrees F., when the pump delivered 16.56 cubic centi- 

 meters of liquid hydrocyanic acid as corresponding to each ounce of 

 cyanid and consequently delivered an amount of gas approximately 

 21 per cent less than that evolved from the pots, as previously 

 explained. 



Table I. Comparative Scale-Kill at Temperatukes 65° to 70° F. Between 98 Per Cent Liquid 

 Hydrocyanic Acid and Pot-Generated Gas. The Liquid Hydrocyanic Acid was Used at 

 THE Rate of 16.56 Cubic Centimeters as Equivalent to 1 Ounce Sodium Cy.vnid and on 

 THIS Basis the Same Dosage Schedule was Followed. 



An examination of this table shows the results with liquid hydro- 

 cyanic acid at this strength to be better at the bottom of the trees 

 than for the pot-generated gas, although toward the top of the trees 

 the reverse is true, a decidedly greater percentage of scale being killed 

 at this latter part in the case of the pot-fumigated trees. The total 

 result for the whole tree is slightly favorable to the pot treatment and 

 shows that, under the stated conditions, 16.56 cubic centimeters of 

 liquid hydrocyanic acid is insufficient to produce results equivalent 

 to 1 ounce of sodium cyanid in pot-generation. 



Other experiments with medium-sized to large trees were performed 

 against the purple scale at the higher temperatures of fumigation, 

 using in some cases 21 to 22 cubic centimeters of liquid hydrocyanic 

 acid as equivalent to the ounce of sodium cyanid, and where this dos- 

 age rate was applied in connection with the same schedule followed 

 in securing the results presented in Table I the mortality average 

 above 99 per cent. Since the average mortality of purple scale under 

 certain conditions was shown to be 94.6 per cent with 16.56 cubic cen- 

 timeters of high purity liquid hydrocyanic acid as equivalent to the 

 ounce of sodium cyanid, and other experiments against this insect 

 conducted under practically identical conditions with 21 to 22 cubic 



