119 



These experimeuts, of course, are too limited to be used for general 

 deductions, but tliey show in tlie first place the great difficulty of kill- 

 ing the particular scale experimented ujion, and also that peach trees, 

 in the dormant winter condition, can stand apiDlications to the trunk 

 and lower limbs of excessively strong mixtures, even pure kerosene 

 oil, with no great danger. The fact that the pure emulsion was more 

 prom])t in its effect than the pure oil is explained by the fact of the 

 emulsion being thicker and therefore longer in drying up, while the 

 oil, Avhicb was of good illuminating quality, evaporated very rapidly. 

 The use of applications as strong as the last two can hardly be recom- 

 mended except in unusual cases of injury, where the "kill-or-cure" 

 method is the only feasible one. Winter treatment, however, will be 

 of value in a good many cases, notably with plants having very thick 

 and copious leaf-growth, rendering it impossible to spray them thor 

 oughly during the summer, and with insects the life history of which, 

 and the nature of the plant they infest, make summer treatment imprac- 

 ticable or unadvisable. Winter treatment of deciduous trees has the 

 advantage also that it requires very much less liquid to wet a tree. 



Experience icith particular scale insects. — Reference has already been 

 made to winter treatment for the new peach scale, Diaspis lanatus. 

 Spring or summer treatment of this scale was very satisfactory in its 

 results. In the first place, this scale was very uniform at W^ashington 

 in the period of hatching, the first young appearing April 30 and prac- 

 tically all emerging during the first week in May. The standard kero- 

 sene-soap emulsion was applied on the afternoon of May 7, and an 

 examination the following morning showed that all the scales which 

 had escaped from beneath the mother scales had been killed. Most of 

 those beneath the scales were also destroyed, the general escape of 

 the larvte having loosened the old scales so that the insecticide pene- 

 trated beneath them. Following the application there was a very long 

 period during which no rain fell, giving the insecticide a favorable 

 opportunity to affect the plant, but no injury whatever resulted. The 

 young scale insects were destroyed in twenty-four hours, and after this 

 period rain would have been of advantage in freeing the plants from 

 further action of the oil. The application was not repeated, and on 

 the 22d of May a few living young were found beneath some masses of 

 old scales. The habit of the young of this species seems to be to aban- 

 don the old scale and seek a new location entirely free from the pro 

 tection of the mother scale; but in some few cases this had not been 

 done, and young protected under masses of old scales had escai)ed the 

 application. A few old scales were also observed at this date still liv- 

 ing, and without any signs of the formation of eggs in their ovaries. I 

 am of the opinion that these scales, which ultimately died before mid- 

 summer, weie nonfertilized females, and this condition accounts for 

 the prolongation of their existence. 



