THE MONTHLY BULLETIN. 395 



The ro,.t :\|ihiils suffer but little from natural enemies, a single Scymnus larva 

 being the only predator observed by the writer, while no parasitic enemies were 

 ever enconntered. The young larva; are very flat and without doubt penetrate the 

 soil throughout the root system. Also the aphids can live under extremely moist 

 conditions, provided the roots are not decayed. 



Control. 



Trees may be safely disinfected in airtight houses or boxes with hydrocyanic acid 

 gas. Three quarters of an ounce sodium cyanide or one ounce potassium cyanide 

 should be used for each 100 cubic feet of air space within the fumigatorium and 

 fumigation should last 45 minutes. For orchard treatment a contact insecticide 

 that will dissolve the wax secretions is desirable. This should be applied in a 

 shallow basin around the trunk. Experiments with miseible oil, kerosene oil emul- 

 sion and distillate oil emulsion proved successful. Miseible oil was used at 

 strengths of 1/12. 1/20, 1/2S, and 1/40. The two first proved successful and the 

 third partially so. At strengths of 1/12 and 1/20 occasional burning of surface 

 roots resulted, but the main roots escaped injury and for three months after treat- 

 ment the infestations remained very small. Kerosene oil emulsion was tested at 

 tine.' strensths. 10. 15 and 20 per cent. Three months after the applications all 

 the treated trees with one exception were free from aphis to a depth of one foot, 

 the exception consisting of one small colony on a tree treated with 15 per cent 

 emulsion. Three check trees were heavily infested. At 15 per cent and 20 per 

 eent strengths some surface roots were burned. Treatments with distillate oil 

 emulsion included strengths of 1A per cent. 3 per cent, 4A per cent and 6 per cent. 

 Yearling orchard trees were given one gallon of wash. Except for the weakest 

 strength results showed that the aphids were killed as far down in the soil as the 

 insecticide penetrated, in most cases all the insects on the tree were destroyed. 

 In other eases, however, those on the lower roots were not killed and it was evident 

 that one gallon was not quite sufficient to reach the lowest roots. 



Carbon bisulphide 30 cc, 20 cc. and 10 cc. per tree was applied with a pal 



' ' » to yearling orchard trees. Each application was made from 8 to 12 

 inches from the tree trunk, was of 5 cc. charge, and was released 6 inches below 

 the soil surface. The condition of the soil was good for this treatment. Examina- 

 tion made ten days after treatment indicated that 10 cc. was not satisfactory, 

 and that at thr two other strengths the aphis were either killed or weakened and dis- 

 colored, except that out of the four trees treated with 20 cc. one had a small healthy 

 infestation on fibers 14 inches from the soil surface. The use of carbon bisulphide 

 in the orchard is somewhat risky, occasional trees having been killed outright from 

 treatments of 30 cc. 



Nnrsery seedlings treated with one injection of cc. carbon bisulphide injected 

 six inches from the trunk and about five inches below the soil surface were 

 freed of aphis. Even as small a dose as 2 cc. destroyed all the aphids 

 on 5 out of trees. Injections made one foot from the trunk were ineffective. 

 The seedlings were treated in Octoher and no ill effects on the trees could be traced 

 to the insecticide. However, at this time of year the trees were growing but little. 

 and had they been treated earlier in the year when the trees were in full growth 

 root injury mitrht have resulted. If nurseries are to be treated in summer with 

 earhon bisulphide a few trees should first be tested for possible injury. 



The writer believes that trees infested with the woolly aphis should receive treat- 

 ment in April or May and should he examined during July and August and if 

 necessary treated again. In most cases a single application will not kill or drive 

 off all the root aphids on a tree so that in course of time the infestation will 

 increase again. In the treatments with kerosene oil emulsion and miseible oil it 

 was found that this subsequent increase was very slow — three months after the 

 application in no case could an infestation of injurious proportions be found. A 

 yearling orchard tree requires from li to 2 gallons of insecticide, older trees up to 

 four years require about a gallon for each year of their age. but the amount varies 

 with the manner of root growth, trees with deep roots requiring more wash than 

 those with shallow roots. Trees over four years of age rarely need treatment and 

 thorough treatment of them is rendered difficult by reason of the spread of the root 

 system. - 



