332 INSECTICIDES, FUXGICIDi:S, AND WEED KILLERS. 



solutions of 3-3-5 per cent of whale oil, a dose which has no action 

 on adults. Mixtures of soap and insecticides have a more decided and 

 radical action, but they also must be applied at the time when the deli- 

 cate larvcC issues from the winter egg. This moment varies with the 

 different plant lice to siich an extent that the time of treatment must 

 be varied according to the species which it is desired to exterminate. 

 One of the most energetic insecticides, and also the least injurious to 

 trees, is that i-ecommended by Nessler, consisting of soft soap, ethyl, and 

 amyl alcohol : Dissolve 5 lb. of soft soap in 6^ gallons of rain water, 

 add, after cooling, 2 gallons of ordinary 90 per cent alcohol and 1 

 gallon of amyl alcohol. A mixture of 3 lb. of soft soap and 6 lb. of 

 am^'l alcohol in 10 gallons of water acts similarly. These insecticides 

 are applied by the brush, such as they ai-e, in winter during the 

 hatching of the eggs, on all the nodosities and cankers produced 

 by this aphis. It is well to prune the tree and to clean the trunk and 

 the large branches before treatment ; then the whole tree is sprayed 

 with a solution diluted with an equal part of rain water. Summer 

 treatment with this insecticide is not sufficient to kill the adult. 

 Sorauer recommends a mixture of 50 oz. of soft soap, 2 oz. of carbon 

 ■disulphide, and 6^ gallons of water. Muhlberg recommends a mixture 

 with tobacco : 3 \h. of tobacco, 5 lb. of amyl alcohol, 2 lb. of ordinary 

 alcohol (formula 9, p. 329). If this last preparation infallibly kills the 

 louse it also injures the buds and the leaves, especially when growing, 

 whilst mixtures of alcohol and soap of equal strength have not this 

 drawback. 



Coccides (cochineals). — All cochineals are exterminated like the 

 Aspidiotus perniciosus, Comstock (San Jose louse). Cochineals with a 

 protective shield resist soap solutions, even concentrated, and insecticide 

 mixtures containing soap, better than plant lice. As with the woolly 

 aphis, it is best to attack the larvas at the moment they are hatched, 

 and when they issue from the protective shell of tlie dead mother. 

 Pure soap solutions used against the San Jose louse some days before 

 the fall of the leaf and a little before flowering, in the spring, were 

 found quite satisfactory l)y Marlatt and Smith. As already seen the 

 former obtained with a 24 per cent solution more than 97 per cent of 

 dead cochineals. Smith, with whale oil soap of 20-30 per cent, up to 

 100 per cent of killed ; with 20 per cent of white soap, strengthened by 

 a little carbonate of potash, 85 per cent. Whale oil soap is the most 

 energetic of all ; it is now considered as a specific against cochineals. 

 A tepid solution of soap applied on the young larvic in spring kills them. 

 (He experimented on the cochineal of the rose laurel.) A hot solution 

 was used with success by Frank and Kruger. It is necessary to repeat 

 this last treatment until the cochineals are exterminated. Unfortun- 

 ately the soap solution to be effective must be applied of such a strength 

 that it always injures the tree. Winter treatment with 18-30 per 

 cent of soap always diminishes the blossom ; flowering often does not 

 occur at all ; the peach is peculiarly sensitive thereto. This drawback 

 may be avoided, according to Alvood, if the treatment be only applied 

 in spring, after the formation of the fruit-buds and at the time of iheir 

 swelling ; they are then not so sensitive to the action of soap. Smith 



