291 



where they are exposed directly to the sun and the hot dry air of 

 summer. This should be done in the early summer so as to expose 

 the pupae for as long a period of hot weather as possible. It has 

 been found that 70 to 100 per cent, of the pupae are killed by this 

 treatment of the stubble. 



Jones (P. R.). The Selection of Petroleum Insecticides from the 

 Commercial Point of View. — Mthly. Bull. Cal. State Conmiiss. 

 Horiic, Sacramento, vii, no. 4, April 1918, pp. 189-191. 



The three chief types of petroleum insecticides are described under 

 the headings of mechanical mixtures, mechanical emulsions and 

 miscible or soluble oils. It is pointed out that owing to the uncer- 

 tainty in appearance of different insect pests from one season to another, 

 it is nearly always necessary for a manufacturer to make plans ahead 

 and manufacture a certain stock that can be despatched quickly to 

 meet whatever emergency in the nature of insect infestation may 

 arise. Frequently these insecticides when manufactured are not 

 required and have to be held over until the following year. It is 

 alwavs necessary also for the manufacturer to put in an excessive 

 emulsifier in order to overcome hardness in water or carelessness in 

 mixing by the consumer. An oil spray that might be satisfactory 

 in an experiment station, therefore, might not have great commercial 

 possibilities. Petroleum insecticides require more expert field service 

 than any other class, and while miscible oils may be high in initial 

 cost, they have greater efficiency and fewer failures in the field. They 

 also have less tendency to break down on the tree than those of the 

 mechanical emulsion t}^e ; they are consequently more efficient and 

 cause less injury to trees if the right oil is used in manufacture and 

 the correct dosage in application. The mechanical type of emulsion 

 can only be used with success locally ; but if growers had sufficient 

 entomological and chemical training, or could secure extensive field 

 service from universities, experiment stations or horticultural officers, 

 and were able to buy raw ingredients at a sufficiently low price, 

 mechanical emulsions" would certainly be the cheapest kind to use. 



Gray (G. P.). Wettable Sulfurs.— 3///i^y. Bull Cal. State Commiss. 

 Hortic, Sacramento, vii, no. 4, April 1918, pp. 191-192. 



While such solutions of sulphur as the lime-sulphur spray have 

 long been in use, they cannot he used on all plants for fear of injuring 

 the foliage. Dry sulphur, which is less active, has recently been used 

 extensively on plants with delicate foliage, but there are certain 

 objections to its application. When dusted upon crops that are 

 soon to be harvested, the pickers complain of its irritating effect 

 upon the eyes. In windy locaUties, a great deal of the sulphur applied 

 is apt to be blown off the fohage. In order to obviate this, the dust 

 application is often carried out in the morning while the dew is on 

 the plants ; this restricts the operation to a limited time. To over- 

 come these objections, sulphur has been mixed with water and applied 

 as a spray. Sulphur, however, is not easily wetted, and in order 

 to counteract the aversion of sulphur for water, without otherwise 

 modify-ing its properties, a number of substances such as soap, flour 

 paste, oleic acid, glue, dextrin, diatomaceous earth and others, have 



(C479) b2 



