166 MASS. EXPERIMENT STATION BULLETIN 179. 



in controlling aphids and thrips, but killed only 50 per cent, of the actively 

 feeding mites. At the above strength this spray severely injured cucumber 

 foliage, and even when diluted to 1 part oil in 100 parts of water, injury 

 still occurred. 



(h) Arlington Oil and Black-LeaJ-Jfi . — Formula: oil, 1 part to 125 

 parts of water; Black-Leaf-40, 1 part to 2,000 parts of water. This com- 

 bination spray is much more active than the ingredients used separately, 

 but is injurious to the cucumber foliage. 



(c) Kerosene Emulsion. — This is recommended as being efficient in 

 controlling red spiders, but it severely injures tender foliage. 



2. Sprays containing Vegetable Oils, (a) Lemon Oil. — This is manu- 

 factured by the Lemon Oil Company, Baltimore, Md., and is at present 

 sold at 11.75 per gallon in 5-gallon lots. It is a completely saponified 

 oil soap, and is guaranteed to contain the following ingredients: — 



Per Cent. 



Soap, . • 6 



Vegetable oil, . . . " 3^ 



Potassium carbonate, .......... J 



Terabenthine (Tiirpentine?), ......... 5 



Water (not over), . . . . . . . . . .85 



Of the many commercial insecticides used experimentally in the control 

 of red spiders this proved the most satisfactory. 



Results. — Used at the strength of 1 part lemon oil in 20 parts of water, 

 or 1 pint in 2^ gallons of water, it killed all actively feeding mites, as 

 well as those in the quiescent stage, without injuring the foliage. The 

 eggs are not materially affected by this spray. If young potted cucumber 

 plants are dipped in the above mixture some injury will result to the 

 terminal growing point, but if the plants are sprayed this injury does not 

 occur. 



During the spring and summer months of 1916 this spray was thoroughly 

 tried out on a commercial scale, and proved to be very satisfactory, but 

 its expensiveness precludes its free use as a general spray for red spiders. 



(b) Ex-periments on the Duplication of Lemon Oil. — With the co- 

 operation of Dr. E. B. Holland of the Massachusetts Agricultural Experi- 

 ment Station a number of spray materials were made in order to deter- 

 mine the killing agent in lemon oil, and for the purpose of duplicating 

 the efficiency of this oil by a substitute which would be less expensive. 

 The following table will briefly show the composition of these mixtures 

 and their relative effectiveness in controlling red spiders: — 



