INSECT ENEMIES AND THEIR CONTROL 



115 



of each triangle may be ascertained by multiplying the height 

 of the perpendicular side of the triangle by the length of the 

 base line and that product by the length of the house. This 

 total divided by two will give the capacity of the triangle. If 

 the eaves are not on a level, the space may be divided into 

 rectangles and triangles and the cubic contents of the house 

 calculated similarly to the foregoing method. 



Miscellaneous insecticides, in addition to those pre- 

 viously described in this chapter, are sometimes em- 

 ployed in the treatment of greenhouse vegetable crops. 

 Kerosene emulsion is a 

 standard spray for the 

 control of aphids, 

 though the liquid to- 

 bacco preparations are 

 generally preferred for 

 use in the greenhouse. 

 Arsenate of lead, when 

 an arsenical poison is 

 needed, is most satis- 

 factory for greenhouse 

 purposes. Various 

 soaps and soap prep- 

 arations, some of them 

 proprietary, are useful 

 in checking the ravages 

 of certain insect pests. 

 It will seldom be nec- 



however tO Use 



Fi 37. Galls on cucumber roots produced 

 . by nematodes. 



any of these materials 



if the major treatments previously described are thorough 



and timely. 



The spraying apparatus for greenhouse use should be 

 light and convenient to operate. The various forms of 

 knapsack sprayers are sometimes employed. Automatic 

 tank pressure sprayers are becoming popular. Some 

 growers prefer bucket pumps, but they are not the most 



