TROPICAL AGRICULTURAL METHODS 27 



the weeds and kill them out by shading, after which the cover 

 crop itself may be plowed under or cultivated into the soil in 

 order to improve the physical condition of the soil. 



In localities of excessively high rainfall it often happens 

 that the rain occurs daily and almost continuously for periods 

 of several months. Under such conditions it is impossible 

 to destroy weeds by cultivation, and cultivation, moreover, in- 

 jures the texture of the soil when it is in a muddy condition. 

 In Hawaii the use of a spray of arsenite of soda has found 

 great favor as a weed destroyer under such circumstances. 

 It has been used for this purpose for six years or more on 

 thousands of acres of land devoted to rubber ranching, sugar 

 cane, and pineapples, and in all cases with satisfactory results. 

 The spray is prepared by boiling two pounds of sal soda and 

 one pound of arsenic in a gallon of water until the mixture is 

 clear. The mixture is then diluted to make from 20 to 24 gal- 

 lons pf spraying material. If desired, seven ounces of caustic 

 soda may be used in the place of two pounds of sal soda. For 

 the successful application of this spray it is merely necessary 

 to have a few hours of weather without rain. The spray is 

 applied to the green growing parts of the weeds and produces 

 the effect of prompt burning of the foliage and tender stems. 

 Special machinery has been devised which prevents the spray 

 from coming in contact with sugar cane, pineapples, or other 

 crops. The cost of application even on rough land has been 

 found to be about $1.25 an acre. Arsenite of soda destroys 

 all ordinary herbaceous weeds and has also been found to kill 

 wild raspberries, Lantana, and various other weedy shrubs. 



Insects, like weeds, are busy the year round in tropical coun- 

 tries. The cost of making frequent applications of insecticides 

 month after month and the impossibility of applying insecti- 

 cides under any circumstances to sugar cane and certain other 

 tropical crops have necessitated the adoption of other methods 

 than artificial insecticides for the control of injurious insects. 

 One method which has perhaps come most prominently to pub- 



