1909.] PUBLIC D0CUMP:NT — No. 31. 11 



zation and freezing, if thorougli, are effective. The introduction 

 of trap crops, such as mustard or rape, is useful. 



10. Weeds in walks, roadways, tennis courts, and poison ivy 

 about trees or near houses or walls, can be destroyed by the use 

 of arsenic compounds, among the most effective being arsenate 

 and arsenite of soda. 



17. Many weeds can be destroyed by spraying the foliage 

 with a solution of sulfate of iron, while some of the commer- 

 cial preparations are effective weed killers. 



18. Some of the insects most destructive to greenhouse crops 

 can be destroyed by fumigation with hydrocyanic acid gas, and 

 such fumigation should be carried on on clear nights without a 

 moon, or on cloudy nights at a house temperature of 55° to 65°, 

 followed by complete ventilation and a rather low temperature 

 in the house the next day. 



