1909.] PUBLIC DOCUMENT — No. 31. 67 



and about 10 gallons applied to the square rod, weeds are not 

 likely to come in again for a few years. 



A few applications will kill poison ivy about trees, near 

 houses, on walls, etc., but only large trees should be treated, 

 otherwise injury to the tree might result. The treatment of a 

 space 2 feet wide around a large tree will not injure the tree. 

 This method of treating ivy in the open fields and mowings is 

 not advisable, as it is too expensive, since the amount necessary 

 to kill ivy in such locations would render the treated land use- 

 less for several years. The best way to exterminate ivy in 

 mowings is by j)lowing up the land and planting it for a few 

 years. 



In one experiment where we made applications of arsenate 

 of soda, carbolic acid, white arsenic and sal soda to a mowing 

 filled with ivy, at the rate of 1 to 20 and 10 gallons to the 

 square rod, we found that the ivy was not permanently exter- 

 minated, although both the ivy and grass were temporarily 

 killed. The plots treated with white arsenic and sal soda 

 showed the efi'ect of the treatment six years afterward, but it 

 did not kill out all the ivy or all the grass. Four other plots 

 of poison ivy were treated with 10, 20, 30 and 40 per cent, 

 solutions of crude nitrate of soda, at the rate of 10 gallons per 

 square rod. This treatment destroyed the grass and the tops of 

 the ivy plants soon after application, and the stronger the 

 solution used the more marked was the effect. A month later, 

 however, all the plants showed a deep green color, and the 

 grass and ivy thrived more luxuriantly than before. 



From these experiments it is evident that arsenic compounds 

 are the most effective poisons for plants.-^ Solutions of such 

 substances as arsenate and arsenite of soda, corrosive sublimate 

 and arsenic sulfide are most effective ; they penetrate the soil to 

 some extent and kill the roots. It would appear, moreover, that 

 these substances do not leach out of the soil like some others 

 and are for this reason probably more permanent in their ef- 

 fect. There are other substances which are effective in destroy- 

 ing foliage, and for the complete elimination of certain weeds 

 they do the work. 



• Prof. L. R. Jones, who has experimented with various weed killers, found certain 

 arsenic comiiounds liest adapted for killing M'eeds. Twelfth Annual Report, Vermont 

 Agricultural Experiment Station, 1889. 



