8 



At this Station experiments have been carried on with arse- 

 nite of soda in testing the effect of this chemical upon a number 

 of weeds, including oi (Stacliytarpheta dichotoma), lantana, 

 spurge (Euphorbia peplus), pualele or sow thistle, pig-weed, 

 purslane, cockle-bur (Xanthium strumarium) , glue (Acacia far- 

 nesiana), dodder, Japanese nut-grass, honohono (Commelina 

 nudiflora), crotalaria and other weeds. In these experiments 

 the stock solution, as described above, was dissolved in from 15 

 to 20 parts of water. The effect of the spray was manifest in 

 most instances within 2 or 3 hours, but on Japanese nut-grass 

 the leaves did not turn brown until the second day. On all of 

 these weeds the leaves and stems ultimately died as a result of 

 a single application. 



In spraying alfalfa infested with dodder the alfalfa was 

 killed as well as the dodder. In this respect the results were the 

 same as those obtained with spraying with iron sulphate. The 

 leaves and small stems of lantana were destroyed by a single 

 application, but for the complete destruction of the plant a sec- 

 ond, third or even fourth treatment was found necessary. With 

 sow thistle, although apparently destroyed, it seemed to recover 

 rather promptly and grew up again from the base of the plant. 

 Similar results have been had in Xahiku in spraying this plant. 

 Some difficulty is likely to be experienced in destroying hono- 

 hono on account of the fact that in dense patches it is hard to 

 reach all portions of the plant with the spray and two or three 

 applications may be necessary. Japanese nut-grass, although 

 entirely destroyed above ground by the arsenite of soda spray, 

 promptly grew up again from the underground bulbs without 

 showing any serious diminution of vigor. In previous experi- 

 ments of the Station it was found possible to destroy this plant 

 with carbon bisulphide, but this chemical is too expensive for 

 use on a large scale. Judging from the experiments which have 

 thus far been made, the best way to destroy this weed economi- 

 cally is to shade it out by using pigeon-peas and allowing them 

 to occupy the ground for a year or more. 



In the practical application of arsenite of soda on a large 



