1920.] PUBLIC DOCOIEXT — No. 31. • 33a 



of the potatoes in the different ph)ts. Satisfactory protection 

 from insects was also obtained with all three of the arsenicals, 

 which appeared to act with about equal rapidity, and no foli- 

 age injury followed the use of either spray. Indeed, the three 

 materials appeared to be ecpially good in every way except as 

 to suspension quality and cost. 



As regards suspension, the arsenate of calcium settled toward 

 the bottom of the spray tank the most rapidly; the magnesium 

 arsenate was a little slower in this regard; while the lead ar- 

 senate remained unsettled much longer than the others. This 

 is a point definitely in favor of the lead arsenate, unless the 

 pump used is equipped with a thoroughly effective agitator, 

 when it becomes of less importance. As regards expense of 

 these materials, based on average quotations for 1919, the cost 

 of 50 gallons of spray for the lead arsenate used was 66 cents; 

 for the magnesium arsenate, 50 cents; and for the calcium ar- 

 senate, 45 cents. 



These tests, so far as they go, would seem to favor the use 

 of calcium arsenate as being equally effective with the other 

 materials, and costing less. Other facts must be considered, 

 hovv-ever. The first is that the results of one set of tests never 

 supply information enough from which to draw safe, general 

 conclusions. Another is that tests of calcium arsenate alone 

 have shown that it burns foliage badly, and must be comibined 

 with considerable excess lime if this is to be prevented. In 

 the above tests the Bordeaux mixture supplied this excess of 

 lime. A third point is that these results were obtained with 

 potatoes, and enough testing on other plants has been done to 

 indicate that the results here reported may not hold at all for 

 at least some other kinds of plants. They do indicate, how- 

 ever, so far as a single experiment goes, that spraying potatoes 

 with 4-4-50 Bordeaux mixture combined with powdered ar- 

 senate of lime will give as good results as arsenate of lead or 

 arsenate of magnesium, and at a lower cost. Whether repeti- 

 tions of this experiment in other seasons and under varying 

 weather conditions will give the same results cannot now be 

 foretold. 



Sulfoleuvi. — Tests of this material, which is claimed to be a 

 miscible oil containing a considerable per cent of sulfur in solu- 

 tion, were made mainly to determine its effectiveness against 



