yo MAINE AGRICUI,TURAI, EXPERIMENT STATION. I913. 



It was in connection with these comparisons that the lack of 

 an-unsprayed check-plot was most apparent. Apparently when 

 plots A and C are compared, 4 pounds of arsenate of lead were 

 decidedly more effective in scab control than standard dilution 

 lime-sulphur plus 2 pounds of arsenate of lead. If 4 pounds of 

 arsenate of lead exerts so decided a fungicidal eft'ect, is it not 

 possible that the amount of scab on plot E, sprayed with 2 

 pounds of arsenate of lead alone, is considerably less than would 

 have developed on an unsprayed plot? • If such is the case its 

 use as a check plot does not measure the true fungicidal value 

 of sprays used on the other plots. Similarly how much of the 

 fungicidal value of lime-sulphur combined with arsenate of lead 

 is due to the presence of the last named material? There is, 

 one outside factor which may have exerted an influence on the 

 apparent effectiveness as a fungicide of the heavy application 

 of arsenate of lead. As is illustrated on p — ■ the nine trees in 

 this plot were at the corner of the orchard and were thus much 

 better exposed to the sunlight than those on the other plots. 

 However it does not seem that this location with regards light 

 is sufficient to account for the recorded differences. 



Experiments with Different Arsenicaes in Combination 

 WITH Lime-Suephur. 



The ordinary arsenate of lead paste commonly used for or- 

 chard spraying is a very variable substance. Some lots as pur- 

 chased may be quite soft and carry a considerable percentage of 

 water. Other lots, sometimes from the same manufacturer, are 

 received in the form of a rather dry, sticky paste. This varia- 

 tion in composition may cause considerable variation in the 

 amount of arsenate of lead actually used in the spray no matter 

 how careful the user is to accurately weigh the quantity taken. 

 Also considerable difficulty is frequently experienced in disolv- 

 ing the arsenate of lead paste, particularly that which has par- 

 tially dried out, so that it will mix thoroughly and well with 

 the spray. Certain manufacturers are now selling a dry arsenate 

 of lead in powder form which dissolves readily and quickly in 

 water and which, if not adulterated, should always carry the 

 same amount of poison pound for pound. Arsenite of zinc is 

 also being sold as a substitute for arsenate of lead. 



