44 Maine; agriculturai, e;xperime;nt station. 19 14. 



the mustard and probably would seriously injure the potatoes 

 as well. 



In order to ascertain the effect of spraying potato plants with 

 sulphate of iron one plot each of Irish Cobbler and Green 

 Mountain potatoes were planted on June 10, 19 13. Each plot 

 contained four rows of about 250 feet in length. 



Other than the spraying with sulphate of iron the treatment 

 of these potatoes was in every way the same as that of other 

 potatoes grown in 1913. The land was prepared by plowing 

 and harrowing to make a good seed bed. Medium sized, 

 healthy, sound tubers were used for seed. The seed was treated 

 with formaldehyde for fungi. Fertilizer at the rate of i/CX) 

 pounds per acre, carrying 4 per cent nitrogen, 8 per cent avail- 

 able pihosphoric acid and 7 per cent potash, was applied at 

 planting and at first cultivation. 



The plants appeared July 2 and three days later the soil was 

 hilled around them. On July 8 the plants were 2 to 4 inches 

 above ground. Although there were no plants of either kind of 

 mustard on the plots they were sprayed tv\dce on July 8 with a 

 solution of 100 pounds of iron sulphate in 50 gallons of water. 

 In 24 hours all the tissue that had been hit by the spray had 

 turned black. These blackened portions of the leaf surface 

 later shrivelled and were brown. No plants were completely 

 killed. 



On July 10 a sulky cultivator was used, straddling each row. 

 On July 12 the plants had recovered somewhat and were grow- 

 ing. The tops were sprayed for the second time July 14. But 

 one application was made this time. This spraying had the 

 same effect as the first except that the plants did not seem to 

 recover as rapidly. Five days later, however, the tops showed 

 signs oi recovering. On July 25 the field was cultivated and 

 sprayed with bordeaux mixture and Arsenoid. On July 30 

 hardly any trace of the spray injury was visible. 



The plants started blossoming August 4, 20 days later than 

 other potatoes of the same variety planted on the same date. 

 On August 13 the tops were from 12 to 16 inches in height and 

 still blossoming. At this time, compared with other Irish Cob- 

 blers and Green Mountains planted at the same date, the tops 

 and tubers were smaller and the period of blossoming later. 



