8 UNIV. OF X. IT. AGR. EXPERIMENT STATION [Bulletin 2;]^ 



ference in yields ])etween the two groups of fields was very small. Com- 

 mercial dusts cost about 20 percent more than the sprays for the same 

 areas. Because of ease of application and the manner in which it fits into 

 present practices, dustiiii^- is more freciuently done on the smaller areas. 

 Dusts are more efifective on moist plants and may be applied when the hay 

 is too wet to handle. Si)rayinfi^. however, must be done when the plants are 

 dry. which often interferes with the hayin"- and consequently may be 

 delayed. (PurncU Fund.) 



WHY DOES POTATO SEED RUN OUT? 



Attemjjts to develop jjotato seed stock in southern New Hampshire have 

 thus far failed, due to deterioration from leafroll : and studies have been 

 conducted by O. liutler, comi:iaring- seed at East Kingston and Northwood 

 with northern-grown seed at Cole1)rook. 



At Northwood a plot was established in 1926, as there was some reason 

 to believe that the locality, while situated in the same county as East King- 

 ston, was better suited to seed growing because of its higher elevation. The 

 seed planted in 1!>2() ]-)roduced 4.48 percent leafroll plants, but no mosaic 

 was detected. In 1!»27 the seed was carefully greened before planting and 

 3.57 percent weak-.sprouted tubers were removed. The amount of leafroll 

 that developed in the field was 2.75 percent ; in cither words, the stock was 

 better than it had been the year before. Yet the seed saved from the plot, 

 when greened in 1!)2.S. was found to contain 39.3 jiercent weak-sprouted 

 tubers. The stock was worthless. 



At East Kingston potatoes harvested 90 days after planting deteriorated 

 comnletely in 4 years. At Northwood the stock used was worthless after 

 two seasons. 



It is to be noted that at Colebrook, seed from the same original source as 

 was used at East Kingston and Northwood shows after seven years no 

 material deterioration. The question arises whether the difiference may not 

 be due to temperature. The mean temperature during the growing season 

 for the three stations has l)een : Colebrook (4 vears) 15.12° C. ; East King- 

 ston (5 years) 16.78° C. : Northwood (2 years) 16.80° C. 



At East Kingston the mean number of hours per day above 25° C. for 5 

 years has been 2.51 hours per day, at Colebrook 1.6 hours per day. It is 

 to be noted that mosaic plants exposed to a temperature above 25° C. of 1 

 hour per day still show mosaic symptoms, but when the exposure is length- 

 ened they become obscure and eventually disappear. Mosaic is the prevail- 

 ing degeneration disease of potatoes at Colebrook: leafroll is the prevailing 

 degeneration disease at East Kingston and Northwood. The mean 

 number of hours per day the temperature is below 10° C. is apparently of 

 some significance, being 4.3 at Colebrook and 3.1 at East Kingston for the 

 period covered. But for the four years in which we have comparative 

 data, there have been two years in which there were practically twice as 

 many hours per day below 10° C, at Colebrook as at East Kingston, and 

 two years in which the number of hours below 10° C. at both stations was 

 practically the same. Leafroll shows no tendency to increase at Colebrook, 

 but it has shown very marked increase at East Kingston in the two years in 

 which the number of cool hours per day at the latter station was only half 

 the number at the former. (Purnell Fund.) 



