Apr. i, 1931 
Leafroll , Net-Necrosis , and Spindling-Sprout 
77 
centage which resulted in sublot 2, in spite of tuber selection, from 
proximity to a source of virulent aphids. In sublot 1 of lot 1919—21 
roguing produced a greater reduction in leafroll than in sublot 1 of lot 
1919—20, apparently because of a greater distance from entirely leafroll 
stock. 
Table XIII .—Effect of roguing upon percentage of leafroll 
First season. 
Second season. 
Lot No.° 
Variety. 
Per- 
Sublot 
No. 
Rogu- 
ings. 
Total 
Per- 
Location. 
centage 
of leaf- 
number 
of hills. 
centage 
of hills 
roll. 
leafroll. 
1918-4 
f Bliss Tri- 
Aroostook Farm plant- 
}( 6 ) 
/ 1 
I 
!, 33 2 
1,615 
2 
\ umph. 
disease plot, two rows. 
l 2 
O 
8 
(Green 
Aroostook Farm plant- 
1 c 
/ I 
I 
I, 64I 
O. 2 
\ Mountain. 
disease plot, one row. 
/ 5 
l 2 
O 
1,489 
4 
1919-20 
/Irish Cob- 
Aroostook Farm next 
f 1 
2 
1,254 
4 - 7 
1 bier. 
all-leafroll row. 
fAroostook Farm third 
I 5 
l 2 
O 
954 
10 
1919-21 
... do. 
| row from all-leafroll 
( 1 
2 
*,321 
• 5 
3-8 
{ row. 
l 2 
0 
954 
1919-22 
...do. 
Commercial field. 
14 
( 1 
I 
639 
637 
O 
8 
l 2 
0 
0 The year of planting (first season) is given as part of the lot number. 
6 Rogued so late (August 16) that hot weather and age caused many undoubtedly healthy hills to look 
as if possibly leafroll. 
It is noteworthy that in lots 15 and 22 leafroll was entirely eliminated 
from sublot 1 by a single roguing. The marked reduction of leafroll 
in sublot 2 of lot 22 apparently was due to a large percentage of the 
leafroll vines producing tubers weighing less than 2 ounces and to the 
selection of large tubers together with the scarcity of aphids in this field. 
Hence it appears that leafroll may be eliminated from infected stock by 
roguing, provided that such stock is not in close proximity to leafroll 
vines infested with aphids, and may be reduced by discarding small 
tubers. This means that in northeastern Maine leafroll may be con¬ 
trolled more readily than mosaic of potato (19, p. 270). Whether this 
is due to less prevalence of diseased plants or to less susceptibility under 
the existing conditions of aphid infestation remains to be determined 
by further investigation. In either case it would not be advisable to 
expect similar results elsewhere where either diseased plants or aphids 
are more numerous. 
From the data on hill selections (p. 53) it is apparent that this method 
of selection does not necessarily insure stock free from leafroll if such 
selection is practiced near leafroll plants infested with aphids. Hence, 
in view of the fact that elimination of leafroll hills from the seed plot by 
roguing appears to be fully as effective as hill selection, the former method 
of eradication seems the more desirable one. From the results on aphid 
transmission it is very evident that the earlier the diseased plants are 
