22 UNIV. OF N. H. AGR. EXPERIMENT STATION [Bulletin 232 



With the small number of cases in which dusting was practised no 

 material differences in yield appeared as compared with wet Bordeaux 

 sprays. (Purnell Fund.) 



STUDIES OF POTATO LEAF-ROLL 



Difficulties in the way of maintaining potato seed stock in southern New 

 Hampshire have been found by the Experiment Station to be due probably 

 to the spread of leaf-roll. Studies of this disease have been continued in 

 the plots in East Kingston with a view to determining the reason why 

 this disease should be more marked than in the northern sections and 

 whether there is any method of controlHng it. Up to the present time it 

 has been necessary to discourage the growers in the southern part of the 

 state from selecting their own home-grown seed. 



- Comparisons have been made since 1922 with seed grown at East 

 Kingston and seed from the stock as grown at its original source in Maine. 

 Beginning in 1926 it was found that the seed grown in East Kingston and 

 harvested 90 days after planting, which should have given promising 

 results, produced stock so badly affected with leaf-roll as to make it unfit 

 for further use as seed. At the same time stock grown continually at 

 the same source in Maine showed a high per cent of leaf -roll beginning with 

 1925, but did not increase materially in 1926. In 1926 the per cent of 

 leaf -roll in the Maine fields was 12 per cent as compared with 39 per cent 

 at East Kingston. 



During the course of the above experiment it was found that the mean 

 temperature at East Kingston from May when potatoes were ordinarily 

 planted until August when the 90-day stock was harvested and from late 

 June until the middle of September was approximately the same. It was 

 thought, therefore, that immature seed of satisfactory quality might be 

 produced by planting at the end of June and harvesting in late Septem- 

 ber, and in 1925 an experiment was made with this end in view. Seed 

 from northern New Hampshire stock was planted on June 23 and har- 

 vested September 21. The disease record for the plants was: mosaic, 

 0.78 per cent; leaf-roll, 1.17 per cent. In 1926 the stock from the late 

 planted seed showed 42.9 per cent net necrosis, whereas that from the early 

 planted seed showed between 3.2 and 4.6 per cent. 



The removal of tubers affected by net necrosis prior to planting proved 

 a small help, but was by no means sufficient to control the disease. 



Studies of the vigor and method of sprouting of the potato indicate 

 that a very large per cent of leaf-roll tubers may be recognized by the 

 way in which a tuber sprouts. (Purnell Fund.) 



CONTROL OF POTATO TIP-BURN 



The comparison of spraying versus dusting potatoes conducted by 0. 

 Butler showed conspicuously greater resistance to tip-burn on the sprayed 

 plots. An 8-4-50 Bordeaux mixture was applied every fourteen days, 

 or five times during the season, while dust was applied every seven days, 

 i.e., nine times for the season. 



Tip-burn developed quite severely during the summer, and the non- 

 treated and dusted plots were nearly dead on September 1, whereas the 

 plants in the sprayed plot were still green. (State Fund.) 



