Effect of defoliation date on yield and leaf roll incidence in potato

Summary

Defoliation experiments in the lower Fraser Valley of British Columbia showed that in 1961 and 1962 the initial spread of potato leaf roll virus occurred in late June or early July. More extensive spread occurred after July 25 in 1961 and after July 31 in 1962. Since the later spread in each year occurred in fields which were rogued and kept free of aphid colonies, it is presumed that alateMyzus persicae introduced virus from sources outside the test fields.

Normal cropping practices were followed. The mean yield of Netted Gem in 1961 was 116 cwt per acre on July 25, only 35% of that obtained on September 5. Kennebec in 1961 yielded 230 cwt per acre on July 25, 66% of that recorded on August 22. In 1962 mean yield of Netted Gem on July 31 was 134 cwt per acre, 44% of that obtained by September 4. In the same year the mean yield of Kennebec on July 31 was 234 cwt per acre, 72% of that obtained on August 21. The Netted Gem tubers from plants defoliated on July 25, 1961 or July 31, 1962 were somewhat soft after 5 months storage but they germinated well. Kennebec tubers from plants defoliated on these dates were normal.