The effect of insecticides on the spread of potato leaf roll virus in seed potato fields at Pukekohe

In recent years potato seed crops at Pukekohe have shown high levels of leaf roll virus infection, in spite of the use of insecticides. Laboratory and field tests have shown that although insecticides control aphid populations, they do not kill viruliferous insects quickly enough to prevent transmission of leaf roll to potato. High levels of leaf roll were seen in plots of potatoes that had emerged in a peak of aphid flight activity in the second half of November 1969, whereas plots emerging later were relatively free of virus. The evidence suggests that most of the virus seen in seed potato fields is brought there by viruliferous aphids migrating from infected crops in the neighbourhood. Isolation of seed fields from the Pukekohe district is advocated.