Abstract
Abstract A survey of the incidence of cereal aphid infestation in wheat crops during the last two seasons was carried out in Canterbury. This survey revealed large differences in aphid populations, in different districts where varying environmental conditions affected crop growth. Early sowing, vigorous growth, and adjacent shelter led to high aphid numbers in the 1962 season. Cold damp conditions during the winter and spring of the 1963 season prevented any build up of aphid populations and resulted in low levels of barley yellow dwarf virus (BYDV) infection in the following summer. Aphid counts in the spring months were directly related to the subsequent levels of BYDV infection in January. Low crop yields were associated with high virus counts in the 1962 season, particularly in districts which experienced low rainfall in early summer, e.g., Rangiora-Oxford. A high BYDV incidence did not reduce yields below about 35 bushels/ac on the moister and more fertile soils of the Lincoln-Southbridge districts.
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