SUMMARY Sugar beet growers in England have been advised since 1959 to spray their crops with systemic insecticide to control spread of yellows viruses when infestation with the vector aphids (mainly Myzus persicae Sulz.) in May and June reaches 0.25 aphids/plant. The data collected up to 1966 show that aphid infestation at any one time is not proportionally related to eventual yellows incidence. Graphs of mean aphid infestation and yellows incidence in different areas are presented, which are a guide to issuing spray warnings.
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R. Hull (1968) studied this question.