Surveys of sugar-beet seed crops, mangold clamps and weedsin England for aphids and viruses, 1963–73

Abstract

SUMMARYThe annual patterns of infestation of sugar-beet root and seed crops by green aphids (Myzus persicae) and by black aphids (Aphis fabae) were similar, paralleling population changes shown by catches on sticky traps in southern England, but the incidence of yellows in root crops was not correlated with incidence in seed crops in the same year. Few green aphids overwintered on beet-seed plants and the incidence of yellows was consistently low in the main seed-growing areas where all the stecklings are raised under cereal cover crops. Elsewhere, yellows sometimes spread in the autumn and many green aphids occasionally overwintered. Black aphids were seldom prevalent; the severity of attack correlated with the number of eggs laid on spindle (Euonymus europaeus) during the previous autumn.Twenty-two per cent of mangold clamps checked in mid-April contained aphids, but only about 5 % contained M. persicae. Seventeen per cent of the infested clamps contained aphids infective with BMYV and 10% contained aphids infective with BYV. However, the acreage of mangolds grown in England has decreased.Myzus ascalonicus overwintered on weeds more often than M. persicae or other species likely to act as vectors of viruses affecting sugar beet. Forty per cent of samples of some common weeds collected from sheltered sites during mid-April from 1963 to 1973 were infested with aphids, and those on chickweed (Stellaria media), groundsel (Senecio vulgaris) and shepherd's purse (Capsella bursa-pastoris) were commonly infective with yellowing viruses. Weeds are probably a major source of yellowing viruses in southern England.