Integrated control of aphid pests of lettuce [Lactuca sp.] and Brassica crops in the United Kingdom
1999
Collier, R. (Horticulture Research International, Warwick (GB))
Aphids are the major pests of outdoor lettuce and Brassica crops in the UK. The foliage of lettuce crops is infested by three species of aphid (Nasonovia ribisnigri, Myzus persicae, Macrosiphum euphorbiae), whilst the roots are infested by the lettuce root aphid (Pemphigus bursarius). The cabbage aphid (Brevicoryne brassicae) is the major pest of Brassica crops, but they are infested also by M. persicae. Until recently, aphids have been controlled mainly with organophosphorus and carbamate insecticides. However, the range of insecticides available to lettuce and Brassica growers is decreasing. New active ingredients are being considered experimentally, but of these, only imidacloprid is approved, and just as a seed treatment on lettuce. A further problem for growers is that some populations of M. persicae and N. ribisnigri are resistant to one or more insecticide groups. In addition, vegetable growers in the UK are under increasing pressure from retailers, consumers and environmentalists to avoid making routine insecticide applications and to reduce pesticide use. This has stimulated research on integrated pest management systems, where insecticide applications are made according to pest pressure and are integrated, wherever possible, with non insecticidal methods of control. Non-insecticidal methods of control considered include cultivars of lettuce resistant to either foliage or root aphids, entomopathogenic fungi to control P. bursarius, semio-chemicals to manipulate insect behaviour and undersowing crops with clover. Management techniques by which treatments can be targeted include the use of weather data to forecast aphid attacks and careful crop sampling, used in conjunction with tolerance levels, to make spray decisions. The paper summarises some of the techniques under development and discusses longer-term prospects for aphid control in lettuce and Brassica crops.
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