Pea and Bean weevil – Sitona lineatus
Pea and bean weevil is a grey brown weevil with characteristic snout. It feeds on leaves, producing u shaped notches but it is its larvae that produce most of the yield reductions in beans. Eggs are laid on the soil and the larvae hatch, burying into the soil to feed on the roots. Pea and bean weevil can dramatically reduce root nodule formation and thus nitrogen fixation. Figure 1 demonstrates the effects of this pest on nitrogenase activity, the enzyme which fixes nitrogen in the root nodules.
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Figure 1. Effects of pea and bean weevil infestation of nitrogen fixation by field beans at various stages of development 5
[redrawn from data produced by Rothamstead experimental station annual report, 1976. 154]
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Control of pea and bean weevil centres around the adults. Pyrethroid ('Hallmark', 'Dovetail' and 'Decis', cypermethrin (various) 'Contest', 'Fury') insecticides are applied in the spring once leaf notches become apparent. A second application 3 weeks after the first is often beneficial if infestations are high as this controls the adults hatching from larvae, laid as eggs by the first migrators into the crop. Control is generally economic (Figure 2).
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Figure 2. Control of pea and bean weevil in field beans (data from 1981 to 1986)
[Redrawn from data from King, 1981. Proc. 1981 British Crop Protection Conf. 327-31; Rothamstead EHF. Yields of field experiments, 1980. 305-313; Bennison, 1991. Aspects Appl. Biol. (27) 151-55; Raw, 1992. Tests of Agrochem & Cult (13). In Ann. Appl. Biol. (120) 64-65; Bardner et.al., 1983. J. Agric. Sci. (101) 71-80]
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