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E.M. El Banhawy, N. Carter and I.R. Wynne, 1993. Prelimina~' observations on the tx)pulation development of anystid and flee-living mesostigmatic mites in a cereal field in southern England. Exp. Appl. Acarol.. 17: 541-549.The effect of manipulating cereal aphid population development, by either adding aphids or spraying with an aphid-specific insecticide, on the predatory mite fauna was investigated. Populations of the anystid mite, Anystis baccarum (L.), were very small until late June when numbers built up rapidly at the time of the aphid population decline. There was however, no signilicant relationship between aphids and numbers of mites over the whole season. Preliminary eleetrophoretic analysis of two enzymes in the gut of anystid mites indicated that they may have been feeding on thrips, Limothrips cerealium Haliday. The free-living soil Mesostigmata had two population peaks, each related, the first tx)sitively and the second negatively to aphid populations.

S U M M A R YIn experiments at Rothamsted in 1984-86, seven factors, each at two levels, were tested in factorial combination on winter barley (cv. Panda) grown as a third take-all susceptible crop. The factors were seed rate, a growth regulator prior to stem extension, amounts of N in spring, 'winter' nitrogen, an autumn insecticide, a fungicide applied to the seed (' Baytan') and a programme of fungicide sprays in spring and summer. Sowing 50% more seeds than normal increased the number of ears/unit area but had no effect on mean grain yield because grains were smaller. There were, however, significant, but unexplained, interactions between seed rate and the fungicide 'Baytan' applied to the seed. A growth regulator applied prior to stem extension had little effect on crop growth and no significant effect on grain yield. If sufficient N was applied in April there was little benefit from applying 'winter' N (30 kg/ha in November and again in February/March) except in 1985 when the amount of NO 3 -N in the soil, measured in the previous October, was lowest. Insecticide sprays applied in autumn to control the aphid vectors of barley yellow dwarf virus (BYDV) had no significant effect on grain yield but infectivity indices were below the threshold needed for treatment in each year. On average, ' Baytan' applied to the seed increased grain yield by 0-28 t/ha and this was associated with decreases in the severity of take-all. Over the three years, programmes of fungicide sprays, applied during spring and summer, increased grain yield by 0-92 t/ha but the mean response was largest where most N was applied.The experiments also allowed the importance of interactions between different agronomic factors to be examined. A combined analysis of grain yields for all three years (based on 192 plot values) showed that only six 2-or 3-factor interactions, out of the 73 estimated, were significant (P < 005). Two of these interactions reflected variable responses to 'winter' N and fungicide sprays in the three years and three of the remaining four involved 'Baytan'.Additional plots of barley grown after oats had little take-all and yielded 114 t/ha more grain than similarly treated plots grown after barley. These responses were obtained despite evidence that oat residues had adverse effects on the growth of barley seedlings. Additional plots of barley grown after a bare fallow also had little take-all and gave even larger total yields (grain plus straw) than did barley after oats but the mean yield of grain was less than after oats because more of the dry matter after a fallow was straw. In 1984, when take-all was relatively slight, plots after a fallow gave even less grain than plots after barley ( -0-77 t/ha) despite producing 212 t/ha more dry matter in grain plus straw.iNTRnnnrnnN growth has increased and the means to eliminate or I N T R O D U C T I O N ameliorate many constraints on yield have been The husbandry of cereal crops, and of winter cereals developed so that more options are available to in particular, has become m...

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