THE INFLUENCE OF BLACK BEAN APHID, APHIS-FABAE SCOP, AND ITS HONEYDEW ON LEAF GROWTH AND DRY-MATTER PRODUCTION OF SUGAR-BEET

A. fabae populations, started at the 3-4 leaf-stage of sugar beet in the glasshouse and peaking at 3000 individuals per plant, reduced leaf area by 64% at the 14 leaf-stage. The size of the heavily-infested leaves number 5 to 10 was reduced by 80% or more. The rate of leaf growth regained normal values after the aphid populations collapsed, but the infested plants did not make up for the decrease in leaf area production that had been incurred during the infestation. Total dry matter production over a period of 1.5 weeks was reduced by 47%. Honeydew had no effect on leaf size or dry matter production. Sugar beet plants in the field became infested with A. fabae at the 2.3, 4.5 and 6.8 leaf stages. Maximum populations of 800, 2100 and 2200 aphids per plant were recorded, respectively. The pertinent reductions in leaf area were 91%, 67% and 34% at the 10-12 leaf-stage and 79%, 65% and 14% at harvest while the total dry matter produced was reduced by 91%, 79% and 16%. Neighbouring plants of the early-infested sugar beet plants gained significantly higher weights than control plants. Honeydew had no effect on leaf area or dry matter production. The consequences of these results for our understanding of Aphis fabae injury in sugar beet and aphid control in the field are discussed.