The effect of partial defoliation on yield of sugar beet

Sugar-beet plants were defoliated during growth in seven experiments from 1968 to 1974 either (1) by removing each leaf as it became fully expanded or (2) by removing with scissors as soon as possible all leaves except certain groups up to leaf 50 , but mainly 6 to 20 , or (3) by treating the growing point chemically or mechanically in an attempt to stop the production of leaves after the twentieth. Removing mature leaves decreased yields considerably, but removing all leaves except 6–20 did not decrease significantly total dry matter yield of the whole plant and in one experiment increased it by 7% and root weight by 15%. Remaining leaves had a greater photosynthetic efficiency as measured by growth analysis and a ¹⁴C0₂ feeding technique because they were less shaded or there was reduced competition for some nutrient or essential growth component. Additional leaves formed beyond the twentieth resulted in a proportionately lower photosynthetic efficiency of all leaves, but attempts to treat the plant to stop production of new leaves beyond the twentieth were inconclusive.