abstract a field experiment conducted for 2 consecutive years in a semi-arid tropical region of south india investigated the influence of yellowing and crinkling disease, caused by leaf-sucking insects, on the yield and composition of the essential oil of cymbopogon winterianus jowitt (citronella cv. java 2). infected leaves exhibited yellow specks or blotches which in later stages developed into yellow streaks running along the length of the leaves. emerging young leaves were pale green or yellow coloured, twisted, crinkled and developed into whip-like structures. severely diseased plants died. the yellowing and crinkling disease decreased biomass yield in the first and second years of harvesting by 62.8% and 82.7%, respectively. the corresponding decreases in essential oil yield per plant were 62.8% and 79.0%. the essential oil examined by gc and gc-ms from cultivated healthy plants contained citronellal (28.4%), geraniol (24.8%), citronellol (11.8%) and elemol (10.2%). the major components from diseased plants were geraniol (19.0-25.5%), elemol (15.3-20.4%), citronellal (13.4-19.1%) and citronellol (12.9-15.1%). caryophyllene oxide (3.5-6.0%) was an important minor component. copyright (c) 2004 john wiley & sons, ltd.