Weed Population Dynamics and Composition in a Tropical Island Eggplant (Solanum melongena L.) Agroecosystem: Implications for Sustainable Weed Management

Competition between crops and weeds is a huge challenge for eggplant (Solanum melongena L.) farmers in Fiji. The aim of this study was to identify and quantify weed species in major eggplant agroecosystems of Fiji, with a focus on their prevalence, distribution, and seasonal abundance to inform effective and sustainable weed management strategies. The weed population data were used to calculate frequency, abundance, density, relative values, importance value index per species per location, and similarity index of species against each location. In addition, principal component analysis was used to identify key factors influencing weed distribution and abundance. A total of 40 weed species from 18 families were identified across agroecosystems, comprising 24 annual species and 16 perennial species. Overall, weed species composition comprised 27.2% grasses, 25.4% sedges, and 47.4% broadleaves. The predominant weed species were found to be from the Poaceae family, specifically Cynodon dactylon L. Pers. (Couch grass), Echinochloa colona L. Link (Jungle rice), and Eleusine indica L. Gaertn. (Crows foot), while Cyperus rotundus L. (Purple nutsedge) was the major species from the Cyperaceae family. The first two principal components (dry zone PC1 and intermediate zone PC2) explain 55.8% of total variance, highlighting the dominance of sedges like C. rotundus in PC1 and the prevalence of grass species such as E. indica and E. colona in PC2.