Screening of Indian borage [Plectranthus amboinicus (Lour) Spreng], bitter weed [Andrographis paniculata (Burm.f.) Nees] and Southern cone marigold (Tagetes minuta L.) for allelopathic potential against weeds

Several plants express the allelopathic phenomenon through release of allelochemicals. Plants rich in allelochemicals can be used for controlling weeds in organic crop production. Current study was aimed at screening of Andrographis paniculata (Burm.f.) Nees (bitter weed), Plectranthus amboinicus (Lour) Spreng (Indian borage) and Tagetes minuta L.(Southern cone marigold) for allelopathic potential against upland weeds. This study was conducted from February to May 2021 in the Department of Agronomy, College of Agriculture, Vellanikkara, Kerala Agricultural University, Thrissur. The methanol extracts of Tagetes minuta and Andrographis paniculate at 25-30% concentration as preemergence application exhibited allelopathic effect on broad-leavedweeds.