Endogenous pesticides from ten common weed species in the Philippines

Herbicidal activity of the different weed extracts in petri dishes indicated that Portulaca oleracea was the most toxic in terms of inhibiting the growth of pechay (Brassica pekinensis), rice (Oryza sativa), Ipomoea triloba and Echinochloa colona. There was a direct proportional relationship between the degree of growth inhibition and extract concentration. Root elongation was generally more affected than shoot and germination. In some cases, although the seed coat ruptured the seed failed to germinate. Softening of the seeds and eventual rotting were also noted. P. oleracea extract was also promising as post-emergence spray against Cyperus difformis and E. colona but not against I. triloba suggesting selectivity. The affected seedlings were chlorotic. The inhibitor possibly present in P. oleracea extract was not inactivated by agitation and by heat. It was mostly concentrated on the leaves, water extractable, and was not adsorbed by activated carbon. Studies on herbicidal activity involving soil medium or soil exudate and weed residue studies showed lesser inhibitory effects than in the petri plate study. P. oleracea extract was also the most promising fungicide for the control of Helminthosporium maydis and Rhizoctonia solani. Bioassays showed significantly bigger zone of inhibition or reduction of mycelial growth or both on agar culture. In vivo studies with potted corn plants revealed protective and therapeutic effects of P. oleracea extract against H. maydis. Applied one day before inoculation, P. oleracea reduced the number of Helminthosporium leaf spots by 48-50% and reduced the lesion size by 33-47%. Extracts applied a day after inoculation did not affect the frequency of H. maydis lesions. Higher extract concentration of 75% exhibited similar magnitude in reducing lesion size as Benomyl. P. oleracea extracts at 75% also delayed the onset of sporulation and reduced the number of conidia per lesion. Entomological assays showed that concentrated extract of V. cinerea, R. exaltata, E. indica and E. hirta were promising against Musca domestica with mortality rate higher than 50%