Three insecticides viz., carbofuran, endosulfan and quinalphos were assessed for their toxic effects on plant growth and vesicular-arbuscular mycorrhizal (VAM) fungi development in sorghum. Samples of a black alluvial soil, contained in earthen pots, with indigenous VAM populations were drenched with graded concentrations of the insecticides ranging from 0 to 10 kg ha −1 after 30 days (single application), or 30 and 60 days (two repeated applications), of plant growth. Single or two repeated applications of carbofuran at levels of 0.5–2.5 kg ha −1 were non-toxic to plant growth and mycorrhizal development. However, 5 and 10 kg ha −1 levels of carbofuran were phytotoxic and significantly inhibited colonization by VAM fungi. Plant growth and VAM formation were not affected by 0.5 kg ha −1 levels of both endosulfan and quinalphos. Single or two repeated applications of endosulfan, and quinalphos, at concentrations of 5 and 10 kg ha −1, exerted toxicity to the plant growth and VAM fungal colonization.