Effect of some granular insecticides currently used for the treatment of maize crops (Zea mays) on the survival of inoculated Azospirillum lipoferum

Four insecticides, carbofuran, chlormephos, terbufos and benfuracarb, curre ntly used on maize (Zea mays) at sowing, were tested for their compatibilit y with Azospirillum lipoferum strain CRT, used as an inoculant to improve m aize growth and yield. The growth or survival of A lipoferum was studied in the presence of the insecticides: (1) in liquid and solid cultures of the bacteria, (2) when a commercial inoculant (Azogreen-m (TM), Liphatech, Meyz ieu, France) was inoculated directly on insecticide granules, (3) when inoc ulated Azogreen-m granules were mixed with insecticide granules and (4) whe n inoculated Azogreen-m granules were delivered separately to the seed bed. Of the four insecticides tested, only terbufos had a slight effect on grow th of A lipoferum in solid cultures. All the insecticides decreased the sur vival of A lipoferum when the bacteria were inoculated directly on to the g ranules, or when inoculated Azogreen-m granules were mixed with an insectic ide. We hypothesize that the discrepancies between bacterial culture tests and survival studies might be explained by the conditions of desiccation en countered during inoculation of the granules. Desiccation stress could incr ease the toxic effect of the insecticides. We therefore suggest including d esiccation stress in the biotest used to assess inoculant-pesticide compati bility. (C) 2001 Society of Chemical Industry.