Pasteuria penetrans, a biological control agent for root-knot nematodes, has great potential for development as a bionematicide. Previous studies have shown that high nitrogen levels affect the development of root-knot nematodes. The objectives of this study were to determine the effects of various levels of ammonium nitrate and of harvest time on development of P. penetrans. Five levels of ammonium nitrate (0.0, 0.2, 0.4, 0.8, 1.6 g/pot) and five different harvest times (37, 44, 51, 58, 65 days after inoculation) were tested separately with six replicates each for both experiments. Ammonium nitrate adversely affected the development of both M. arenaria race 1 and P. penetrans. A quadratic relationship was established between the number of females per root system and the nitrogen levels. Number of endospores per root system and number of endospores per female were negatively correlated with the nitrogen levels and decreased 1.1 million and 0.013 million, respectively, per 0.1 g ammon
