| Summary: | Two neem-derived pesticides were examined under <i>in vitro</i> and <i>in vivo</i> conditions to test their efficacy in controlling <i>Plasmopara halstedii</i> pathotype 704, a causal agent of downy mildew in sunflower. All the tested concentrations of neem leaf extract and the highest concentration of commercial neem product significantly reduced the sporangial germination under <i>in vitro</i> conditions. In <i>in vivo</i> experiment, 3-days old pre-treated seedlings with both concentrations of neem leaf extract and the highest concentration of commercial product showed a significant reduction in the infection indicating possible systemic effect of neem. When the seedlings were treated following the infection with <i>P. halstedii</i> (i.e., post-treatment), only the highest concentrations of neem leaf extract and the commercial product showed a significant reduction in the infection indicating curative effect of neem. Possibilities for the control of <i>P. halstedii</i> with neem-derived pesticides are discussed.
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