 Millardet is chiefly remembered for his work dealing with plant pests.In the 1860s the vineyards of France were infested by the destructive Phylloxera, an aphid-like pest inadvertently introduced to Europe from the United States.Millardet and fellow botanist Jules Émile Planchon (1823-1888) controlled the infestation by using American grape vines that were resistant to Phylloxera as grafting stock.